Other
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsm22a..01u&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #SM22A-01
Other
2149 Mhd Waves And Turbulence (2752, 6050, 7836), 2407 Auroral Ionosphere (2704), 2764 Plasma Sheet, 2788 Magnetic Storms And Substorms (7954)
Scientific paper
The network of THEMIS all-sky imagers provides an unprecedented opportunity of studying time evolution of multiscale auroral disturbances associated with the magnetospheric substorm onset. In this talk, we report our recent results suggesting a possibility of direct optical monitoring of propagating low-frequency magnetotail disturbances associated with pre- and post-onset conditions. The results show a significant enhancement of spatial and temporal coherence of the growth phase aurora accompanied by increased ambipolar electric field fluctuations in the tail signaling a formation of a thin current sheet about ˜5 minutes prior to the main auroral breakup. During this time, growth phase arcs reveal various forms of azimuthal plasma motion including multiscale turbulence and westward propagating waves with traveling speeds of 2.0 -- 5.0 km/s. The post-breakup auroral dynamics exhibits wave-like forms which typically travel duskward at the velocity 8.0 -- 12.0 km/s, recurrence time 20 -- 30 s. These waves first appear within a local pre-midnight sector (˜1 hour MLT wide) shortly before to the global expansion onset, and they can be reliably detected during the first 10+ minutes following the breakup. The analysis of simultaneous in situ THEMIS measurements suggests that the observed pre-onset wave patterns can be an auroral footprint of flapping oscillations and/or other drift wave modes in the magnetotail which can arguably be related to the development of the initial plasma instability triggering the substorm onset.
Donovan Eric
Liang Jian-Jie
Liu Wende
Mende Stephen
Spanswick Emma
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