Modulation of ionospheric conductance and electric field associated with pulsating aurora
Modulation of ionospheric conductance and electric field associated with pulsating aurora
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DOI：
10.1029/2009ja014683
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发表时间：
2010-03-04
影响因子：
2.8
通讯作者：
Sato, N.
中科院分区：
文献类型：
--
作者：
Hosokawa, K.;Ogawa, Y.;Sato, N.
我们首次提出了电离层参数的准周期调制，这些参数与脉动极光的发生有关，如电子密度、电导和电场。2008年3月，在挪威特罗姆索(北纬69.60度，东经19.20度)上空，使用全天电视摄像机和欧洲非相干散射超高频系统，对脉动极光进行了同时的运动测量。在这次活动期间的一段时间内，亚视在当地时间上午时段(类似于MLT 0500时)观测到脉动极光，周期为8-17 S。在这一区间内，EISCAT得到的原始电子密度存在准周期振荡。E区(95-115公里)较低高度的电子密度在光脉动开始“开启”后立即增加了3-4倍。高度积分的霍尔电导也增加了1.5-2倍，几乎与电子密度的变化一致。电子密度和霍尔电导对脉动极光的响应几乎是立即的。然而，在光学脉动停止后，两者都没有立即降低到本底水平。这主要是因为在这些高度，电子密度通过与周围离子的复合而下降需要几秒钟的时间。有趣的是，基律纳的远程天线进行的电场测量显示，当脉动的极光打开时，电场发生了重定向。我们提出了一个模型，在这个模型中，脉动极光斑块内霍尔电导的增强导致了斑块边缘的电荷积累，然后电场被由此产生的极化电场所修正。用该模型估算的电场调制能很好地再现EISCAT的实际电场观测结果，证实了该模型的有效性。这些结果表明，与脉动极光相关的高能电子沉淀引起的电离对电离层的电导率和电流系统有显著的影响。这种对电离层的修改可能有助于描述脉动极光的形态特征。特别是，电场的改变将影响脉动极光斑块的空间结构，如它们的运动和形状。
We present, for the first time, a quasiperiodic modulation of ionospheric parameters, associated with the occurrence of pulsating auroras, such as electron density, conductance, and electric field. In March 2008, simultaneous campaign-based measurements of pulsating auroras were conducted over Tromso (69.60 degrees N, 19.20 degrees E), Norway, using an all-sky TV camera (ATV) and the European Incoherent Scatter (EISCAT) UHF system. During an interval within this campaign period, pulsating auroras, with periods of 8-17 s, were observed by the ATV in the morning local time sector (similar to 0500 MLT). In this interval, quasiperiodic oscillations were identified in the raw electron density obtained by EISCAT. The electron density at lower altitudes in the E region (95-115 km) was enhanced by a factor of 3-4 immediately after the optical pulsation became "on." The height-integrated Hall conductance was also elevated, by a factor of 1.5-2, almost in harmony with the electron density variation. The response of the electron density and Hall conductance to the appearance of the pulsating aurora was almost immediate. However, both did not decrease to the background level promptly after optical pulsation ceased. This was primarily because it took a few seconds for the electron density to decrease through recombination with ambient ions at these altitudes. Interestingly, electric field measurements performed by the remote antenna at Kiruna showed that redirection of the electric field occurred when the pulsating aurora was "on." We propose a model in which the enhancement of Hall conductance within patches of the pulsating aurora caused charge accumulation at the edges of the patches, and the electric field was then modified by the resulting polarization electric field. An estimation of the electric field modulation with this model well reproduced the actual electric field observations carried out by EISCAT, which confirmed the validity of the model. These results imply that the ionization caused by high-energy electron precipitation associated with a pulsating aurora has a significant effect on the ionospheric conductivity and current system. This modification of the ionosphere may facilitate characterization of the morphological features of pulsating auroras. In particular, modification of the electric field would affect the spatial structure of pulsating aurora patches, such as their motion and shapes.