MIST meeting, London, 26 November 1999

First session

I Krauklis (Department of Space and Climate Physics, Mullard Space Science Laboratory, UCL), O Vaisberg (Marshall Space Flight Centre, Huntsville Alabama) and B Peterson (Lockheed-Martin Space Sciences Laboratory, Palo Alto, California). Preliminary observations of magnetosheath plasma in the mid-altitude cusp by the Polar/TIMAS and Interball Tail/SCA1 experiments during an interval of strongly northward interplanetary magnetic field

During an interval of high solar wind dynamic pressure and strongly northward IMF. The SCA1 plasma experiment on board the Interball Tail spacecraft observed lobe reconnection. At a similar time the TIMAS experiment on board the Polar spacecraft moved out the magnetosphere into a region of stagnant magnetosheath plasma with a pitch angle distribution peaked at 90 degrees. Electron data (HYDRA instrument, PI J. Scudder) was consistent with Polar moving into the cusp region at this time. Coincident with a northward turning of the Z component of the magnetic field measured at Polar (MFI instrument PI C.T. Russell) the magnetosheath plasma started moving in an anti-sunward direction. The rotation of the magnetic field is consistent with Polar crossing the magnetopause into the magnetosheath.

J Rae and M Lester (University of Leicester), J Scudder (University of Iowa, USA), M Grande (Rutherford Appleton Laboratory, Oxon), T Fritz (Boston University, USA) and C T Russell (University of California, USA). Pulsed cusp particles and their ionospheric flow signatures

Previous studies have indicated that ions in the energy range 1-20 keV/Q associated with the cusp observed by Polar pulse on timescales of 2 to 10 minutes. We present a multi-instrument study of these pulsed particle signatures (PPS) and their associated ionospheric flow signatures measured by the CUTLASS HF radars. Pulsed Ionospheric Flows (PIFs) are observed in the CUTLASS field-of-view concurrently with the PPS. Previous observations of PIFs have been identified as the ionospheric signatures of Flux Transfer Events (Provan et al., 1998, Neudegg et al., 1999) at the dayside magnetopause. We discuss the relationship between the particle and flow signatures in terms of a common generation mechanism.

T J Stubbs, P Cargill, (Space and Atmospheric Physics, Imperial College, London SW7 2BZ), M Grande, B Kellett, M Lockwood and C Perry (Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, U.K), Observations of the Northern Polar Cusp with the Polar Spacecraft

This study analyses an extended cusp region on 14th August 1996, where relatively high fluxes of solar wind particles are seen over a period of ~4 hours. This coincided with weak IMF BZ, with varying orientation. Solar wind particles are identified as having high charge state and low energy (1-10 keV/q). We have concentrated on observations of O>2+ and He2+. Using CAMMICE MICS and MFE data from the POLAR spacecraft, together with MFI and SWE data from the WIND spacecraft, it has been shown that the extended cusp regions do not correlate with extended (greater than 3 hours) periods of either northward, anti-sunward, eastward or westward oriented IMF. This suggests that these events are not connected with tail lobe reconnection, as suggested by Grande et al., (1997). The magnetic field measured by POLAR has been compared with the Tsyganenko 1989 (T89) magnetospheric model. The T89 model shows the event occurring on closed field lines in the tail lobe, where solar wind particles are not expected to be present. This disparity is caused by the suppression of open field lines in the T89 model.

M Taylor and P Cargill (Space & Atmospheric Physics, Blackett Laboratory, Imperial College, London, SW7 2BZ). A model of magnetic fluctuations in the cusp

The high altitude cusp is gradually being revealed as a region with magnetic field fluctuations on all scales. We present a simple WKB-based model detailing the interaction of low frequency waves with a cusp-like field geometry. The waves are generated at the magnetopause, and are assumed to move into a region of changing field and plasma. We find the amplitudes of the velocity and magnetic field fluctuations decrease as they evolve through our idealised cusp geometry. Such behaviour implies that, for our model, fluctuations originating from magnetosheath generated disturbances cannot be simply convected into the cusp by a background flow and that fluctuations found within the cusp have a more local origin. We propose to further this model by carrying out a cause and effect type analysis, including source/sink terms within the cusp itself and investigate possible magnetopause candidates for such phenomena.

S Oughton (Department of Mathematics, UCL, UK), W H Matthaeus, G P Zank, D J Mullan and P Dmitruk (Bartol Research Institute, University of Delaware, Newark, DE, USA). Alfven Waves + 2D Turbulence = Coronal Heating?

Numerous attempts have been made to explain why the solar corona is two orders of magnitude hotter than the atmosphere below it. It is generally believed that the coronal magnetic field plays an important role in the heating process, but as yet there are no completely successful models of the process. Here we discuss a highly promising coronal heating model based on driving of quasi-two-dimensional MHD turbulence by LOW-frequency Alfven waves (generated close to the photosphere). The physics behind the model will be presented, along with results from simulations.

W P Wilkinson (School of Computing and Mathematical Sciences, University of Brighton, Lewes Road, Brighton BN2 4GJ, UK), A R Breen, P J Moran, C A Varley and P J S Williams (Department of Physics, University of Wales, Aberystwyth, SY23 3BZ, UK). The Rankine-Hugoniot relations and co-rotating interaction regions in the solar wind

The Rankine-Hugoniot relations specify the conditions that must be satisfied by the physical parameters on both sides of magnetohydrodynamic (MHD) discontinuities. In this paper, we use the Rankine-Hugoniot relations to investigate how the amount of rotation of the magnetic field by an MHD fast shock depends on the Mach number and plasma beta of the upstream flow. We show that, in the high Mach number limit, the maximum rotation of the field at the shock tends to a limiting value of 36.7 degrees. For finite plasma beta, this limiting value is also the highest possible. We discuss the implications of our findings for the standard picture of co-rotating interaction regions in the solar wind.

M Y Gulamali and P Cargill (Space And Atmospheric Physics Group, Imperial College Of Science,Technology And Medicine). A Multiresolution Analysis Of The Solar Wind Magnetic Field Using The Wavelet Transform

We investigate a set of corotating interaction regions observed by the Ulysses spacecraft between July 1996 and June 1997. We use the Haar wavelet transform to perform a multiresolution decomposition of the measured magnetic field. This analysis allows us to investigate fluctuations in the solar wind at different time scales. We find that at scales of ~10 hrs large structural features of the solar wind can easily be discerned. On shorter time scales (~10 min), we find that the fluctuations are characteristic of intermittent MHD turbulence.

S Dalla and A Balogh (The Blackett Laboratory, Imperial College, London). Recurrence in MeV proton fluxes and anisotropies at 5 AU from the Sun

We report the observation of a recurrent pattern in proton fluxes and anisotropies at 5.2 AU from the Sun, made by the Anisotropy Telescopes on board the Ulysses spacecraft between April 1998 and May 1999, during the rising phase of solar cycle 23. The time delay between recurrent features of the pattern is not constant and increases from 122 to 155 days over the three recurrences observed. We discuss a possible connection between these observations and the well documented existence of a 154-day periodicity in the rate of occurrence of solar flares.

M Hopcroft and S C Chapman (Space and Astrophysics Group, Physics Department, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL). 2D Hybrid simulations of the solar wind interaction with a small scale comet

The results of an investigation into the interaction of the super magnetosonic solar wind flow around a small plasma source are presented. The typical pick-up gyroradii of these source ions are of the same scale as the bow shock formed. We wish to identify energy momentum transfer mechanisms that produce the structure observed. Investigations were conducted by means of 2D hybrid numerical simulations which represent spatial co-ordinates in 2D whilst resolving 3D fields, velocities and bulk plasma vector variables. The scheme represents both solar wind protons and source ions with meta-particles advanced by the Lorentz force law, and electrons via fluid equations with no inertial term. Quasineutrality and constant pressure are imposed. The source region consists of an inner dense core and an outer halo, to represent a thermal component and a high energy tail of the sputtered population respectively. We identify a change in bow shock structure between low and high mach number flows. The increased structuring at high flows coincides with an apparent deflected velocity layer behind the shock.

R Bamford, C J Davis, L Cander and L Farr (Rutherford Appleton Laboratory,Chilton, Didcot, OX11 0QX). First results of measurements of the ionosphere during the 1999 Total Solar Eclipse

Reported here are some of the results from a number of the ionospheric instruments making measurements during the August 11th 1999 Total solar eclipse. These include :
-The changes of between 10-30 dB in the signal strengths of MW radio signals from commercial broadcast stations (Figure 1) and radio amateurs using SW.
-Vertical and oblique ionosondes which show changes in electron densities of 20-35% for the different layers of the ionosphere both under the path of totality and in the partial shadow.
-A drop of 18% in the Total Electron Content from a dual frequency GPS receiver located in the 97% partial eclipse..

Radio Luxemburg (1440 kHz) recorded at Birmingham
Figure 1. A plot of the variation in the radio signal of the 1440kHz carrier emanating from Radio Luxembourg and received in the UK during the morning of the total solar eclipse.

E M Clarke (Sheffield Hallam University), C J Davis, M Lockwood, S A Bell and J A Smith (Rutherford Appleton Laboratory). Ionospheric Measurements of Relative Coronal Brightness during Total Solar Eclipses

During the August eclipse this year in Helston, Cornwall, ionosonde measurements were made. Using this data a method has been established which estimates the percentage of unobscured ionising solar radiation at any time during a solar eclipse. An initial comparison of the eclipse on August 11, 1999 and July 9, 1945 has shown a significant difference in ionising radiation, implying structural change in the corona. Further work is being carried out on available historical data in order to determine the relative effects of solar cycle, apparent lunar diameter, and the recently discovered long-term changes in the coronal magnetic field.

T B Jones, T K Yeoman, T D Reid, D M Wright and P J Chapman (Leicester). Did the Total Eclipse of 11th August 1999 produce Atmospheric Gravity Waves?

During the Eclipse period, the Leicester group deployed a number of experiments to search for any wave activity produced by the transit of the dark region over the ionosphere. In particular a short path four station Doppler experiment was deployed in the UK and the frequency changes in a number signals received over longer propagation paths were also measured. A quasi vertical sounder was also in operation at 5 min intervals for several days before and after the 11th. Preliminary analysis of the data from all the instruments indicates that the eclipse day was characterised by an unusually high level of TID activity, whereas the control days before and after the 11th August indicate only few such disturbances. The direction of propagation of the TIDs suggests that the path of totality might be a source region for the atmospheric gravity waves producing these ionospheric signatures.

Second session

N J Mitchell, P J S Williams (Department of Physics, University of Wales Aberystwyth), T R Robinson (Department of Physics and Astronomy, University of Leicester), S Kirkwood (Swedish Institute of Space Physics, Kiruna), D Pancheva and H R Middleton (Department of Physics, University of Wales Aberystwyth). A new VHF radar at Esrange to study mesosphere/lower-thermosphere region coupling and dynamics

A new all-sky meteor-scatter radar was deployed at Esrange (67.9N, 21.1E) in August 1999. The radar is able to monitor the dynamics of the atmosphere at mesosphere/lower-thermosphere heights on a continuous basis. Crucially, the radar represents a significant advance over earlier systems in that it uses an interferometric technique to determine echo heights. This allows investigation of the vertical structure of the motion field with a height resolution of about 2 km and a time resolution of about one hour. The full capabilities of this instrument are described and some initial observations presented.

A M Smith and L Kersley (Aberystwyth Radio and Space Physics Group). Possible polar-patch formation; a multi-instrument case study

Measurements from the ESR, EISCAT and CUTLASS radars and DMSP satellites detectors are used to study the progress of enhanced ionisation density structures in the polar region. It is proposed that the observations show the production of a polar patch with the mechanism of formation possibly being related changes in IMF configuration

A Canals, A Breen, P Moran, and R Fallows (University of Wales. Aberystwyth). Bulk flow speed and Alfvén wave flux in the fast solar wind

The mechanism which causes the acceleration of the fast solar wind is a question which scientists have long been seeking the answer to. Two acceleration models, both which propose that Alfvén waves are the source of the 'push', aim to solve this outstanding problem. One model, proposed by Ofman and Davila, looks at, how the dissipation of low frequency Alfvén waves causes the acceleration. This model predicts a measurable signature in IPS data in the form of a decreasing random velocity perpendicular to the direction of flow and an increasing bulk flow speed, for distances <25 solar R. In this paper, we analyse data from the extensive EISCAT IPS database for predominately fast streams between 1993-1999. We concentrate on a careful and detailed analysis of values for the perpendicular random velocity for distances of up to 50 solar radii.

R Wilson and M K Dougherty (Imperial College, London). Evidence of Low Frequency Waves in Jupiter's Middle Magnetosphere

Previous analysis of Voyager and Ulysses fly-by data indicated ULF waves in Jupiter's magnetosphere. With Galileo having completed over 20 orbits, statistical results can be calculated. In this talk we investigate the presence of 10 to 20 minute waves whose existence were hinted at from previous missions and are now believed to be a global resonance of the magnetosphere.

S A Espinosa and M K Dougherty (Space and Atmospheric Physics, Imperial College, London SW7 2BZ, U.K). Periodic Perturbations in Saturn's Magnetic Field

Analysis of all the existing magnetic field data from Saturn's magnetosphere is carried out. This data arises from the three spacecraft encounters with Saturn (Pioneer 11, Voyager 1 and 2, in 1979, 1980 and 1981 respectively). In order to carry out a direct comparison between the three data sets they are all expressed in the same coordinate system; that of planetocentric spherical polar coordinates for the magnetic field and the SLS (right-hand, 1980.0) system for the trajectory. In the cases of Pioneer 11 (whole encounter) and Voyager 2 (inbound) a bipolar perturbation is observed (with a period close to the planetary rotation period) in the radial and/or azimuthal components of the field. Existing models of Saturn's magnetic field imply a negligible tilt between the rotation and dipole axes and therefore such models cannot explain this periodic perturbation. Possible causes for this feature are discussed.

R E Lowe and D Burgess (Astronomy Unit, Queen Mary and Westfield College, Mile End Road, London E1 4NS). Shock structure and its effect on electron acceleration in Quasi-Perpendicular shocks

Highly energetic electrons near collisionless shocks are widely observed, but the exact electron acceleration mechanism is not completely understood. Simulations of quasi-perpendicular collisionless shocks show ripples in the density and magnetic field moving along the shock ramp. Using a two dimensional hybrid simulation and a test particle code, we examine these ripples and their effect on electron acceleration.

S E Pryse (Aberystwyth Radio and Space Physics Group). Multi-instrument study of magnetopause reconnection footprints in the summertime ionosphere

Results are presented from a multi-instrument study of the response of the summertime ionosphere to an increasingly southward IMF. The progressive equatorward motion of the plasma signature is deduced from observations by several instruments, including the radio tomography system, ESR and EISCAT radars, and DMSP particle detectors.

K A McWilliams and T K Yeoman (Radio & Space Plasma Physics, University of Leicester, Leicester LE1 7RH). Two-dimensional electric field measurements in the ionospheric footprint of a flux transfer event

Line-of-sight Doppler velocities from the CUTLASS HF radar pair have been been combined to produce the first two-dimensional vector measurements of the convection pattern in the ionospheric footprint of a flux transfer event. The motion of the footprint of the newly reconnected flux tube is compared with the ionospheric convection velocity. Very stable and moderate IMF conditions, along with the preceding prolonged period of northward IMF allow us to study in detail the spatial and temporal evolution of the ionospheric response to magnetic reconnection.

N V Nastasyina-Beloff (Space Science Centre, School of Engineering, University of Sussex, Brighton, UK) and P F Denisenko (Institute of Physics, Rostov State University, Rostov-on-Don, Russia). The Resolving Power of the Ionospheric Radio Sounding Methods

Any radio physic experiments aimed at diagnostics of ionospheric parameters contain the inherent random errors of measurements. It happens due to fluctuations of signal in radio equipment and in propagation media. Therefore under solving inverse problems of the ionospheric radio soundings the problem appears to estimate the confidential intervals of determining plasma characteristics from known statistical properties of experimental errors. Generally speaking, the determination of root-mean-squares errors ?(x) occurs more difficult problem than obtaining strictly parameter x. But under some conditions which take place in experiments of topside ionosphere sounding (and in some cases under sounding from Earth's surface) it is possible to find the analytical expressions. It allows to relate the errors of measurements and indeterminacy of diagnosing parameters without any supposes about any height dependencies. In present paper three problems are described: 1) vertical Doppler diagnostics; 2) real heights determination under vertical satellite sounding; 3) diagnostics of effective electron collision frequency by method A1. In all described cases for determination of ionospheric parameters it is necessary to inverse the Volterra integral equations of first kind [1]. This inversion leads finally to linear integral relation of dispersion of searched values with correlation function of measurement errors in radio signal characteristics. The computer simulation has shown that the root-mean-squares errors of determining values depend on signal polarization, frequency range, geomagnetic latitude of observation point and on radius of frequency correlation. Under using waves of ordinary polarization for experimental measurements the errors of diagnostics of searched ionospheric parameters (vertical velocity of plasma motions, real heights or electron collision frequency) increase from magnetic pole to equator. The applying extraordinary polarizing waves for diagnostics gives opposite dependence, i.e. errors are minimal on magnetic equator and maximal in polar ionosphere. On the middle latitudes the root-mean-squares errors of real heights make about 25% from the errors of group paths measurements. Under accuracy of measurements of radio wave absorption 1dB the errors of effective electron collision frequency reach . Under errors of Doppler frequency shift determination in 0,01 Hz the errors of determination of vertical velocity of plasma motion make about 2 m/s. Obtained estimators allow carry out the optimal choice of polarization of sounding signals for getting minimal confidential intervals for diagnosing parameters.
[1] Denisenko P.F., Kuznetsov E.V., Nastasyina N.V., Vodolazkin V.I. Errors in parameters deduced from ionospheric soundings. Data World Center A for Solar-Terr. Phys. Report UAG-105, Boulder, USA, March 1998, PP. 76-81.

Third session

D M Willis (Space and Astrophysics Group, Department of Physics, University of Warwick, Coventry CV4 7AL, UK) and F R Stephenson (Department of Physics, University of Durham, Durham DH1 3LE, UK). Solar and auroral evidence for an intense recurrent geomagnetic storm during December in AD 1128

The earliest known drawing of sunspots appears in The Chronicle of John of Worcester, which was compiled in the first half of the twelfth century. In this medieval chronicle, the Latin text describing the sunspots is accompanied by a colourful drawing, albeit idealized, which shows the apparent positions and sizes of two sunspots on the solar disk. The date of this observation of sunspots from Worcester in England is firmly established as AD 1128 December 8. Assuming that the drawing was prepared fairly carefully, the angular diameters of the two sunspots were approximately 3 arcmin and 2 arcmin in the northern and southern hemispheres, respectively. Similarly, the heliographic latitudes of both sunspots were within the approximate range 25°-35°. About five days after this observation of sunspots on the solar disk, on the night of AD 1128 December 13, a red auroral display was observed from Songdo (modern name Kaesong) in Korea. This auroral observation was recorded in the Koryo-sa, the official Korean chronicle of the period. In addition, between the middle of AD 1127 and the middle of AD 1129, five Chinese and five Korean auroral observations were recorded in various East-Asian histories. These ten oriental auroral records correspond to six distinct auroral events, which provide evidence for recurrent, though intermittent, auroral activity on a timescale almost exactly equal to the synodic solar-rotation period (approximately 27 days). The six distinct auroral events were apparently associated with two series of recurrent geomagnetic storms, both of which were sufficiently intense to produce mid-latitude auroral displays in East Asia. These ancient solar and auroral observations are interpreted in terms of modern understanding of solar-terrestrial physics. Contemporary ground-based and satellite measurements during the last few decades have indicated that recurrent geomagnetic storms are usually a feature of the declining phase of the solar cycle. Moreover, the intensity of such recurrent geomagnetic storms has been classified as moderate rather than intense. The recurrent geomagnetic storms occurring during the interval AD 1127-1129 must have been intense, however, to produce mid-latitude auroral displays over China and Korea. This last statement remains true even after proper allowance is made for the fact that the north geomagnetic pole was situated at East-Asian longitudes during the twelfth century. Therefore, either the two series of recurrent geomagnetic storms occurred near a medieval sunspot maximum or, if they occurred near a medieval sunspot minimum, the overall level of solar activity must have been significantly higher during the twelfth century than it has been during the past four centuries.

W J Wykes, S C Chapman and G Rowlands (Space and Astrophysics Group, University of Warwick, UK). Enhanced Phase Space Diffusion due to Chaos in Relativistic Electron-Whistler Mode Wave Particle Interactions

The chaotic interaction between electrons and whistler mode waves has been shown to provide a mechanism for enhanced diffusion in phase space. Pitch angle diffusion is relevant for the scattering of electrons into the loss cones, thus providing a source for auroral precipitating electrons. A single whistler mode wave propagating parallel to the background magnetic field has resonance with the electrons but the process is not stochastic. The presence of a second, oppositely directed whistler wave has been shown previously to introduce stochasticity into the system, thus enhancing diffusion in phase space. Here we generalise previous work to include relativistic effects. The full relativistic Lorentz equations are solved numerically to permit application to a more extensive parameter space. We consider parameters scaled to intrinsic planetary magnetospheres, for electron populations with 'pancake' velocity distributions i.e. large anisotropies in velocity space. We show that the diffusion is rapid, occurring on timescales of the order of tens of electron gyroperiods, and is strongly sensitive to the wave amplitude, the wave frequency and the perpendicular velocity.

T K Yeoman (Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, U.K), R V Lewis (Ipswich School, Henley Road, Ipswich, Suffolk, IP1 3SG, UK), H Khan (Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, U.K) and J M Ruohoniemi (Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20707, U.S.A). Interhemispheric observations of nightside ionospheric electric fields in response to IMF Bz and By changes and substorm pseudobreakup

HF radar data during equinoctial, small IMF By conditions have enabled the ionospheric convection during the substorm growth phase and substorm pseudobreakup to be studied in both hemispheres. This has revealed both conjugate and non-conjugate convection behaviour during the substorm growth phase and after the pseudobreakup onset. The nightside convection pattern is found to respond promptly to the southward turning of the interplanetary magnetic field (IMF) which impacts on the dusk flank of the magnetosphere due to an inclined phase front in the IMF in the case study presented. The timescale for the response to changes in the IMF By component is found to be a little longer, and the full impact of the IMF By is not apparent in the nightside convection until after substorm pseudobreakup has occurred. The pseudobreakup itself is found to result in a transitory suppression in the ionospheric electric field in both hemispheres. This flow suppression is very similar to that observed in HF radar observations of full substorm onset, with the exception of a lack of subsequent poleward expansion.

H Khan and S W H Cowley (Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK). Effect of the IMF By Component on the Ionospheric Flow Overhead at EISCAT: Observations and Theory

We have analysed a database of ~300 h of tristatic ionospheric velocity measurements obtained overhead at Tromsø (66.3° magnetic latitude) by the EISCAT UHF radar system, for the presence of flow effects associated with the y-component of the IMF. We find that for IMF Bz negative, significant perturbation flows are observed in the dusk and nightside sector, between ~1600 and ~0200 MLT, which are directed eastward for IMF By positive and westward for IMF By negative, and are of magnitude ~20-40 m s-1 per nT of IMF By. At other local times the perturbation flows are smaller and more scattered. Results for IMF Bz positive are overall more scattered, but again indicate the presence of eastward perturbation flows near midnight for IMF By positive, between ~2100 and ~0200 MLT, which are of amplitude ~20 m s-1 nT-1. We have investigated whether these IMF By-dependent flows can be accounted for quantitatively by a theoretical model in which the equatorial flow in the inner magnetosphere is independent of IMF By, but where distortions of the magnetospheric magnetic field associated with a "penetrating" component of the IMF By field changes the mapping of the field to the ionosphere, and hence the ionospheric flow. We find that the principal flow perturbation produced by this effect is an east-west flow whose sense is determined by the north-south component of the unperturbed flow. Perturbations in the north-south flow are typically smaller by more than an order of magnitude, and generally negligible in terms of observations. Using equatorial flows which are determined from EISCAT data for zero IMF By, with corotation added, the theory predicts the presence of zonal perturbation flows which are generally directed eastward in the northern hemisphere for IMF By positive and westward for IMF By negative at all local times. However, although the day and night effects are therefore similar in principle, the model perturbation flows are much larger on the nightside than on the dayside, as observed, due to the day-night asymmetry in the unperturbed magnetospheric magnetic field. Overall, the model results are found to account well for the principal zonal flow effects observed, in terms of the direction and amplitude of the flow perturbations, and the local time of their occurrence. However, the level of agreement is much better for the more ordered IMF Bz negative results than for the more scattered results for IMF Bz positive.

M H Denton, G J Bailey (University of Sheffield), R A Heelis and M Hairston (University of Texas at Dallas). DMSP Observations - Electron temperature, ion temperature, density and concentrations. Results from 0900LT Jan-Jun 1991

Observations of electron temperature, ion temperature, density and concentrations from the DMSP F10 satellite at 0900LT have been analyzed. Averaged profiles have been produced to examine the longitudinal and seasonal effects on the above parameters. Observed features include a region of elevated electron temperature in the northern (summer) hemisphere, sharply separated from 'normal' electron temperature in the southern hemisphere. Such regions only occur during or shortly after significant stormtime activity. Reasons for such features are discussed. In addition, modelling studies have been carried out using the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The model confirms the character of Te and Ti during geomagnetically quiet periods. The rapid changes during stormtime periods are harder to model, and require a better understanding of the low-latitude effects of storms in the F-Region.

J K Hargreaves (Engineering Dept., Univ. of Lancaster, Lancaster, England) and P N Collis (EISCAT Scientific Association, Kiruna, Sweden). Spectrum and dynamics of a weak, night-time precipitation event observed by EISCAT in October 1996

A night-time precipitation event affecting the D region has been studied using electron-density profiles from the EISCAT VHF system and absorption data from the Kilpisjarvi imaging riometer. The study demonstrates how the combination of techniques leads to a clearer picture of events than may be obtained from either one alone. The radar shows a wavelike variation with periodicity about 25 min. Since the imaging riometer shows no evidence of horizontal motion, it is concluded that the slow pulsation is due to variations in the incoming particle flux, not to motion through the beam. The changes in the spectrum of the incoming electrons have been derived from the observed electron-density profiles. The 25-minute periodicity is stronger at altitude 95 km, implying a variation in the flux of ~30 keV electrons. The variation is smaller at greater height (and, therefore, at lower energy). There is good agreement between the absorption calculated from the measured electron-density profiles and that observed directly by the riometer. Whereas the second and third peaks of the fluctuation produce radio absorption mainly in the E region, the first one shows enhanced electron flux above 50 keV and a significant amount of radio absorption in the D region as well.

A J Coates, D R Linder, A M Rymer (Mullard Space Science Laboratory), M Grande (Rutherford Appleton Laboratory), K Svenes, B Narheim (Norwegian Defence Research Establishment), D T Young (University of Michigan, USA) and the CAPS team. Cassini electron spectrometer observations during the 18 August 1999 Earth swingby

An overview of the Cassini Plasma Spectrometer results during the Earth swingby is given concentrating on the electron spectrometer results. This high velocity (10 Re per hour) cross section through the Earth's magnetosphere included unexpected features, such as a narrow electron beam, in addition to the anticipated boundaries and regions such as the bow shock, magnetopause, plasmasphere, ionosphere and plasma sheet. The magnetosphere was in an active state at the time due to a high speed solar wind stream. Preliminary results and interpretations are discussed.

R H A Iles, A D Johnstone, A N Fazakerley and P Bühler (Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT). Relativistic Electron Flux Enhancements in the Outer Radiation Belt

Currently the process of relativistic electron flux enhancements in the outer radiation belt is not very well understood. However, these high energy electrons pose a serious threat to satellites as well as manned space missions. Occasional unpredictable increases in the flux of this electron population have in the past damaged and disabled satellites. The high cost of the launch and building of satellites therefore acts as a strong incentive for research into the satellite's operational environment. This study uses data from the two UK built, DERA satellites, STRV-1a and STRV-1b, which sweep the radiation belt four times per day from L = 1.1 out to L = 7 on highly elliptical, near-equatorial orbits. The instruments used are the Cold Ion Detector (CID) on board STRV-1a, from which the background counts are used as an electron count rate monitor, and the Radiation Environments Monitor (REM) which is on board STRV-1b. An initial study used data from both CID and REM to investigate a number of relativistic electron enhancements during the first six months of 1995. An attempt was made to find possible correlations with the solar wind conditions, IMF-Bz, Dst and Kp. Our results show that in many cases the acceleration mechanism within the magnetosphere appears to be related to solar wind speed, but is not so strongly dependent on the ring current. These results prompted a more extended analysis with an aim of verifying our initial findings, and to gain further insight regarding the mechanisms that lead to a relativistic electron enhancement. The extended study uses data from the CID instrument over a period of about four years from February 1994 until March 1998. This interval was chosen as it is a period of solar minimum during which we expect there to be a higher frequency of high speed solar wind interactions than during the solar cycle average. It will also be easier to isolate individual events as the magnetosphere is generally less disturbed during this period and solar wind variations are more clearly defined.

A Lawrence, M Jarvis, M Rose, M Clilverd (British Antarctic Survey) and M Taylor (Utah State University). Implementation of an airglow imager in Antarctica

Observations of airglow can reveal intensity fluctuations generated by gravity waves propagating in the mesosphere and lower thermosphere. A CCD imager, designed for observing airglow, is to be deployed at Halley, Antarctica in January 2000 for specifically observing these small-scale gravity waves. The continuous operation of this apparatus at Halley will provide a unique southern hemisphere high-latitude dataset with which to study the variability and seasonality of these phenomena and will also provide a comparison between northern and southern hemisphere gravity wave activity. .

D Rees (Center for Atmospheric and Space Science, Utah State University, USA, and Hovemere Ltd., UK), M Conde (Geophysical Inst., University of Alaska, Alaska, USA), U Brandstrom and A Steen (Swedish Inst. of Space Physics, Kiruna, Sweden). Daytime ground-based optical imaging of the aurora

Aurorae, spectacular phenomena in the polar night sky, also provide a convenient projection of the effects of complex and energetic plasma processes within the outer magnetosphere. Much has been learned about the ionosphere and magnetosphere from night-time auroral images. However, similar imaging is extraordinarily difficult by day, due to the overwhelming background of atmospherically-scattered sunlight. This is unfortunate, since many plasma processes related to the aurora, in addition to the interactions between the electrodynamics and energetics of the auroral ionosphere with the polar thermosphere may be unique to the sunlit ionosphere. A visible-light image of the aurora at l630 nm wavelength was obtained from Kiruna, Sweden, at sunset on May 2, 1999, by an imaging spectrometer featuring excellent spectral resolution and out-of-band rejection. This is the first such image obtained from the ground under near-daytime conditions. These observations were obtained as a test of principle during development of a prototype Daytime Auroral Imaging instrument. Even this prototype instrument has adequate sensitivity to detect the normal OI(1D-3P) dayglow emission at l630 nm against the intensity of the daytime sky. This technique holds great promise for future ground-based studies of the magnetosphere is processes which are mapped to the daylit ionosphere. There are also a number of very significant applications to studies of the low and mid- latitude thermosphere and ionosphere, in addition to studies of the polar aurora under daytime and summer-time conditions.

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