### Parallel Session P28: 1045-1230, Thursday 15th April 2010

#### General MIST Science Session 2 (MIST)

Location: G226

Abstract:

Magnetospheric-Ionospheric-Solar-Terrestrial (MIST) research concerns physical processes within the Sun-Earth system, other solar system bodies and exo-planets; in particular the solar/stellar wind, moons and planetary atmospheres and magnetospheres. The MIST general session is designed to address those aspects of current MIST research not explicitly covered in other sessions, such as neutral atmosphere science, ULF waves and wave-particle interactions, auroral and ionospheric electrodynamics, and ground-based studies of the coupled magnetosphere-ionosphere system. All researchers who are interested in any aspect of MIST science are therefore invited to take part.

Organisers:

• Adrian Grocott (University of Leicester)
• Emma Woodfield (University of Lancaster)
• Andrew Fazakerley (University College, London, MSSL)

#### Talks

 15 April, 10:45 SCANDI: All-sky view of meso-scale spatial structure in the thermosphere and ion-neutral coupling over SvalbardTimothy Spain (UCL) 15 April, 11:05 Observations and modelling of artificial D-region heating seen by ARIESAndrew Senior (Lancaster University) 15 April, 11:20 Observations of double-peaked HF radar spectra due to mixed echoes from natural and artificial plasma irregularitiesHannah Vickers (University of Leicester) 15 April, 11:35 Overview of low energy electron observations in the vicinity of Saturn's moon EnceladusSheila Kanani (Mullard Space Science Laboratory) 15 April, 11:50 Evidence for the occurrence of ~10.6h magnetic field oscillations in Saturn’s equatorial magnetosphereGabby Provan (University of Leicester) 15 April, 12:05 Magnetospheric-period oscillations in Saturn's equatorial magnetosphere and open tail lobes throughout the Cassini missionDavid Andrews (University of Leicester) 15 April, 12:20 Poster adverts

#### Posters

Tracking solar wind structures from the Sun through to the orbit of Mars
Anthony Williams (University of Leicester)

SuperDARN observations of the sub-auroral convection response to enhanced geomagnetic activity

Interpolation of external magnetic fields over large sparse arrays using Spherical Elementary Current Systems
Ciaran Beggan (British Geological Survey)

Combining incoherent scatter radar data and IRI2007 to monitor the open-closed field line boundary during substorms.
Emma Woodfield (Lancaster University)

An estimation of the Carrington flare magnitude from solar flare effects (sfe) in the geomagnetic records
Ellen Clarke (British Geological Survey)

Towards modelling of high latitude magnetic fields from satellite data
Gemma Kelly (University of Liverpool)

The drift of auroral radio absorption patches observed by imaging riometer
John Hargreaves (University of Lancaster)

Nature of the ring current in Saturn’s dayside magnetosphere
Stephanie Kellett (University of Leicester)

#### Talk Abstracts

SCANDI: All-sky view of meso-scale spatial structure in the thermosphere and ion-neutral coupling over Svalbard
Spain, Timothy, A. L. Aruliah, H.-C. I. Yiu, I. McWhirter, E. M. Griffin, A. Charalambous, M. Kosch, L. Baddeley, V.S.C. HowelI, I. McCrea
UCL
15 April, 10:45

The UCL Scanning Doppler Imager (SCANDI) is an all-sky Fabry-Perot Interferometer that is located at the Kjell Henriksen Observatory on Svalbard near the EISCAT ESR radars. It provides routine nighttime observations of the two most prominent auroral and airglow emissions at 630nm or 557.7nm. These allow measurements of thermospheric winds, temperatures and intensities at around 240km and 120km altitude, which roughly correspond to the F- and E-region ionosphere. It is one of 3 existing SDIs in the world; the other two are the original Alaskan SDI and Mawson, Antarctica SDI. Recently the first conjugate study of the upper thermosphere was made by comparing the SCANDI with the Mawson SDI. These instruments have upset the standard assumptions of a slowly varying thermosphere. EISCAT-SCANDI experiments using high temporal and spatial resolution measurements have shown localised rapid responses to ionospheric variability (10s of minutes over a few hundred kilometres horizontal distance), but also an underlying inertia. The effects of this behaviour appear in unexpected amounts of heating and acceleration of the upper atmosphere, and have consequences for feedback mechanisms through the neutral wind dynamo.

Observations and modelling of artificial D-region heating seen by ARIES
Senior, Andrew, M. J. Kosch, F. Honary
Lancaster University
15 April, 11:05

Artificial radio wave heating of electrons in the D-region is used as a diagnostic technique for studying polar mesospheric summer echoes, a radar phenomenon caused by minute ice particles in the vicinity of the mesopause. Recent studies of the heating using the cross-modulation technique found that models used to predict the heating overestimated the observed cross-modulation by a factor of 1.5-2.5. The Advanced Rio-Imaging Experiment in Scandinavia (ARIES), a high-resolution imaging riometer system, observed changes in the ionospheric absorption of cosmic radio noise during D-region heating. These observations have been compared to predictions from a similar model to that used when analysing the cross-modulation results. Provisional results show that the model overestimates the change in cosmic noise absorption by a factor of about 2. These results lead us to question the validity of the usual models of D-region heating by powerful HF radio waves.

Observations of double-peaked HF radar spectra due to mixed echoes from natural and artificial plasma irregularities
Vickers, Hannah, Terry Robinson
University of Leicester
15 April, 11:20

CUTLASS HF backscatter targets may be artificially induced through the use of the EISCAT high power ionospheric heating facility at Tromsø, Northern Norway. Plasma irregularities created in this way are known to be highly field-aligned and usually possess low spectral width. In the vicinity of natural waves and irregularities under more disturbed geophysical conditions however, the spectral width of artificial irregularities as deduced by the standard SuperDARN ‘FITACF’ analysis, can be sometimes appear to be broadened. In this work, we present such observations and employ the Burg maximum entropy analysis method to CUTLASS HF radar spectra, combined with standard ‘FITACF’ parameters and DMSP satellite measurements to show how mixed artificial and natural HF echoes from spatially separated sources can give rise to double-peaked spectra as a result of detection at the edges of antenna main lobe

Overview of low energy electron observations in the vicinity of Saturn's moon Enceladus
Kanani, Sheila, Geraint Jones, Gethyn Lewis, Chris Arridge, Andrew Coates, Dave Young
Mullard Space Science Laboratory
15 April, 11:35

Enceladus resides deep within Saturn's magnetosphere. The magnetospheric plasma incident on the satellite is absorbed, forming a thermal plasma wake downstream of the moon, and a cavity in higher energy populations. When the Cassini spacecraft crosses Enceladus's L-shell, these cavities are observed as brief dropouts in energetic particle fluxes, or microsignatures, most clearly observed by the Magnetospheric Imaging Instrument (MIMI). A survey of thermal plasma observations by the Cassini Plasma Spectrometer (CAPS) instrument has revealed the existence of various features in low energy electrons close to the times of microsignatures, or immediately before or after their occurrence. These features vary; some present themselves as a set of discrete spikes, covering electron energies of 9-15 eV and lasting, intermittently, up to tens of minutes. Other show evidence of injection events close to the moon's orbital plane. We present the results of a survey of these perplexing features, suggest possible causes for their occurrence and discuss results from close Enceladus flybys.

Evidence for the occurrence of ~10.6h magnetic field oscillations in Saturn’s equatorial magnetosphere
Provan, Gabby, D.J. Andrews, S.W.H. Cowley, M. K. Dougherty, L. Lamy
University of Leicester
15 April, 11:50

Andrews et al. (2008) and Provan et al. (2009) reported Cassini observations of near-planetary period magnetic field oscillations in Saturn’s near-equatorial magnetosphere, and showed that their period was closely similar to the slowly-varying period of ~10.8 h determined by Kurth et al. (2008) from modulations of SKR radio emissions. Kurth. et al (2008) further reported that these emissions also exhibited a second period of ~10.6 h. Further investigation by Gurnett et al. (2009) revealed that the ~10.6 h modulated emission originates from the Northern hemisphere, whilst the ~10.8 h modulated emission originates from the Southern hemisphere. Andrews et al. (2008) and Provan et al. (2009) also found significant ‘jitter’ in the phases of the equatorial oscillations, and presented evidence that much of this is not due to measurement errors but has a real physical cause. Here we show that this phase ‘jitter’ is due to the superposition in the equatorial magnetosphere of field oscillations at the Southern period with weaker oscillations at the Northern period. We determine the relative amplitudes of these oscillations, and the phase of the Northern period oscillations relative to the Northern SKR modulation.

Magnetospheric-period oscillations in Saturn's equatorial magnetosphere and open tail lobes throughout the Cassini mission
Andrews, David, S.W.H. Cowley, L. Lamy, G. Provan
University of Leicester
15 April, 12:05

We present new results of analysis of the near-planetary period oscillations in Saturn's magnetic field, employing all available Cassini data obtained to date, including during the recent Saturn equinox. In this analysis we use a new fit to the previously studied spatial variations in the phase of these oscillations, and deduce secular changes in their periodicities. Pre-equinox these equatorial magnetic field oscillations are found to be consistently in phase with those observed on Southern-hemisphere open field lines, and hence with the dominant component of the Saturn kilometric radiation (SKR) emission. Meanwhile, field oscillations on open field lines in the planet's Northern hemisphere are consistently found to be in phase with the weaker, longer-period component of the SKR. Near equinox, we have now observed a rapid decrease in the period of the equatorial field oscillations. Consequences of these new findings are discussed.

#### Poster Abstracts

Interpolation of external magnetic fields over large sparse arrays using Spherical Elementary Current Systems
Beggan, Ciaran, Sam McLay
British Geological Survey

Interpolation of the magnetic field disturbances to a point remote from an observatory can be achieved by employing the latitudinal-weighted arithmetic mean of the field as measured at two observatories, one to the north and one to the south of the point of interest. An alternative technique for interpolating external magnetic field disturbances across large spatial areas can be achieved with the Spherical Elementary Current System (SECS) method using data from ground-based magnetic observatories. The SECS method represents complex electrical current systems as a simple set of equivalent currents placed at a specific height in the ionosphere. The magnetic field recorded at observatories can be used to invert for the electrical currents and subsequently used to interpolate or extrapolate the magnetic field across a large area. We show that inverting for induced subsurface current systems in addition to ionospheric current systems can result in strong improvements to the estimate of interpolated magnetic field, particularly in the radial component of the field. We demonstrate that relatively few observatories are required to produce an estimate which is better than the null hypothesis (i.e. assuming no change in the field) or interpolation using latitudinal weighting of data from other observatories. We further investigate the application of the SECS method in mid- to high geomagnetic latitudes using a series of observatory networks to test how well the external field can be interpolated over large distances.

An estimation of the Carrington flare magnitude from solar flare effects (sfe) in the geomagnetic records
Clarke, Ellen, Craig Rodger (University of Otago), Mark Clilverd (BAS), Thomas Humphries (BGS), Orsolya Baillie (BGS), and Alan Thomson (BGS)
British Geological Survey

In this study we review previous work to estimate the magnitude of the Carrington solar flare (1 September 1859) and re-examine observations of solar flare effects (sfe) on the Kew and Greenwich Observatory magnetograms. A data base of more recent events is constructed from: existing sfe data available on-line; magnetic observatory yearbooks; sfe data collected and processed by Ebro Observatory; additional scaling of events using one-minute values from various INTERMAGNET and WDC magnetic observatories; and GOES X-ray flux data. We investigate four of the largest events in detail and also the statistical relationship between sfe magnitude and X-ray flux with respect to solar zenith angle and geomagnetic latitude and use the results to estimate the size of the Carrington flare.

SuperDARN observations of the sub-auroral convection response to enhanced geomagnetic activity
Grocott, Adrian, M. Lester, S.E. Milan, T.K. Yeoman
University of Leicester

A recent addition to the Super Dual Auroral Radar Network (SuperDARN), the Blackstone radar is located at ~50 degrees magnetic north, ~10 degrees equatorward of its auroral counterparts. At this latitude the radar regularly makes observations of plasma convection equatorward of the main auroral oval. These observations reveal low velocity sub-auroral ionospheric scatter that is well correlated with both the ring current (SYM-H) and auroral electrojet (AE) indices indicating it is responding directly to geomagnetic activity. In this paper we present some statistical verification of this relationship, and investigate the time delay between the auroral enhancements and the sub-auroral convection response. In addition, we present some near-conjugate THEMIS observations of a magnetospheric substorm which suggest a direct relationship between localised substorm activity and the observed sub-auroral dynamics.

The drift of auroral radio absorption patches observed by imaging riometer
Hargreaves, John, M. J. Birch, B. J. I. Bromage
University of Lancaster

The phenomenon of drifting patches of auroral absorption, first recognised in the 1960s, is here illustrated in recent observations with an imaging riometer in northern Finland. Possible causes are considered, using incoherent-scatter observations from EISCAT and F-region velocities from SuperDARN.

Nature of the ring current in Saturn’s dayside magnetosphere
Kellett, Stephanie, C.S. Arridge, E.J. Bunce, A.J. Coates, S.W.H. Cowley, M.K. Dougherty, A.M. Persoon, N. Sergis, R.J. Wilson
University of Leicester

Determination of the physical nature of Saturn's ring current, i.e., the actual combination of currents associated with the inertia of the near-corotating plasma and hot particle effects, has been the subject of much debate for almost 30 years.

Here we investigate the nature of the ring current in Saturn’s dayside magnetosphere using magnetic field (MAG) and plasma particle (CAPS, MIMI and RPWS) data from two typical near-equatorial passes of the Cassini spacecraft spanning the radial range between ~3 and ~20 $R_S$ ($R_S$ is Saturn's equatorial radius, equal to 60268 km). Physically, the plasma currents that form the ring current are due to one or more of three possible effects; the spatial gradient of the perpendicular plasma pressure, the anisotropy of the plasma pressures parallel and perpendicular to the field lines, and the inertia of the flowing (near-corotating) plasma. We examine plasma parameters obtained by Cassini for each pass and compare the azimuthal current density profiles deduced with those obtained from current disk modeling of the magnetic field perturbations.

We show that the current associated with the $P_{\rm perp} > P_{\rm para}$ pressure anisotropy of the warm water group ions is important inside $\sim 10 R_S$, cancelling a significant fraction of the otherwise dominant inertia current inside $\sim 6 R_S$. The overall total current density profile is then found to be similar to that produced by the pressure gradient current, but augmented in strength by factors of ~1.5-2.0 by the difference between the inertia and anisotropy currents. The deduced current density profiles are in good agreement with the gross features of the profiles deduced from current disk modeling, though with the current density then falling more steeply with radial distance than the $1/r$ dependence assumed in the model.

Towards modelling of high latitude magnetic fields from satellite data
Kelly, Gemma, Richard Holme, Alan Thomson
University of Liverpool

Recent low-Earth orbit satellite missions have provided a wealth of high quality data allowing for improved models of the near-Earth geomagnetic field. However, understanding in the high latitude regions is lagging behind due to the complexity of the processes and interactions in this region. We investigate residuals between some recent models (CHAOS-2, T01 and CM4) and data from the CHAMP and Ørsted satellites, with the aim of investigating how well the models fit the data, particularly regarding the high latitude regions.

By looking at the residuals on an orbit-by-orbit basis we have shown that all three models show very similar features in the residuals. We can identify current sources that are consistent in time and co-latitude, even at very quiet times (Kp < 2o, night-side only). There is also some correlation between the size of the residuals and level of activity indicated by the PC and AE indices. When investigating two-day averaged residual plots the auroral oval can be identified, and there are enhanced residuals over the polar caps, for both quiet and disturbed times. This information will be fed into a method for improving geomagnetic field models at high latitudes.

Tracking solar wind structures from the Sun through to the orbit of Mars
Williams, Anthony, A.O. Williams, N.J.T. Edberg, S.E. Milan, M. Lester, M. Franz
University of Leicester

With no direct upstream monitors of the solar wind at either Venus or Mars, the solar wind inputs to the plasma environments of both planets must be inferred. We present a method, using a combination of images from the Heliospheric Imagers (HI) on the Solar Terrestrial Relations Observatory (STEREO) and in-situ measurements from the Advanced Composition Explorer (ACE) situated at Earth’s L1 point to track the progression of Corotating Interaction Regions through the inner heliosphere, and to predict their arrival at Venus and Mars. We show the results of this method for solar minimum from 1 July 2007 to 31 July 2008, demonstrating that there is good agreement between expected arrival times and observed enhanced activity at each planet.

Combining incoherent scatter radar data and IRI2007 to monitor the open-closed field line boundary during substorms.
Woodfield, Emma, J.A. Wild, A. Senior, A.J. Kavanagh
Lancaster University

The size of the polar cap, and hence the amount of open magnetic flux contained within it, is a very important quantity when it comes to understanding the substorm process as well as reconnection rates in general. Ground-based proxies of the open-closed field line boundary (OCFLB) have therefore been of great interest in recent years. In this work we build on previous studies by Aikio et al (e.g. Ann. Geophys., 24, 1905-1917, 2006) which use a combination of EISCAT electron temperature measurements from the mainland and Svalbard to track the motion of the OCFLB. We demonstrate whether using the International Reference Ionosphere model (IRI2007) can enhance this method and make it applicable to other incoherent scatter radars. In particular we make use of EISCAT data to investigate the electron temperature signatures of the OCFLB during a large number of substorms.