日侧伴随电子加速的离子上行事件的分布特征

The characteristics of the dayside ion upflows associated with electron acceleration

本文基于2005年1月和7月DMSP F13卫星的观测数据,研究了日侧伴随电子加速的顶部电离层离子整体上行事件的分布特征.结果表明,离子上行主要发生在磁纬70°~80°MLAT范围内,加速电子磁层源区对应低纬边界层和等离子体片边界层;冬季上行存在明显的"晨昏不对称性",主要发生在晨侧(06∶00—09∶00 MLT),夏季上行主要发生在磁正午(09∶00—15∶00 MLT),以磁正午为中心近似呈对称分布,并且冬季离子上行发生率显著高于夏季;离子上行发生率在中等地磁活动时期显著增强,上行区域随着地磁活动的增强向低纬度方向扩展;行星际磁场Bx>0时,对应等离子体片边界层13∶00—18∶00 MLT和06∶00—09∶00 MLT区域内上行发生率增加,行星际磁场By的方向会导致上行高发区以磁正午为中心发生反转,行星际磁场南向时,上行发生率增强;冬季离子上行平均速度高于夏季.

Based on the observations from the DMSP F13 in January and July 2005,the statistical characteristics of the bulk ion upflow events associated with dayside electron acceleration at high-latitude topside ionosphere are studied.The results show that(1)the ion upflow mainly occurs in the geomagnetic latitude(MLAT)range of 70°~80°,and the magnetospheric source region of the accelerated electron corresponds to Low Latitude Boundary Layer(LLBL)and Boundary Plasma Sheet(BPS).(2)The dawn-dusk asymmetry is obvious in winter season,with the ion upflows mainly occurring on the dawn side ionosphere(06∶00—09∶00 MLT).But the ion upflows in summer mainly occurs at the magnetic noon(09∶00—15∶00 MLT),with a symmetric distribution centered at the magnetic noon.(3)The occurrence of ion upflow in winter is significantly higher than that in summer,and is significantly enhanced during the period of moderate geomagnetic activity.The upward region expands to the lower latitude when the geomagnetic activity is enhanced.The effect of interplanetary magnetic field(IMF)components has also been studied in this paper.When IMF Bx is positive,the upflow occurrence increases in the 13∶00—18∶00 MLT and 06∶00—09∶00 MLT,which are regions corresponding to the BPS.The direction of IMF By may lead to the high-incidence area reverse at the prenoon or postnoon region.The occurrence of ion upflows increases significantly when IMF is southward.The average velocity of ion upflows in winter is significantly higher than that in summer.