Millennium MIST 11th - 13th April 2000
Imperial College, London

[Report published in Astronomy & Geophysics 41, 4.28-4.30 (August 2000)]

A. Programme B. Report C. Abstracts

Millennium MIST 11th - 13th April 2000
Meeting Report

by N F Arnold (University of Leicester) and P Cargill (Imperial College)

Published in Astronomy & Geophysics 41, 4.28-4.30 (August 2000)

The first meeting of the new millennium saw another packed programme of the highest quality with a poster session again being needed to accommodate all of the contributions. Andy Smith (British Antarctic Survey) chaired the first session with a series of presentations on upper atmospheric science. Eoghan Griffin (University College, London) compared neutral winds from a number of sources. Differences in location exceeded those due to solar variability over two solar cycles, but the latter was still significant. Having added a number of chemical constituents to the Coupled Mesosphere and Thermosphere model, Matt Harris (UCL) considered the impact of energetic particle precipitation. Significant changes to important species were noted during active periods. He+ ions were added by Chris Wilford (Sheffield) to the Sheffield coupled thermosphere-ionosphere-plasmasphere model. The simulated ion concentrations agreed well with satellite observations.

Andrew Lawrence (Cambridge) studied planetary waves in the Southern Hemisphere and compared the findings with observations in the mesosphere and ionosphere. It was possible to characterise the vertical and latitudinal propagation of these waves. The variation of vertical velocities measured by the European Incoherent Scatter Radar allowed Vicky Howells (Rutherford Appleton Laboratory) to examine the spectrum of gravity waves near the mesopause. None of the current theoretical models were able to predict the observations correctly.

The SuperDARN HF radar network uses meteor trails in the near ranges to deduce wind speeds and diffusion rates. Peter Cook (Leicester) described the calibration of one of these radars by comparing the results with a purpose-built meteor radar. Neil Arnold (Leicester) used a model of the upper atmosphere to demonstrate how geomagnetic activity in the thermosphere could affect the propagation of planetary waves. The winter stratospheric circulation was found to be particularly sensitive.

The second session on the ionosphere was chaired by Mark Lester (Leicester). Henry Rishbeth (Southampton) reminisced over the F-layer dynamo theory invoked 30 years ago to explain satellite observations of super-rotation. Subsequent wind measurements indicated that the rotation was smaller than expected, leading to a puzzle that has yet to be resolved. Standing in for Stuart Robertson (Southampton), Alan Aylward (UCL) introduced a new set of instruments installed on Svalbard to measure the cusp and auroral oval. The eclipse of August 11th 1999 was used as part of its validation procedure. The ESR itself was scanning along the North-South meridian in a paper by Adam Smith (Aberystwyth). The impact of reconnection from the magnetosphere on the ionosphere was examined under a variety of solar wind conditions.

Huiyu Tao (Lancaster) reported the detection of a Pi2 pulsation during a substorm onset using the IRIS riometer. Strong absorption prevents measurements from being made by HF radars at the same time. Down in the Southern Hemisphere, two overlapping SuperDARN radars were employed by Gareth Chisham (BAS) to investigate poleward moving line-of-sight 'flow bursts'. Much of the enhancement was due to a change in the direction of the convection reversal boundary. The first day of the meeting was concluded by Emma Woodfield (Leicester). She examined the use of the spectral width parameter from the CUTLASS Finland radar as an indicator of the position of the ionospheric footprint of the open/closed magnetic field line boundary.

The meeting resumed on Wednesday morning with Ian Mann (York) chairing proceedings on a variety of solar-terrestrial topics. A new instrument for the passive monitoring of the top side ionosphere using radio frequency waves was described by Péter Bakki (Budapest). A spectrum analyser was used to resolve different sources and estimate the electron density from the absorption of signals by the ionosphere. Mark Lester (Leicester) described ionospheric flows during a substorm from both an orbiting auroral imager and the SuperDARN radar chain. In conjunction with the Scandinavian magnetometers, it was possible to examine the convection pattern in detail.

Iain Coleman (BAS) examined reconnection on the dayside magnetopause where the solar and geomagnetic fields are oppositely aligned. Using a model of the Earth's magnetic field it was possible to construct an ionospheric footprint and compare it with radar observations to test competing theories. Two papers from York considered the acceleration of electrons in the near-Earth environment by ULF waves during geomagnetic storms. First off, Rod Matthie reported a causal connection between large pulsations observed from magnetometer data and enhanced fluxes of electrons. Then Louis Ozeke presented corroborative modelling evidence. The 'bounce resonance' equation supported the observed characteristics of these pulsations, such as their monochromatic nature and localisation in both space and time.

Studies of Ulysses spacecraft data from Imperial College carried us through to the interval. Dorian Clack reported on observations of large-scale corotating shock orientations. The magnetic planarity in the vicinity of the forward and reverse shocks was compared with previous studies. Geraint Jones found evidence for the presence of comet Hyakutake's tail at a considerable distance from the nucleus. This made it the longest comet tail every recorded.

Steve Schwartz (Queen Mary and Westfield College) took over the reins after coffee. Sandra Chapman (Warwick) explored the applicability of an avalanche model to the dynamic activity present in the Earth's magnetosphere. Auroral data obtained from the Polar spacecraft divided the energy distribution internally generated and externally forced components. Nick Watkins (BAS) sought self-organised criticality within the magnetosphere through the AE geomagnetic index and the solar wind. He demonstrated that these systems possess power law distributions consistent with either SOC or turbulent systems.

Tim Horbury (QMW) made use of three spacecraft to deduce structures in the geospace environment on a scale of around 105 km. Results provided new estimates of the relative abundances of tangential and rotational discontinuities in the solar wind. Murtaza Gulamali (IC) investigated co-rotating interaction regions as seen by Ulysses at mid-latitudes. Results from a magnetic cloud embedded within a rarefaction region of the CIR were presented. Phil Moran (Aberystwyth) discussed radio scintillations generated by fluctuations in the Interplanetary Magnetic Field. Combining the measurements from two radio telescopes allowed the solar wind velocity to be measured under a variety of conditions.

Having explained to the audience what a two and a half dimensional magnetohydrodynamic code was, Joachim Schmidt (IC) simulated coronal mass ejections to investigate their interaction with the solar wind. He showed that the direction of alignment was critical in determining interactions with the wind. John Sherman (RAL), a representative from STARLINK, spoke to the MIST community about the new arrangements for PPARC computing provision. The changes will take effect in April 2001.

Refreshed by lunch and conversation, the afternoon programme started with a series of brief talks about the forthcoming CLUSTER II space mission and other new science initiatives. It was chaired by Peter Cargill (IC). André Balogh (IC) introduced the community to the mission. He explained that delays of several months are being experienced due to thruster problems. Mike Hapgood (RAL) discussed the constraints on data transmission and instrument resolution given the provision of a single receiving station in Spain. The UK online data facility was demonstrated by Steve Schwartz (QMW). Mike Lockwood(RAL) presented an overview of the scientific potential of the CLUSTER mission. Mark Lester (Leicester) outlined SPEAR a new active radar for probing the upper atmosphere and magnetosphere being constructed for deployment within the polar cap. Andy Smith (BAS) reviewed the new experiments being introduced in the Antarctic by the British Antarctic Survey. A report of improvements to the EISCAT facilities both on the mainland and on Svalbard was made by Ian McCrea (RAL). Finally, Farideh Honary (Lancaster) discussed the possibility of acquiring a new riometer facility with high spatial resolution and energy discrimination.

The final oral session of the day was chaired by Chris Owen (MSSL). Stephen Topliss (MSSL) reported particle population observations of the Cusp during Northward IMF from the POLAR satellite. Several events exhibited secondary populations with an increase in energy with latitude leading to a 'butterfly' dispersion pattern. Matt Taylor (IC) investigated the interactions between the cusp region of the Earth's geomagnetic field and Alfvénic waves. A combination of the conservation of energy and the occurrence of Kelvin-Helmholtz instabilities balanced the decay and growth mechanisms.

Nigel Meredith (MSSL) examined the spatial and temporal distribution of whistler mode chorus in the inner magnetosphere from satellite data. The acceleration of electrons in the radiation belt by these waves is consistent with the observations. Rosalind Mist (MSSL) used Geotail satellite data to study the 2-D distribution of ions in the Earth's distant plasma sheet. Additional multiple scattering from Fermi-type processes was required to account for the data. Malcolm Dunlop (IC) made use of Equator-S crossings of the Earth's magnetopause to suggest that most of the time the plasma depletion layer is either narrow or absent. The detection of ion cyclotron waves was found to be a useful indicator of this layer.

There was extensive time available for viewing the posters during coffee and lunch breaks and after the close of the afternoon session. All sessions were well attended and provided a focus for numerous lively discussions. Richard Balthazor (Sheffield) presented results from the CTIP model in which thermospheric heating due to upward-propagating plasma waves were included. The preliminary results suggest that this new physics can remove discrepancies in existing models. Sandra Chapman (Warwick) presented new developments in her work on virtual reality. She showed examples of how VR can be used to help understand complex systems such as the motion of particles in a current.

Gareth Chisham (BAS) presented results on the response of HF radar spectral boundary width to a switch in IMF By. An equatorward bulge of the polar cap boundary occurred in association with changes in the dayside reconnection rate. Toby Clark (BGS) showed results obtained from instruments installed by Scottish Power to measure Geomagnetically Induced Currents in their portion of the UK grid. He presented a comparison of their measurements with magnetic field variations measured at UK magnetic observatories. Elizabeth Clark (RAL) presented results of ionospheric observations during solar eclipses since 1932. She showed that there was evidence for a long-term increase in the Sun's coronal intensity at EUV and X-ray wavelengths.

Silvia Dalla (IC) presented further results on long-term periodicities in solar energetic particle fluxes at large heliocentric distances. Evidence now seems to exist for periodicities of protons in the 30 - 125 MeV range and electrons in the 2-10 MeV range. Jackie Davies (Leicester) discussed EISCAT VHF observations in a poleward-expanding auroral bulge. She showed that in two cases the electron temperature boundary was straddled by a narrow band of enhanced ion temperature indicative of high electric fields needed for current continuity. Malcolm Dunlop (IC) presented new models for the warped Jovian current sheet. An extensive parameter variation was presented in order to fit the data from the various spacecraft passes through the Jovian magnetosphere.

Markus Fraens (QMW) discussed the properties of magnetic depressions in the solar wind. The depressions were modelled in terms of both MHD models of solitary waves and a kinetic description, and a comparison with spacecraft data was presented. Mike Kosch (MPAe) presented results concerning observations of HF-induced airglow by DASI and CUTLASS. He noted that the development and fading of airglow patches could be observed with an intensity up to 100 Rayleighs. Ian Krauklis (MSSL) presented two-point observations of lobe reconnection. Using data from the Polar and Interball spacecraft, he showed that the observations were very similar despite a spacecraft separation of 2 Re. Elizabeth Lucek (IC) presented results of magnetopause crossings obtained by the Equator-S mission. She showed that a significant number of crossings show no real structure on sub-second scales, and that there is some evidence for the generation of electromagnetic lower hybrid waves.

Nick Mattin (BAS) presented a new data access and browsing system (DABS). The system provides a single web-based interface to the last 5 years of BAS data held in upper atmosphere databases. George Millward (UCL) presented results of CTIP modelling of the influence of tidal forcing on equatorial vertical ion drift. The calculated drifts were found to be in good agreement with empirical data based on radar measurements. Ingo Mueller-Wodarg (UCL) presented a 3-D general circulation model of Titan and Triton. These are the only terrestrial-sized moons in the solar system with a nitrogen-rich atmosphere, and show significant differences from the Earth's thermosphere.

Richard Rijnbeek (Sussex) presented models for magnetic reconnection in accelerating plasmas. Using a time-dependent Petschek model, he showed that for high speed plasma flows, destruction and subsequent reformation of a current sheet could occur. Andy Smith (BAS) presented results from observations of post-midnight VLF, magnetic and Pi2 substorm signatures. The results were interpreted in terms of a substorm current wedge with an approximately westward electrojet poleward of Halley. Peter Cargill on behalf of Tim Stubbs (IC) presented results of energetic particles seen by the CAMMICE instrument on Polar. A dawnside asymmetry was seen in particles with energies in the range 1-35 KeV and this was interpreted in terms of the convection electric field in the magnetotail.

The first session of the last day was chaired by Malcolm Dunlop (IC). Emma Bunce (Leicester) reported a local time asymmetry in the equatorial current sheet of Jupiter's magnetosphere as measured by a series of planetary encounters. These results implied a significant divergence of the azimuthal equatorial current. Robert Wilson (IC) investigated 10-20 minute period ULF waves in Jupiter's magnetosphere as seen by Galileo. These waves were found to be prominent in the perpendicular magnetic field component and independent of local time and radial distance from the planet.

Stéphane Espinosa (IC) analysed magnetic field data from spacecraft encounters with Saturn and found a perturbation with a period close to that of the planetary rotation period. A mechanism involving the 'ballooning' of the field and plasma was proposed. Abigail Rymer (MSSL) reported an unusually strong electron beam observed in a Cassini particle detector during the recent flyby of the Earth. As only a few pitch angles recorded this beam, there was a distinct possibility that there was a problem with the detector.

Michelle Dougherty (IC) described the deployment of the Cassini magnetometer leading up to the Earth swingby. The high velocity of the probe as it passed by the Earth provided a unique snapshot of the magnetosphere. Paul Birch (Warwick) presented modelling results from simulations of the lunar wake using a 1-D particle-in-cell code. It was possible to study both electron and ion infilling within the Moon's shadow and the results agreed well with the observations.

The final session of the conference was chaired by Alan Aylward (UCL). Ranvir Dhillon (Leicester) described the properties of field aligned irregularities generated by the EISCAT heater and seen in the CUTLASS radars. These irregularities are considerably better correlated than their natural counterparts making them more effective targets for studying the ionosphere. Yuanzhi Su (Sheffield) used the SCTIP model to explain an observed asymmetry in electron densities between the hemispheres. At high altitudes the difference appeared to be due to neutral wind variations whilst at low altitudes differences in mean molecular mass and density were responsible.

Csaba Szombathy (Budapest) described the results of some terrestrial tests of a new space instrument to study the ionosphere via analysing the radio spectrum. The eclipse of 1999 provided an ideal opportunity to monitor the signal strength variations from several sources. Ingo Mueller-Wodarg (UCL) used the CTIP model to investigate the role of tides as a thermospheric 'spoon', mixing up the heterogeneous upper atmosphere. Asymmetries in the seasonal circulation pattern contributed to height variations in the resultant mean molecular mass.

Mark Dieckmann (Linkoeping) described the behaviour of low velocity waves generated by a plasma sounder instrument on board spacecraft. One category referred to as Q-resonances are probably generated by the strong turbulence excited by the sounder itself. Mike Kosch (MPAe) reported observations of the thermospheric ion drag time constants from two ground based instruments and compared the results with previous satellite readings. The neutral wind takes up to six hours to acquire most of the momentum from the ionosphere.

Anasuya Aruliah (UCL) described attempts to model the neutral wind inertia to changes in the ionosphere immediately after the termination of a geomagnetic storm. A comparison with ground-based instrumentation revealed an unexplained discrepancy between the two. Tim Yeoman (Leicester) used measurements of ULF waves from CUTLASS to infer their phase evolution. Combining the information from three distinct wave types allowed the drift-bounce resonance interactions that caused the waves to be determined. The meeting concluded with thanks to the contributors, and especially to Peter Cargill, the local organiser.

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