Bow shock crossings detected during the Cassini flyby of Jupiter (December 2000) indicate that this boundary was relatively inflated during the early and late phases of the encounter. A variety of magnetic signatures indicate a wide range in angle between the solar wind field and the local shock normal. The time variation in this angle is generally consistent with a shock surface model similar to that derived for the Voyager / Pioneer encounters. Cassini data indicate that the solar wind pressure varied by an order of magnitude during the early phase of the flyby (up to Jan 18 2001), and that consequently the bow shock itself was in a highly dynamic state.

The nature of the Jovian bow shock has been explored by seven spacecraft to date, including Galileo which orbited the planet from December 1995 to September 2003. However, the dusk flank from 200 to 1000 Jovian radii had not been sampled prior to the Cassini swing-by in late 2000/early 2001. We present measurements of the absolute electron temperature and density jump, and magnetic field transition at the Jovian bow shock. We discuss how these parameters vary with distance down the dusk flank, with solar wind Alfven number and with magnetosonic Mach number. Electron temperature and magnetic field transitions are observed to vary with distance from the planet, with Alfven and with magnetosonic Mach numbers. We use a magnetohydrodynamic bow shock model to compare the bow shock locations as observed at Cassini with bow shock surfaces derived from the model for the observed solar wind pressure. Although the model is not intended to be extended past 150 R_J the predicted and observed bow shock locations compare surprisingly well out to over 600 R_J. We also compare the solar wind pressure observed at Cassini with values for pressure inferred from the model for the observed bow shock locations. We find that the model generally over-estimates the pressure within 400 R_J and underestimates at distances beyond this. Our observations are given a standardised frame of reference by dividing the bow shock location [x, y] co-ordinates by the bow shock stand off distances derived from the model. This normalised dataset is used to compare the observed electron temperature transitions with those inferred from a gas-dynamic model of total temperature transition across the Earth’s bow shock. We find the change in the temperature transition is 20% lower than predicted by the model. We also use the model to infer an average solar wind Mach number of 5.1 which is around half the observed average values (Alfven Mach number 8.3 and magnetosonic Mach number of 12). No correlation was found of electron density or density transition with distance, which is surprising as several models exist describing the expected density decrease with distance down the magnetosheath. Where velocity data is available we show that the electron heating at these shocks scales with the difference of the squares of solar wind bulk flow and magnetosheath speed (v_u²-v_d²), as has been shown to be the case at Earth. We also find that the electron density and magnetic field magnitude show a weaker but still significant correlation with v_u²-v_d².

The thermospheres of the outer planets have temperatures far in excess of those expected if solar heating is the principal energy source. A possible source of this missing energy is precipitation of energetic particles in the high-latitude auroral regions. However, auroral energy can only heat the whole thermosphere if it is redistributed by equatorward winds. Coriolis forces may act as a barrier to this process. Simple experiments with general circulation models allow us to assess the effectiveness of auroral heating as a global heat source and examine the atmospheric motions that it may produce.

The UCL Mars model is a self consistent global model of the thermosphere which numerically solves the energy, momentum and continuity equations. It enables study of the dynamics, energetics and composition of the neutral and plasma gases. The recent addition of an ionosphere into the global model has yielded interesting results, the main validation of this work has been carried out using data from the Radio Science experiment onboard Mars Global Surveyor.

Self-consistent non steady-state model of magnetic reconnection was developed. Feedback structure of the reconnection was revealed. Such feedback causes reconnection rate pulsations with a time period proportional to the diffusion region size. Though the model of the diffusion region used in this study was very simple, the origins of the feedback in the reconnection process are much more general. We believe that the existence of the feedback connection between inflow and outflow regions can possibly explain bursty, impact behavior of the magnetospheric reconnection.

During the recovery phase of a substorm occurring on the 1st September 2002 the four Cluster spacecraft were located in the plasma sheet. The FGM magnetic field data from the four spacecraft observe a cavity of close to zero magnetic field which passed over the four spacecraft, travelling Earthwards. A detailed study of this event is now underway and we present preliminary observations from FGM, CIS, PEACE and RAPID instruments.

This paper further addresses the issue of nightside flow bursts which occur during intervals of northward but strongly B_y-influenced IMF. Recent discussions of such bursts concerned intervals during which the IMF B_y component was negative. The present study concerns an interval of B_y-positive IMF which occurred on 20 March 2002 (0100 - 1200 UT). During the interval B_y increased steadily from ~2 to 12 nT, whilst the B_z component decreased steadily from ~10 to 0 nT. There was thus a ~6 h sub-interval during which the IMF clock angle remained between 30° and 60°, such that moderate dayside reconnection and open flux production was maintained. It is found that flow bursts of a similar size and speed to those observed under B_y negative (~1000 m/s, spanning 2-3 h of MLT in the midnight sector) also occur when B_y is positive. However, the direction of east-west flow is reversed, indicating that they are driven by processes in the magnetosphere which are directly related to the orientation of the IMF. It is suggested that they are caused by a reconfiguration of an asymmetric tail resulting from prolonged dayside reconnection with a B_y-dominated IMF. This is consistent with previous suggestions that they are associated with convective transport following reconnection in the more distant tail. Analysis of ground magnetic data, auroral images and geosynchronous particle data also show associated features, but indicate that the flow bursts are not directly associated with substorms.

We present a case study of the global plasma flows observed during an interval of continues northward interplanetary magnetic field (IMF) which lasted in excess of ten hours. The plasma flow vectors were observed by the Northern hemisphere SuperDARN radars, and global convection flow patterns were obtained using the map-potential analysis tool. During the first four hour of our case study, the IMF B_y component dominated the IMF B_z component, during the next few hours the opposite was true. This change in the IMF conditions was associated with large scale re-configuration of the global convection flow patterns, from a twin-cell convection configuration with anti-sunward flow over the polar cap and return flow at lower latitudes, to a four cell convection pattern where reverse convection flow is observed over the polar cap. The plasma flow observed during our entire northward IMF interval was not steady-state, but showed clear evidence of time-dependent pulsing. We will present global convection maps showing pulsed dayside flows observed during interval of reverse convection over the polar cap.

The International Ionospheric Tomography project comprises receiver chains in Scandinavia, Greenland and Alaska and can provide near-simultaneous images of the large-scale plasma distributions in three different longitude sectors. Tomographic reconstructions of the wintertime dayside ionosphere are presented under conditions of stable, positive IMF B_z. The chains can simultaneously measure the ionospheric structure in the dawn, noon and post-noon magnetic sectors. The spatial distributions of the plasma over an extended region of the northern hemisphere are discussed in the light of the likely high-latitude plasma convection for the IMF condition.

A meteor radar has been installed on Ascension Island (8ºS, 14ºW). Routine data collection began in October 2001. Here we present observations of the 12- and 24-hour tides made in the 13-month period Oct 2001 - Oct 2002. The dominant motion is found to be the 24-hour tide, which sometimes has monthly-mean amplitudes in excess of 50 m/s. The 8- and 12-hour tides are also observed, but are generally much weaker with typical monthly amplitudes of about 5 m/s and 10 m/s respectively. In the case of the dominant 24-hour tide, a clear seasonal cycle is evident. Maximum monthly-mean tidal amplitudes are reached in October 2001, however this maximum is not repeated in 2002 indicating considerable inter-annual variability. Small tidal amplitudes are observed in December, June/July and September. In all seasons the amplitude of the 24-hour tide generally reaches a maximum at heights near 95 km- which is just below the equatorial mesopause. In the case of the 12-hour tide, amplitudes are generally weaker, but the amplitudes increases throughout the height range observed and are greatest during the autumnal and winter months (March to August). The largest 12-hour tidal amplitudes occur around the autumnal equinox, and this maximum appears related to a stronger feature observed at higher latitudes. Comparisons with the latest NCAR HAO Global Scale Wave Model reveal significant discrepancies between the observed tidal amplitudes and the model predictions. Both the 12- and 24-hour tides display dramatic variability on time scales of ~ 1 - 30 days. The variability is often quasi-periodic and suggests coupling between tides and planetary waves is a major cause of short-term variability for equatorial tides.

The equatorial mesosphere and lower thermosphere are home to a rich variety of unique atmospheric phenomena. A meteor radar has been deployed on Ascension Island (8S, 14W) in the equatorial Atlantic to measure horizontal winds in the height range ~ 80-100 km. Routine height and time resolutions of ~ 3 km and 1 hour, respectively. The radar was deployed in 2001 and near-continuous measurements are available from October of that year. Data of this sort are ideal for investigating the mean winds, tides and planetary waves that dominate the dynamics of this part of the atmosphere and couple it to the regions above and below. In this presentation, the radar is introduced and its performance and capabilities described. One of the dynamical features being investigated is a conspicuous class of wave observed with a period of about three days and amplitudes that can reach several tens of m/s. The waves are strongly intermittent and have distinctive properties, including oscillations which are strongly polarised in the zonal direction, and phase slopes that indicate they have ascended from below. The unusual characteristics of these waves suggest that they are equatorially trapped Kelvin waves originating in the lower atmosphere. Their limited amplitude growth with height indicates momentum transfer into the mean flow takes place. The behaviour and nature of these waves is described and their possible role as drivers of the equatorial circulation is considered.

Atmospheric gravity waves play a vital role in maintaining the temperature and wind structure of the mesosphere and lower thermosphere, and in driving the global residual circulation in this region. Their small scale size means that they cannot be resolved by global atmospheric models, so instead their effects are parameterised. A new parameterisation, based upon the work of Medvedev & Klaassen 2000, has been incorporated into the UCL CMAT model. Recent results from this model will be presented.

The first tristatic Fabry-Perot Interferometer (FPI) measurements of the neutral atmosphere co-located with tristatic measurements of the ionosphere made by the European Incoherent Scatter (EISCAT) radar were carried out during the nights of the 27th and 28th February 2003. Tristatic measurements mean that there are no assumptions of uniform wind fields and ion drifts, nor zero vertical winds. Independent thermospheric measurements reduce the need for models of the neutral atmosphere and derivation of neutral parameters from ionospheric measurements. The FPIs are located close to the 3 radars of the EISCAT configuration in northern Scandinavia, which is a region well covered by a network of complementary instruments. These provide a larger scale context within which to interpret our observations of mesoscale variations on the scales of tens of kilometres spatially and minutes temporally. Initial studies indicate that the thermosphere is more dynamic and responsive to ionospheric forcing than expected. Calculations using the tristatic volume measurements show that the neutral wind dynamo contributes an average of around 40% of Joule heating during the first night of observation, by both enhancing and reducing the effective electric field by up to several 10’s of percent. Comparison of EISCAT ion temperatures at an altitude of 240 km with FPI neutral temperatures show some anomalous differences (T_i around 200 K below T_n for up to 30 minutes on the first night) that is inconsistent with energy transfer, but may probably be accounted for by height variations.

Statistical observations of the subauroral polarization stream using the large Millstone Hill incoherent scatter radar (two solar cycle) has been carried out. The SAPS is a broad persistent region of ring current induced electric field can be seen equatorward of the normal two cell ionospheric convection pattern, across the night sector to dawn. This feature is overlap with the storm enhanced density feature, which has been mapped closely to the plasmaspheric tail as seen by the EUV image from the IMAGE spacecraft. SAPS statistics has been used by the modelling community to model the time evolution of the plasmaspheric tail. Initial study using EUV image, DMSP drift meter, and the mainland UK tomographic is being conducted to understand the longitudinal difference in the coupling of the plasmasphere to the middle ionosphere.

Pitch angle and energy diffusion rates for scattering by whistler mode chorus waves are proportional to the wave magnetic field intensity and are strongly dependent on the frequency distribution of the waves and to the ratio between the electron plasma frequency (f_pe) and the electron gyrofrequency (f_ce). Relativistic electrons interact most readily with lower-band chorus (0.1 < f/f_ce < 0.5) and energy diffusion leading to local acceleration to relativistic energies is most effective in regions of low f_pe/f_ce. We perform statistical studies of data from the CRRES mission and show that, outside of the plasmapause, both fpe/fce and lower-band chorus activity are dependent on magnetic activity with regions of low f_pe/f_ce and enhanced lower-band chorus activity occurring over a wide range of geospace during active conditions (AE > 300 nT). Enhanced waves in these regions could play a major role in electron acceleration to relativistic energies during periods of prolonged substorm activity.

Results are presented from a study of the northern magnetospheric cusp crossed by the 4 Cluster satellites during 16:25-17:55 UT on 18 April 2002 when a moderate geomagnetic storm was in progress, solar wind dynamic pressure was rather low and IMF B_z was suitable (southward) for reconnection in the dayside magnetopause. The satellite orbit and data from the FGM, CIS, PEACE, STAFF and WHISPER instruments reveal that the satellites have crossed through a structured exterior cusp. Three distinct anti-sunward ion flow events of duration about 1.5, 17.5 and 19.0 minutes, with bulk flow roughly parallel to the magnetopause surface, are detected in the cusp region. The ion density in the events measured by one of the satellites (C3) is up to 10 times less than that measured by other satellites (C1 and C4, no data from C2), which seems to arise from the low northward-westward flow encountered by C3 compared to C1 and C4. The sharp inward/outward walls of the anti-sunward flow events are detected with expected/reversed time sequence by the 4 satellites, with time delays of up to 10 sec./4 sec. That suggests reversed accelerated plasma flows inside the events compared to the flows outside the events, with faster acceleration closer to the inward walls. The magnetic field fluctuations in B_y (~ 50 nT) associated with the anti-sunward ion flow events are found to be nearly twice as strong as those in B_x and B_z, suggesting strong field-aligned currents.

We have analysed high-resolution Cluster magnetic field data during three high-altitude cusp crossings in 2001 and 2002. The Cluster separations for these crossings varied between 100 and 600 km and therefore provided an unique opportunity to study wave properties at different length scales. In the cusp Cluster sees frequent intervals of magnetic field fluctuations with clear peaks in power close to the local ion cyclotron frequency, and both left and right-handed polarisations. At large separations the power seen at different spacecraft can differ by orders of magnitude. For smaller separations, the power seen at the four spacecraft agrees better but still shows some differences. For all separations there was no significant correlation between the signals seen at different spacecraft, indicative of very local structure. The origin of the waves appears to lie in highly filamented sheared plasma flows present in the cusp.

In January and early February 2002, orbital manoeuvres were in progress to alter the Cluster constellation size. At times, the four Cluster spacecraft were arranged along a line, rather than in the more usual equilateral tetrahedron as they crossed the magnetopause. The configuration allows simultaneous observations of any magnetopause boundary layers, the magnetosheath and of flux transfer events (FTEs) at various distances from the magnetopause, as well as the consequences of any in- or outward magnetopause motion. Such a configuration existed on the 25th January 2002 as the spacecraft were inside the magnetosphere approaching the magnetopause after passing through the northern high latitude cusp travelling outbound. The PEACE electron spectrometers on the four spacecraft all observed a series of transient bursts of magnetosheath-like plasma. One such event, at about 10:08 UT is accompanied on some of the spacecraft by a signature in the magnetic field magnitude similar to a crater-type FTE (taxonomy by Paschmann et al. [1982], Elphic [1995]), but without a bipolar signature in the inferred magnetopause normal direction. This event is shown to be incompatible with an FTE interpretation, but the magnetosphere plasma motion and magnetic field variations are shown to be consistent with motion around a moving boundary disturbance caused by a pressure pulse.

The ion outflow from the cleft/cusp region is one of the main contributors of ionospheric ions in the magnetosphere. Previous studies show that upflowing ions mainly come from the latitudinally-localised region near the equatorward boundary of the cusp. Inside this region the intense perpendicular heating of the ions was observed as well as electrostatic and electromagnetic wave activity. Based on Cluster PEACE and CIS particle data, we discuss three mid-altitude cleft/cusp crossings with different locations and properties, concentrating mainly on particle behaviour inside the heating region. Our study shows that the location of the region with the most intense ion heating is well correlated with uni- or bi-directional soft (<500 eV) electron beams, presumably from magnetopause reconnection. We found an electron parallel anisotropy threshold which could play a role in the modulation of the local ion transverse heating. We also discuss the correlation between the ion heating, suprathermal electron bursts and different wave modes.

Solar energetic particles (SEPs) accelerated during flares and coronal mass ejections can escape from the solar atmosphere and propagate through interplanetary space. Studies of the relative timing between flare onset and particles reaching a detecting spacecraft in interplanetary space, have shown that the arrival of the first SEPs is often much later than expected from a scatter free propagation model. We compare SEP onset times at the Wind and Ulysses spacecraft, during periods when they were at widely separated locations in space. We discuss the interpretation of these data in terms of (a) delayed SEP acceleration, for example by a coronal mass ejection driven shock, and (b) particle scattering in interplanetary space.

A survey of the non-radial flows (NRFs) during nearly five years of interplanetary observations revealed that approximately half of the large (> 100km/s) NRFs can be readily associated with ICMEs. Furthermore, the very strongest NRFs are all ICME-driven. Conversely, the average maximum non-radial flow speed upstream of ICMEs is ~ 100 km/s, and just over one third of all ICMEs are preceded by large (> 100km/s) NRFs. The next step is to understand the upstream flow deflections in terms of the large-scale structure of the driving ICME. We look at a single example in detail, before showing a summary of the results for five fast moving magnetic clouds. Using variance analysis it is possible to infer the local axis orientation of a magnetic cloud, and qualitatively estimate the point of interception of the spacecraft with the ICME. The upstream flow deflections are in agreement with the points of interception predicted by variance analysis. Thus we conclude that the upstream flow deflections are in accord with the current concept of the large-scale structure of an ICME: a curved axial loop connected to the Sun, bounded by a curved (thought not necessarily circular) cross-section.

Simulations of plasma flows in the plasma sheet suggest that shear flow away from the midnight sector generates field-aligned currents [Birn and Hesse, 1996]. A survey for intervals when Cluster was located in the deep plasma sheet and observed a flow shear was performed. Using high-resolution 3D data from Cluster's Plasma Electron And Current Experiment (PEACE) and derived electron velocity moments the effect of flow shears on field-aligned flows within the plasma sheet is discussed. The difficulties in observing flow-shear generated currents against those associated with the plasma-sheet boundary layer are illustrated. The scale size of the observed flow shears and their role in field-aligned current generation is discussed.

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