[Report published in Astronomy & Geophysics 44, 1.30-1.31 (February 2003)]
by J A Wild (University of Leicester)
Published in
Astronomy & Geophysics 44, 1.30-1.31 (February 2003)
This year's one-day autumn meeting of the MIST (Magnetosphere,
Ionosphere and Solar-Terrestrial) community was held on 22
November 2002 at the Geological Society, Burlington House. Jim
Wild reports.
The morning session of the meeting began under the
chairmanship of Ingo Mueller-Wodarg (University College
London). Jonathan Eastwood (Imperial College) presented
observations of Ultra Low-Frequency (ULF) waves in the
foreshock standing upstream of the Earth's magnetosphere.
Employing plasma and magnetic field data from the
four-spacecraft Cluster mission he was able to compare the
properties of the observed waves using single and
multi-spacecraft analysis techniques. Transferring the
discussion to the interior of the magnetospheric cavity, Gary
Abel (British Antarctic Survey) discussed why it is that the
energy dispersion observed in substorm-injected electrons is
not reflected in substorm-enhanced whistler waves. He
demonstrated that the evolution of whistler mode waves
would be controlled by a number of factors such as the
electron energy distribution function, as well as diffusion
and propagation effects. By studying over 800 electromagnetic
ion cyclotron wave events observed by the CRRES spacecraft
Nigel Meredith (Mullard Space Science Laboratory) was able to
demonstrate that pitch-angle scattering due to wave-particle
interactions with electrons of less than 2 MeV are found
within the local time range 13-18 MLT for L > 4.5. He went on
to show that these electrons are only subject to strong
scattering over a small fraction of their drift orbits,
resulting in drift averaged scattering lifetimes in
the range several hours to a day. Youra Taroyan (Sheffield)
addressed the shortcomings of many descriptions of long-period
magnetic pulsations. By adopting a unified approach, rather
than the separate treatment of the problems of wave excitation
and resonant coupling, a new field line resonance excitation
mechanism was presented that goes some way to reconciling some
of the discrepancies between waveguide/cavity
mode theories and observations.
In the first of three talks on the neutral atmosphere, Alison
Dobbin (UCL) discussed recent
developments in the Coupled Middle Atmosphere and Thermosphere
(CMAT) model. The consequences of removing gravity wave drag
and auroral momentum and energy inputs from the model were
presented and compared with a staged turn-on of each
individual process. It was suggested that during periods of
low solar and geomagnetic activity, the dynamics of the middle
atmosphere are influenced by the ionosphere above 100 km.
Balan Nanan (Sheffield) presented incoherent scatter radar
observations of variations in the diurnal mean wind velocity,
and the amplitude and phase of tidal effects in the
mid-latitude thermosphere. He reported that mean wind
velocity and tidal amplitudes decrease with increasing solar
activity and that the rate of decrease is notably faster for
stronger tides. Scott England (Leicester) went on to discuss
results from the newly developed Stratosphere to Thermosphere
Energy Variability Experiment (STEVE). After outlining the
model, the results of an investigation into the impact of
gravity waves on the dynamics of the mesosphere and lower
thermosphere using various gravity wave parameterisations in
the model were presented. Moving on to issues of
magnetosphere-ionosphere coupling, Jim Wild (Leicester)
employed ground- and space-based observations of the auroral
ionosphere to investigate the motion and size of the polar cap
during BY dominant (BZ positive) Interplanetary Magnetic Field
(IMF) conditions. He reported that the poleward boundary of
the ultraviolet aurora, as observed from space, was displaced
significantly equatorward from the open/closed field line
boundary measured by the plasma instruments on the Cluster,
DMSP, and FAST spacecraft and suggested caution in the use of
UV auroral images in defining such boundaries.
Following lunch, Nigel Meredith (MSSL) took the chair.
Ricky Sims (Aberystwyth)
continued the discussion of the location of the open/closed
boundary during IMF BZ positive conditions. Using EISCAT
Svalbard radar observations of ion temperature and flow
velocity in the dayside summer ionosphere, he demonstrated the
existence of open flux tubes convecting rapidly away from a
high latitude reconnection site and made comparisons with the
Tsyganenko magnetic field model configuration in that
region. Crossing to the magnetotail, Jason Dewhurst
(MSSL) presented a statistical
investigation into the thinning and expansion of the plasma
sheet during magnetospheric substorms using data from the
Cluster PEACE instrument. In addition to the expected
Z-component motion, he reported a significant Y-component
motion during substorms when observed in the dusk sector and,
on average, differences (~ 10%) between the average plasma
sheet thinning and expansion velocities.
Bogdan Hnat (Warwick) presented the first of two talks to
address the multi-fractal nature of variations in geophysical
time-series. A model-independent technique of differencing
and rescaling was described that identifies self-similarity in
the Probability Density Fluctuations (PDF) in the solar wind
plasma parameters observed by the WIND spacecraft. The
discussion was continued by Sandra Chapman (Warwick) who
applied the finite size scaling technique to quantify the
statistical properties of the fluctuations in the AU, AL and
AE indices and the epsilon parameter that quantifies energy input
from the solar wind to the magnetosphere. She reported that
the exponents required to rescale the PDF of the fluctuations
are the same for all of these quantities, that self-similarity
was evident in each, and suggested that this placed important
constraints on current models of the coupled solar
wind/magnetosphere system. In the next presentation, Steve
Ellacott (Brighton) discussed the results of a theoretical
study in which the evolution of a Maxwellian ion velocity
distribution transmitted through a stationary 1-D
perpendicular model shock profile was investigated. By using a
Lagrangian/Hamiltonian formulation of the ion equations, he
demonstrated that it is possible to reproduce the stretching
and rotation effects observed in such ion velocity
distributions. Whilst the resultant velocity distribution
remains Gaussian in the low-temperature limit, this was found
not to be the case for higher temperature. In the final talk
to report on recent developments in modelling and simulation,
Katariina Nykyrib (IC) presented the results
of MHD simulations of magnetic reconnection inside small-scale
filamentary field and current structures that develop at the
flank magnetopause due to the Kelvin-Helmholtz instability.
She explained that due to the small scale of these current
structures the MHD approximation is invalid, and
that the Hall term of Ohm's law must be included. The
subsequent results of 2-D Hall-MHD simulations were presented
and compared with those from plain 2-D MHD models. Chris
Owen (MSSL) presented
electron and magnetic field observations from a different
reconnection region, this time in the Earth's magnetotail.
Using multi-spacecraft data from the Cluster mission, the
possible signatures of Hall currents in the vicinity of a
reconnection X-line were reported and compared with previous
single spacecraft studies. Whilst similarities with these
earlier studies were demonstrated, is was not clear whether or
not subtle differences observed during this event could be
reconciled in the framework of the model inspired by previous
observations.
The final session of the meeting, with Gary Abel (BAS) in the chair,
was devoted to planetary
science. James Scuffham (IC) reported on
the development of a magnetic field model of Mercury,
beginning with an overview of the limited observations of the
planet's magnetic field. He went on to discuss the
applicability and modifications required of existing
Terrestrial magnetospheric models in order to describe realistically
the Hermean magnetic field,
and what differences are expected between the two systems.
Switching attention to Jupiter, Jon Nichols (Leicester)
presented a study of magnetosphere-ionosphere coupling in the
Jovian magnetosphere. By considering the breakdown in
corotation of plasma originating from the moon Io, he
demonstrated that magnetosphere-ionosphere coupling currents
are generated and presented a realistic model of the system.
Paul Hanlon (IC) used magnetic field
observations from the Galileo mission to Jupiter to
investigate the structure of the current carrying plasma sheet
that dominates the Jovian magnetosphere. By studying many
plasma sheet encounters with the spacecraft, he concluded that
at distances of less than ~ 30 Jupiter Radii (RJ) from the
planet the plasma sheet is ~ 4-6 RJ thick, whilst the motion
of the plasma sheet due to the rotation of the planet
introduced large uncertainties in this estimate at greater
distances. Continuing the discussion of planetary
magnetospheres, Giacomo Giampieri (IC)
exploited magnetic field data from the Voyager 1 and 2, and
Pioneer 11 encounters with Saturn in order to formulate a
mathematical description of the Kronian ring current system.
By comparing the resulting model's parameters for the three
spacecraft flybys, he suggested a possible deviation from the
axial and planar symmetries assumed in the model. Ingo
Mueller-Wodarg (UCL) presented the
expected thermospheric effects at Titan when the moon is
eclipsed as it passes behind Saturn. This event, which occurs
every 15 years, was simulated using a general circulation
model that indicated a drop in the thermospheric temperature
of ~ 20 K and the stimulation of globally propagating waves.
Finally, Tracy Moffat (UCL)
presented the results of recent updates to the UCL 3-D
numerical model of the Martian thermosphere. The developments
allow for increased flexibility and more realistic
descriptions of the physical processes involved. She went on
to demonstrate that the model results compare favourable with
existing models whilst offering a variety of potential
advantages in the future. The meeting concluded with thanks
to all the contributors and chairmen.
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