Abstract Based on the Defense Meteorological Satellite Program (DMSP) observations during Solar Cycle 23, this paper examines solar activity dependence of ionospheric bulk ion upflow events (IUEs) in the Southern Hemisphere (SH). Much previous similar work was conducted over the Northern Hemisphere (NH) with measurements from European Incoherent Scatter (EISCAT). To eliminate the influence of geomagnetic disturbance on IUEs, we pick out observations during geomagnetic quiet periods (with Kp ≤ 2+). Results show that, ion upward densities and fluxes are dramatically elevated at times of high solar activity (HSA) but ion upward drifts and occurrences are increased at times of low solar activity (LSA) in the SH, which is consistent with the situation in the NH. The ratios between HSA and LSA for these four parameters (IUEs’ density, flux, upward drift and occurrence) are ~2.71, ~1.98, ~0.76 and ~0.57, respectively. Furthermore, lower flux event takes place frequently at LSA as the background ion density is low but the upward drift is large, while higher flux event happens commonly at times of HSA accompanied by high ion density but low upward velocity. Quantitatively, an increase in unit of solar activity (characterized by P index) causes a 4.2×108 m−3 increase in ion density and a 1.2×1011 m−2·s−1 enhancement in upward flux, together with a 0.6 m·s−1 and 0.02 % decrease in ion upward velocity and uprate, respectively. The acceleration from the ambipolar electric field is thought to be a possible mechanism affecting the dependence of IUEs on solar variations. For HSA, the acceleration from the ambipolar electric field weakens, but a large number of background ions provide abundant seeds for acceleration and upflow, which maintains a high IUE flux. It is inferred that upflow events and upward drifts are inhibited by the enhanced ionospheric background density.

中文翻译：

---

地磁静止期太阳活动对电离层离子上升流的影响：DMSP 观测

摘要 基于国防气象卫星计划 (DMSP) 在太阳活动周期 23 期间的观测，本文研究了南半球 (SH) 电离层体离子上升事件 (IUE) 对太阳活动的依赖性。之前许多类似的工作是在北半球 (NH) 上进行的，测量结果来自欧洲非相干散射 (EISCAT)。为了消除地磁扰动对 IUE 的影响，我们选取​​地磁静默期（Kp ≤ 2+）的观测值。结果表明，在高太阳活动（HSA）时，离子向上的密度和通量显着升高，而在太阳活动低（LSA）时，离子向上漂移和出现的次数增加，这与 SH 中的情况一致。 NH。这四个参数（IUE 的密度、通量、向上漂移和发生率）分别为 ~2.71、~1.98、~0.76 和 ~0.57。此外，由于背景离子密度低但向上漂移大，低通量事件经常发生在LSA，而高通量事件通常发生在HSA伴随着高离子密度但低向上速度的时间。从数量上讲，太阳活动单位（以 P 指数为特征）的增加导致离子密度增加 4.2×108 m-3，向上通量增加 1.2×1011 m-2·s-1，同时增加 0.6 m· s-1 和 0.02% 的离子上升速度和上升率分别降低。双极电场的加速被认为是影响 IUE 对太阳变化依赖性的一种可能机制。对于 HSA，来自双极电场的加速减弱，但是大量的背景离子为加速和上流提供了丰富的种子，从而保持了高 IUE 通量。推测上升流事件和向上漂移受到增强的电离层背景密度的抑制。