A. Programme B. Report C. Abstracts

MIST meeting, 26 November 2004
Meeting Report

by
Neil Arnold (University of Leicester)

Published in Astronomy & Geophysics 46, 3.36-3.37 (June 2005)

The annual one-day meeting of the MIST (Magnetosphere, Ionosphere and Solar-Terrestrial) community was held on the 26th November, 2004 at the Geological Society, Burlington House. The first session of the meeting was chaired by Peter Cargill (Imperial College). A number of crossings of Saturn's outer magnetosphere were analysed by Nick Achilleos (IC) during Cassini's orbit insertion. Models allow the dynamic variability to be mapping into a global picture of the magnetosphere. There was evidence of sub-corotation of the magnetospheric plasma relative to the planet at distances of greater than 5 Saturn radii. Hazel McAndrews (Mullard Space Science Laboratory) reported on the initial results from the Cassini electron detector at the magnetopause of Saturn. It was found that within the magnetosheath there were episodes where the plasma was intermediate between being within and outside the magnetosphere. Plasma transfer could be related to either steady state reconnection or diffusion across the boundary.

An investigation of upstream waves from the bowshock and the magnetosheath region of Saturn using the Cassini magnetometer was presented by Cesar Bertucci (IC). Streams of plasma moving away from the bowshock created a 'foreshock' that modified the velocity distribution function. First observations of low frequency waves connected to the bowshock were achieved. Chris Smith (University College London) proposed auroral heating and ion drag as possible mechanisms for the imbalance between radiative transfer estimates of Jovian thermospheric temperatures and observations. If variable electric fields were used, then there was an increase in the amount of energy available without affecting the ion drag, so a net effect could be achieved.

Chris Arridge (IC) described how a global model of Saturn's magnetospheric field could be used to help interpret the observed data and to infer the global structures from in situ observations. Starting from a model of the internal planetary field and an azimuthal current disk, magnetopause currents were included to extend the applicability of the model to higher latitudes and greater distances from the planet. Observations of magnetic anomaly signatures in Mars Express data were considered by Yasir Soobiah (MSSL). In the absence of a strong planetary magnetic field, only residual crustal forces remain, but these are sufficient to influence the solar wind close to the planetary surface. The spacecraft could descend to an altitude of 300 km from a highly elliptical orbit, which was sufficient to detect ionospheric and sheath plasma. The fields focused or defocused the plasma population.

In the first of three talks from the University of Warwick, Sandra Chapman reflected on particle-in-cell simulations of reforming perpendicular shocks. Reflection of plasma from a shock boundary resulted in heating of the plasma in front of the shock. It was found that a fraction of the plasma could undergo significant accelerations and that going from hydrogen to helium ions could also increase the energies available to the plasma. Bogdan Hnat attempted to distinguish between solar wind and internal magnetospheric processes in determining the short time scale (less than a few hours) variability of the geomagnetic indices using the Fokker-Planck scaling approach. Self-similar statistics appeared to give a good approximation within this time frame regardless of solar activity levels. Lastly, Tom March described how 'mutual information' between geomagnetic indices and the solar wind as seen by the WIND spacecraft could have implications for propagation time estimates. The method allowed non-linear relationships to be tested. Out of five schemes for estimating solar wind propagation times were investigated, the one assuming a fixed orientation consistent the Parker Spiral orientation gave the best agreement.

After the lunch break, Richard Balthazor (Sheffield) took over the chair. Simon Child (IC) considered two years of Ulysses observations of the heliospheric current sheet at solar maximum to help understand the topology of the heliospheric magnetic field. Heliospheric current sheet encounters distributed across a wide range of latitudes indicated that there was an enhanced spread in the observed elevation angle of the orientations with increasing latitude. This result was consistent with a single highly tilted HCS. Ranvir Dhillon (Leicester) described the first EISCAT Svalbard Radar observations of SPEAR enhanced ion and plasma lines. There was clear evidence for the excitation of the parameteric decay instability as well as the so- called purely growing mode. There was no clear evidence of the ion line overshoot that was a recurrent feature of the Tromso heater facility. Balazs Pinter (Sheffield) modelled the sub-auroral polarization streams using the Coupled Thermosphere Ionosphere Plasmasphere (CTIP) model in the mid-latitude ionosphere. These features may raise the peak free electron concentrations by an order of magnitude, with a considerable impact on TEC measurements and radio wave propagation directions.

A study of the geometry of artificial plasma irregularities produced by RF heating was presented by Harmaninder Shergill (Leicester), in order to test the upper hybrid resonance theory of heater irregularity generation. The CUTLASS HF radar provided the patch size determination as a function of frequency and ionospheric conditions. Atousa Goudarzi (Leicester) described how the SuperDARN radar and DMSP satellites could be used to identify the location of the open-closed field line boundary of the Earth's magnetic field in response to magnetic reconnection. When the IMF was northward, the boundary moved polewards compared to southward conditions. During transitions, the response was found to be much quicker in the northern hemisphere.

Stuart Thom (Sheffield) used the CTIP model to study the refilling of the plasmasphere following a geomagnetic storm. The model results were compared with IMAGE light intensity maps of scattering from helium ions. Density variations were found to be strongly related to solar wind changes. Silvia Dalla (Manchester) updated the community on progress in building a grid of inter-operating data archives and software tools by the AstroGrid consortium. Several examples of usage relevant to the UK MIST community were presented.

The chairman of the third and final session was Ranvir Dhillon (Leicester). Tim Yeoman (Leicester) announced the first observations of SPEAR-induced coherent backscatter. High power HF radio waves from this facility generated artificial irregularities that could be observed by the CUTLASS radars several thousand kilometres away. These irregularities provided a means of accurately measuring the winds in the ionosphere, providing evidence of ULF waves. Richard Balthazor (Sheffield) presented evidence of transonic neutral wind flows in the thermosphere that had been observed by the Dynamics Explorer 2 satellite. Using the CTIP model, large electric fields were shown to be able to create strong ion drift flows. The process was highly non-linear but it was found that neutrals could propagate at velocities greater than the speed of sound.

Jim Wild (Leicester) revised time-of-flight calculations for high latitude geomagnetic pulsations using a realistic magnetospheric magnetic field model. The Cluster spacecraft observed standing Alfvèn waves with speeds dependant on the strength of the magnetic fields and the plasma density and from this the time-of-flight between conjugate points could be calculated. The period of the pulsations was found to increase towards higher latitudes. Nigel Meredith (British Antarctic Survey) had carried out a preliminary investigation of PEACE particle data during Cluster perigee passes. This data had been highly contaminated with electrons from the outer radiation belt in spite of a high thickness of shielding. However, using data from a higher energy detector and given geometric factors from the second detector, it was possible to remove much of the contamination.

The meeting ended with three presentations from MSSL. Yulia Bogdanova presented a possible mechanism for the formation of the stagnant cusp observed by Cluster at high-altitudes at a time close to noon. Stagnant conditions were found to last for approximately one hour during a period of stable lobe flux reconnection. Continuous particle injections were observed at dawn from IMAGE satellite data, whilst the SuperDARN radar network showed two reconnection sites at dawn and dusk. Aurelie Marchaudon described observations of flux transfer events by the Double Star spacecraft and injections by Cluster on the dawnside flank of the magnetosphere. Many of these events were observed and their impact on the ionosphere using the SuperDARN network was discussed. There was a good agreement between the two, aiding an understanding of the injection mechanism. Ilya Alexeev presented Cluster observations of plasma sheet electrons during a substorm. Multiple crossings during substorm onset revealed a possible wave propagating across the plasma sheet. Parallel electric currents were investigated. The anisotropy was believed to be related to the electron temperature. The electron distribution was not consistent with a simple adiabatic theory of electron heating during the substorm.

Throughout the duration of the meeting there was an opportunity to view three posters. Nanan Balan (Sheffield) described Cluster southern magnetospheric cusp crossings during geomagnetic storms. Ion densities increased by more than two orders of magnitude, ion temperatures increased by a factor of ten whilst the ion velocities turned strongly southwards. Brigid Cooling (Queen Mary and Westfield College) modelled the magnetosheath at the magnetopause to allow for a prediction of the motion of open flux tudes along the magnetopause during dayside reconnection events. The model hadbeen tested across a wide range of IMF orientations. Oleg Pokhotelov (Sheffield) discussed halo instabilities in space plasmas. A fully kinetic theory of mirror-type modes accounting for finite ion Larmor radius effects in non-Maxwellian space plasmas had been developed. From this a dispersion relationship may be obtained, revealing two different instabilities.

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