[Report published in Astronomy & Geophysics 46, 4.18-4.21 (2005)]
by N F Arnold and Andrew Lyons (University of Leicester)
Published in Astronomy & Geophysics 46, 4.18-4.21 (2005)
The magnetosphere, ionosphere and solar-terrestrial physics community gathered at Selwyn College, University of Cambridge for three days between Tuesday 5th April and Thursday 7th April 2005. Neil Arnold and Andrew Lyons report.
The first session of the meeting was chaired by Andy Smith (British Antarctic Survey) and featured results from a number of ongoing planetary missions. Andrew Coates (Mullard Space Science Laboratory) presented early results from the Cassini Plasma Spectrometer (CAPS). Solar wind pressure was shown to control the aurora in Saturn's ionosphere. The planet's inner magnetosphere was found to be mainly composed of water ions from the icy satellites whilst its ionosphere near the rings was dominated by molecular oxygen. Abigail Rymer (MSSL) described how the CAPS experiment revealed classical signatures of hot ions and electrons undergoing adiabatic drift dispersion in Saturn's inner magnetosphere. She found that the inferred time since injection was usually less than one Saturn rotation.
Pioneer, Voyager, and Cassini magnetometer data was used by Christopher Arridge (Imperial College) to derive the equatorial current density in the kronian magnetosphere. He compared the estimated current density with previous empirical values and models of the current sheet. Hazel McAndrews (MSSL) had also made use of the CAPS instrument on Cassini to compare and contrast the wakes of the moons Dione and Enceladus on the magnetosphere of Saturn. The latter moon had carved out a depletion region in the trapped high energy particles of the radiation belt.
Alexandra Law (Imperial College) described how Titan usually orbits within Saturn's magnetosphere, giving rise to a magnetic wake in the rapidly rotating plasma field. The first three targeted flybys made by Cassini allowed the response of the magnetosphere around Titan to changes in the solar wind to be examined. Christopher Smith (University College London) explained how the addition of steady Joule heating and ion drag into the upper atmospheres of Jupiter and Saturn were not sufficient to account for the observed high thermospheric temperatures. By introducing fluctuations about the mean electric field, there was a significant increase in the heating.
A session on atmospheric waves, winds, tides and temperatures back on Earth was chaired by George Millward (UCL). Nick Mitchell (Bath) announced the installation of a new meteor radar at the BAS station at Rothera in the Antarctic. Preliminary results from the radar were presented describing the mean flow, planetary wave activity and daily-mean temperatures measured in the late-summer mesopause region. Alan Aylward (UCL) described the latest developments with their Coupled Mesosphere and Thermosphere model. The new version will include a self-consistent middle atmsophere and a more accurate representation of the Earth's magnetic field, in addition to greatly increased flexibility and ease of use compared with earlier versions.
Henry Rishbeth (Southampton) introduced the Bastille Day storm of July 2000 and other large geomagnetic storms to show evidence of large increases of F2-layer electron density at low and middle latitudes. His talk discussed the physics of storm-enhanced electron densities (SED) and in particular the suggestion that plasma originating in equatorial latitudes may be transported to the polar cap. The European incoherent scatter radar (EISCAT) was used by Eoghan Griffin (UCL) to calibrate Fabry-Perot Interferometer measurements of neutral temperatures in the thermosphere within the polar cap and at the edge of the auroral oval. Subsequent FPI data could now be normalised under a wide range of solar-terrestrial conditions.
The first session of Wednesday was chaired by Nick Mitchell (Bath) and considered topics in ionospheric research. George Millward (UCL) described how current ionospheric models were being modified to include observed magnetic field lines instead of a dipole field representation. The next stage of the project, in which the new ionosphere was fully coupled to a global model of thermospheric electrodynamics was also discussed. Alan Wood (University of Wales Aberystwyth) explained how a 'tongue-of-ionisation' (TOI), comprising dayside plasma entrained in the high-latitude convection, was believed to be responsible for density enhancements in the polar ionosphere. Observations of TOI were presented from a sequence of satellite passes monitored by the UWA radio tomography chain and supporting radar observations.
Co-ordinated observations from the EISCAT heating facility at Tromso and the CUTLASS Finland HF radar were presented by Harmaninder Shergill (Leicester). Using a variety of experimental configurations, the geometry of the resultant patches could be used to determine the observed power distribution. Terry Robinson (Leicester) described the new SPEAR high power radio wave facility on Svalbard. The first observations of artificially stimulated plasma line emissions were recorded along with field-aligned plasma density irregularities observed by the CUTLASS radar.
Alexandra Cran-McGreehin (St Andrews) presented analytical work based on a model which derived the non-linear current voltage relationship for the downward field-aligned auroral current region. The peak in the ratio of the magnetic field to electron density plays an important role in determining the conductivities present. Silvia Dalla (Manchester) described how Virtual Observatories (VOs) are being developed all over the world to enable seamless access to a diverse range of astronomical datasets. AstroGrid, the UK contribution, will include datasets from the Solar System Data Centre. A science case aimed at following coronal mass ejections (CMEs) through their evolution was presented.
The second session of the day was chaired by Abigail Rymer (MSSL) on the sun's atmosphere and the solar wind. Richard Henwood (Rutherford Appleton Laboratory) described a new tool to reconstruct solar images from the Greenwich Sunspot Group Reports which enabled large magnetic storms to be related to unaided observations of sunspots. This work substantiated a technique used to identify possible intense historical geomagnetic storms based on two millenia of coincident sunspot and auroral observations from East Asia. Simon Child (IC) used fifteen years of Ulysses data to better understand the heliospheric current sheet (HCS) observed over most solar latitudes. He found that the Ulysses data were consistent with a single highly tilted HCS at solar maximum, but that there was also substantial local structure within individual sector boundary crossings.
Sandra Chapman (Warwick) applied the concept of self-similarity to reveal scaling in the structure functions of density fluctuations in the solar wind. The results were compared with passive scalars obtained in other turbulent systems. The two data sets were not coincident, implying limitations with the present assumptions. Phillip Newman (Brighton) described how the reflections of a proportion of ions from the solar wind, at the Earth's bow shock, contribute to thermalization from high Mach number trajectories. Results on the effect of the magnetic field direction and the curvature of the shock were discussed for cylindrical and spherical shock geometries and compared to those for a planar shock.
The afternoon sessions were devoted to the impact of the four Cluster spacecraft to magnetospheric boundary layer science. James Wild (Leicester) was in the chair. Melissa Longmore (Queen Mary College, London) presented the results of a statistical survey of the moments of the plasma distribution within the magnetosheath using four years of Cluster orbital coverage to characterise its flow and density. She noted a deceleration of the flow at higher latitudes close to the magnetopause, resulting in sub-Alfvénic flow near the cusp. Ian Bates (Sheffield) used Cluster data to investigate the redistribution of energy by the solar wind around the magnetopause, in particular the exchange between plasma particles and the wave field. Cluster allowed an improvement on earlier 'two-point' measurements of energy transfer in the plasma and more meaningful estimates could now be made.
Yulia Bogdanova (MSSL) described Cluster observations of two distinctive boundary layers in the dayside mid-altitude cusp under a range of solar wind and IMF conditions. The first consisted of soft magnetosheath electrons and high-energy boundary plasma sheet ions and the second was a mixture of both ions and electrons with magnetostheath energies. Panagiota Petkaki (BAS) presented an analysis of electric and magnetic waves measured by STAFF instruments on the Cluster spacecraft during several current sheet crossings. She found that the electric and magnetic wave power decreased considerably at all frequencies when the magnetic field strength approached zero.
The chair for the last session of the day was Chris Owen (MSSL). Hina Khan (European Space and Technology Centre, The Netherlands) presented observations from the Electric Field and Waves (EFW) instrument on Cluster during an outbound pass as the satellite traversed the high-latitude cusp and magnetopause boundary. Several flux transfer events resulting from reconnection were observed on either side of the magnetopause boundary and she presented a detailed analysis of these events. Robert Fear (MSSL) carried out a statistical survey of high-latitude flux transfer events using the Cluster spacecraft. The majority of these events occurred when the IMF was southward, but a significant number were observed under the opposite conditions. The latter were consistent with generation via lobe reconnection by the magnetosheath and the magnetosphere.
Andrew Fazakerley (MSSL) reported on how the Chinese Double Star mission has provided an unprecedented opportunity to monitor the low- latitude dayside magnetosphere boundary layer in conjunction with simultaneous observations of the high-latitude boundary layer by the quartet of Cluster spacecraft. The spacecraft observed ongoing reconnection on the dayside magnetopause. James Wild (Leicester) presented the first space- and ground-based study exploiting data from the coordinated Cluster and Double Star missions, in order to investigate dayside magnetic reconnection. In-situ observations of magnetosheath flux transfer events combined with measurements of flows in the high-latitude northern hemisphere ionosphere indicated pulsed magnetic reconnection during an interval of steady IMF.
On the final day of the meeting, Gareth Chisham (BAS) chaired a session on signatures of magnetic reconnection in the ionosphere. Mark Lester (Leicester) reported on observations of ionospheric flow by the Tasman International Geospace Environment Radar (TIGER) during a substorm expansion phase made in conjunction with Geotail observations far downtail from Earth. Enhanced earthward flows observed by Geotail were coincident with a localized vertical-like flow region observed by TIGER. Gabrielle Provan (Leicester) described how density fluctuations in the solar wind resulted in quasi-periodic variations in the solar wind dynamic pressure and IMF. At this time, the Northern Hemisphere SuperDARN radars observed bursts of high-latitude high-velocity plasma flow. Also, the IMAGE spacecraft observed correlated fluctuations in the brightness of the dayside proton auroral spot.
Hongqiao Hu (Leicester/Polar Research Institute of China) explained how, during IMF conditions that were expected to favour Southern Hemisphere high latitude reconnection at equinox, a four-cell convection pattern was observed and lasted for more than 2 hours in the Northern Hemisphere. Accompanying the pulsed reconnection, poleward moving radar aurora and anti-sunward ionospheric flow bursts were observed Atousa Goudarzi (Leicester) considered the ionospheric flow response to reconnection during different interplanetary magnetic field conditions, utilising the SuperDARN radars in both hemispheres. Asymmetries in the IMF could be studies over both hemispheres. Complementary spacecraft data made it possible to determine the location of the boundary between open and closed magnetic field lines.
Elerie Pryse (Aberystwyth) employed ion drift measurements by the EISCAT Svalbard radar to identify the polar cap open/closed field- line boundary. Coincident particle flux observations from over- passing satellites could provide characteristic energies of the closed magnetic field energetic electrons at the boundary along with a population of softer precipitating magnetosheath particles. Amin Aminaei (Lancaster) analysed over 400 absorption spike events using the IRIS riometer and described four distinct categories relating to various magnetic reconnection conditions. The distribution of these events according to seasons and their dependencies on geomagnetic activity and solar wind conditions were presented.
The final session was chaired by Hina Khan (ESTEC). Nanan Balan (Sheffield) described the effects on the magnetosphere, ionosphere and ground magnetic field of the passage of strong solar winds during a magnetic storm. Observations from the ACE upstream monitoring spacecraft, Geotail and Cluster indicated significant enhancements in densities and electron/ion temperatures which were similarly recorded by EISCAT and the Tromso magnetometer chain. Nigel Meredith (BAS) used CRRES satellite data to estimate the timescale for the decay of the flux of energetic electrons in the Earth's outer radiation belt during and after episodes of enhanced magnetic activity. The decay appeared to occur in the plasmasphere and that whistler mode emissions, which resonate with electrons in the appropriate energy range, may be responsible.
Richard Horne (BAS) used the Halloween storm of 2003, where the outer radiation belt was depleted and reformed closer to the Earth, as a rare means of testing leading theories of electron acceleration mechanisms. It appeared that wave acceleration was a primary mechanism and this may hold true on other planets in the solar system. Gary Abel (BAS) described over ten years of Antarctic measurements of Substorm Chorus Events. Many events were associated with drift echoes of substorm injected electrons rather than the initial injections themselves. The drift echoes may present favourable conditions for the generation of whistler mode chorus.
Andrew Kavanagh (Lancaster) presented both ground and space based observations of energetic electron precipitation during 'sawtooth' events and compared them with established patterns from individual substorms. He showed that for the cases studied, there was little difference between precipitation patterns during isolated substorms and during sawtooth events, consistent with the view that sawtooth events were periodic substorms. Paul Henderson (MSSL) presented a preliminary analysis of flux rope-like structures in the Earth's near tail observed by Cluster during the 2003 tail season. Properties of the ropes were investigated using multi spacecraft techniques in a time of small separation between spacecraft. This allowed a good determination of the currents through the Cluster tetrahedron.
A number of posters were displayed during the meeting and time was devoted to discussing the contents with the authors. Gary Abel (BAS) applied observed solar wind power inputs into a minimal substorm model of the evolution of the global dynamical state of the magnetotail using only three simple rules. Chris Arridge (IC) presented a global model of the Kronian magnetospheric magnetic field that extended the internal field plus disc model to include the whole of the dayside magnetosphere and far into the night-side. Alan Aylward (UCL) described how the EISCAT radio wave heater could generate an abrupt increase in the returned power from Polar Mesospheric Summer Echoes as the heater was switched off.
Nanan Balan (Sheffield) presented the first simultaneous mesopause and thermospheric wind observations from the MU radar during moderate to high solar activity conditions. Ian Bates (Sheffield) applied correlation dimension analysis to an implementation of a magnetic field reversal model to show that the dimension of the dynamics does not agree with that calculated from the dataset of electrojet indices. Mathew Beharrell (Lancaster) had studied the geomagnetic solar flare effect, employing SAMNET magnetometer and satellite data and revealed a clockwise current vortex over Scandinavia at the beginning of the flare.
Charlotte Beldon (Bath) described how horizontal winds in the mesosphere and lower thermosphere have been measured by a VHF meteor radar based in UK over a 16-year interval. The complete data set has been used to investigate the terdiurnal and quartdiurnal tides. Andy Breen (Aberystwyth) reported how an upgrade to the EISCAT radar, in combination with the MERLIN radio telescope system, improved the velocity resolution obtained by the interplanetary scintillation technique. Elizabeth Chambers (Sussex) revealed how some of the electron count distributions from the PEACE instrument on board Cluster had non-Poissonic autocorrelation functions over short timescales.
Gareth Chisham (BAS) presented the results of a statistical intercomparison between SuperDARN and Defense Meterological Satellite Program (DMSP) spacecraft estimations of the location of the open- closed field line boundary. Olli Jokiaho (Southampton) presented measurements of neutral temperatures in the thermosphere above Logyearbyen in Norway using the High Throughput Imaging Echelle Spectrograph (HiTIES).
Andrew Lyons (Leicester) introduced a new coupled model of the middle and upper atmosphere of the Earth and described how it was to be used to investigate geomagnetic influences on the neutral atmosphere down to the tropopause. Balazs Pinter (Sheffield) examined the effects of Sub-Auroral Polarisation Streams (SAPS) on the mid-latitude ionosphere with the Coupled Thermosphere Ionosphere Plasmasphere model (CTIP), comparing the results with the Utah State University TDIM model. David Sandford (Bath) explained how the signature of the lunar tide has been identified in the mesopause region over both Castle Eaton in the UK and Esrange in Arctic Sweden. The structure of this tide was discussed over a solar cycle.
Jo Sullivan (Southampton) described a project to look at the recent phenomenon of NEIALs (Naturally Enhanced Ion-Acoustic Lines) observed in power density spectra recorded at the EISCAT Svalbard Radar (ESR) and their relationship to other optical auroral phenomena. Emma Woodfield (Liverpool) provided a summary of the current progress of magnetic field modelling in the magnetosphere and ionosphere as part of the GEOSPACE consortium to exploit vector magnetic data from satellites and so improve our understanding and modelling capability for the Earth's entire magnetic field from the core to the magnetosphere. Ping Yin (Bath) used GPS dual-frequency observations to produce electron density distribution with a 4-D tomography inversion. He reported dramatic uplifts of F2 layer heights at mid- latitudes during the November 2003 storm.