FG10. Diffuse Auroral Precipitation
There were four separate breakout sessions devoted to the Diffuse Auroral Precipitation Focus Group at the 2008 GEM workshop
Thu, 26 June, 10:30 a.m. - 12:15 p.m
Contents
DAP 1: "Electron Pitch-Angle Scattering: Wave Observations and Theory"
Co-chaired by Richard Thorne and Nigel Meredith
This session was well attended (30-40 participants) and examined the global morphology and variability electrostatic electron cyclotron harmonic (ECH) and electromagnetic whistler mode chorus plasma waves, which are capable of interacting with plasma sheet electrons, leading to precipitation into the atmosphere. Theoretical calculations of pitch-angle scattering rates from each class of wave, under different levels of geomagnetic activity, were also presented to assess their potential contribution to the global pattern of diffuse auroral precipitation.
- Nigel Meredith presented a statistical analysis of ECH and upper band chorus from CRRES wave observations.
- Binbin Ni presented plasma sheet electron scattering by upper and lower band chorus and showed that such waves could induce strong diffusion scattering over the energy range between 100 eV to a few keV.
- Richard Thorne presented ECH scattering rates and showed that such waves could contribute to the scattering of lower energy electrons.
- Richard Quinn presented Jay Albert’s approximate calculations for chorus scattering and showed that this could lead to far more rapid computation.
- Eric Donavan presented observations for Laila Andersson, which showed evidence for two difference mechanisms for electron scattering.
- Ted Fritz presented evidence for butterfly distributions of energetic electrons in the auroral zone.
Over the next year much better observational models for the global distribution of each class of scattering wave will be made available, which can be used to better quantify the rate of plasma sheet electron scattering.
Thu, 26 June, 1:30 - 3:00 p.m.
DAP 2: "The Origin of Diffuse Auroral Structure"
Co-chaired by Eric Donovan and Mike Henderson.
This session was well attended (30-40 participants) and explored the origin of spatial structure and temporal variability of the diffuse aurora.
- Eric Donovan presented evidence for patches of diffuse auroral emissions, which exhibit temporaly pulsations at a variety of time scales ranging from >1 Hz to Pi2 frequencies.
- Mike Henderson showed observations of Giant Undulations on the equatorward edge of the diffuse aural zone, and suggested that these were associated with SAPs flows in the dusk sector.
- Sarah Jones presented evidence (for Mark Lessard) of pulsating aurora with ~ 10 sec period, and suggested that this was associated with modulation of the cyclotron resonant instability.
- Tom Sotirelis described the global distribution of precipitating electrons observed on low altitude satellites.
- Eric Donovan presented evidence for Harlan Spence of Omega bands observed in the inner magnetosphere.
The talks highlighted three important aspects of diffuse aurora structure: 1) the spatio-temporal evolution of boundaries; 2) the spatio-temporal modulation of precipitation, particularly in the case of patchy-pulsating aurora; 3) the importance of global models of the precipitation due to diffuse aurora that would incorporate some information about structure. In addition, it was decided that we are uncertain as to whether pulsating aurora are always embedded in larger-scale diffuse aurora, nor whether or not patches in the diffuse aurora may be formed as a consequence of parallel acceleration.
It was agreed by those present that activities in the near future should focus in particular on global models of diffuse auroral precipitation, and on advancing our understanding of patchy and pulsating aurora. It was asserted that these two themes offer promise for better quantifying, for example, global distributions of conductivity that are used in global simulations.
Thu, 26 June, 3:30 - 5:00 p.m.
DAP 3 (Joint with FG on Near Earth Magnetosphere): "Plasma Sheet Ion Scattering"
Co-chaired by Shawn Young and Hyojin Kim
The equator-ward edge of the diffuse proton aurora provides information on current sheet scattering associated with stretching of the magnetic structure in the magneto-tail. Ion precipitation can also be associated with features of the ring current.
- Yongliang Zhang presented evidence of ion precipitation observed in TIMED/GUVI and DMSP/SSUSI data. The data provides global information on equatorward boundary of proton current sheet scattering and on the scattering process for ring current ions.
- Simon Wing discussed observational information on the b2i boundary of isotropic ion precipitation.
- Eric Donovan described the use of FAST satellite data to determine the transition from isotropic scattering to weak scattering near the edge of the proton diffuse aurora. He also showed that there was some inconsistency between the isotropic boundary location and the expectations from energy-dependent current sheet scattering on the dayside.
Fri, 27 June, 10:30 - 12:15 p.m.
DAP 4: "Planning session for 2008-2009 activities"
Co-chaired by Jacob Bortnik and Tom Sotirelis.
In this session Jacob Bortnik and Tom Sotirelis discussed available data sources on waves and precipitating particles. This information will be place on the GEM/Wiki web site. Plans and objectives for the next year of the campaign were also formulated.
