Simultaneous observations of ESF irregularities over Indian region using radar and GPS
Simultaneous observations of ESF irregularities over Indian region using radar and GPS
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DOI：
10.5194/angeo-26-3197-2008
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发表时间：
2008-10
影响因子：
1.9
通讯作者：
S. Sripathi;S. Bose;A. Patra;T. Pant;B. Kakad;A. Bhattacharyya
中科院分区：
文献类型：
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作者：
S. Sripathi;S. Bose;A. Patra;T. Pant;B. Kakad;A. Bhattacharyya
本文利用位于低纬Gadanki（13.5° N，79.2° E，低纬6.3° N）的MST雷达（53 MHz），对赤道扩展F（ESF）期间L1频率（1.575 GHz）上的总电子含量（TEC）和GPS振幅振荡的时空变化进行了同步观测。特别是，TEC和L-波段的纬度和经度范围内进行了研究，在印度地区的不同类型的ESF结构观测使用MST雷达在低太阳活动期间的2004年和2005年。同时雷达和GPS观测在严重的ESF事件在午夜前的小时显示，显着的GPS L波段振荡，TEC的耗尽，和TEC指数（DROTI），这是一个衡量TEC的波动，在低纬度地区获得的双导数与雷达回波的出现在Gadanki相吻合。正如所料，在午夜前的雷达图上，当不规则物到达较高的高度时，在较高纬度的L波段信号上会观察到强烈的反气旋。相反，当雷达回波仅限于较低的高度时，发现弱的反气旋，其纬度范围很小。在磁静期，我们记录了羽状雷达回波在午夜后的一段时间，是没有L-波段的闪烁。利用VHF闪烁观测的光谱斜率和互相关指数，我们认为这些不规则性可能是“死”或“化石”气泡，它们只是从西方漂来的。这种情况是一致的观测，其中抑制前反转增强（PRE）在向东电场中的电离层观测赤道F层的高度，也发生在雷达观测相对于午夜前的时间段的低谱宽。然而，没有L-波段反射在午夜后的事件，当雷达观察到的羽状结构和反射记录在VHF波段，提出了问题的不规则性的演变过程。一个可能的解释是，虽然小尺度（~3米）的不规则性是通过在千米尺度大小的不规则性壁上生长的二次波产生的，但在这种情况下，瑞利-泰勒不稳定性本身的演变并没有延伸到几百米尺度大小的不规则性，这些不规则性在L波段信号上产生闪烁。
In this paper, we present simultaneous observations of temporal and spatial variability of total electron content (TEC) and GPS amplitude scintillations on L1 frequency (1.575 GHz) during the time of equatorial spread F (ESF) while the MST radar (53 MHz) located at Gadanki (13.5° N, 79.2° E, Dip latitude 6.3° N), a low latitude station, made simultaneous observations. In particular, the latitudinal and longitudinal extent of TEC and L-band scintillations was studied in the Indian region for different types of ESF structures observed using the MST radar during the low solar activity period of 2004 and 2005. Simultaneous radar and GPS observations during severe ESF events in the pre-midnight hour reveal that significant GPS L band scintillations, depletions in TEC, and the double derivative of the TEC index (DROTI), which is a measure of fluctuations in TEC, obtained at low latitudes coincide with the appearance of radar echoes at Gadanki. As expected, when the irregularities reach higher altitudes as seen in the radar map during pre-midnight periods, strong scintillations on an L-band signal are observed at higher latitudes. Conversely, when radar echoes are confined to only lower altitudes, weak scintillations are found and their latitudinal extent is small. During magnetically quiet periods, we have recorded plume type radar echoes during a post-midnight period that is devoid of L-band scintillations. Using spectral slopes and cross-correlation index of the VHF scintillation observations, we suggest that these irregularities could be "dead" or "fossil" bubbles which are just drifting in from west. This scenario is consistent with the observations where suppression of pre-reversal enhancement (PRE) in the eastward electric field is indicated by ionosonde observations of the height of equatorial F layer and also occurrence of low spectral width in the radar observations relative to pre-midnight period. However, absence of L-band scintillations during post-midnight event, when radar observed plume like structures and scintillations were recorded on VHF band, raises questions about the process of evolution of the irregularities. A possible explanation is that whereas small scale (~3 m) irregularities are generated through secondary waves that grow on the walls of km scale size irregularities, in this case evolution of the Rayleigh-Taylor instability itself did not extend to irregularities of scale sizes of a few hundred meters that produce scintillation on a L-band signal.