Precursor signatures and evolution of post‐sunset equatorial spread‐F observed over Sanya
Precursor signatures and evolution of post‐sunset equatorial spread‐F observed over Sanya
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DOI：
10.1029/2012ja017820
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发表时间：
2012-08
影响因子：
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通讯作者：
Guozhu Li;B. Ning;M. Abdu;W. Wan;L. Hu
中科院分区：
文献类型：
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作者：
Guozhu Li;B. Ning;M. Abdu;W. Wan;L. Hu
[1]最近对赤道扩展F(ESF)前兆特征的个例研究表明，大尺度波结构(LSWS)与赤道纬度ESF发展之间存在一一对应关系。本文研究了2011年9-10月地磁平静和扰动条件下，位于磁赤道以北13°的三亚地区(18°N，109°E)的低频驻波及其ESF的发生和发展。数字探空仪(DPS-4D)的高时间分辨率电离图提供了卫星跟踪测量，用于指示低地表面波的发生。利用同一地点的GPS闪烁和甚高频相干雷达回波测量，以及电离图中的距离类型扩展F(RSF)，确定了局地ESF活动的发展。此外，还利用三亚甚高频雷达东西向五波束扫描测量数据分析了建立ESF发展初始条件时的纵向差异。观测期间LSWS与ESF活动的相关研究为LSWS是ESF发展的必要前兆提供了确凿的证据。结果表明，当F层经历日落后突然上升(PSSR)时，LSWS和ESF几乎是一对一的关系，揭示了将F层抬升到足够高高度的纬向电场(Pre)反转前增强的强度是控制日落后ESF产生的一个重要参数。然而，在没有PSSR的情况下，ESF和GPS闪烁并不总是发生在LSWS出现之后。有时LSWS事件先于底型扩展F(BSF)的产生，而BSF并没有垂直发展成ESF和雷达羽流。这一结果可能表明，在不明显、微弱甚至适度的预条件下，仅有LSWS的出现可能不足以产生日落后导致电离层闪烁的F区不规则性。除了LSWS以外，还有更多的因素可能对导致电离层闪烁的ESF不稳定性的增长起到至关重要的作用。
[1] Recent case studies on the precursor signatures of equatorial spread-F (ESF) have shown a one-to-one correspondence between the large-scale wave structures (LSWS) and ESF development at equatorial latitude. In this study, the LSWS and the onset and development of the ESF are investigated over Sanya (18°N, 109°E), a station located at 13° north of the magnetic equator, during both geomagnetic quiet and disturbed conditions in September–October 2011. High-time-resolution ionograms from Digisonde Portable Sounder (DPS-4D) provided the satellite trace measurements that were used to indicate the occurrence of the LSWS. The development of local ESF activity was identified using GPS scintillation and VHF coherent radar echo measurements from the same site, together with the range type spread-F (RSF) in ionograms. Additionally, the Sanya VHF radar five-beam scanning measurements in east–west direction were used to characterize the longitudinal difference in establishing the initial conditions for ESF development. Correlative studies between the LSWS and ESF activities during the observational period offer consolidated evidence that the LSWS is a necessary precursor for the ESF development. It is shown that the LSWS and ESF have nearly a one-to-one relationship when the F layer undergoes an abrupt post-sunset rise (PSSR), revealing that the magnitude of the pre-reversal enhancement in zonal electric field (PRE) that elevates the F layer to a high enough altitude is an important parameter controlling the generation of post-sunset ESF. However, in the absence of the PSSR, the ESF and GPS scintillation did not always occur following the appearance of LSWS. Sometimes the LSWS events preceded the generation of bottom type spread-F (BSF) that did not develop vertically into ESF and radar plumes. This result may indicate that under inexpressive, weak, or even moderate PRE conditions, the appearance of the LSWS alone may not be sufficient to produce the post-sunset F region irregularities responsible for ionospheric scintillations. More factors, other than the LSWS, could play crucial roles favoring the growth of ESF instabilities responsible for ionospheric scintillations.