[Report published in Astronomy & Geophysics 42, 4.18-4.20, (2001)]
by N F Arnold (University of Leicester) and I R Mann (University of York)
Published in Astronomy & Geophysics 42, 4.18-4.20, (2001)
The magnetosphere, ionosphere and solar-terrestrial physics community gathered at the Department of Chemistry, University of York from 9-11th April 2001.
The first session of the meeting was convened by its host, Ian Mann (York). To mark the successful deployment of the four CLUSTER II spacecraft, the first eleven papers were devoted to early scientific returns from the mission. Andrew Fazakerley (Mullard Space Science Laboratory) presented measurements of electron velocity distributions from the Plasma Electron And Current Experiment. He described the efforts to calibrate the four instruments. The first simultaneous observations of magnetic fields both at the magnetopause and in the magnetosheath using the Cluster spacecraft were presented by Elizabeth Lucek (Imperial College). Variations between instruments was marked normal to the magnetosheath boundary.
Malcolm Dunlop (IC) investigated the magnetopause dusk flank and boundary layer using the fluxgate magnetometer. A magnetic storm compressed the magnetopause which permitted a detailed analysis of the magnetopause boundary layer. PEACE observations of electrons in the dayside magnetopause region were reported on by Chris Owen (MSSL). He identified transient bursts of magnetosheath-like plasma in the data suggestive of flux transfer events with periods of order 4-8 minutes. Jonathan Eastwood (IC) used the fluxgate magnetometer to investigate the structures in the solar wind and magnetosphere. In particular a sector boundary in the solar wind was observed as the spacecraft entered and left the magnetosheath.
Two papers from MSSL focused once more on the PEACE instruments. Matthew Taylor described observations of electrons in the northern cusp region. He found an example of two spacecraft entering the open closed boundary layer whilst the other two remained outside. Ian Krauklis combined PEACE and FGM measurements from two spacecraft to observe the mid-altitude cusp. The open - closed boundary was seen to erode due to low latitude reconnection. Enhancements in density may have been related to field aligned currents and flux transfer events.
After the interval, Chris Owen took the chair. Tim Horbury (IC) presented observations of the magnetic field at the bowshock. Detailed observations of a number of parameters around the bowshock could be estimated. Whistler waves were observed that varied rapidly in response to changing IMF conditions. Ian Bates (Sheffield) used the wave field decomposition method developed for the AMPTE pair of spacecraft to determine the wave dispersion relation for Cluster. The technique was well suited to the study of magnetosheath waves.
Jim Wild (Leicester) studied flux transfer events at the high latitude magnetopause from Cluster and ground-based instrumentation. Bipolarisations of the magnetic field, indicative of FTEs were observed and the radars observed pulsed poleward moving flows. Co-coordinated ground magnetometer and Cluster data were also employed by Ian Mann to study Kelvin-Helmholtz instabilities driven by solar wind impulses. During intervals of fast solar wind speed, the instability can bathe the flank magnetosphere with low frequency wave power.
Moving away from Cluster, Iain Coleman (British Antarctic Survey) presented a study of magnetic field line draping in the dayside magnetosheath using Geotail and Wind spacecraft data. The relationship between the solar wind and the magnetopause became more complex moving from the sub-solar point to the flanks. Bridget Cooling (Queen Mary and Westfield) described results from a three-dimensional model of open flux tubes along the magnetopause, which was used to estimate the location of reconnection and the asymmetries between the Parker spiral direction and seasonal asymmetries of polar convection.
The last paper of the day was given by Mervyn Freeman (BAS). He examined the influence of the solar wind on the scaling properties of energy dissipation in the magnetosphere, using the AE index of ionospheric currents. The time series was found to have fractal properties indicating turbulence. John Sherman (Rutherford Appleton Laboratory) updated the MIST community on Starlink services that are now available and invited STP suggestions towards forthcoming infrastructure plans. A highlight of the meeting was the inauguration of the MIST five-a-side football tournament; a trophy was presented to the winning team at the conference dinner.
The second day of the meeting was brought to order by Alan Aylward (University College London). David Rees (Utah/Hovemere) described a double etalon Fabry-Perot interferometer for studying the dayside aurora using the oxygen green line. He presented results from several aurora in addition to day-glow in a two-dimensional full sky image. Proton aurora observations from Svalbard using a number of ground and space based instrumentation were described by Stuart Robertson (Southampton). A shock event was monitored and the first measurements of the backscatter Doppler shift of the hydrogen-beta line in the cusp were reported.
Steve Maple gave the first of three talks from Lancaster. He used the sky map of the 38.2 MHz Imaging Riometer for Ionospheric Studies (IRIS) to determine the distribution of cosmic noise intensity. The map is used to generate the quiet day curves. Carlos del Pozo used IRIS and EISCAT radar observations over three years to assess the correspondence between absorption, electric field strength and conductivity during substorm activity and E-region instability conditions. John Hargreaves examined the fine structure in auroral absorption 'spike' events, where there is a peak lasting only for a minute or two at a substorm onset. Pi2 periodicities of 15 60 seconds were seen using wavelet analysis.
An adaptive model of the ionosphere using radio tomography was described by R. Dabas (National Physical Laboratory, India). The technique demonstrated a role for tomography in near-real-time ionospheric mapping for radio broadcasting applications. Henry Rishbeth (Southampton) explained how the seasonal asymmetry in the f2 layer could not be explained by the eccentricity of the Earth s orbit around the Sun. Tides may well account for this phenomenon. Simulations of integrated oxygen emissions from the Coupled Middle Atmosphere and Thermosphere general circulation model were presented by Alan Aylward (UCL) and compared with Fabry-Perot interferometer results from Sweden and Norway.
Mark Lester (Leicester) took over the chair till lunch time. A report of progress on a major upgrade to the CUTLASS HF radar system was made by Tim Yeoman (Leicester). Very good correspondence between the new, independent operating modes was obtained, but some data contamination needed to be resolved. Mervyn Freeman (BAS) presented a unified model of the response of ionospheric convection to changes in the interplanetary magnetic field. He used the model to test two conflicting theories of magnetic reconnection.
Four talks were devoted to the scientific exploitation of SuperDARN HF radar data. Kathryn McWilliams (Leicester) presented the first two dimensional electric field measurements of anti-sunward ionospheric flow bursts within the footprint of newly reconnected magnetic flux. She used the twin CUTLASS radars in conjunction with Defense Meteorological Satellite Programme data. Gareth Chisham (BAS) tested competing hypotheses of reconnection during large IMF By conditions as observed by SuperDARN HF radar measurements of the ionosphere. It was found that the anti-parallel merging hypothesis matched the data far better than the subsolar merging hypothesis. Adrian Grocott (Leicester) presented observations of substorm excited flows in the high latitude ionosphere using the radar network, magnetometer and spacecraft data. He provided evidence that convection flows could be driven by nightside reconnection. Finally, Emma Woodfield (Leicester) carried out an inter-hemispheric statistical study of nighttime spectral width distributions observed by two of the radars. There were many similarities but dawn-dusk asymmetries and seasonal variations observed at Iceland were not seen at Syowa.
Gary Abel (BAS) compared the statistical occurrence of Pulsed Ionospheric Flows seen in the ground to flux transfer events observed by spacecraft. Power spectra indicate the former have a turbulent 'pink noise' distribution indicative of self organised criticality. Hina Khan (Leicester) presented a study of the dynamic cusp during strong IMF By conditions using multiple ground and space based instruments. Poleward moving ionospheric flows coincided with enhanced density and ion temperatures, associated with pulsed dayside reconnection. The morning session was concluded by Steve Morley (Southampton) who discussed the different origins of 'sawtooth' cusp features in the ion dispersions observed by DMSP as it crossed the northern cusp region. Changes in the signatures were likely to be due to a change in the reconnection rates encountered at different satellite passes.
Proceedings for the first session of the afternoon were directed by Tim Yeoman (Leicester). Lewis Ozeke (York) described how asymmetric ionospheric conductivities could influence the generation of poloidal Alfvén waves and generate modes that are not permitted in the symmetric case. The so-called 'drift-bounce' mechanism may be an important factor in ring current decay processes. An extensive survey of POLAR satellite ion distribution data had been carried out by Lisa Baddeley (Leicester) to identify the energy sources for particle-driven ultra low frequency waves. Signatures on the spacecraft were then compared with ground-based magnetometer and radar observations of the waves.
Magnetometer data featured prominently in the next three talks. Joe Mathews (York) was interested in large scale ionospheric pulsation events. The observations indicated that the perturbation was probably caused by the fundamental mode of oscillation of drifting ring current ions. Zoe Dent (York) employed the cross-phase technique to obtain the eigenfrequency of the magnetic field line from two meridionally spaced magnetometers. From this it was possible to estimate the plasma density in the equatorial plane and then compare the results with in situ spacecraft data. Julia Rees (Sheffield) analysed magnetic field data using the wavelet transform technique. From this it was possible to monitor the erosion of the plasmasphere following a magnetic storm. A simple convection model was not sufficient to explain the results.
Andy Smith (BAS) described a campaign in the Antarctic to study the bursts of whistler mode chorus waves that propagate to the ground following the injection of clouds of energetic electrons around midnight during the substorm expansion phase. Clare Watt (BAS) investigated the breakdown of idealized magnetohydrodynamics within space plasmas when resistivity becomes important. The inclusion of electro-static ion acoustic waves indicated that simple models significantly under-estimated the true extent of the process.
Tuesday afternoon continued with a poster session. In the first of two Cluster papers, Andy Buckley (Sussex) highlighted the first results from the Digital Wave Processing experiment (DWP) particle correlator and showed electron time structuring during both natural and plasma sounding events. Then Malcolm Dunlop (IC) presented first results from Cluster FGM show-casing how to use four-point magnetic field data to analyse the 3D structure and motion of discontinuities (discontinuity analyser) and electric current densities (curlometer).
Simon Foster (Southampton) showed that there was a strong correlation between the latitudinal spread in sunspot groups and the flux emergence rate. The increase in coronal source flux inferred from sunspot group observations matched the century timescale increases in solar flux. Continuing on the theme of the drivers of geomagnetic activity, Abigail Rymer (MSSL) presented multi-point measurements of the evolution of a CME propagation speed from 0-5 AU, using SOHO, Cassini, ACE spacecraft and Earth orbiting satellites. Youra Taroyan (Sheffield) then examined the energy injection into the magnetosphere resulting from a resonant flow instability. He showed that these surface wave resonant flow instabilities could occur for shear flows below the Kelvin-Helmholtz threshold.
Turning attention inside the magnetosphere, Dave Milling (York) showed how the magnetometer cross-phase technique can be used to infer the position of the plasmapause and track its motion through the day. Moving lower into the atmosphere, Mick Denton (Aberystwyth) demonstrated an excellent agreement between the results from the Coupled-Thermosphere-Ionosphere-Plasmasphere (CTIP) model and tomographic measurements of the high-latitude ionosphere. Chris Wilford (Sheffield) outlined the recent extension to the CTIP model with the inclusion of He+ ions. The revised CTIP code was validated by comparison with data from DMSP.
Mervyn Freeman (BAS) was the chair for the concluding series of talks for the day. FAST satellite data had been employed by Sophie Cash (Leicester) to characterise the effects of 3 Hz modulated ionospheric heating of the E-region at Tromsö and the subsequent launch of ULF waves. Variations in the electric field measurements and a downward electron flux from a height of 3500 km were observed. The Tromsö heater was also used by Farideh Honary (Lancaster) to examine artificially induced airglow emissions in the oxygen red and green lines. Several theories had been proposed to account for these emissions. Significant levels of electron temperature enhancement were detected at the same time. Richard Horne (BAS) presented a paper on behalf Nigel Meridith (MSSL). They had examined the link between enhanced substorm activity and electrons accelerated to relativistic energies. Using CRRES satellite data, they showed that wave-particle interactions were responsible for the acceleration within the storm time convection electric field. Richard Horne had also looked at the pitch angle distribution of energetic electrons from CRRES during an acceleration event in the outer radiation belt. Pitch angle scattering appeared to be consistent with the data.
A new auroral signature of solar wind pressure pulses from the South Pole was described by Mike Pinnock (BAS). Dynamic pressure variations in the dayside magnetopause generated an equatorial spur in the green atomic oxygen emission line. Alan Rodger (BAS) continued on the theme of ionospheric signatures of pressure pulses with a consideration of travelling convection vortices. The hemispheric asymmetry in the magnetometer and riometer data may be ascribed to the propagation of Alfvénic waves from the sub-solar point. The IRIS riometer was used by Andrew Kavanagh (Lancaster) to investigate a solar wind pressure pulse. In addition to high absorption readings at the riometer, the STARE radar observed flow decreases and a loss of backscattered power, whilst magnetometers suggested Kelvin-Helmholtz instabilities.
The chair of the first session of the final day was Farideh Honary (Lancaster). An overview of the new BAS Geospace-Atmosphere Transfer Functions programme was given by Martin Jarvis, whereby the Antarctic between 60 200 km was to be studied to determine long-term trends and contrast it with the Arctic. The region is special because it is dynamically isolated from the rest of the atmosphere in winter. Owen Jones (BAS) described how the Imaging Doppler Interferometer could be used to measure winds in the upper mesosphere and lower thermosphere. There was good agreement between this instrument and a dedicated meteor radar. In particular, confidence in the results above 90 km was increased by the study.
Mark Clilverd (BAS) described how an MF radar at Rothera, Antarctica was used to investigate whether the echoes in the upper mesosphere were consistent with Polar Mesospheric Summer Echoes. Many of the measurements were more consistent with turbulent diffusion from gravity waves. Patrick Espy (BAS) used a CCD all-sky imaging camera at Halley, Antarctica to observe optical airglow emissions. Under good viewing conditions, atmospheric gravity waves were found to be very common in the winter with fewer waves observed in the summer. Robert Hibbins (BAS) described in more detail how the all-sky camera was able to extract the airglow data from the background signal that included stars. It was then possible to obtain the relevant gravity wave parameters.
Andy Lawrence (Cambridge) presented a gravity wave ray-tracing model that was used to simulate the horizontal and vertical propagation from the surface up to mesospheric altitudes. The ray paths and momentum fluxes provided an estimate of their source and energy distributions. George Millward (UCL) presented model simulations of the thermosphere, ionosphere, plasmasphere and electrosphere during a geomagnetic storm. More detailed electrodynamics compared with earlier models resulted in a more rapid response in the atmosphere to the perturbation.
Richard Balthazor (Sheffield) described how high speed ion flows could be sustained in the upper atmosphere using the CTIP model. Supersonic shock fronts could generate heating comparable to that associated with particle precipitation. Yuanzhi Zu (Sheffield) used the Sheffield University Plasmasphere Ionosphere Model to examine the subauroral topside ionosphere during a severe geomagnetic storm. The plasmapause was found to move to a very low L shell.
The final session of the meeting was chaired by Tim Horbury (IC). Mai Lam (BAS) analysed the impact of Forbush decreases in galactic cosmic rays on the atmosphere over the South Pole. No observable effects were found, contradicting the results of an earlier study at Vostok 1000 km to the north. Mike Kosch (Lancaster) provided a critical evaluation of the horizontal thermospheric winds measured by the Fabry-Perot interferometer located at Skibotn, Norway. During geomagnetic storms, the vertical wind becomes an important factor.
Michael Mendillo (Boston University) compared the ionospheric variability of Mars and the Earth. Mars Global Surveyor provided a number of radio occultation opportunities to measure the ionosphere whilst the spacecraft was aerobraking into orbit. Andrew Coates (MSSL) described the first results from the CAPS electron spectrometer on board the Cassini spacecraft as it passed Jupiter on the way to Saturn. The planet's bow shock was greatly expanded compared with the Voyager encounters due to changes in the solar wind. Stan Cowley (Leicester) outlined his predictions for the behaviour of Jupiter's magnetosphere and its influence on the ionosphere, as Cassini passed by the planet. The position of the auroral oval should be affected by the strength of the solar wind.
Matthew Owens (IC) examined the relationship between the peak magnetic field intensity and peak ion velocity of the solar wind as seen by the ACE spacecraft. Knowing the velocity of solar emissions, it becomes possible to predict the magnitude of the subsequent magnetic field perturbations as experienced by the Earth. Andy Breen (Aberystwyth) compared the large-scale structure of the solar-maximum solar wind determined by the interplanetary scintillation technique and in situ spacecraft measurements. Results were particularly good at slow velocities.
Three talks from Imperial College brought the meeting to a close. Alan Rees reported on a preliminary survey of magnetic clouds observed by the Ulysses spacecraft as it passed from high solar latitudes to the south pole of the Sun. 32 clouds were observed where smooth magnetic field rotations with a duration of several days occurred. Jonathan Gloag discussed the limitations of shock parameter calculations in describing heliospheric shock waves. Over 100 shocks were observed by Ulysses; more than half appeared to indicate a breakdown in the MHD approximation. Murtaza Gulamali observed MHD turbulence at the Ulysses spacecraft. A numerical simulation was used to test several wave generation mechanisms, including solar coronal convection outwards into the solar wind and localised instabilities causing a turbulent energy cascade.
The meeting concluded with thanks to all participants, particularly the local organiser Ian Mann.