低纬电离层南北半球不对称性研究

It has been found that the relative strength of the EIA crests between northern and southern hemispheres is affected by many factors, such as the trans-equatorial neutral wind, the neutral composition (O/N2) variation, the vertical E×B plasma drift and the consequent fountain effects. It is generally considered that the transition of relatively stronger crest from the winter hemisphere to summer hemisphere, which generally occurs in the afternoon, is closely associated with the decrease of the trans-equatorial neutral winter in the afternoon. A few works have been simulated the north-south asymmetry of the EIA crests, but only using the pure ionospheric model without considering the ion-neutral coupling effects. However, the relative roles are not clear , for the neutral wind on plasma horizontal transportation and on changing plasma loss rate through driving the ionosphere upward or downward, as well as neutral composition and E×B drift. Therefore, the mechanisms of the EIA hemispheric asymmetry needs further investigation. On the other hand, I recently found through global occultation observation that in March equinox, evident double crests of hmF2 occurred at around ±10° geomagnetic latitude (MLAT) with a trough over the magnetic equator, while in solstices only one crest was observed in the summer hemisphere. To investigate the mechanisms of the above phenomena, I would carry out a series of theoretical simulation, using TIEGCM, which is a time-dependent, self-consistent, three-dimensional and physics-based model of the global thermosphere/ionosphere system. The aim of the present study is to ：(1) Quantitatively investigate on the relative roles of all mechanisms that involved in the EIA crests asymmetry by doing TIEGCM simulation;(2) Obtain more accurate latitudinal structure of hmF2 and its seasonal variation over low latitudes in the Asian sector through ionosonde observation; (3) Clarify the mechanism on the hmF2 crests over low latitude and the hmF2 crest hemispheric asymmetry through TIEGCM simulation.

电离层F2层电子密度赤道异常驼峰的南北半球不对称性可由跨赤道中性风、大气成分、电场漂移及其相关的赤道喷泉效应等多种因素引起。以往研究大多认为冬夏半球驼峰不对称性的改变与午后中性风的减小密切相关，且相关理论研究一般采用的是非耦合电离层模型。然而，风场通过电离层动力学输运与改变电离层化学损失过程的相对贡献，以及中性成分、电场漂移等影响程度尚不清楚。此外，申请人最近已发现低纬度电离层F2层峰高在春秋季也出现驼峰结构，而在夏至和冬至不对称，仅在夏季半球出现单峰。申请人拟基于三维自洽的热层-电离层电动力学耦合模型开展系统理论模拟研究，甄别中性风、中性大气成分和电场漂移等因素对电子密度南北不对称的相对贡献；并借助测高仪观测，进一步分析赤道峰高纬度结构及其随季节的变化，结合数值模拟探索赤道区域峰高异常结构和南北半球不对称的形成机制。

申请人基于三维自洽的热层-电离层电动力学耦合模型（TIEGCM）和其它低纬模型，对以往发现的南北半球赤道异常（电子密度驼峰和电离层峰高）的半球不对称现象及其形成机制开展系统的理论和模拟研究，从而甄别中性风、中性大气成分、赤道喷泉效应以及暴时效应等因素的相对影响；并对上述低纬电离层不对称性的变化特征开展深入的研究。该项目计划在四年内完成。在项目实施过程中，围绕上述既定目标，四年内首先开展了电离层热层重要能量来源—粒子沉降能量分布与变化的研究。在此基础上，借助TIEGCM和其它低纬模型，对低纬电离层不对称性开展控制实验，定量分析了跨赤道中性风、中性大气成分、赤道喷泉效应以及暴时效应等因素的影响。进一步地，研究了包含低纬在内的全球背景下电离层热层的极区能量来源，多种新现象和形成机制，得出了低纬电离层过程在全球系统耦合中的响应和形成机制。这些研究工作均按计划陆续在四年项目执行期内完成，取得了一系列新的成果。项目的一切费用均未超出预算。以上研究成果丰富，在地学高水平杂志发表SCI论文21 篇，其中有8篇第一或通讯作者论文，且该项目均为第一标注。培养了博士毕业生2名 （周苏、李娜）和在读博士、硕士研究生三名（李振兴，汪令敏，黎中黎）。协助培养了两名博士后工作人员。