Plasmaspheric storm time erosion
Plasmaspheric storm time erosion
复制标题
等离子层风暴时间侵蚀
DOI：
10.1029/1999ja900497
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发表时间：
2000
影响因子：
--
通讯作者：
N. Thomson
中科院分区：
文献类型：
--
作者：
M. Clilverd;B. Jenkins;N. Thomson
异常低的哨声模式群延迟时间观测的甚低频多普勒接收机在法拉第，南极洲，和达尼丁，新西兰，磁暴。这些通常是由等离子体层附近的电子浓度耗尽L=2.4，而不是由VLF波的传播path. Using的数据集，几乎是连续的，因为1986年，我们发现，在风暴期间的耗尽在1995年的太阳活动极小期显着比在1986年的最低。法拉第的事件研究表明，风暴引起的电子浓度损耗在1986年约为2倍，在1995年约为3-4倍，与一年中的时间无关。然而，这两个地点观察到的消耗比1958年和1961年使用自然哨声观察到的要深得多（即，2-4与1.3相比）。利用谢菲尔德大学等离子体层电离层模式（SUPIM）研究了哨声模式观测到的等离子体层电子浓度耗尽的可能原因。热层参数，包括所有高度中性氢和氧浓度的减少，受到了正常水平10倍的扰动。然而，27小时后产生的等离子体层消耗仅为10%的量级。因此，数据中观察到的消耗不太可能仅仅是热层变化造成的。此外，一管等离子体在1000 m s−1的赤道赤道向E × B漂移速度的影响下被移动到更高的L壳层，并显示出大约2倍的耗尽水平。虽然使用漂移管模型有可能产生等离子体层浓度耗尽，但耗尽比观察到的要小，并且所需的向外E × B漂移速度比先前在L=2.4时报道的大2倍。因此，管漂移机制是在L=2.4处观察到的等离子体层电子浓度耗尽的主要原因是不可能的。虽然没有机制是明确确定在这项研究中，本文提出的地面结果表明，类似的结构和规模的侵蚀水平的电子浓度分布的ISEE 1卫星在1983年的磁扰动之后，从而提供了一个长期的等离子体层侵蚀的记录。
Unusually low whistler mode group delay times are observed by VLF Doppler receivers at both Faraday, Antarctica, and Dunedin, New Zealand, following magnetic storms. These are typically caused by plasmaspheric electron concentration depletions near L=2.4 and not by changes in the VLF wave propagation path. Using a data set that is almost continuous since 1986, we find that depletions during storms in the solar minimum of 1995 are significantly deeper than in the minimum of 1986. Event studies at Faraday show that the electron concentration depletions caused by storms were about a factor of 2 in 1986 and a factor of 3–4 in 1995, independent of the time of year. However, the depletions observed by both sites are significantly deeper than those observed in 1958 and 1961 using natural whistlers (i.e., factors of 2–4 compared to 1.3). The Sheffield University Plasmasphere Ionosphere Model (SUPIM) has been used to investigate possible causes of the plasmaspheric electron concentration depletions observed in the whistler mode data. Thermospheric parameters, including a reduction in the concentration of neutral hydrogen and oxygen at all altitudes, were perturbed by a factor of 10 from their normal levels. However, the plasmaspheric depletions produced were only of the order of 10% after 27 hours. It is unlikely therefore that thermospheric modifications alone are responsible for the depletions observed in the data. Additionally, a tube of plasma was moved to higher L shell under the influence of an equatorial meridional E × B drift velocity of 1000 m s−1 and showed levels of depletion of about a factor of 2. Although it is possible to generate plasmaspheric concentration depletions using the drifting tube model, the depletions are smaller than those observed and the outward E × B drift velocity needed is a factor of 2 greater than those reported previously at L=2.4. It is therefore unlikely that the tube drifting mechanism is the principal cause of the observed plasmaspheric electron concentration depletions at L=2.4. Although no mechanism is clearly identified in this study, the ground-based results presented in this paper indicate erosion levels of similar structure and magnitude to electron concentration profiles from the ISEE 1 satellite in the aftermath of magnetic disturbances during 1983, thus providing a long-term record of plasmaspheric erosion.