[Report published in Astronomy & Geophysics 43, 1.23-1.24 (February 2002)]
by N F Arnold (University of Leicester)
Published in Astronomy & Geophysics 43, 1.23-1.24 (February 2002)
The annual one-day meeting of the MIST (Magnetosphere, Ionosphere and Solar-Terrestrial) community was held on the 23th November 2001 at the Geological Society, Burlington House. Gareth Chisham (British Antarctic Survey) was the chairman for the morning session. Michele Dougherty (Imperial College, London) took advantage of the Cassini spacecraft flyby of Jupiter to carry out simultaneous measurements of the solar wind and Jovian magnetospheric conditions. She reported the first observations of northward Interplanetary Magnetic Field conditions leading to magnetopause erosion during reconnection. Using previous spacecraft flights through the Jovian current sheet, Jonathan Nichols (Leicester) was able to deduce a model of the planet s magnetic field. He then compared the resulting angular momentum and auroral electron precipitation with those generated by a simple dipole magnetic field. It was found that the self-consistent model was able to account for the location and intensity of the planet s auroral oval.
Christina Pagel (Imperial College) examined the heliospheric magnetic field observed between the north and south poles during the recent fast latitude scan of the Ulysses spacecraft. The level of magnetic fluctuations was found to be greatest in the polar regions during solar minimum and lower towards the solar equator and at solar maximum. Holger Schmitz (Warwick) made use of fully kinetic particle-in-cell simulations of high Mach number shock waves to reveal a non-thermal downstream electron energy distribution with a high energy tail in the bow shock of Mercury. He found that electrons could become trapped at the foot of the shock where they could become accelerated by an electric field before leaving the phase space hole.
Several studies from Imperial College made use of data from the Ulysses spacecraft. Jonathan Gloag examined aspects of the detailed structure of weak interplanetary shock waves. He observed behaviour that appeared to depart from classical magnetohydrodynamic theory in that there were often significant delays between the times of the deflection of the magnetic field and times of the change in the magnitude of the field fluctuations. The unique heliospheric polar orbit of Ulysses provided Geraint Jones with data from a rapid 10 month scan at both solar minimum and then five years later solar maximum. During solar minimum, the dipolar solar magnetic field was clearly seen with a low latitude heliospheric current sheet. During 2001, Ulysses sampled the Sun s magnetic polarity at all latitudes while it was undergoing a reversal. Bogdan Hnat (Warwick) examined the statistical properties of the interplanetary magnetic field. He found that a single scaling parameter can be used to adequately describe its behaviour on timescales of less than 26 hours. Over longer periods, the behaviour was more complex and suggested a possible multi-fractal character.
Attention was shifted to the ionosphere by Ranvir Dhillon (Leicester) as he described the effect of varying the scanning angle of the Tromso ionospheric heater in the generation of artificial backscatter in the CUTLASS Finland HF radar. It was found that the power was intensified in the direction along the Earth s magnetic field and that as the scan period was reduced below a minute, there was a reduction in the resulting backscattered power related to the timescale of the excitation and decay processes. Eoghan Griffin (University College London) discussed the implications for the thermosphere of observed small scale structure in the ionospheric convection flows and related joule heating as observed by the CUTLASS HF radar. He suggested that a high resolution Scanning Doppler Imager would complement the ionospheric measurements in this region.
After lunch, Eleri Pryse (Aberystwyth) took the chair. Richard Sims (Aberystwyth) presented evidence for a tongue-of-ionisation in winter over Svalbard whereby cold plasma had been transported from sub-auroral latitudes into the polar cap during southward IMF conditions. He made use of a range of ground- and space-based instrumentation, to show that numerical models were not yet able to simulate these phenomena. The first measurements of F-region ion temperatures using a Fabry-Perot interferometer were described by Mike Kosch (Lancaster). Night time singly ionised oxygen, formed by auroral particle precipitation, provides the optical source. On three nights, there was excellent agreement between the European Incoherent Scatter radar 300 km away and the interferometer.
Chris Wilford (Sheffield) reported on improvements to the Arecibo radar s ability to measure concentrations and temperatures of H+ and He+ up to altitudes of 2000 km. For the first time it was possible to compare these values with in situ measurements from satellites. These observations indicated significant layering of He+ around 700 km. Initial results from the coupled thermosphere ionosphere plasmasphere (CTIP) model have been able to reproduce this feature. Jackie Davies (Leicester) described joint EISCAT/CUTLASS radar observations of ionospheric signatures of dayside transient reconnection. On the morning of 23rd November 1999, the IMF was strongly southward and a series of poleward-propagating F-region electron density enhancements were seen. These features appeared to originate from around the open/closed field line boundary of the magnetosphere/ionosphere system following flux transfer events in the magnetosphere.
The Earth s magnetosphere, as seen by the Cluster spacecraft, was the subject of the talk by Jonathan Eastwood (Imperial). The behaviour of the magnetosheath region was compared with conditions upstream in the solar wind that were observed by the ACE spacecraft at the first Lagrangian point. Two magnetic field reversals took place on 13th February 2001 and statistical analysis techniques were used to determine the evolution of the field between the two spacecraft. Youra Taroyan (Sheffield) was interested in the generation of magnetohydrodynamic waves at the Earth s magnetopause. The existence of a finite non-uniform layer between two semi-infinite homogeneous regions permitted several resonances to occur. Whilst Kelvin-Helmholtz instabilities tended to favour high velocities, resonant flow instabilities were found to become significant at much lower flow speeds.
Kathryn McWilliams (Leicester) discussed a magnetospheric flux transfer event that was seen by the Geotail spacecraft as it passed through the dawn magnetopause and its impact on the ionosphere. The SuperDARN network of HF radars was able to monitor the convection flow conditions in the vicinity of the spacecraft s ionospheric footprint. Changes in the orientation of the IMF during this interval influenced the location of the merging sites in the ionosphere. Silvia Dalla (Imperial) examined the distribution of solar energetic particles as seen from the two Helios spacecraft within the Earth s orbit and also from the Ulysses spacecraft at a much greater distance from the Sun. It was found that large events of high energy coming from the Sun take longer to decay at greater distances from the Sun than would be predicted from theoretical magnetic bottle models.
The final session of the meeting was chaired by Mike Kosch (Lancaster). A force-free flux rope model was used by Adam Rees (Imperial) to determine the gross properties of magnetic clouds observed by Ulysses. Over the duration of the mission so far, cloud properties were sampled over a wide range of heliographic latitudes and solar conditions. There appeared to be preferred cloud orientations that were independent of the latitude. Mathew Owens (Imperial) analysed three years of solar wind data from the ACE spacecraft to investigate the relationship between magnetic field intensities and solar wind speeds. He showed that the correlation between the two quantities increased as the threshold value of magnetic field intensity was raised, indicating that some of the high-speed and low field observations may be associated with off-axis flux ropes.
Keisuke Hosokawa (Kyoto and Leicester) carried out an inter-hemispheric comparison of spectral width boundaries as observed by the SuperDARN radars. At equinox, the correlation between the magnetic latitudes of these conjugate boundaries is excellent and both hemispheres show the same response to magnetospheric reconnection. A difference of 10 minutes in the response time to a substorm between the two radars used in the study can be attributed to the effects of a significant asymmetry in the IMF. Lisa Baddeley (Leicester) reported the use of high resolution artificial targets for the CUTLASS Finland HF radar, generated by the high power heater at Tromso, to observe high wave-number ULF waves. Simultaneous observations from the CAMMICE instrument on the Polar spacecraft indicated a departure from a Maxwellian ion distribution at 10 keV, consistent with energy transfer from the particles to these waves via the drift-bounce resonance process.
Cathryn Mitchell (Bath) described the synthesis of multi-instrument total electron content measurements to generate three dimensional images of the ionosphere. Results from the USA and European regions demonstrated the potential of imaging from the auroral regions to the equator. During a magnetic storm on 15th July, 2000, an electron density depletion over the European sector was seen to extend down to 44°N. Sandra Chapman (Warwick) rounded off the presentations with a provocative talk about the use of the statistics of extremal events to characterise the game of football. It was found that the top English league over the past thirty years produced an uninteresting negative binomial distribution, whilst worldwide domestic leagues produced a long, non-Gaussian tail. These techniques can be applied to the likelihood of extreme events in plasma transport, including the coupled Sun-Earth system. The meeting concluded with thanks to all the contributors and chairmen.
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