Constraining the substorm problem using ULF wave techniques

Details Constraining the substorm problem using ULF wave techniques Constraining the substorm problem using ULF wave techniques

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm52a..07r&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM52A-07

Physics

2744 Magnetotail, 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 2790 Substorms

Scientific paper

Using ground-based magnetometers from CARISMA and THEMIS and in-situ magnetic observations by THEMIS and GOES, we present the results obtained from an objective wavelet-based technique to determine the first onset of ULF wave activity during expansion phase onset on the ground and in space. We validate ground-based ULF timing against the large-scale IMAGE FUV and smaller-scale THEMIS ASI auroral observations. We find clear, coherent and repeatable characteristics of these ULF waves on the ground indicating a localized onset epicentre that provides a clear and strong constraint on the location in time and space of expansion phase onset. Specifically, we show that the onset of long-period Pi1/short-period Pi2 ULF waves commence at an epicentre in the ionosphere which is co-located in time and space with the development of spatially-localised, latitudinally narrow small-scale undulations on a faint isolated arc several degrees equatorward of the pre- existing discrete auroral arcs. These optical undulations have a periodicity in the same Pi1 frequency band as the magnetic perturbations. During this activity, the pre-onset poleward discrete arc system remains spatially and temporally distinct from, and quasi-stable and unaffected by, the rapid dynamics of the new more equatorward auroral activity during the first the 2-3 minutes following onset. These optical and magnetic manifestations of expansion phase onset initiation may represent a characteristic ionospheric signature of a near-Earth plasmasheet instability. An alternate scenario is that reconnection in a severely stretched geometry produces these signatures, but in that case the stability and magnetospheric location of the more poleward arc system mapping to the plasmasheet must be explained. Regardless, the combination of high cadence and spatial resolution magnetic and optical measurements such as those outlined here provide a remarkably tight constraint on the mechanisms responsible for the initiation of substorm onset We outline the characteristics of ULF pulsations in both the Pi1 and Pi2 bands in the nightside ionosphere and magnetosphere during substorms. We describe the use of these techniques in creating a substorm onset database during the THEMIS era for use by the scientific community. Finally, we detail the development of a Canadian AE calculation that will be routinely available at the Canadian Space Sciences Data Portal (www.cssdp.ca)

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