Vertical rise velocity of equatorial plasma bubbles estimated from Equatorial Atmosphere Radar (EAR) observations and HIRB model simulations
Vertical rise velocity of equatorial plasma bubbles estimated from Equatorial Atmosphere Radar (EAR) observations and HIRB model simulations
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DOI：
10.1002/2017ja024260
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发表时间：
2017-06
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影响因子：
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通讯作者：
S. Tulasi Ram;K. Ajith;T. Yokoyama;M. Yamamoto;K. Niranjan
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文献类型：
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作者：
S. Tulasi Ram;K. Ajith;T. Yokoyama;M. Yamamoto;K. Niranjan
2010年5月至2013年4月期间，利用位于科托塔邦的47 MHz赤道大气雷达（EAR）的二维扇区图估算了赤道等离子体气泡（EPB）的垂直上升速度（Vr）和最大高度（Hm）。总共观测到86个EPB，其中68个是日落后EPB，其余18个EPB是在午夜左右观测到的。与日落后时段观察到的 EPB 垂直上升速度 (~45-265 m/s) 相比，午夜前后观察到的 EPB 垂直上升速度明显较小 (~26-128 m/s)。此外，在午夜左右，EPB 的垂直增长在相对较低的高度停止，而大多数 EPB 在日落后的时间被发现已经增长到超过了 EAR 的最大可检测高度。采用不同背景条件的三维数值高分辨率气泡（HIRB）模型来研究控制 EPB 垂直上升速度和最大可达高度的可能因素。 EAR 观测在日落后和午夜时段估计的上升速度总体上与 HIRB 模型中 EPB 的非线性演化一致。由于背景电场较弱和背景离子密度水平降低，在气泡内的弱极化电场方面讨论了午夜时段 EPB 较小的垂直上升速度 (Vr) 和较低的最大高度 (Hm)。
The vertical rise velocity (Vr) and maximum altitude (Hm) of equatorial plasma bubbles (EPBs) were estimated using the two‐dimensional fan sector maps of 47 MHz Equatorial Atmosphere Radar (EAR), Kototabang, during May 2010 to April 2013. A total of 86 EPBs were observed out of which 68 were postsunset EPBs and remaining 18 EPBs were observed around midnight hours. The vertical rise velocities of the EPBs observed around the midnight hours are significantly smaller (~26–128 m/s) compared to those observed in postsunset hours (~45–265 m/s). Further, the vertical growth of the EPBs around midnight hours ceases at relatively lower altitudes, whereas the majority of EPBs at postsunset hours found to have grown beyond the maximum detectable altitude of the EAR. The three‐dimensional numerical high‐resolution bubble (HIRB) model with varying background conditions are employed to investigate the possible factors that control the vertical rise velocity and maximum attainable altitudes of EPBs. The estimated rise velocities from EAR observations at both postsunset and midnight hours are, in general, consistent with the nonlinear evolution of EPBs from the HIRB model. The smaller vertical rise velocities (Vr) and lower maximum altitudes (Hm) of EPBs during midnight hours are discussed in terms of weak polarization electric fields within the bubble due to weaker background electric fields and reduced background ion density levels.