Ground-based and in-situ timing of substorm expansion phase onset: Locating the initiation region and determining the timescale of magnetosphere-ionosphere coupling

Details Ground-based and in-situ timing of substorm expansion phase onset: Locating the initiation region and determining the timescale of magnetosphere-ionosphere coupling Ground-based and in-situ timing of substorm expansion phase onset: Locating the initiation region and determining the timescale of magnetosphere-ionosphere coupling

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsm21a..05r&link_type=abstract

American Geophysical Union, Spring Meeting 2009, abstract #SM21A-05

Physics

2736 Magnetosphere/Ionosphere Interactions (2431), 2744 Magnetotail, 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 2790 Substorms

Scientific paper

Despite the characterisation of the auroral substorm more than 40 years ago, controversy still surrounds the processes triggering substorm onset initiation. 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. Furthermore, we show that the onset of ULF wave activity in space occurs contemporaneously with the onset of ULF wave activity on the ground, suggesting that magnetosphere-ionosphere coupling may occur remarkably fast during the onset process, perhaps by means of energetic electron precipitation that have been accelerated via shear Alfvén waves. Furthermore, 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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