We present observations of a duskside shock aurora occurred on 21 April 2001 by the SuperDARN radar at Syowa Station and the all-sky camera at Zhongshan Station （ZHS） in Antarctica when the radar was operated in fast-scan mode covering the ZHS region. With the two independent data sets, we examine ionospheric plasma convection and aurora arising from a sudden impulse （SI） event associated with an interplanetary shock. During the transient shock compression, the aurora was quiescent without any optical emission at the preliminary impulse of the SI. About 7 min later, a new thin auroral arc with brighter emissions and a lifetime of -14 rain expanded westward from the region above ZHS during the main impulse of the SI. SuperDARN radar line-of-sight measurements showed periodical oscillation in the flow direction with ultra-low-frequency waves having a period of -8 min during the shock compression. We suggest that downward field-aligned current during the preliminary impulse stage of the SI was the main driver of the first plasma flow reversal, and the subsequent new discrete auroral arc may be associated with field-aligned acceleration in the region of the main impulse related upward field-aligned currents. The ground magnetometer observations suggest that the oscillation of the ionospheric convection on the duskside was associated with field line resonance activity.
LIU JianjunHU HongqiaoHAN DeshengLIU YonghuaZHANG QingheAkira S Yukimatu
Using high temporal resolution optical data obtained from three-wavelength all-sky imagers over six winters continuously at Yellow River Station （78.92°N,11.93°E） in Arctic,we statistically investigated the dependence of location of poleward moving auroral forms （PMAFs） on the interplanetary magnetic field （IMF） B z and B y components as a function of MLT and MLAT under stable IMF conditions.It is found that more PMAFs occurred in lower latitude for Bz＆lt;0 and there was less evident IMF B y-related prenoon-postnoon asymmetry for Bz＆lt;0 than for Bz＆gt;0.We found that the PMAFs were distributed over a wide range of MLT when Bz＆lt;0,which indicates that the reconnection X-line might spread like an ’S’ shape.However,during northward IMF,PMAFs were observed predominantly prenoon for IMF By＆gt;0 and postnoon for IMF By＆lt;0 associating with the effect of the high-latitude reconnection,which is largely consistent with the theoretical model of the convection flow.
Based on the fuzzy local information c-means （FLICM） clustering algorithm, a new method is developed for extracting the equatorward and poleward boundaries of the auroral oval from images acquired by the Ultraviolet Imager （UVI） aboard the POLAR satellite. First, the method iteratively segments the UVI image with the FLICM clustering algorithm, according to an integrity criterion for the segmented auroral oval. Then, possible gaps in the extracted auroral oval are filled, based on prior knowledge of its shape. To evaluate the method objectively, the extracted boundaries are compared with the precipitating electron boundaries determined from DMSP satellite precipitation particle data. The evaluation results demonstrate that the proposed method generates more accurate auroral boundaries than traditional methods.
WANG QianMENG QingHuHU ZeJunXING ZanYangLIANG JiMinHU HongQiao
