[Report published in Astronomy & Geophysics 44, 3.26-3.28 (2003)]
by N F Arnold (University of Leicester)
Published in Astronomy & Geophysics 44, 3.26-3.28 (2003)
The first session was chaired by Steve Milan (Leicester). Emma Bunce (Leicester) compared the Jovian and Kronian magnetosphere-ionosphere coupling currents. In Jupiter, breakdown in the co-rotation of ion flow leads to the creation of this current, with the moon Io providing the bulk of the plasma. In spite of rapid rotation in Saturn, currents generated in this fashion have been calculated to be far too faint to be important. Instead it was proposed by Stanley Cowley (Leicester) that the main auroral oval is associated with the ring of upward field-aligned currents that border the polar cap, driven by the solar wind. He presented a theoretical model of Saturn's polar ionospheric flows and their relation to the main auroral oval.
The recent flyby of Jupiter by Cassini, which acted as an upstream monitor, allowed Paul Hanlon (Imperial College) to analyse a compression event within the outer Jovian magnetosphere that was observed by the Galileo spacecraft. He reported externally driven super-rotation of the magnetosphere. Paul then gave a second talk on the structure of the Jovian plasma sheet. Its thickness was found to be fairly constant out to thirty Jovian radii and then became progressively thicker with distance. The plasma sheet was found to lag the magnetic equator by a delay time comparable to the Alfvenic wave propagation speed.
Moving closer to home, Henry Rishbeth (Southampton) presented a day by day comparison of the Mars and Earth ionospheres for the month of March 1999. He used Mars Global Surveyor electron density profiles. The two planets' E- and F1-layers were found to be reasonably similar, suggesting that interplanetary space weather was possible. James Scuffham (IC) modelled Mercury's magnetosphere in anticipation of a planned mission to the planet in the near future. The inputs to the model were based on observations from Mariner 10 and knowledge of the behaviour of the Earth's magnetosphere. Mercury has a small dipole field, so during high IMF, the magnetopause can be just one tenth of the planet's radius away from its surface.
After a short break, Emma Bunce took over the chair. Adam Rees (IC) discussed observations of magnetic clouds made by the Ulysses spacecraft. These clouds were often associated with smooth rotations of the magnetic field and enhanced amplitudes that could be approximated by a force free flux rope model. On several occasions, double flux rope structures were observed, suggesting that the spacecraft had passed in and out of the cloud at two different points. Simon Foster (Southampton) had analysed the correlation between total solar irradiance and the coronal source flux. He obtained monthly values going back over 150 years. Following consideration of sunspot areas, faculae networks and the total irradiance, he concluded that changes to the quiet Sun emission rate was likely to be the most significant factor.
Matthew Owens (IC) examined the SOHO observations of coronal mass ejections (CMEs) at the Sun's surface and the subsequent in situ measurements made by the ACE spacecraft to understand better the causes of deviations from the normal transit time curves. Several suggestions for improving the CME arrival time prediction skill were made. Jonathan Eastwood (IC) described Cluster multi-spacecraft observations of the ion cyclotron resonance in the terrestrial foreshock. He examined ultra low frequency (ULF) waves with periods of approximately 30 seconds. The waves deviated from the field aligned direction by as much as 20 degrees due to the influence of the background magnetic field and solar wind flow vectors.
The fluxgate magnetometers on board Cluster were also used by Katarina Nykyri (IC), who reported magnetic field observations of the high altitude cusp on 17th March 2001. A high altitude cusp crossing could be identified by a region of significant turbulence, indicating a dynamic region, even though the solar wind conditions were quiet. The first day's proceedings were rounded off by Robert Fear (Mullard Space Science Laboratory). He presented Cluster PEACE observations of electron signatures near the cusp magnetopause. On 25th January 2002, a suspected flux transfer event (FTE) was observed just inside the cusp that was believed to be evidence of reconnection between the magnetosphere and the magnetosheath. A flow vortex consistent with an FTE was also recorded.
The first session of the second day was chaired by Adrian Grocott (Leicester). Iain Coleman (British Antarctic Survey) was interested in the emergence of large-scale reconnection structures on the dayside magnetopause. He noted that in spite of a high level of magnetospheric turbulence, large scale structures appeared due to the fractal nature of the noise. As a consequence, there was a degree of correlation between different spatial scales. Panagiota Petkaki (BAS) considered the role of anomalous resistivity in reconnecting non-Maxwellian plasmas. Near the magnetopause boundary idealised magneto-hydrodynamics does not always apply. Also, wave-particle interactions, such as those related to current driven ion acoustic waves tended to have a Lorentzian distribution rather than a Maxwellian one.
Yulia Bogdanova (MSSL) reported Cluster observations of electron distributions in the Earth's magnetic tail during a substorm. Bidirectional field aligned electron beams were observed, following intervals of bursty bulk flows. As the length of the electron path decreased, the energy increased during a rapid reorientation of the Earth's magnetic field in response to the onset of the substorm. Natalie Draper (Leicester) reported on a magnetospheric substorm event that took place on 1st September 2002. The study made use of Cluster, ACE and IMAGE spacecraft in conjunction with ground-based instrumentation. The SuperDARN radars generated ionospheric convection maps that depicted the evolution of the current flow at the same time as the spacecraft probed the conditions in the magnetotail.
Gary Abel (BAS) investigated the variations of multi-scale ground magnetic fluctuations and radar velocity data between different geophysical regions. He wanted to assess the relative importance of the intrinsic plasma environment and the solar wind driver in determining the Earth's magnetosphere. Power law like power spectra were obtained to better understand models of the magnetospheric convection. Mervyn Freeman (BAS) reported on a minimal substorm model that could be used to explain the observed statistical distribution of times between substorms. He assumed that the delay in the response of the magnetosphere to solar wind forcing was due to a configurational constraint on the system. The model produced a probability distribution that compared favourably with the distribution of observed substorms.
The second session of the morning was chaired by Ranvir Dhillon (Leicester). Peter Damiano (St. Andrews) described a one-dimensional hybrid MHD-kinetic model of electron dynamics in standing shear Alfven waves. A link between these waves in the Earth's magnetic field and auroral arc formation was discussed using the model. Strong field line convergence resulted in strong parallel electric current densities and associated high energy electron beams. Hannah Scoffield (Leicester) had carried out an investigation of ULF waves using CUTLASS radar and FAST satellite data. She had combined the large scale structure of ULF wave events with small scale measurements made on 14th December 1999. A theoretical model fitted the large scale structure quite well, but a lot of small scale detail still needed to be accounted for.
Tim Yeoman (Leicester) was interested in the attenuation of ULF wave signatures between the ionosphere and the ground. F-region currents shield the ground from small scale structures. The extent of the attenuation is a function of the ionospheric conductivities and the wave length scale size. To be able to test the current theories it was necessary to make use of high quality electric field data. Ashwini Sinha (Leicester) made use of the Green's function technique to study the geomagnetic field line response to solar-wind pressure variations at the magnetopause boundary by assuming idealistic ionospheric conditions. The fundamental mode responded more readily in the rigid boundary case, whilst the second harmonic dominated in the free case.
Danny Summers (Memorial University of Newfoundland, Canada) presented observational, theoretical and modelling evidence to explain how large numbers of relativistic 'killer' electrons were generated in the magnetosphere. He proposed the energization of relatively low energy electrons by means of resonant interactions with whistler mode chorus waves. Nigel Meredith (MSSL) presented further detailed evidence for chorus-driven electron acceleration to relativistic energies in the Earth's outer radiation belt. Relativistic electrons were observed during moderate and strong storm conditions over much of the radiation belts, provided substorm activity reached a certain threshold. Weak storms were confined to the outer regions of the belts and few relativistic electrons were present.
After lunch, Darren Wright (Leicester) took over the chair. Stuart Thom (Sheffield) detailed a comparison of He+ in the plasmasphere between the Coupled Thermosphere Ionosphere Plasmasphere model and extreme ultraviolet data from the IMAGE satellite. The model was shown to be very useful for inverting the images from the EUV data. A dark 'shoulder' in the emission brightness around dawn that co-rotated with the Earth through the dayside was clearly apparent. Steve Milan provided evidence for high aspect angle irregularities observed in the HF radar backscatter from the E region electrojet. Backscatter is usually aligned along magnetic field lines. The azimuthal dependences appeared to be consistent with the direction of the convection electric fields rather than the expected drift convection. These findings were complemented by a theoretical analysis of this new class of backscatter by Terry Robinson (Leicester). He indicated that the feedback processes that destabilised these irregularities were associated with the heating effect of parallel electron currents in the collision dominated lower ionosphere.
Sophie Cash (Leicester) had modelled the ionospheric Alfven resonator, with the assistance of ground-based instrument data to define the cavity structure. When the refractive index changed, Alfvenic waves partially reflected and this trapping produced resonance. She used EISCAT electron density profiles to estimate the Alfven wave speed in the cavity and the size of the cavity. Ranvir Dhillon (Leicester) reported descending electron density signatures associated with radar-induced ionospheric heating. Maximum heating was observed by the EISCAT incoherent scatter radar in the field aligned direction. The descent was possibly related to enhanced absorption of the heater beam at lower altitudes. Nikolai Borisov (Leicester) discussed the stationary state and relaxation of artificial irregularities excited in ionospheric heating experiments. During heating, filaments of 4 - 6 m were generated that exhibited an electron density depletion of up to 30 %. As the heater was turned off there was a two-stage relaxation for structures that were less than 10 m across.
The final session of the day was chaired by Kathryn McWilliams (Saskatchewan, Canada). Kaido Kaal (Lancaster) employed data from the IRIS riometer to estimate the energy of energetic protons entering the Earth's atmosphere. A magnetospheric particle tracing model was used to investigate the origins of different energies of protons as they passed through the geomagnetic field. Roman Makarevitch (Lancaster) investigated the relationship between the velocities of absorption patches and moving E and F region structures as observed by the IRIS riometer and the CUTLASS and STARE radars. Observed reversals of meridional flows were believed to be due to Interplanetary Magnetic Field reversals. The measured absorption was strongly influenced by E-region electric field heating.
Anastasia Stockton-Chalk (Southampton) described a new technique for observing proton aurora. The Spectrographic Imaging Facility, located at Svalbard, Norway, provides high temporal and spatial resolution data. Doppler shifted hydrogen profiles provide a unique method of analysing incoming, energetic protons. Jim Wild (Leicester) announced the availability of two years of co-ordinated SuperDARN radar and Cluster spacecraft observations of the magnetosphere and the associated ionospheric footprint region. 229 intervals of favourable conjunctions at high time resolution have been generated to date. Most of the regions of the magnetosphere have now been sampled by Cluster at a range of local times and spacecraft configurations.
Chris Thomas (Leicester) reviewed progress towards the completion of SPEAR, a new high-powered HF ionospheric heater and low power radar system, which is being deployed within the Polar Cap. SPEAR will generate artificial irregularities for the CUTLASS HF radars and will perform a variety of space plasma experiments. Tony van Eyken (EISCAT Scientific Association) reported on the plans for EISCAT in the future after more than 20 years of successful operation, as its current operational agreement is scheduled to expire in 2006.
The first session of the final day was chaired by Gabby Provan (Leicester). Scott England (Leicester) described numerical simulations of atmospheric gravity wave damping of the global circulation in the upper mesosphere and lower thermosphere. Recent advances have made it possible to incorporate physically realistic representations of these waves into the models for the first time. This process could enhance the ability of solar activity to modify the stratosphere. David Nunn (Southampton) considered the impact of polar mesospheric summer echoes on VLF propagation. Since fractional depletions in electron density near the mesopause of 90 % have been observed in the summer these phenomena could affect VLF propagation. Theoretical considerations indicated that this was possible under certain conditions.
Tommi Karhunen (Leicester) ended the session with a talk on the use of CUTLASS radar ground scatter data to measure travelling ionospheric disturbances (TIDs). A three-dimensional ray tracing model in the presence of a TID was compared with an event observed in the CUTLASS data to generate relevant parameters such as the amplitudes and wave lengths of the principal components of the underlying waves.
Over an extended coffee break, delegates had an opportunity to view a series of posters. Lisa Baddeley (Leicester) presented a study of magnetospheric plasma populations as a potential source of energy for high azimuthal wavenumber pulsations and found that the energy dissipated was in good agreement with the radar observations of the sink in the ionosphere. A large scale ULF wave event was the subject of an investigation by Tim Yeoman (Leicester). CUTLASS radar and IMAGE magnetometer data on the ground were gathered during a FAST satellite overpass. The ionospheric measurements were compared with the in situ field and particle data.
Darren Wright (Leicester) reported high resolution observations of ULF waves by the CUTLASS radars during an interval of ionospheric heating by the EISCAT high power heating facility. These waves were seen to increase the observed radar spectral widths due to ion-cyclotron wave activity. Jason Dewhurst (MSSL) made use of the Cluster spacecraft Plasma Electron and Current Experiments to determine the passage of the plasma sheet lobe boundary during a magnetospheric substorm. Some implications for possible substorm triggering mechanisms were discussed.
Richard Jones (Aberystwyth) used the LASCO instrument on SOHO and radio scintillation measurements from EISCAT and MERLIN to study interplanetary coronal mass ejections. Results of several case studies were presented and the effects of different CME geometries were discussed. Mario Bisi (Aberystwyth) displayed the latest results from the study of the interaction regions that occur when streams of fast solar wind catch up with regions of slow solar wind. The EISCAT radar provided the interplanetary radio scintillation measurements.
David Nunn (Southampton) displayed the results of detailed numerical modelling of Trimpis observed on the Antarctic Peninsula. Trimpis are short term variations in the amplitude and phase of VLF or LF transmissions, usually induced by lightning flashes. Adrian Grocott (Leicester) presented a detailed study of the coincident Cluster and ground-based observations of a 'bursty bulk flow' event in the near-Earth central plasma sheet. The data was consistent with small scale transport of plasma towards the Earth.
The final session of the meeting was chaired by Jim Wild. Mike Lockwood (RAL) stood in for Katie Throp (Southampton). He described how the study of proton aurora could provide useful information concerning magnetospheric reconnection variations. Strong signatures in the solar wind were related to subsequent proton precipitation on 26th November 2000. The change in the solar wind pressure and magnetic field direction suggested a travelling convection vortex. Gareth Chisham (BAS) measured the reconnection rate in the dayside ionosphere during an interval of Northward IMF. He used the Northern Hemisphere SuperDARN radar network to observe the high latitude ionospheric convection electric field. Satellite and radar observations were then employed to infer the location of the reconnection site. He proceeded to estimate the reconnection electric field strength and the associated reconnection potential.
Steve Morley (Southampton) described a numerical representation of the Cowley-Lockwood conceptual model of the ionospheric response to time-dependent magnetospheric reconnection. He used the model to address the question of whether the observed changes to the convection pattern were a consequence of localised expansion or part of a global response. Kathryn McWilliams discussed a multi-instrument study of the dayside magnetosphere during a particularly favourable interval. October 4th 2002 saw a rare conjunction of spacecraft and ground-based instrumentation in the Scandinavian sector. A significant magnetospheric storm was taking place and a number of poleward moving phenomena were detected by the radars at this time. Gabby Provan (Leicester) rounded off the meeting with a statistical study of high-latitude plasma flow during magnetospheric substorms. She had made use of SuperDARN convection flows from a few years of data to track the ensemble behaviour of the ionosphere at different stages in the evolution of these storms.