Observational Properties of 15MLT-PCA in the Southern Hemisphere and the Switching Effects of IMF B_y on 15MLT-PCA Occurrence

Based on Special Sensor Ultraviolet Spectrographic Imager on Defense Meteorological Satellite Program spacecraft (DMSP/SSUSI) observations in the Northern Hemisphere, a particular polar cap arc observed at similar to 1,500 magnetic local time (MLT) sector was identified and was named 15MLT-PCA. A 15MLT-PCA model proposed for the Northern Hemisphere suggests that the 15MLT-PCA is caused by a lobe reconnection related to the tilt angle and lobe field line twisting due to a long-lasting positive interplanetary magnetic field (IMF) B-y condition. However, it is unclear if the 15MLT-PCA can be observed in the Southern Hemisphere and how the IMF B-y influences its occurrence and location. Using the long-term DMSP/SSUSI observations in the Southern Hemisphere, we confirmed that the 15MLT-PCA could be observed in the Southern Hemisphere in summer under long-lasting negative IMF B-y and predominantly positive IMF B-x. The ion energy dispersion and some other statistical properties are also investigated. Further, we showed that the IMF B-y has a switching effect on the occurrence of the 15MLT-PCA using multiple cases. We found that the 15MLT-PCA disappear as soon as the IMF B-y changed to an unfavorable condition, but it seems that the favorable conditions need to be maintained for similar to 1 hr for the occurrence of 15MLT-PCA. We also found that the IMF B-y magnitude is well correlated to the MLT location of the 15MLT-PCA. We suggest that all the results support the 15MLT-PCA model and imply that a magnetotail lobe reconnection should be common in the summer hemisphere because the well-known Parker Spiral favors meeting the model's IMF requirements.