极盖区等离子体云块近十年研究进展

Recently research advances on the polar cap patches

极盖区等离子体云块是一种经常出现在极区电离层F层的高密度块状结构,其电子密度一般是背景电子密度的两倍及以上,水平尺度约为100~1000 km.极盖区等离子体云块的产生及演化过程可以示踪磁层-电离层/热层耦合过程中的能量及动量传输过程.同时,这种电子密度不均匀体(尤其是其边沿区域)对跨极盖区的无线电波传播具有很强的干扰,经常影响无线电通讯导航定位等应用.因而,极盖区等离子体云块研究不仅是空间物理领域的热点问题,而且也是空间天气监测及准确预报等应用的重要基础.本文简述了近十年来极盖区等离子体云块的研究进展,主要内容包括:概括了极盖区等离子体云块几种可能的形成机制;提出了极盖区冷/热等离子体云块的分类研究;统计了极盖区等离子体云块的时空分布特征及其对外部条件的依赖性;追踪了极盖区等离子体云块的完整演化过程;最后,讨论了极盖区等离子体云块引起的离子上行现象及电离层闪烁效应.

The polar cap patch is a common ionospheric structure.It often appears in the F region of the ionosphere over the polar caps;these patches are usually characterized by electron densities that can be even twice greater than that of the surrounding area.Untangling the formation and evolution of the polar cap patch can unveil the transportation of energy and momentum through magnetosphere-ionosphere-thermosphere couplings.However,owing to their wide horizontal reach(~100~1000 km),these high electron density structures greatly obstruct radio wave propagation over the polar cap,particularly at their edges,seriously impeding efforts tied to communication,navigation,and positioning.Therefore,the study of polar cap patches is not only of significance within space physics but also of great value within the context of space weather monitoring and prediction.In this paper,recent progress in polar cap patch research is summarily reviewed.The focus of our review includes the possible mechanisms underlying the formation of the dominant dayside reconnection;the recently proposed sunward return flows,likely produced by the nightside reconnection or other processes;and the newly defined patch-polar cap hot patch and its dependencies on various factors(e.g.,solar&geomagnetic activities,local plasma transport,and particle precipitation).We will also delve into patch occurrences,as they relate to spatiotemporal dynamics as well as the interplanetary magnetic field conditions.We will also comprehensively review the evolutionary process tied to the Dungey convection cycle,as it moves from the dayside to the nightside and finally as it exits the polar caps,initially modulated by the pulsed nightside reconnection and then sunward transportation by the return flow.Lastly,we will detail the effects of ion upflow and ionospheric scintillation associated with the polar cap patch.For each subject,we will provide a detailed account of progress that has been made and its corresponding prospects.