Observational Properties of 15MLT‐PCA in the Southern Hemisphere and the Switching Effects of IMF B<sub>y</sub> on 15MLT‐PCA Occurrence
Hui‐Ting Feng, Desheng Han, Hui‐Xuan Qiu, Run Shi, Huigen Yang, Yongliang Zhang
Abstract
Abstract 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 ∼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 ∼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.