Lakeland MIST 13th - 15th April 1999

Charlotte Mason College, Ambleside


Tuesday 13 April

Session 1: Aurora /Optical

B S Lanchester, K J F Sedgemore-Schulthess (Soton), A Otto (Fairbanks), M H Rees (Soton), H Zhu (Fairbanks), and I W McCrea (RAL). Optical and radar observations of filamentary aurora - evidence for strong field-aligned currents?

Optical images of the field of view over the EISCAT radar showed that an arc system made up of several parallel arcs passed through the beam at 2230 UT. High resolution images showed the filamentary structure within these arcs. Radar measurements showed fast convection close to the filamentary structure. The changes in electron temperature and density close to and within the auroral filaments have been modelled with a one-dimensional transport and ion chemistry code. The results indicate that an additional heat source is required to account for the observed changes. We suggest that Ohmic heating in a strong field-aligned current layer is that heat source. This conclusion is supported by results from a two-dimensional simulation model.

H Zhu (Fairbanks), B S Lanchester (Soton), A Otto (Fairbanks), M H Rees (Soton), and D Lummerzheim (Fairbanks). Simulation of field-aligned current formation and associated ionospheric structure.

Field-aligned currents facilitate the coupling between the Earth's magnetosphere and the ionosphere. We have developed a new two-dimensional simulation code which includes ionospheric transport as well as ion inertia to model electromagnetic processes of the magnetopshere-ionosphere coupling. Our results illustrate the propagation of field-aligned current layers into the ionosphere and the subsequent intensification of the current. The model results show the density depletion and enhancement at the base of down- and upward directed field -aligned current layers. The results also demonstrate the formation of new field-aligned current filaments as a result of sharp precipitation boundaries. It should be emphasized that the model does not use the commonly applied steady state assumptions. Therefore it is particularly well suited for the simulation of rather small spatial and short temporal scales.

M J Kosch (MPAE), C del-Pozo, F Honary, N Stamatiou (Lancaster), and T Hagfors (MPAE). Images of the optical aurora, riometer absorption and characteristic energy of the precipitating particles.

Recordings of auroral optical emissions at 557.7 nm are made from Skibotn, Norway (69.350 N, 20.360 E), using the Digital All-Sky Imager (DASI). The images give estimates of the precipitating patterns of soft electrons (< ~8 keV). Recordings of cosmic radio noise absorption at 38.2 MHz are made from Kilpisjarvi, Finland (69.050 N, 20.790 E) using the multi-beam Imaging Riometer for Ionospheric Studies (IRIS). These images give estimates of the precipitating patterns of hard electrons (> ~30 keV). The ratio of absorption to the square root of optical intensity is an approximate indicator of the characteristic energy of the precipitating electrons. Using this, high resolution maps of the characteristic particle energy can be generated within the combined observation area of DASI and IRIS (67.8-70.20 E, 17.75-23.750 N). The EISCAT radar (69.590 N, 19.230 E) makes accurate electron density measurements with altitude at one point within the common field of view of DASI and IRIS. This profile can be inverted to compute the equivalent energy spectrum of the precipitating electrons. Both methods are compared and discussed using the night of 13-14 February 1996 as an example.

A L Aruliah, and I McWhirter (UCL). Proposed observations of Meso-scale neutral wind flows at high-latitudes using all sky and tristatic Fabry-Perot Interferometers.

Overlapping FPI fields of view have indicated that there is considerably more variation in the spatial behaviour of the neutral winds than has been presumed. Although the long-term average behaviour of the neutral winds show a spatial scale size of several hundreds of kilometers, as expected, night by night comparisons of data from sites at Kiruna and Kilpisjarvi, which are only 150km apart, show a large number of differences. In particular, narrow regions of heating can be seen in the response of the vertical winds. The increased temporal resolution achieved with our recent generation of FPIs, which use CCD detectors, also reveal rapid and sharp changes in the wind field which will have repercussions for the way in which energy is dissipated in the upper atmosphere. This paper will present plans for making tristatic measurements of the neutral wind with FPIs and also plans to build a new all-sky imager which uses state-of-the-art detector technology.

A D Aylward, A L Aruliah, I C F Mueller-Wodarg (UCL). Neutral wind dynamo contribution to the high-latitude energy budget.

The contribution of the neutral wind dynamo to the high-latitude energy budget is beginning to be acknowledged as significant. A few model simulations have been published indicating that the neutral wind contributes several tens of percent of the total electromagnetic energy flux in the upper atmosphere. However, the usual assumption used in empirical measurements made at high latitudes is to set the neutral wind to zero because it is presumed that the magnetospheric dynamo overwhelms the neutral wind dynamo at these latitudes. This assumption also greatly simplifies the calculations required. In this paper we will investigate the energy budget using ionospheric measurements made with the EISCAT and ESR radar, together with neutral wind measurements made with FPIs at Kiruna and Longyearbyen. The campaign has been named SP-UK-FLYE. The calculation requires knowledge of the height profile of the neutral winds which the FPIs cannot provide. However, this can be provided by the CTIP model since the FPIs can measure the neutral winds at 240km and the radars can provide neutral winds at around 100km and consequently, these measurements can be used to anchor the model simulations.

E Griffin (UCL). Thermospheric meridional neutral wind climatologies from radar and airglow measurements.

The existence of long term databases of both radar data from the EISCAT system and airglow measurements from Fabry-Perot interferometer (FPI) measurements at Kiruna has allowed comparison of climatologies for thermospheric meridional neutral winds derived from the radar data and measured by the FPI. The results of these comparisons and the conclusions that follow are presented.

D M Willis (Warwick), and F R Stephenson (Durham). Simultaneous auroral observations described in the historical records of China, Japan and Korea from ancient times to AD 1750.

Early auroral observations recorded in various oriental histories are examined in order to search for examples of strictly simultaneous and indisputably independent observations of the aurora borealis from spatially separated sites in the Far East. In the period up to AD 1750, only six examples of such simultaneous and independent auroral observations have been found. These occurred during the nights of AD 1101 January 3 1, AD 1138 October 6, AD 1363 July 30, AD 1582 March 8, AD 1653 March 2, and AD 1730 February 15. On the night of AD 1101 January 31, the aurora borealis was observed simultaneously and independently from sites located in China, North China and Korea. On the night of AD 1138 October 6, the aurora borealis was observed simultaneously and independently from sites in China and Korea. The aurora borealis was definitely observed on the following night from at least one site in England and may also have been observed on the same night from at least one site in eastern Europe. On the night of AD 1363 July 30, the aurora borealis was observed simultaneously and independently from sites in China and Japan; moreover, it was seen again three nights later from a separate site in China. On the night of AD 1582 March 8, the aurora borealis was observed simultaneously and independently from sites in China and Japan. The aurora borealis was definitely observed two nights earlier from several sites in Europe and there is some evidence that it was also observed in Europe on the same night as in the Far East. On the night of AD 1653 March 2, the aurora borealis was observed simultaneously and independently from sites in China and Japan. On the night of AD 1730 February 15, the aurora borealis was observed simultaneously and independently from sites in both China and Japan, as well as being observed independently on the same night from many sites in Europe.

The independent historical evidence, describing the simultaneous occurrence on these six nights of mid-latitude auroral displays at more than one site in the Orient, provides incontrovertible proof that auroral displays actually occurred on these occasions. This conclusion is corroborated by the excellent level of agreement between the detailed auroral descriptions recorded in the different oriental histories, which furnish essentially compatible information on both the 1 colour (or colours) of each auroral display and its position in the sky. In addition, the occurrence on three of the six occasions of auroral displays in Europe, within two days of simultaneous auroral displays in the Far East, suggests that many of the mid-latitude auroral displays recorded in the oriental histories are associated with major geomagnetic storms.

Session 2: Mesosphere / Thermosphere

P J S Williams (Aberystwyth), M Kunitake (CRL), Steffan Buchert (STELab), Tony van Eyken (EISCAT). A comparison of tidal and quasi-tidal oscillations in the lower thermosphere as measured simultaneously by EISCAT at Longyearbyen and TromsÆ .

Incoherent-scatter measurements of ion velocity, made by the EISCAT radars observing along the magnetic field line, have been used to determine the meridional component of neutral wind velocity at a number of separate heights over the range 90 km to 120 km. Frequency analysis has been used to determine the amplitude and phase of the most prominent components at each height, including those with periodicities of 24, 12 and 8 hours. Since August 1998 such measurements have been made simultaneously at both Ramfjordmoen (69.6 degrees North) and at Longyearbyen (78.2 degrees North). For each component and at each height the ratio of the amplitudes observed at the two stations have been determined, as well as the differences in phase. The results have been compared with predicted values for tidal modes in an attempt to distinguish global modes and quasi-tidal oscillations at high latitudes.

V Howells, N J Mitchell, A G Beard (Aberystwyth), H G Muller (Cranfield). Diurnal-,semidiurnal- and planetary-wave-period modulation of gravity-wave activity in the mesosphere and lower thermosphere.

Meteor radar wind measurements were made over the UK from June 1989 to October 1994. The radar infers horizontal-wind velocities and although gravity waves cannot be measured directly, the variance of the veloctites gives an indication of the gravity-wave activity during the morning in winter and in the afternoon in summer. A time-series analysis reveals strong modulation of the gravity-wave variance at tidal and planetary-wave periods. The seasonal behaviour of the modulation is investigated

H R Middleton, N J Mitchell, A G Beard, P J S Williams (Aberystwyth) and H G Muller (Cranfield). The 16-day planetary wave in the mesosphere and lower thermosphere.

A meteor radar located at Sheffield in the UK has been used to measure wind oscillations with periods between 10 - 28 days in the mesosphere/lower-thermosphere region at 53.5oN, 3.9oW from January 1990 to August 1994. The data reveal a motion field in which wave activity occurs in episodes lasting generally for less than two months and which occur over a broad range of frequencies. A seasonal cycle is apparent in which the largest amplitudes of up to about 14 m/s are observed from January to mid-April. A minimum in activity occurs in late June to early July followed by a second, smaller, maximum in late summer/autumn where amplitudes reach up to 7 - 10 m/s. Considerable interannual variability is apparent and wave activity is observed in the summers of all the years examined, suggesting that the westward phase of the equatorial QBO does not completely prevent inter-hemispheric ducting of the wave from the winter hemisphere, or that it is generated in situ.

D Pancheva, A G Beard, N J Mitchell (Aberystwyth) and H G Muller (Cranfield). Climatological characteristics of non-linear coupling between tides and planetary waves.

Meteor-scatter radar measurements have been used to investigate the non-linear coupling of tides and planetary waves in the mesosphere/lower-thermosphere region over the period 1990-1994. A bispectral analysis reveals that strong coupling occurs with the semidiurnal tide, but that the coupling with the diurnal tide is very weak. Confirmation of the non-linear nature of the interaction is provided by the detection of the predicted secondary waves. The studied interval suggests an asymmetry in the strength of the interaction, with the zonal component being the most strongly interacting in most, but not all, cases. The bispectra reveal that many components of the planetary-wave field are involved, and the signature of non-linear interaction is seen at wave periods of 2, 4-6, 8-10 and 16 days. There is also evidence of interactions at periods of 25-28 days

M J Harris (UCL), N F Arnold (Leicester), A D Aylward, I. Mueller-Wodarg (UCL). Modelling the upper mesosphere / lower thermosphere : A new coupled general circulation model.

The Upper Mesosphere Lower Thermosphere (UMLT) is an important transition region in the coupling of the upper and middle atmospheres. In order to help study the dynamics and energetics of this system, a 3-D time dependent Coupled Mesosphere and Thermosphere model (CMAT) has been developed, extending and updating the existing thermospheric code to incorporate mesospheric dynamics and energetics. Accurate radiative heating efficiencies used within the model have been shown to generate a temperature inversion layer layer near the mesopause. Preliminary comparisons between model output and observations will be presented.

D Rees (Hovemere Ltd). The current and future capability of the ALOMAR facility in northern Scandinavia for studies of stratospheric and mesospheric / lower thermospheric dynamics and energetics.

The ALOMAR Observatory, near the Andoya Rocket Range, Northern Norway (WE, 69oN), is an International Facility which already contains three fully operational high-performance Lidar Systems and two capable radars (MST and W). During 2000, a new "metal" lidar system is anticipated to be introduced by colleagues from the USA, providing ALOMAR with the unique capability to measure simultaneous profiles of wind, density and temperature profiles of high accuracy, vertical and temporal resolution from the tropopause up to above 110 km altitude, 24 hours per day, year around, combining the lidar and radar systems.

A preview of some of these novel capabilities and studies, using the existing lidar and radar systems, will be provided. We will also highlight some of the unexpected advantages and new science results coming from the very successful efforts to develop a daytime capability for the major detection channels of the ALOMAR Rayleigh / Mie / Raman Lidar.

Stratospheric wind measurements from the Doppler Wind capability of the ALOMAR Lidar have been subjected to a series of intercomparison and validation programmes, using measurements from the nearby MST radar, radiosonde and rocket flights. In turn, the lidar-based stratospheric wind measurements are being used currently to describe and evaluate the stratospheric transport terms appropriate for studies of stratospheric ozone above Northern Scandinavia during the winter and spring periods in 1997, 1998 and 1999.

Wednesday 14 April

Session 3: Ionosphere I

G Provan, T K Yeoman , M Lester (Leicester), J M Ruohoniemi and R Barnes (John Hopkins). How to image large-scale ionospheric convection patterns using the SuperDARN radars.

Super Dual Auroral Radar Network (SuperDARN) is a global network of I-IF radars, with potential for observing and predicting the space we~ environment. 'Me SuperDARN radars provide information on the high-latitude ionosphere in the Northern and Southern hemisphere, obtaining the ExB drift of ionospheric plasma by scattering radio waves off F region irregularities. The SuperDARN radars am arranged such that observations in common-volume am am bidirectional and the 2D EXB velocity can be resolved unambiguously. By merging measurements from all the radars in the Northern hemisphere, direct mapping of the convection can be extended to almost 12 hours of magnetic local time. However, although the two-dimensional velocity at a point can only be unambiguously resolved if two or more radars make simultaneous measurements, all the available line-of-sight velocity data serves to constrain the possibilities for the large-scale convection velocity. The pattern that is most consistent with the measurements can be determined by mathematical fitting. This is the basis of the map_potential model, described by Ruchoniermi and Baker (1998) as "..a method of filtering. combining and reducing data from the SuperDARN radars which optimizes the mapping of large- scale convection pattern." The Leicester group now have this model and it is available to other workers within the community. This talk aims to give an introduction to the map_potential model and how to use it

P B Byrne, N F Arnold , T R Robinson, and M Lester (Leicester). Routine generation of meteor scatter parameters from the CUTLASS HF SuperDARN Radars.

The following study presents an evaluation of the use of the CUTLASS HF SuperDARN radars for roles normally associated with dedicated meteor radars. The immediate aim of the research carried out to date is to generate meteor scatter data products as a matter of routine, during normal CUTLASS operations. This meteor data provides a convenient tracer of the neutral wind velocity at the upper mesosphere - lower thermosphere (UMLT) boundary. As such, the data returned is important in that it contains information on the coupling across the UMLT boundary. Techniques have been developed which can successfully detect and identify various sources of contamination in the meteor data returned by the CUTLASS Finland radar. This contamination would lead to an inaccurate measurement of the wind velocity. These sources are: ionospheric scatter including sporadic-E, ground scatter, geomagnetic pulsations and scatter from behind the radar. Additionally, other contamination mechanisms have been suggested which warrant further study.

M Pinnock, A S Rodger, (BAS). On the use of SuperDARN HF radar backscatter characteristics for determining the noon polar cap boundary.

Previous work has demonstrated a link between the equatorward edge of cusp particle precipitation, detected by satellites and ground-based optical measurements, and the eqautorward edge of HF radar backscatter in the noon sector showing large Doppler spectral widths. The radar Doppler spectral width data has been used as a proxy for the location of the polar cap boundary (PCB), and this data used to measure the flow of plasma across the PCB and hence derive the reconnection electric field in the ionosphere. This work has used only single radar data sets with a field of view limited to ~2 of MLT. In a case study using 4 of the SuperDARN radars we examine the Doppler spectral width boundary determined over 6 h of MLT around the noon sector and its relationship to the convection pattern. The variation with longitude of the latitude of the Doppler spectral width boundary shows a characteristic (and predicted) bay like feature. This feature is shaped by the variation with longitude of the poleward flow component of the ionospheric plasma flow and may be understood in terms of the well known cusp ion time-of-flight effects. Using this interpretation we derive the cusp ions time-of-flight over a 40 minute period and find that it shows variations which appear to follow the IMF clock angle, with longer times of flight when IMF Bz goes to zero or positive compared with the IMF Bz negative periods. This characteristic may be explained by the magnetopause reconnection site moving from the sub-solar point to higher latitude, and consequent lower ion energies being injected at the magnetopause. Our results reinforces the intimate link between cusp particle precipitation and the Doppler spectral width data, in particular when time-of-flight effects on the cusp ions are taken in to account.

C F del Pozo, F Honary, S Marple (Lancaster), and E Nielsen (MPAe). Initial results of the CASE experiment for the study of auroral absorption during E-region instability conditions.

The initial results of the CASE experiment combining IRIS, EISCAT and the two coherent radars from STARE, for the simultaneous observation of the auroral absorption events during Farley-Buneman instability conditions in the E-region, are presented. EISCAT measures various physical parameters in the D and E regions, as well as the electric field, which allows the identification of instability conditions and the definition of the F-B instabiliy cone. It also allows the estimation of the electron precipitation spectrum and the height and width of the absorption layer above Tromsø. By comparing the 2-D images from IRIS and STARE observations the study of the spatial extent and structure of the ‘instability’ patches, as well as the temporal evolution of the absorption signatures (and their correspondence with the irregularities’ velocity distribution provided by STARE) is carried out.

M J Birch, J K Hargreaves (UCLan), G J Bailey (Sheffield). Electron content by GPS observation: Correction of oblique observations to zenithal.

A major question in measuring electron content using GPS satellite transmissions is the altitude to be used in correcting oblique measurements to equivalent zenithal values. Standard practice has been to use an altitude of 300 to 400 km., but analysis of data obtained at Lancaster has indicated that a considerable greater altitude would beappropriate. The paper will discuss the use of the Sheffield University Plasmasphere and Ionosphere Model to support (or otherwise!) this conclusion.

R L Balthazor, R J Moffett (Sheffield), L Kersley, E Pryse, C Mitchell, M Williams (Aberystwyth). Modelling the mid-latitude ionospheric trough with the Sheffield coupled thermosphere-ionosphere-plasmasphere model.

The Sheffield coupled thermosphere-ionosphere-plasmasphere model has been used to model the mid-latitude ionospheric trough along the line of longitude 18 degrees East from 1995 day 326 to 1995 day 332, an extended period of extremely quiet activity followed by a burst of intense activity. The model has reproduced well the position of the trough and the electron density equatorward of the trough as measured by the Aberystwyth tomographic receiver chain. The modelled electron density poleward of the trough is found to be critically dependent on the precipitation model used, with a model based on DMSP satellite data found to reproduce observations better than a model based on TIROS data. There is found to be little dependency of the position of the trough on the high latitude circulation pattern.

R Dhillon, S E Milan, and T R Robinson (Leicester). A Comparison between radar signatures of the Farley-Buneman and the electron Pedersen conductivity instabilities.

Recent theoretical and experimental work directed towards the D-region and lower E-region, at altitudes of around 80-95km, has indicated the existence of a new type of plasma instability. This instability, the Electron Pedersen Conductivity Instability (EPCI), excites waves that propagate preferentially along a direction parallel to the bisector between the electric field and ExB directions. The differences between radar backscatter signatures for the EPCI and the more widely known E-region Farley-Buneman Instability (FBI) are discussed and characterised. The data were collected using CUTLASS, a bistatic component of the HF SuperDARN array with sites in Iceland and Finland, and STARE, a bistatic coherent scatter radar with sites in Finland and Norway. A summary of previous experimental studies, providing possible confirmation of the EPCI, is also presented.

Session 4: Ionosphere II

I K Walker (Aberystwyth), J Moen (UNIS), S T Berry, L Kersley (Aberystwyth), and D A Lorentzen (UNIS). Dayside precipitation and the possible formation of polar-cap patches.

The paper describes experimental observations of enhancements in F-region electron density created by particle precipitation at the entry to the polar-cap convection flow. Two case studies are discussed of measurements of red-line auroral emissions and electron density structures imaged by radio tomography. Differences between the examples are related to IMF conditions and it is shown that one of the structures in particular has characteristics and potential lifetime consistent with those of patches found in the central polar cap.

Y Z Su, G J Bailey (Sheffield), and K I Oyama (ISAS). Equinoctial asymmetry in the low-latitude topside ionosphere.

In this study, the differences of the electron density and temperature in the low-latitude topside ionosphere at March and September equinoxes are investigated using observations made by the Hinotori satellite. The observations show that there is an equinoctial asymmetry in electron density. In the southern/northern hemisphere, the electron densities are higher at September/March equinox than at March/September equinox. The equinoctial asymmetries become stronger with increasing latitude for both hemispheres. The behavior of the observed electron temperature is controlled by the electron density. The mechanism of the equinoctial asymmetry is investigated using a global model, the Coupled Thermosphere Ionosphere Plasmasphere Model.

A M Smith, S E Pryse(Aberystwyth), and J Moen (UNIS). Ionospheric response to changes in IMF clock angle.

Sharp transitions in the IMF components measured by the WIND satellite give rise to clear ionospheric responses. Optical measurements by the meridian scanning photometer at Ny-Εlesund show changes in the type of auroral emission that can be explained in terms of the variations in IMF clock angle. Line-of-sight plasma flows measured by the CUTLASS Finland radar also showed distinct responses to the clock angle. The relative response time of the two sets of ionospheric measurements to the changes in IMF is discussed.

G Chisham, M Pinnock, A S Rodger, I J Coleman (BAS), A Thorolfsson, J C Cerisier (CETP-SM). High-time resolution SuperDARN radar observations of the dayside convection response to changes in IMF.

A.D.M. Walker Department of Physics, University of Natal, Durban, South Africa. We present data from two of the southern hemisphere SuperDARN radars describing the high-latitude ionosphere's response to a change in the IMF By direction during a period of steady IMF Bz southward. Data from the WIND and GEOTAIL spacecraft describe the solar wind while the FAST satellite provides a snapshot of the convection reversal boundary region in the radars' field-of-view. Data from the northern hemisphere SuperDARN radars provides a conjugate view of the event. The radars were operating in a special mode which gave high time resolution data (30 s) on 3 beams with a full scan every 3 minutes. The location of the radars in the noon time sector gave a detailed observation of the change in the ionospheric convection pattern as IMF By changed from negative to positive. In particular the development of the westward edge of the afternoon convection cell is observed in the radars' field-of-view. Detailed study of the phase velocity of the changes in the ionospheric convection pattern will be presented. The plasma flow burst behaviour around the event is also studied and found to confirm the results of previous work which shows such bursts originating well equatorward of the convection reversal boundary. The observations are examined in the context of current ideas about the mapping of the magnetopause merging line to the ionosphere and the causes of plasma flow bursts.

K A McWilliams, T K Yeoman, G Provan (Leicester). A statistical study of the occurrence rates and repetition frequencies of pulsed ionospheric flows in the dayside auroral zone.

A study has been performed on the occurrence of pulsed ionospheric flows as detected by the CUTLASS Finland HF radar.  These flows have been suggested as being created at the ionospheric footprint of newly-reconnected field lines, during episodes of magnetic flux transfer into the terrestrial magnetosphere - flux transfer events or FTEs.  Two years of both high-time resolution and normal scan data have been analysed in order to perform a statistical study of the occurrence rate and repetition frequency of the pulsed ionospheric flows.  These statistical results obtained from ionospheric flows are compared to occurrence rates and repetition frequencies of FTEs derived from in situ spacecraft data.

T D G Clark, E Clarke, and A W P Thomson (BGS). Geomagnetic Induced Current (GIC) risk in the UK : 1. Magnetic variations.

Using data from the three UK magnetic observatories, GIC risk in the UK is assessed. Known examples of GICs in the power grid are discussed in relation to the geomagnetic variations observed. A simple measure of the power of the magnetic field variation is presented, which can be used to determine the risk according to season and local time. Monitoring and forecasting of this power index is suggested as a means of preventing damage to high-cost equipment.

D Beamish, T D G Clark, E Clarke, and A W P Thomson (BGS). Geomagnetic Induced Current (GIC) risk in the UK: 2. Surface electric fields.

A simplified three-dimensional geology model is used to provide an indication of the surface electric field in the UK for various amplitudes and wavelengths of the external magnetic field variation. It is found that the conductivity contrast between seawater and the on-shore geology, in particular, produces enhanced E-fields around the coast. We discuss how the geophysical model may be used with network models of, for example, power grids and pipelines, to calculate levels of geomagnetically induced currents.

Session 5: Magnetosphere I

M Mendillo (Boston). Magnetospheric-Ionospheric interactions, ionospheric imaging of magnetospheric boundaries.

An all-sky imaging system operating at a sub-auroral site (Millstone Hill, MA) has recorded a rich set of emission structures throughout the past solar cycle. At 6300 A, three distinct features have been seen in a dataset that now exceeds 1000 nights of operation: airglow, diffuse aurora, and stable auroral red (SAR) arcs. These features typically have mean emission heights of 300 km, 200 km, and 400 km, respectively. In 75 case studies of evenings with both diffuse aurora and SAR arcs, the equatorward edge of the diffuse aurora and the central latitude of the SAR arc have been mapped along geomagnetic field lines to the equatorial plane. The respective L-value locations of both features are, within statistical uncertainties, essentially identical (typically, L ~ 3). This implies that the inner edge of the plasma sheet (source of diffuse aurora) and the ring current/plasmapause interaction region (source of SAR arcs) are coincident sites in the magnetosphere. A persistent shortfall in model estimates of brightness for faint SAR arcs using the thermal excitation mechanism may be resolved by a modest source of 6300 A generated by proton precipitation.

M H Denton ,Y Z Su ,G J Bailey (Sheffield), K I Oyama (ISAS). A modified plasmaspheric thermal conductivity: Theory, observations and model results.

Plasmaspheric closed field line models solve equations of continuity, momentum and energy balance to calculate parameters such as ion and electron temperatures, concentrations and field-aligned fluxes. The electron temperature calculated in this way is typically much lower than that measured by satellite instruments at altitudes above 1000km. A density dependent thermal conductivity defined by Mayr et al (1973) has been introduced into SUPIM (Sheffield University Plasmasphere Ionosphere Model). The theoretical derivation of this conductivity is described and comparison made between observations and model values obtained using SUPIM.

R Andre, M Pinnock (BAS), J P Villain (LPCE/CNRS), and Hanuise (LSEET/CNRS). Characteristics of the SuperDARN spectra and their relationship to magnetospheric processes.

Coherent HF radars use ionospheric irregularities (scale length ~ 15 m) as tracers of the plasma motion, deriving the average line of sight velocity from a complex autocorrelation function (ACF) which is computed from the emission of a multipulse sequence. A linear analysis determines the line of sight Doppler velocity and the spectral width from the temporal evolution of the phase and of the power.

When the spectrum deduced from the ACF comprises only one component, an enhancement in Doppler spectral width is usually interpreted as an increase in velocity fluctuations in the sampled volume. But the topology of the large-scale electric field projeted to the ionosphere can also increase the spectral width in regions where large velocity gradients are expected. Using the Heppner and Maynard convection model, we show that the width of the velocity distribution can be of the order of 200 m/s in the convection reversal.

When the spectrum comprises several components, the temporal evolution of the phase is no longer linear, and the power is also modulated by the second component. These multi-component spectra are due to a multi-peaked velocity distribution function observed during the integration time. We show that a time-varying electric field with a high-frequency, like the Pc1 pulsations which are commonly observed in the dayside, can explain several multi-component spectra.

Because the linear analysis of the ACF gives us some keys to distinguish the ACFs with respect to their characteristics (multi-component spectrum or not, high spectral width or not), one can classify them. This classification has been applied to a large database constructed from the data collected by 6 SuperDARN radars in the northen hemisphere during the winter 1996. Here, we show that the ACF characteristics are not randomly distributed, but are localized in very specific regions. We show that the geometrical effects cannot explain the high-spectral width values observed, and we conclude by making some connection between either soft electron precipitation or time-varying electric fields, and the ACFs characteristics presented above.

I Krauklis, A Johnstone (MSSL), W Peterson (Lockheed). Acceleration of ionospheric O+ in the LLBL and Cusp regions observed by Polar/TIMAS.

A common observation by the Polar/TIMAS instrument during LLBL and Cusp crossings is the close association of the energy of the up-going ionospheric O+ with the injected H+ populations. We present a summary of 10 cusp crossings where the IMF was southward. In the LLBL the average O+ acceleration was 0.5 kms-2, with the bulk velocity of the O+ consistently less than the H+ in this region. Once in the Cusp the O+ attained the same bulk velocity as the up-going H+ bulk velocity within 260±100s. Observation of the O+ temperatures reveal a monotonic relation between bulk velocity and temperature. Also the T||/T_|_ ratio of the injected and mirrored H+ is elevated in comparison to the down-going injected H+. These observations are consistent with wave-particle interactions accelerating and heating the O+ population in the LLBL and the Cusp region.

J Storey, M Lester (Leicester), C T Russell (UCLA),T A Fritz (Boston), M Brittnacher (Washington), J B Blake (Aerospace Corp.), and J Scudder (Iowa). Plasma sheet variations during substorm activity: Observations on 17th May 1996.

This presentation details the initial results obtained from a study of an interval of substorm activity observed in the high-latitude plasma sheet by the Polar spacecraft, during a pass over the Scandinavian sector on 17th May 1996. In this interval the spacecraft passes from a magnetic latitude of 44° at 20:00 UT, down to 20° by 22:30 UT. The study makes use of the CAMMICE instrument on board the Polar spacecraft, specifically to investigate any substorm related plasma flows. Other Polar instruments from which data have been used include two other particle instruments, Hydra and CEPPAD, and the Ultra-Violet Imager (UVI), which provides images of the auroral zone throughout the interval and hence shows ground signatures of the plasma flows observed in situ. Other instrumentation includes the WIND magnetometer and the IMAGE and SAMNET magnetometer chains. These instruments provide background data sets that are used to confirm the presence of substorm activity and give the timing of the onset of any such activity. The particle instruments observe PSBL signatures twice during this interval. The first entry into the PSBL is due to a slight re-configuration of the field geometry caused by pseudobreakups occurring at 20:48 and 21:00 UT. The continuing growth phase causes the tail field lines to become more tail-like resulting in the spacecraft exiting the plasma sheet, before the expansion phase onset results in the spacecraft observing CPS ions at 21:45UT.

A J Smith, M B Grieve, M A Clilverd, and C J Rodger (BAS). A quantitative estimate of the mean annual ducted whistler power propagating within the field of view of the VLF receiver at Halley, Antarctica.

It is known that wave particle interactions between whistler mode waves and trapped electrons in the magnetosphere frequently lead to wave amplification accompanied by pitch angle scattering of gyroresonant electrons and their precipitation into the ionosphere. This is accepted as an important loss process for trapped electrons in the 10-100 keV range. However the relative importance of different classes of whistler mode wave, principally plasmaspheric hiss, chorus, and lightning generated whistlers, has remained somewhat uncertain. Of particular interest is what effect lightning, and the whistlers generated by it, have on the radiation belts. Burgess and Inan [J. Geophys. Res., 98, 15643, 1993] have estimated electron lifetimes of ~5 x104 days at L=2.24 leading them to conclude that lightning may have a comparable effect to plasmaspheric hiss as a loss process for radiation belt electrons. This estimate was however based at least partly on estimates of whistler rates and numbers of components per whistler published in the early 1960s from whistler observations made during the International Geophysical Year (1957-58) using relatively simple receiving equipment running on an infrequent sampling format.

In this paper we revisit this subject using modern digital whistler recordings from Halley station, Antarctica, (76degS, 27degW, L~4.3). We have used a statistical approach to estimate the total annual wave energy in lightning whistlers which arrived in the field of view of the Halley receiver in the frequency range 3-5 kHz. A separate estimate is made for both local day and night conditions. We have based the study upon a representative sample of randomly chosen days in 1996 which were constrained to have the same distribution of geophysical activity (SKp) as the year as a whole. For these days we estimated the ducted wave power for each component of observed multicomponent whistlers by combining the measured intensities with a model to represent the propagation losses between the duct and the receiver. We also used multicomponent whistlers to investigate the latitudinal variation in the duct emission power for whistlers which had propagated over the range L=2.9 to 4.7. During magnetically quiet periods, a general decrease with increasing L was found, confirming the results of Clilverd and Horne [J. Geophys. Res., 101, 2355, 1996]. It is expected that the results reported here will provide useful input parameters for realistic modelling of whistler wave-electron interactions and in assessing the role of lightning in the loss of trapped electrons from the radiations belts.

Session 6: Magnetosphere II

M Grande, M Carter , C H Perry (RAL). Correlation between DST and relativistic electrons during magnetic storms.

We examine the relationship between variations in Dst and the relativistic electron flux during magnetic storms. We have used relativistic electron data from the CRRES and Polar satellites and the LANL geosynchronous satellites, and correlated this with a high time resolution version of Dst. We see evidence that negative excursions in Dst during all phases of major storms corresponds to significant reductions in the flux of radiation belt electrons. Similarly increases in Dst correspond to increases in the radiation belt electron population. We will show case histories, and examine more generally the correlation, and its possible causes. We include a superposed epoch analysis of the effect of substorms on the relativistic electron population in the radiation belt, and will thus test the hypothesis that substorms are instrumental in causing the increase in the radiation belts. Results for substorm and relativistic energy electrons will be compared.

K Mills , and A N Wright (St. Andrews). Azimuthal phase speeds of FLRs driven by Kelvin-Helmholtz unstable waveguide modes.

A model for the coupling of unstable fast cavity modes to field line resonances (FLRs) is presented. We consider a bounded, non-uniform magnetospheric flank separated from a semi-infinite, field-free, flowing magnetosheath by an infinitely thin magnetopause. Fast cavity modes may become unstable for sufficiently high flow speeds, and we find that, for any flow speed, there is a common phase speed at which all the harmonics have their maximum growth rate. The common phase speed is independent of the equilibrium structure within the magnetosphere, and is determined by the local structure at the magnetopause. We perform a local analysis of the reflection and transmission of modes at the magnetopause. By requiring the spontaneous radiation of modes from the magnetopause, we may predict a phase speed at which we would expect the maximum growth rate to occur for any set of parameters. These predicted phase speeds are found to be in good agreement with both those found by our model and observations of FLRs that are observed simultaneously.

I R Mann (York), A N Wright (St. Andrews). Diagnosing PC5 magnetospheric waveguide mode excitation mechanisms.

Compressional modes supported by a waveguide with a free magnetopause boundary have characteristics which are strongly local time and solar wind speed dependent, being either leaky, trapped, or energised by the magnetosheath flow. Using a theoretical treatment, we show how the characteristics of multiple harmonic field line resonances (FLRs), driven by the waveguide modes, can be used to diagnose their energy sources. Using observations previously reported in the literature, we show examples of this diagnostic analysis and conclude that the dawn/dusk asymmetry in Pc5 FLR characteristics may be linked to different excitation mechanisms operating either side of noon. In particular, we suggest that the majority of dawn-side FLRs may be excited by waveguides modes which are amplified through the action of over-reflection at the magnetopause.

R A Mathie (York), F W Menk (Newcastle, Australia), I R Mann, and D Orr (York). Discrete field line resonances and the Alfven continuum in the outer magnetosphere.

Using Pc5 pulsation events observed with the IMAGE magnetometer array, we demonstrate that mHz frequency field line resonances (FLRs) represent local enhancements in the background Alfven continuum of field line eigenfrequencies. By comparing resonance profiles for a typical event with the continuum frequency profile determined using cross-phase techniques, we show that pulsation frequencies as low as 1-2 mHz can couple to high latitude FLRs on high latitude closed field lines. We also suggest that the transition to open field lines on days of higher geomagnetic activity may lead to a breakdown in pulsation characteristics at the highest latitudes of the IMAGE array. In addition, we show evidence of the U-shaped diurnal variation in field line eigenfrequency and suggest that this is primarily due to field line stretching, epsecially on the magnetosphere flanks.

T I Woodward, M W Dunlop (IC), A N Fazakerley (MSSL), and N Sckopke (MPAe). Magnetosheath structure just upstream of the magnetopause.

It is well known that the flow of the magnetised solar wind over the Earth's magnetosphere establishes an intricate system of upstream wave-fronts and shocks. In the framework of MHD theory, the bow shock is formed by the fast mode, while physical conditions for the Alfven and slow mode waves to stand in the flow behind the bow shock (but upstream of the magnetopause) exist. It is the purpose of the current study to use data from the dual spacecraft AMPTE IRM/UKS mission to identify and analyse the structure of low frequency, wave-like structures recorded in the data from regions upstream, but adjacent to, the magnetopause. Evidence for a plasma depletion layer, slow/Alfven mode standing front, as well as mirror mode-like compressional structures in the local noon region has been reported previously. Here we investigate their relationships to each other in this and the dawnside regions.

Poster Previews:

I C F Mueller-Wodarg (UCL), H Rishbeth (Soton). Thermospheric meriodional circulation and its effect on composition.

Thermospheric circulation is driven by solar EUV heating, with a contribution at high latitudes of magnetospheric sources. At equinox, the dayside upwelling and nightside downwelling hardly disturb the diffusive balance, while at solstice the prevailing summer- to winter circulation leads to transport of gases in the meridional direction, thus generally upsetting diffusive balance. As a result, the thermospheric composition is more molecular at equinox. This semiannual composition change accounts for semiannual variations of F2-layer electron density at low latitudes as well as part of the semiannual changes in neutral density. To show this, we present results from the Coupled Thermosphere-Ionosphere-Plasmasphere Model (CTIP).

D Rees (Hovemere Ltd). Recent observations of momentum coupling in the high latitude thermosphere and ionosphere and ionosphere by doppler imaging systems.

Within the Polar Cap and Auroral Oval, magnetospheric electric fields generate a large and highly variable momentum source for the thermosphere through momentum coupling from the rapidly-moving ionospheric plasma to the neutral gas via ion drag. Two Doppler Imaging Systems, one located at Kiruna, Northern Sweden, and the second in Svalbard, have provided a series of graphic illustrations of the development of complex thermospheric flow patterns during a series of geomagnetic disturbances during the past two years of increasing solar and geomagnetic activity.

M A Clilverd, C J Rodger, and N R Thomson (BAS). Investigating seismo-ionospheric effects on a long subionospheric path.

We examine the possibility of earthquake precursors influencing the subionospheric propagation of VLF transmissions. We consider the long (12Mm) path from NE USA to Faraday, Antarctica during 1990-1995 and investigate the subionospheric amplitude variation of signals from the NAA communication transmitter (24.0kHz, 1MW) in Cutler, Maine, with particular emphasis on possible changes induced by seismic events occurring in South America. We have analysed the changes in timing of modal minima generated by the passage of the sunrise terminator over the Andes i.e. the 'VLF Terminator Time' (TT) method. The anomalous variations in timing throughout the year are of similar size and occurrence frequency to those previously reported i.e. 0.5-1 hour and 1-2 per month. However, we find that in these anomalous cases, the time of the sunrise modal minimum does not change significantly, but rather, the minimum becomes insufficiently deep to be detected, and the time of the next nearest minimum is logged. Our analysis indicates that the occurrence rate of successful earthquake predictions using the TT method can not be distinguished from that of chance. Additionally, the level of false earthquake prediction using the TT method is high.

J A Wild, T K Yeoman (Leicester), P E Eglitis (Uppsala /FMI), and H J Opgenoorth (SISP/FMI). Multi-instrument observations of omega-bands and their associated magnetic signatures.

High time resolution data from the CUTLASS Finland radar during the interval 19:00 UT 10/05/98 - 04:00 UT 11/05/98 are employed to characterise the ionospheric electric field due to an omega band at a resolution of 45 km over a latitudinal extent of 5 degrees. E-region observations from the STARE Norway VHF radar operating at a resolution of 15 km over a comparable region are also incorporated. These data are combined with ground magnetometer observations from several magnetometer networks. This allows the study of the ionospheric equivalent current signatures and height integrated ionspheric conductivities associated with omega bands as they propagate through the field of view of the CUTLASS and STARE radars. The high time resolution and multi-point nature of the observations leads to a refinement of the previous models of omega band structure.

I J Coleman, M Pinnock, and A S Rodger (BAS). Ionospheric footprint of the magnetopause merging line as predicted by the anti-parallel merging hypothesis.

The anti-parallel merging hypothesis holds that reconnection takes place on the dayside magnetopause where the solar and geomagnetic fields are oppositely directed. We have mapped the predicted merging regions to the ionosphere (using the Tsyganenko 96 magnetic field model). We will present the resulting shape, width and latitude of the ionospheric dayside merging region in both hemispheres, showing its seasonal and diurnal dependence as well as its conditioning by the IMF clock angle and other solar wind parameters. These predictions have implications for the conjugate electric fields in the northern and southern cusps, as measured by the SuperDARN HF radars for example.

J A Davies, T R Robinson, D M Wright, A J Stocker, R Dhillon (Leicester), F Honary (Lancaster) and M T Rietveld (EISCAT). EISCAT UHF observations during an F-region ionospheric modification experiment from the October 1998 UK Campaign.

Results from the UK campaign at Tromso on 6 October 1998 illustrate a significant effect on the incoherent scatter returns measured by the EISCAT UHF radar between about 260 and 300 km altitude during artificial modification of the F-region at a frequency of 4.05 MHz. The ion-line enhancement, observed within this height range, persisted for the entire duration of ten consecutive heater-on periods, each lasting 250 seconds and separated by an off period of 250 seconds. The altitude profile of backscattered ion-line power exhibits a double-peaked form, with the maximum power increased by a factor exceeding 100 compared to unmodified conditions; this increase in power is associated with enhancement in spectral power at the speed of both up- and down-going ion-acoustic waves. The effect is attributed to the transmitted radio frequency being near the third harmonic of the electron gyrofrequency - albeit tentatively due to the absence of data from support instrumentation. The double-peak in the power profile is suggested to result from the frequency of the heater pump wave being close to the F-region critical frequency, i.e. close to penetration.

S E Milan, M Lester, S W H Cowley (Leicester), M Brittnacher (Washington). Convection and auroral response to a southward turning of the IMF: possible POLAR UVI, CUTLASS and IMAGE signatures of flux transfer events.

The first spacecraft-borne imager observations of the optical manifestation of flux transfer events are presented. POLAR UVI poleward-moving auroral forms (PMAFs) are observed in conjunction with PMAFs in HF radar backscatter and PC5 pulsations in ground-based magnetometers. The combined radar and optical observations suggest that the PMAFs can be 2500 km in length. A general antisunward expansion of each PMAF is interpreted as an expansion of the reconnection X-line along the flank of the magnetopause.

T K Yeoman (Leicester), I R Mann (York), G Chisham, M P Freeman (BAS). Sunward convection and global magnetospheric oscillations driven by lobe reconnection during an extended period of northward IMF.

We present observations from an interval of 11 hours of almost continuously nothward IMF which suggest that lobe reconnection may have provided a powerful internal source for global magnetospheric oscillations. The interval is between around 2200 UT on the 19th, and 0900 UT on the 20th, March 1995. From 0400 UT, the SuperDARN Finland radar records good backscatter from high latitudes, and shows a well developed high latitude convection pattern consistent with clockwise flow driven by lobe reconnection under By positive conditions in the northern hemisphere. At around 0900 UT, the Finland radar again observes velocities consistent with continuing lobe stirring, however between the two radar observations the spectral widths suggest that the polar cap has contracted. The radar also detects intervals of convection consistent with four cell convection between these two times. Coincident observations from the IMAGE magnetometer array show the existence of two wave packets of discrete spectrum Pc5 waves, between 0300-0500 UT and 0600-0800 UT, having dominant period of around 512s and 430s respectively. Complex demodulation analysis reveals clear field line resonances (FLRs) in both cases, the first at 73 and the second at 75 degrees geomagnetic. The waves provide an excellent closed field line diagnostic which also show the polar cap to be strongly contracted at this time, the IMAGE estimates of the last closed field line being consistent with those inferred from the Finland radar spectral widths. Whether the northwards motion of the FLR is caused by contraction of the polar cap, or occurs due to local time changes in magnetic geometry is not clear. Unfortunately, the southern hemisphere radar at Halley has insufficient backscatter at polar cap latitudes to confirm whether or not the sunward convection which would be required to generate new closed flux and hence to contract the polar cap was occurring in the southern hemisphere during this interval. Interestingly, however, between 0300-0500 UT and at lower latitudes, the Halley radar does observe ULF wave activity coherent with and of the same period as the waves seen by IMAGE around 6 hours of local time away in the opposite hemisphere. The same wave packet was also seen near the equatorial plane on the dawn flank by Geotail. This shows the ULF waves to be truly global in nature. Since the solar wind speed is relatively slow, and the ram pressure relatively constant, we believe that the waves were not driven directly by the solar wind. Our observations suggest that lobe reconnection may have been responsible and that it may provide a powerful internal source for global magnetospheric oscillations.

D A Neudegg (Leicester), U Auster (Braunschweig), W Baumjohann (MPE), S W H Cowley (Leicester), J Bochner (MPAe), K H Fornacon (Braunschweig), E Georgescu (MPE / ISS), G Haerendel (MPE), and M Lester, S Milan (Leicester), B Nikutowski (MPAe), and T K Yeoman (Leicester). A survey of magnetopause FTEs and associated flow bursts in the polar ionosphere.

Using the Equator-S spacecraft and SuperDARN HF radars an extensive survey of bursty reconnection at the magnetopause and associated flows in the polar ionosphere has been conducted. Flux transfer event (FTE) signatures were identified in the Equator-S magnetometer data during periods of magnetopause contact in January and February 1998. Assuming the effects of the FTEs propagate to the polar ionosphere as geomagnetic field guided waves, appropriate field mappings to the fields of view of SuperDARN radars were performed. The radars observed discrete ionospheric flow channel events (FCEs) of the type previously presumed to be related to pulsed reconnection. FCEs were associated with ~80% of the FTEs. Exemplary case studies will be shown.

S N Walker, M A Balikhin (ACSE), B Lembege (CETP-UVSQ). The spatial sizes of electric and magnetic field gradients in a simulated shock.

The scales of the electromagnetic fields at the front of a supercritical quasiperpendicular bow shock have been studied using the results of a $2 1/2$ dimensional, fully electromagnetic relativistic particle code. The results imply that nonadiabatic motion of the electrons should be observed. Such nonadiabatic motion was observed by by considering the trajectories of individual electrons.

P J S Williams (Aberystwyth), C F del-Pozo (Lancaster), and E Nielsen (MPAe). The observed components of velocity measured by STARE inside and outside the instability cone as predicted by EISCAT for observations during the 1988 ERRIS campaign.

From EISCAT observations of the electric field and the electron and ion temperatures in the auroral E-region we can predict whether velocities observed by the two stations of STARE lie within or outside the 2-stream instability cone. Theory also predicts the way the measured component of velocity varies with direction and this is different within the cone, where it is largely determined by the ion-acoustic velocity, and outside the cone, where it is determined by ExB drift. The observations, when averaged to reduce stochastic noise, show good agreement with the theory.

N Achilleos and T Stallard (UCL). Jupiters's Auroral Electrojet: Modelling

We have made use of the dynamic component of JIM (Jovian Ionospheric Model) to make several models of Jupiter's auroral electrojet. We have produced each model by varying the electric potential drop across the width of the auroral oval between 1.0E4 V and 1.0E6 V. We show the resulting profiles of ion density and velocity as a function of altitude, as well as the neutral velocity profiles from the model thermosphere. The ions move at speeds of several hundred metres per second, with the neutral wind speeds being typically 20 per cent of this figure. We use the velocity profiles to distinguish the altitudes of transition between flows which are dominated by electrodynamic and by gas dynamic / Coriolis forces.

T Stallard, S Miller, N Achilleos, and D Rego (UCL). H3+ Spectroscopy of the Jovian aurora.

Using the CSHELL instrument on the NASA IRFT, it is possible to observe the infrared emission of H3+ in the Jovian ionosphere. This gives us information on the morphology of the aurora, and using spectra, it is also possible to detect and measure the associated auroral electrojet.

Gareth Lawrence (Birmingham). The Atmospheric X-Ray Observatory (AXO)

AXO is a non-ESA mission, with UK involvement currently being proposed for PPARC Bi-lateral funding. Launch is scheduled for late 2002 into a low-earth, circular, polar orbit. The primary scientific objectives are X-ray and optical observations of thunderstorm-related phenomena known as sprites, blue jets and elves; however, a secondary program to study the aurora and gravity waves is also included. UK funding towards - and hence UK involvement in - this mission may be influenced by the expected level of scientific interest within the greater UK STP community.

Thursday 15 April

Session 7: Solar-wind/ Magnetosphere

M Balikhin, S N Walker, and H Alleyne (ACSE), M Dunlop (IC). Problem of the identification of low frequency waves in the magnetosheath.

The dispersion relation of waves observed in the Earth's magnetosheath was determined using data from the AMPTE UKS and AMPTE IRM satellites. It was shown that the observed waves are propagating in the sun-ward direction but are convected towards the magnetopause by the plasma flow. As a result, the observed waves are quasi-standing in the flow. These waves have been previously identified as either slow or mirror modes depending upon which set of dimensionless transport ratios have been used. These waves may also be an experimental observation of the MIAOW waves identified in the hybrid simulations. The observed waves posses short wavelengths, which have the same order of magnitude as proton Larmor radius. Thus they may only be studied analytically within the framework of the kinetic approximation. These waves can be a result of boundary conditions at the magnetopause. The discrepancy with previous experimental findings based on dimensionless ratio (transport ratio) methods, which identified these waves as non-propagating, can be attributed to the basic assumption of the previous studies that large amplitude waves observed in magnetosheath should posses the same dimensionless characteristics as analytically derived for linear waves of infinitesimally small amplitudes.

S N Walker, M Balikhin (ACSE), M N Nozdrachev (IKI). Ramp nonstationarity and the generation of whistler waves upstream of a strong quasiperpendicular shock

Nonlinear processes which occur in the plasma turbulence upstream of the quasiperpendicular supercritical shock were studied by application of high order spectral analysis to the INTERBALL magnetic field data. The results obtained assume the observed turbulence is generated as a result of the decay of a nonlinear wave, originating in the processes of the nonlinear dynamical evolution of the shock ramp.

I Bates, M Balikhin, H Alleyne(ACSE), M Dunlop (IC). Experimental method for identification of dispersive three-wave coupling in space plasma.

The concept of the transfer function was applied to identify linear and nonlinear processes in the magnetosheath region, just downstream of the earth's quasiperpendicular bow shock. The results of the study show the existence of two unstable frequency regions. Analysis of AMPTE UKS and AMPTE IRM data suggests that these instabilities are related to the unstable ion distribution just after the shock front. As the satellites penetrate deeper into the magnetosheath the growth rates of the instability decrease. Further penetration leads to stabilisation of these instabilities.

D Coca, M Balikhin, S A Billings, O Boaghe (ACSE), and M Dunlop (IC). Nonlinear processes in low frequency turbulence upstream of the quasi-parallel part of the terrestrial bow shock: A NARMAX approach.

AMPTE UKS and AMPTE IRM magnetic field data have been used to study nonlinear processes in the vicinity of the terrestrial bow shock. The waves, observed initially at AMPTE UKS were later recorded by AMPTE IRM after being convected trough plasma. Assuming that the plasma between two satellites is a nonlinear system the NARMAX method was used to identify a nonlinear model that can predict accurately the wavefield at the downstream satellite AMPTE-IRM given the observations recorded upstream by AMPTE-UKS. By decomposing the model into its linear and nonlinear components it is shown that, in acordance with a previous study, the dynamics of SLAMS is mainly determined by linear plasma instability. The importance of the nonlinearity is however apparent in the transfer of the energy of the SLAMS to higher frequency whistler fluctuations. Nonlinear interactions are particularly important on the steeper part of the SLAMS. The nonlinear model was also used to compute higher order frequency transfer functions which describe the linear, quadratic and cubic interactions between the waves.

O M Boaghe, M Balikhin, S A Billings, H Alleyne (ACSE). NARMAX approach to the magnetosphere dynamics.

A data based nonlinear dynamics approach has been used to model the global dynamics of the terrestrial magnetosphere. The magntosphere was considered as a ""black box "" input-output nonlinear system. The product of the solar wind velocity and southward component of the magnetic field was considered as an input and measurements of the Dst index as an output. The nonlinear dynamical relation between these input and output sequences was derived using the NARMAX approach. The resulting polynomial model was used to forecast the evolution of the Dst index outside of the interval which was used for derivation of the model. It is shown that such a forecast is in good agreement with actual behaviour of Dst. The derived polynomial model was then used to calculate the nonlinear transfer function and an analogue model. The latter was used to identify types of physical nonlinearities which were significant in the evolution of Dst.

M Taylor, and P Cargill (IC). Plasma flows in the high altitude cusps.

Using a quasi-one dimensional form of the MHD equations, a model of supersonic solar wind plasma flow in the high altitude cusp region is presented. The cusp is approximated by a triangular well where flow is rarefied and accelerated into the cusp indentation by means of an expansion wave. The case of the closed magnetosphere is simulated by aligning the magnetic field perpendicular and parallel to the plasma flow along the magnetopause. An approximation to the open magnetosphere is carried out with various incliniations of the magnetic field with respect to the plasma flow. Study of the fast mode expansion in this case has unearthed singularities within the modified MHD equations, limiting the ability of the flow to undergo maximum expansion. Investigation of this behaviour has been carried out over a wide range of plasma betas.

R T Mist, and C J Owen (QMW). A simple model of plasma mantle particle distributions during periods of high-latitude reconnection.

Hirahara et al. (1997) have previously reported observations of double ion beams close to the magnetopause in the geomagnetic tail. These observations were interpreted as evidence for the occurence of high-latitude reconnection poleward of the cusp. We test this conclusion by presenting a simple, time-dependent model of the structure of the lobe magnetopause and plasma mantle during the switch from southward IMF/dayside reconnection to northward IMF/high-latitude reconnection. In particular, we address the motion of the plasma entering the magnetosphere from the magnetosheath, along field lines that may have been opened as a result of either subsolar or high-latitude reconnection, or both. We use the model to make predictions of the velocity distributions of these particles within the entry layer just inside the magnetopause. We compare these results to the observations made by Geotail close to the distant tail magnetopause, and show that the model successfully predicts the bulk velocities and densities of the observed plasma populations. Hence, on the basis of this model, the observed double ion beams do indeed appear consistent with the occurrence of high-latitude reconnection.

S M Topliss, A D Johnstone (MSSL), W K Peterson (Lockheed), A J Coates (MSSL), C A Kletzing (Iowa). Charge neutrality in the mid-altitude cusp.

The POLAR spacecraft crosses the earth's magnetospheric cusp region at mid-altitudes (5-8 Re) in the northern hemisphere. The TIMAS and HYDRA instruments provide the three dimensional velocity distributions of mass resolved ions and electrons at 1.5 to 3 s resolution. We have used data from these instruments to investigate 13 noon sector cusp crossings. Our investigation focuses on the physical processes responsible for maintaining charge neutrality in the region where solar wind electrons, but not solar wind ions, are encountered by the POLAR spacecraft.

Session 8: Spacecraft observations

A Fazakerley (MSSL), and M Hapgood (RAL). Looking forward to Cluster II.

Cluster II is due for launch in mid-2000, with operations commencing about 3 months later. This talk seeks to inform the wider MIST community about the new mission. Among other things, it will highlight changes from Cluster I (for those who were familiar with Cluster), discuss the expected nature of conjunctions with Svalbard and describe the data products which will be made generally available. We hope to encourage and inform those who may be interested in science involving Cluster, both in the space-based and ground-based communities.

A M Buckley, M P Gough (SSC). Simulations of wave-particle interaction measurements to be made by Cluster.

The study of Wave - Particle Interactions (WPIs) are important in space because on a microphysical level they provide a mechanism for both stochastic disordering processes in plasmas (e.g pitch angle scattering / particle diffusion/ wave dispersion / energy dissipation ) and a mechanism for collective ordering processes (e.g. beam formation /wave mode generation / particle acceleration/ energization ). As part of the Cluster II Digital Wave Processing experiment, direct measurements are made of modulations in the plasma electron population resulting from WPIs and short time particle bursts. These measurements will be performed simultaneously on each of the 4 Spacecraft comprising the Cluster II mission (the spacecraft separation will vary between a few hundred km in the cusp to several Re in the tail). The amplitude of modulation is measured as a function of wave frequency (detection range: 1.4 - 41 KHz, which encompasses fpe/fce frequencies), and electron energy (detection range:0.6 eV to 26 KeV) using the auto-correlation technique. The auto-correlation technique is fast and compact in on board computation and robust against noise. An outline of the Cluster II particle correlator is presented together with simulations of the response to particle modulation in the presence of Poisson noise. Studies are also made of scenarios for the types of WPIs likely to be encountered in various space plasma boundaries and regions and the associated scale lengths and velociy phase space structures. The Cluster Particle Correlator measurements exemplify the interplay between microscopic behaviour (i.e. kinetic WPI measurements) and macroscopic behaviour (i.e. spatially separated measurements) which may mediate cross-scale, self-consistent feedback processes involving WPIs.

R B Horne (BAS), and R M Thorne (UCLA). Electron pitch angle diffusion by ECH waves.

Electrostatic electron cyclotron harmonic (ECH) waves cause pitch angle scattering of 1-10 keV electrons and contribute to the diffuse aurora. It has also been suggested that they contribute to the formation of highly anisotropic pancake distributions observed near the magnetic equator outside the plasmapause. We present pitch angle diffusion calculations based on quasi-linear theory to evaluate this suggestion. We show that the diffusion rates for ECH waves generated at (n+0.5)fce by a loss cone distribution peak close to the loss cone but are very small for wider pitch angles. This suggests that diffusion caused by the growth of ECH waves cannot be responsible for the formation of pancakes. However, we show that if the wave spectrum is peaked at frequencies just below the harmonics of the electron gyrofrequency then pitch angle diffusion is very large for a range of pitch angles just outside the loss cone up to 80 degrees or so. These conditions occur after wave propagation in a nonhomogeneous medium. We argue that ECH waves can form highly anisotropic pancake distributions as the waves are damped, and not as they grow, after propagation in a non-homogeneous medium.

N P Meredith (MSSL), R B Horne (BAS), and A D Johnstone (MSSL). The temporal evolution of injected electron distributions in the inner magnetosphere.

The temporal evolution of injected electron distributions in the inner magnetosphere in the energy range 100 eV < E < 30 keV are examined using data from the CRRES satellite. Equatorial electron distributions and concomitant wave spectra on the night side of the Earth over a range of L-values, 3.8 < L < 6.8, are studied as a function of time since the end of the previous injection event as determined from the AE index. Pancake electron distributions are seen to develop from injected distributions that are nearly isotropic in velocity space. Outside L = 6.0 the pancakes develop on a time scale of approximately 5 hours. Strong ECH and whistler mode waves are associated with the injected distributions and exponential fits reveal wave amplitude decay time constants of 4.3 +/- 0.5 and 4.9 +/- 0.6 hours respectively. Inside L = 6.0 the situation is complicated by the proximity of the plasmapause and inward convection times that may increase significantly with decreasing L-value. Outside L = 6.0, the fitting analysis shows that in the marginally stable state the phase space density contours lie approximately along the curves for diffusion by whistler mode waves determined independently from the wave data, but inside L = 6.0 the pancakes tend to be more sharply peaked at 90 degrees to the field. The results suggest that whistler mode waves play a dominant role in shaping the final distribution outside L = 6.0, whereas inside L = 6.0 the ECH waves also play a significant role.

E A Lucek, M W Dunlop, A Balogh, P J Cargill (IC), W Baumjohann (MPE). Magnetic field signatures observed by Equator-S in the dawn-side magnetosheath.

The Equator-S satellite was well placed to observe waves in the dawn-side magnetosheath, relatively near the magnetopause. Mirror-like signatures, characterised by highly compressive fluctuations in |B|, were observed during 12 of the orbits when the satellite passed into the magnetosheath. Some intervals of mirror-like activity are long, up to 5 hours, and observations cover 0600 - 1040 LT. Analysis of these signatures shows that they occur under conditions when the field has a draped configuration, and that the fluctuations lie in a plane parallel to the observed magnetopause boundary. Typically, mirror-like activity is observed almost up to the magnetopause, which is suggestive of a poorly developed or absent plasma depletion layer. The plasma depletion layer is not expected to be well developed ahead of a high shear magnetopause boundary, but the magnetopause crossings associated with these mirror-like signatures occur under a range of shear conditions. It is suggested, therefore, that the apparent lack of a plasma depletion layer may be ascribed to the location of the satellite on the dawn flank. A more detailed analysis of the region between the magnetopause and the start of the mirror-like signatures is presented in order to better examine any signatures immediately adjacent to the magnetopause. In particular a search is made for electromagnetic ion cyclotron waves which are usually a characteristic of the plasma depletion layer.

G A Abel, A D Johnstone, and N P Meredith (MSSL). The acceleration of field aligned electrons observed by the LEPA instrument on CRRES.

Low energy (100ev - 10keV) field aligned electrons are often observed by the Low Energy Plasma Analyzer (LEPA) on the CRRES satellite. These electrons usually occur in bursts of less than 10 minutes duration and are bi-directional though not always equally. The counterstreaming electrons appear to be scattered out of the loss cone while gaining energy. The total increase in energy may be more than an order of magnitude while the pitch angle increases to about 60 degrees. The acceleration is seen mostly perpendicular to the field direction, with a smaller increase parallel to the field. Theoretical diffusion curves for the resonant interaction between electrons and whistler mode waves have been suggested by Summers et. al, 1998. These curves are distinctly different from the diffusion paths seen in the LEPA data. The diffusion paths suggested by Summers et. al, 1998, assume that the dispersion relation of the plasma is dominated by the cold plasma. We show that in the case of counter streaming beams this is not the case, and that the diffusion curves may well be different under this regime.

J Rae, M Lester (Leicester), J Scudder (Iowa), T Fritz (Boston), M Grande (RAL), C T Russell (UCLA). Statistical study of pulsed particle signatures in the cusp region as observed by the Polar satellite.

We present a multi-instrument statistical study of pulsed particle signatured associated with the cusp as observed by the Polar satellite. Particle fluxes in the 1-50 keV range are found to pulse on varying timescales, and are dominated by particles of solar wind origin. The location in MLT and MLAT of these signatured are investigated over a period of 2 months. The dependence of these pulsing particle signatures on IMF conditions is also investigated. These observations are discussed in terms of possible flux transfer events occurring at the magnetopause.

Session 9: Sun and Planets I

M Lockwood, R Stamper, M N Wild (RAL) and T G Clark (BGS). The change in the suns’ coronal magnetic field since 1868.

A homogeneous sequence of data on geomagnetic activity extends back to 1868 (covering 12 sunspot cycles) and is characterised by a rise in average values since the turn of the century. Near-Earth interplanetary space has been routinely monitored since 1964, giving data from the last 3 sunspot cycles. We show that the largest factor contributing to the rise in geomagnetic activity since 1964 is an upward drift in the magnitude of the IMF. Out-of-ecliptic observations by the Ulysses satellite have shown that the latitudinal gradients in the IMF are small, from which we deduce that the total open magnetic flux of the sun has risen by a factor of 1.4 since 1964. We derive and use three highly significant correlations to extrapolate back to 1868: we find that the solar coronal source flux has increased by a factor of 2.3 since 1901.

G R Lawrence (Birmingham). LASCO observations of coronal mass ejections.

The Large Angle Spectrometric COronagraph, aboard the SOlar and Heliospheric Observatory, has been imaging the solar corona (almost) continuously since 1996. We discuss some of the insights into the physics of coronal mass ejections provided by this unique instrument. Complimentary results from other instruments aboard SOHO will also be discussed.

R A Fallows, A R Breen, P J Moran, C A Varley and P J S Williams (Aberystwyth). Factors controlling the level and scale of interplanetary scintillation.

The scintillation index of a particular radio source is a straightforward calculation made using obersvations of interplanetary scintillation. Previous observations have been made using large radio telescopes capable of observing a large number of sources, but with little or no knowledge of physial parameters along the line of sight. In contrast, EISCAT observations are used to derive a number of solar wind parameters. In this paper, the scintillation index of a number of sources is compared to the level of scintillation due to fast and slow streams along the line of sight, and distance from the Sun. A comparison with scintillation due to co-rotating interaction regions will also be investigated.

D Clack, and R J Forsyth (IC). The orientation of CIRs inferred from Ulysses magnetic field data.

The three-dimensional nature of the interface between slow and fast streams in the solar wind leads to an interaction region in interplanetary space that is inclined with respect to the solar equator. Ulysses measurements of the magnetic field within CIRs has revealed evidence of the field vectors being strongly confined to a plane for periods ~1-2 days. Using a least squares planar fit and minimum variance analysis of these planar structures we have attempted to determine a systematic pattern in the overall orientation of CIRs.

R Wilson, M Dougherty (IC), and M Kivelson (UCLA). Evidence for low frequency waves in Jupiter’s middle magnetosphere.

Previous work on Jupiter's middle magnetosphere from Voyager and Ulysses data suggested the existence of waves of approximately 80, 40 and 15 minute periods. Analysis of Galileo's data reveal that 10 to 20 minute waves are found in abundance in the nightside middle magnetosphere, along with indications of 80 and 40 minute waves. This work carries out a power spectra analysis of a number of the Galileo orbits, highlighting regions of intense activity in ultra low frequency waves.

P Petkaki, and M Dougherty (IC). Ion cyclotron waves in the Jovian magnetosphere.

Magnetometer data from the Ulysses Jupiter flyby is examined, and in particular middle magnetosphere observations near the magnetodisk both during the inbound and the outbound trajectory. Ion cyclotron waves are searched for in the heavy ion gyrofrequency regime (SO2, SO+, S+, O+ and S++). Power spectral peaks in the ion cyclotron frequency range in the Ulysses magnetometer data have been found in the past. Here we thoroughly examine the high resolution 1 sec data, with ion cyclotron waves signatures being observed on several occasions both close to the magnetic equator and at some distance from it. Rippling and warping of the magnetodisk, as observed by Ulysses, could be the cause of such ion cyclotron signatures arising some distance from the magnetic equator. Lower mass ions are observed further away from the planet and the heaviest mass ion signatures only appear close to the Io torus. Polarization analysis of the observations are also presented and theoretical implications of the wave signatures discussed.

Session 10: Sun and Planets II

F W Taylor (Oxford ). Mars Climate Surveyor: Progress and plans.

Mars Climate Surveyor was launched from Cape Canaveral on 11th December 98 and will arrive at Mars on 25th September 1999. The payload consists of atmospheric sounding instrumentation developed and built at Oxford, at JPL, Pasadena, and in Russia. The paper will describe the status of the mission and its scientific objectives.

B Peters, A D Aylward (UCL). A Martian global TGCM 2: Gravity waves and solar wind.

A self-consistent global three dimensional model of the upper Martian thermosphere has been written to study the dynamics, temperature, composition and transport of the neutral and plasma gases. It deals with three major species, CO2, N2, O and four minor species solving versions of the time dependant momentum, energy and continuity equations. A comprehensive radiation scheme is included, dealing with EUV solar heating and radiative transport between the atmospheric layers. Here, the interaction of the upper atmosphere with the solar wind has been examined, as has the effects of gravity waves on the temperature and wind structures.

H Rishbeth (Soton / Boston), R V Yelle (Boston) and M Mendillo (Boston). Dynamics of Titan’s thermosphere.

An analysis of the equation of motion for Titan's thermosphere suggests that the wind system is mainly controlled by the nonlinear "curvature" terms, unlike the Earth's thermospheric wind which are controlled by ion-drag and coriolis force. Assuming a day night temperature difference of 25K, we find that Titan's thermospheric winds are typically 100 m s-1, as compared to Earth's thermospheric winds of order 50 m s-1. We speculate on the electrodynamics of Titan's thermosphere and the tides due to Saturn

I C F Mueller-Wodarg, A D Aylward (UCL), R V Yelle, and M Mendillo (Boston). The thermosphere of Titan simulated by a global 3-dimensional time-dependent model.

Titan, the largest Moon of Saturn and second-largest satellite in our solar system, has an atmosphere similar in many respects to that on Earth. In order to understand better similarities and differences in the atmospheric dynamics, energetics and composition on Titan and Earth, we have adapted the terrestrial Coupled Thermosphere-Ionosphere Model (CTIM) into the first global 3-dimensional time-dependent general circulation model of Titan's thermosphere. We present results from simulations for quiet and active solar conditions, comparing the factors controlling dynamics and energetics in Titan's thermosphere to those found on Earth.

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Affiliation abbreviations:


Department of Physics, University of Wale, Aberystwyth


Automatic Control and Systems Engineering, University of Sheffield

Aerospace Corp.

The Aerospace Corporation, USA


British Antarctic Survey


British Geological Survey


University of Birmingham


Boston University, USA


Technische Universitat von Braunschweig, Braunschweig, Germany


Centre d’etude des Environnements Terrestre et Planetaires, Saint-Maur, Cedex, France


Centre d’etude des Environnements Terrestre et Planetaires, Velizy, France


Centre National de le Recherche Scientifique, France


University of Cranfield, RMCS Shrivenham


Communication Research Laboratory, Hiraiso, Japan


University of Durham


EISCAT Scientific Association


University of Fairbanks


Finnish Meteorogical Institute, Finland

Hovemere Ltd

Hovemere Ltd. Keston, Bromley, Kent


Imperial College, London


Russian Space Research Institute, Moscow


University of Iowa, USA


Istitute of Space and Astronautical Science, Japan


ISS, Bucharest, Romania

John Hopkins

Applied Physics Laboratory, The John Hopkins University


Communication Research Centre, University of Lancaster


Department of Physics and Astronomy, University of Leicester


Lockheed Martin Palo Alto Res. Lab.


Laboratoire de physique et chimie de l'environnement


Laboratoire de sondages electromagnetiques de l'enviroment terrestre


Max-Planck Institute Fur Aeronomie, Katlenburg-Lindau, Germany


Max-Planck Institut for Extraterrestrische Physik, Garching, Germany


Mullard Space Science Laboratory


University of Newcastle, Australia


Atmos. Ocean. and Planetary Physics, Oxford University


Astronomy Unit, Queen Mary and Westfield College, London


Rutherford Applenton Laboratory


Upper Atmosphere Group, Dept. of Applied Maths., University of Sheffield


Swedish Institute of Space Physics, Sweden


University of Southampton


Space Science Centre, University of Sussex

St. Andrews

University of St. Andrews


Solar Terrestrial Environment Lab, University of Nagoya, Japan


Atmospheric Physics Lab, University College London


University of California, Los Angeles, USA


University of Central Lancashire


University Courses in Svalbard, Longyearbyen, Norway


Uppsala University, Sweden


University of Warwick


University of Washington, USA


Magnetospheric Physics Group, Department of Physics, University of York

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