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
Poleward moving auroral forms （PMAFs） are statistically investigated by using 6 winters continues high-quality...
Z. Y. Xing 1,2 H. G. Yang 2 D. S. Han 2 Z. S. Wu1 Z. J. Hu2 Q. H. Zhang2 H. Q. Hu2 B. C. Zhang2 J. M. Liu2 and D. H. Huang2 1. School of Science, Xidian University, Xi''an, China, 710071. 2. SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai, China, 200136.
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<0 and there was less evident IMF B y-related prenoon-postnoon asymmetry for Bz<0 than for Bz>0.We found that the PMAFs were distributed over a wide range of MLT when Bz<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>0 and postnoon for IMF By<0 associating with the effect of the high-latitude reconnection,which is largely consistent with the theoretical model of the convection flow.
