Optical and SuperDARN Signature Associated With SC/SI
SATO, N.(1), Y. MURATA (1), H. YAMAGISHI (1), A- S. YUKIMATU (1), M. WATANABE (1), Yang HUIGEN (1,2), Liu RUIYUAN (2), M. LESTER (3), J-P. VILLAIN (4), and F. J. RICH (5)
(1) National Institute of Polar Research, Tokyo
(2) Polar Research Institute of China, Shanghai
(3) University of Leicester, UK
(4) LPCE/CNES, France
(5) USAF Research Lab., USA
It has long been known that sudden positive changes in solar wind dynamic pressure trigger the geomagnetic sudden commencement (SC). The ground level magnetic field shows systematic variations with latitude and local time that reflect the transmission of complex signals through the magnetosphere and the earth-ionosphere waveguide. SCs drive magnetopause motion, ground magnetic pulsations, optical auroral enhancement etc. The geomagnetic response to a sudden expansion of the magnetosphere is called negative geomagnetic sudden impulse (SI-). Although many investigators have analyzed SCs, detailed analyses of SI-s have not been made except by Araki and Nagano {1}, and to our knowledge no report on their relationship to the optical aurora has been made. The purpose of this paper is to study the response of optical/particle auroras, the magnetic variations, and HF radar signatures associated with the solar wind negative/positive pressure impulse. An example of negative SI-occurred on 3 August 1997. We examined this event in detail using the data obtained by all-sky TV cameras at Zhongshan in Antarctica, SuperDARN HF radars over the northern and southern polar regions, magnetometer networks at IMAGE and Greenland, by referring in situ satellite data located in the solar wind (WIND), magnetosheath (GEOTAIL), magnetosphere (LANL-1, GOES-8) and ionosphere (DMSP-F13). The following interesting characteristics are found; 1) sudden enhancement of an east-west-aligned discrete aurora occurred associated with the SI-. 2) Quasi-periodic (~10 minutes) variations were found in optical intensity, HF radar power and magnetic variations. 3) Upward field-aligned current and inverted 'V' electron precipitation corresponded to the region of the optical aurora. 4) SuperDARN data showed that the convection reversal boundary located at ~ 80 MLAT in the 16-18 MLT sector at the SI- onset and the boundary moved poleward after the SI-. 5) Spatial and temporal variations of the convection boundary were consistent with the magnetic variations at IMAGE and Greenland network.
{1} Araki, T. and H. Nagano, Geomagnetic response to sudden expansions of the magnetosphere, J. Geophys. Res., 93, 3983-3988, 1988.
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