极区上行离子对地磁活动和季节变化响应的统计分析

利用DMSP F13卫星离子漂移速度测量数据和Wind卫星行星际磁场测量数据,对极区顶部电离层离子整体上行进行研究,主要考察平静期和磁暴期离子上行强度,以及不同行星际磁场方向和季节对离子上行的影响。研究发现,无论是南半球还是北半球,磁暴期的上行发生率都超过平静期;无论磁暴期还是平静期,南半球在北向行星际磁场时上行发生率高于南向行星际磁场、北半球在南向行星际磁场时上行发生率高于北向行星际磁场,且该结论在磁暴期比平静期更为明显;南半球平静期在北向行星际磁场和南向行星际磁场时冬季的上行发生率都远高于夏季,超过2倍,北半球平静期在北向行星际磁场和南向行星际磁场时夏季的上行发生率高于冬季。

The geomagnetic activity and seasonal variations of upward ions in the polar ionosphere: A statistical analysis

Based on a large dataset of ion drift velocity measurements onboard the DMSP F13 satellite and interplanetary magnetic field measurements onboard the Wind satellite,a study is made of the plasma bulk upward flowing ions in the topside polar ionosphere,with an emphasis on the quiet-time and storm-time changes in the distribution of upward occurrence and the impact of different interplanetary magnetic fields and seasons on the upward occurrence.The results show that the storm-time occurrence possibility of upward events is higher than that during quiet times in both the Southern Hemisphere and Northern Hemisphere.In the Southern Hemisphere and north of the interplanetary magnetic field,the possibility of upward events is higher than south of the interplanetary magnetic field;and in the Northern Hemisphere and south of the interplanetary magnetic field,the possibility of upward events is higher than north of the interplanetary magnetic field.These conclusions are more obvious in the magnetic storm period than the quiet period.Seasonally,in the Southern Hemisphere,upward events in winter are twice as likely as in summer,and this is the case during quiet times and north of the interplanetary magnetic field as well as during storm times and south of the interplanetary magnetic field.Mean while,in the Northern Hemisphere,the possibility of upward events in summer is greater than in winter,and this is true for quiet times north and south of the interplanetary magnetic field.Large amounts of energetic particles are propagated by the dayside soft precipitating particles (1 keV for ions and 100 eV for electrons) and night side auroral sub-storm particle in jections.This causes the moment transfer and heating of the cold plasma in the polar cap area by fractional heating and the ambipolar diffusion topside the F region of the ionosphere.At the same time,plasma waves,such as extremely low-frequency broadband waves,and ion cyclotron and lower hybrid waves,are involved by the convective velocity shear and plasma instability.Therefore,the cold upflows could be heated into thermal upflows at first,to reach a higher altitude,where they can be accelerated by the plasma waves into super thermal ions.In this paper,the occurrence frequency of upflow events during magnetically quiet periods is less than that during magnetically disturbed periods.This phenomenon can be explained by this mechanism.The seasonal variations of upward ions are discussed in this paper,in that the occurrence frequency in local winter is higher than in local summer in the Northern Hemisphere.However,the opposite is true in the Southern Hemisphere.This conclusion is consistent with previous studies in which it was reported that seasonal variations in ionospheric upflow do indeed exist and that the occurrences are closely related to solar activity and the interplanetary magnetic field.Under conditions of solar illumination,the enhanced solar extreme ultraviolet radiation ionizes the neutral gas.The conductivity of the ionosphere increases,while at the same time the cross-polar cap potential difference decreases.Therefore,the occurrence frequency of upflows is small in local summer compared with local winter.