[Report published in Astronomy & Geophysics 42, 1.27-1.28 (February 2001)]
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by N F Arnold (University of Leicester)
Published in Astronomy & Geophysics 42, 1.27-1.28 (February 2001)
The annual one-day meeting of the MIST (Magnetosphere, Ionosphere and Solar-Terrestrial) community was held on the 24th November, 2000 at the Geological Society, Burlington House. Disruption on the rail network made it difficult for a number of people to attend from the remoter parts of the United Kingdom and imaginative means of transport were employed by many. However, the organiser, Andy Smith (British Antarctic Survey), managed once again to put together a schedule containing 27 presentations over the gamut of the community's interests.
The morning session was chaired by Peter Cargill (Imperial College) and the proceedings commenced with two talks from members of the IC group. Tim Stubbs presented a POLAR satellite study of fully ionised helium and the asymmetry in its population between dawn and dusk. The imbalance was not associated with the Interplanetary Magnetic Field (IMF) conditions but was instead related to particle energy flux levels and the competing forces that they were subjected to within the magnetosphere. High time resolution Equator-S satellite observations of magnetopause crossings were presented by Elizabeth Lucek. When the IMF was orientated in the southward direction there was a distinct separation between the growth in the amplitude of the magnetic field and its rotation, whereas in the northward state, the two parameters were collocated. Electrostatic waves were detected during these crossings on a number of occasions.
Gabby Provan (Leicester) used the SuperDARN network of HF radars and satellite measurements to map the Northern Hemisphere high latitude ionosphere. A complete Dungey cycle of the creation and destruction of open magnetic flux within the magnetosphere was observed. On the dayside there was an episode of reconnection, whilst on the nightside, there was a substorm. Hina Khan (Leicester) reported on the Cassini spacecraft flyby through the Earth's magnetosphere in conjunction with simultaneous observations from other satellites and ground based instruments. The short transit time of the spacecraft through the magnetosphere presented a rare opportunity to monitor the large-scale response to several substorm intervals.
Thermospheric airglow measurements in Northern Europe were reported by Eoghan Griffin (University College London). He carried out an intercomparison of Fabry-Perot Interferometer temperatures with Incoherent Scatter radar observations and empirical model data. It was found that the latter tended to underestimate thermospheric temperatures, especially during periods of high geomagnetic activity. On the other side of the world, Andrew Lawrence (BAS) was preparing to use an airglow imager to study atmospheric gravity waves. To assist in this task he had performed some ray-tracing studies to estimate the geographical distribution and potential source regions of these waves. The theme of atmospheric modelling was continued by two talks from UCL. Matt Harris had extended the Coupled Thermosphere Ionosphere Plasmasphere model to include the mesosphere and part of the stratosphere. This model simulated tidally induced variations in exothermic chemical heating and its subsequent impact on the general circulation. A new model of Titan's thermosphere was described by Ingo Mueller-Wodarg. It successfully accounted for the observed 2-3 hour lag between tidal heating and constituent distributions. Vertical diffusion time-scales were of the right order to account for much of this delay.
Emma Bunce (Leicester) analysed data from the magnetometers from four flybys of Jupiter to derive the divergence of the equatorial current in the dawn sector of Jupiter's magnetosphere. The energy flux into the planet's ionosphere that completes the global electric circuit was confined to a narrow band at 16 degrees from the pole and provided an explanation of the planet's auroral oval. Magnetometer data, this time from Ulysses was employed by Pangiota Petkaki (IC) to investigate the middle Jovian magnetosphere close to the plasma sheet. Analysis revealed transverse waves with frequencies between the gyrofrequencies of SO+ and S+ and it is possible that the technique may be used to derive the composition of other heavy ion contituents. The morning session was brought to a close by Mark Lester (Leicester) describing a new enhancement to the CUTLASS HF radar system. Stereo-CUTLASS will be able to perform two independent observations simultaneously, thereby increasing its sensitivity and/or introducing a second mode of operation that emphasises a different geographical region or frequency domain. Preliminary tests indicated that only relatively minor technical issues needed to be ironed out.
Sandra Chapman (Warwick) took the chair for the post-lunch session. Emma Woodfield (Leicester) processed the extensive CUTLASS HF radar statistical database to examine the statistical distribution of returned echo spectral widths. Their variations with local time and season provided clues about the characteristics of the magnetospheric low latitude boundary layer and the dayside cusp. Magnetic field fluctuations from the Ulysses spacecraft were analysed by Christina Pagel (IC) to determine intermittency in heliospheric turbulence. The shape of the power spectrum makes it possible to differentiate between different models of turbulence. Richard Fallows (Aberystwyth) used the radio interplanetary scintillation technique to study the solar wind. The fast solar wind was found to accelerate quite smoothly within 10 solar radii, whilst the slow wind was more variable and the process continued out to 30 solar radii.
More Ulysses observations from Imperial College were presented by the next two speakers. Murtaza Gulamali looked at magnetohydrodynamic turbulence in co-rotating interaction regions. These CIRs were found to be sensitive to magnetic field magnitude, Alfvènicity and variations in the solar cycle. Geraint Jones found unusual magnetic fluctuations in the high latitude heliosphere which were consistent with passage of the spacecraft through the tail of a comet. As no observed comet has yet been forthcoming, the measurements were used to estimate a possible orbit. The Cassini flyby of the Earth was the focus of the talk by Gary Abel (Mullard Space Science Laboratory). He looked at bidirectional lobe electrons using the CAPS instrument on board. Much of the behaviour was expected but there was a surprising lack of field aligned electrons in the Earth's magnetosheath. Two talks concerning the SuperDARN HF radar followed from the Leicester group. Adrian Grocott discussed a study of magnetotail reconnection. The ionospheric convection cell was enhanced in the pre-midnight sector when the interplanetary magnetic field was northward. Kathryn McWilliams compared ground based radar observations of the dayside aurora with spacecraft ultraviolet data under a range of interplanetary magnetic field conditions. When the y-component of the field was positive, the response was collocated. During negative intervals the radar aurora was seen to be poleward of the ultraviolet images. The last speaker of the session was Ian Krauklis (MSSL). He had analysed POLAR spacecraft measurements of cusp ion velocity dispersion during northward IMF and found a very strong time dependence. There were systematic magnetic local time asymmetries due to lobe reconnection in the sub-alfvènic magnetosheath.
The final session of the meeting was chaired by Mark Lester (Leicester). Adam Rees (IC) reported Ulysses spacecraft observations of magnetic clouds during solar maximum. These were generated by coronal mass ejections and so their frequency of occurrence was dependent on the level of solar activity and heliospheric latitude. Particle-in-cell simulations of the solar wind in the lunar shadow were introduced by Paul Birch (Warwick). Counter-streaming electrons at the edge of the lunar shadow were created which induced a two-stream instability in the centre in accord with WIND spacecraft observations. More detailed studies required the addition of another dimension to the model.
Returning to Ulysses, Jonathan Gloag (IC) looked for slow-mode shocks in the solar wind data and identified three candidates out of 130 shocks. Their short-lived nature and the difficulty of detecting them at current temporal resolution suggested they were commonly underestimated. Tim Horbury (IC) used a number of spacecraft to refine the prediction of arrival time of southward magnetic field turnings at the Earth's ionosphere. Most of these turnings were tangential rather than rotational and so a single spacecraft could be used in the estimate with 86% predicted correctly to within 10 minutes of actual arrival times from the first Lagrangian orbit.
Geraint Jones stood in for Silvia Dalla (both IC) who was unable to present her paper on extreme anisotropy particle events seen by Ulysses in person. Four high isotropy events in four years were observed at a range of latitudes, mostly at relatively high heliospheric latitudes, whilst five extremely anisotropic events were seen close to the ecliptic plane. Possible explanations for these findings were given. Andrew Kavanagh (Lancaster) made use of ground-based riometer and satellite observations of a polar cap absorption event to identify the location of the absorption and proton cutoff latitudes. These indicated the lowest latitudes where the Earth's magnetic field was able to repel incoming solar particles.
Simulations of the recovery of He+ following a geomagnetic storm were reported by Chris Wilford (Sheffield) using the Sheffield University Plasmasphere Ionosphere Model. These results were compared with satellite observations. He+ was seen to recover much more quickly than O+ and H+ as the former responded to photo-ionisation whilst the latter two were involved in charge exchange processes. Sandra Chapman (Warwick) concluded the meeting with a review of mathematical attempts to represent the complexity of the magnetosphere and thus to identify recurrent behaviours such as self-organised criticality. It is important to be able to make the distinction between a complex system and one that is merely complicated. Globally averaged magnetospheric quantities yield a single parameter and so are likely to be of greatest assistance in characterising the system.
The meeting concluded with thanks to all the contributors, chairmen and organiser Andy Smith.