COSMIC/FORMOSAT‐3 observations of equatorial F region irregularities in the SAA longitude sector
COSMIC/FORMOSAT‐3 observations of equatorial F region irregularities in the SAA longitude sector
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DOI：
10.1029/2010ja015618
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发表时间：
2010-11
影响因子：
--
通讯作者：
C. Ko;H. Yeh
中科院分区：
文献类型：
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作者：
C. Ko;H. Yeh
[1]利用COSMIC/FORMOSAT-3GPS掩星探测的电离层电子密度和S4闪烁指数资料，研究了南大西洋磁异常（SAA）所在经度扇区（0° <$75 °W）的赤道F区不规则（F）的形态。2006年4月14日发射进入低地球轨道，由六颗卫星组成的宇宙星座每天提供对1800公里以下高度电离层的全球测量。大的数据集使我们能够统计相关的电子密度耗尽和GPS L1闪烁的研究，这使得全球和高度分布的不规则性进行检查。在太阳活动极小期和地磁平静期条件下，发现日落后的闪烁事件在北方冬季月份（D月）集中在SAA经度扇区，而在相反的季节（J月）在同一经度扇区几乎消失。D月平均的Nmax和Hmax分布表明，不规则性主要发生在底侧F区（200-350 km高度）和低磁纬地区，靠近Nmax和Hmax最大值的位置。这是一致的早期postsunset的不规则性，在该地区产生的等离子体向上漂移已大大增强。通过研究全球电子密度和闪烁事件分布的UT快照，发现仅在D个月期间，在SAA经度扇区的日落终止器、向西下降的地磁场、强闪烁事件和密度耗尽之间存在强的空间相关性，其中E区日落终止器最有可能平行于赤道纬度的磁场方向。在这个经度部门的密度耗尽结构的范围内的两个postsunset电离增强带（EIA），延伸到中央SAA和共轭区域，分别。这样的功能提供了进一步的证据表明，由于在SAA附近的粒子诱导电离的增强的电导率梯度贡献额外的电场增强在赤道F区域。在日落线附近的耗尽区的墙壁，显着的水平密度梯度存在于向西和向南的方向，由于太阳落山和SAA电离增强，分别。水平密度梯度与反平行（东北）的中性风在D个月的组合，可以有助于额外的增长率，以产生的对流层。这些COSMIC观测不仅证实了日落赤道电动力学在控制安静时间的季节性和纵向发生中起着关键作用，而且还揭示了季节性电离层对SAA中高能粒子降水的响应可以显著影响SAA经度扇区中的电离层形态。
[1] The data of ionospheric electron density and S4 scintillation index from COSMIC/FORMOSAT-3 GPS occultation soundings are used to study the morphology of the equatorial F region irregularity (EFI) in the longitude sector (0°∼75°W) where the South Atlantic magnetic anomaly (SAA) is located. Launched into low Earth orbits on 14 April 2006, the six-satellite constellation COSMIC provides daily global measurements of the ionosphere at altitudes below ∼800 km. The large data set enables us a statistically correlative study of electron density depletion and GPS L1 scintillation, which allows the global and altitudinal distributions of irregularity to be examined. Under solar minimum and geomagnetic quiet conditions, postsunset EFI/scintillation events are found to concentrate in the SAA longitude sector during northern winter months (D months), but nearly disappeared in the same longitude sector during the opposite season (J months). The D months’ average pattern of EFI reveals that most of irregularities occurred in the bottom side F region (200–350 km altitude) and at low magnetic latitudes adjacent to the locations of the maximum postsunset Nmax and Hmax. This is consistent with the early postsunset irregularities that are generated in the region where plasma upward drifts have been greatly enhanced. By examining the UT snapshots of the global distributions of electron density and scintillation events, strong spatial correlations are found to exist among the sunset terminator, the westward declined geo-magnetic field, strong scintillation event, and density depletion in the SAA longitude sector only during D months, where the E region sunset terminator is most possibly parallel to the magnetic field direction at equatorial latitudes. Density depletion structures within this longitude sector were bounded by two postsunset ionization enhancement bands (EIA) that extended over central SAA and its conjugated region, respectively. Such features provide further evidence that the enhanced conductivity gradients due to particle induced ionization in the vicinity of SAA contribute additional electric field enhancements in the equatorial F region. At the walls of the depletion region near the sunset lines, prominent horizontal density gradients exist in both westward and southward directions due to sun setting and SAA ionization enhancement, respectively. The combination of horizontal density gradients with antiparallel (north-eastward) neutral winds during D months can contribute additional growth rate to the EFI generation. These COSMIC observations not only confirm that the sunset equatorial electrodynamics plays a key role in controlling the seasonal and longitudinal occurrences of the quiet time EFI, but also reveal that seasonally dependent ionospheric responses to the energetic particle precipitation in SAA can affect considerably the morphology of EFI in the SAA longitude sector.