赤道异常的经度效应

比较赤道异常北峰北坡上磁纬靠近但经度不同台站的f₀F₂月中值的差别,比较中国东部电离层垂测站链与日本垂测站链的f₀F₂月中值的差别,可以研究东亚地区赤道异常随经度的变化.结果表明,冬季,赤道异常北峰在日本扇区的强度大于中国东部地区;反之,夏季赤道异常北峰在中国东部地区的强度大于日本扇区,并且两个扇区北峰结束的纬度冬天低于夏天.     

赤道异常的经度效应

比较赤道异常北峰北坡上磁纬靠近但经度不同台站的f0F2月中值的差别,比较中国东部电离层垂测站链与日本垂测站链的f0F2月中值的差别,可以研究东亚地区赤道异常随经度的变化.结果表明,冬季,赤道异常北峰在日本扇区的强度大于中国东部地区;反之,夏季赤道异常北峰在中国东部地区的强度大于日本扇区,并且两个扇区北峰结束的纬度冬天低于夏天.     

CSES卫星观测的赤道电集流特征

本文利用2018年8月到2019年12月期间我国张衡一号电磁监测试验卫星(CSES)所观测的地磁数据,反演了赤道电集流(EEJ)电流密度的纬度剖面;通过选取的4729个清晰的EEJ事件,分析了在地方时(LT)14:00附近的EEJ特征.研究结果表明：在地磁平静期间,CSES卫星观测的EEJ电流密度的峰值位于磁赤道附近,其平均幅度约为27 mA·m^-1.该幅度小于CHAMP和Swarm卫星的观测结果,这与2018—2019年期间太阳活动水平较低(平均F_10.7指数约为70 sfu)有关,此外也与CSES轨道所处的地方时相关.平均而言,EEJ的主瓣宽度约为4°,主瓣和旁瓣的峰值电流密度之比约为2.7;在本文所关注的事件中,东向EEJ事件约占83%,西向EEJ事件约占17%;这个比例与CHAMP卫星的观测结果稍有不同,与14:00 LT附近西向EEJ出现的概率较低有关.东向EEJ的峰值电流密度对经度、季节和太阳辐射水平有显著的依赖性.EEJ峰值密度随经度变化呈现明显的4波结构,可归因于低层大气非迁移潮汐的作用.EEJ峰值电流密度有明显的季节依赖,其幅度在春秋分较大,冬夏季较小.在2018—2019年期间,尽管太阳活动水平较低,EEJ峰值密度随太阳辐射水平的增加而增加.

     

东亚扇区赤道异常北峰的移动规律

本文利用冲绳、台北、广州、海南四个电离层垂测站的f0F2月报表资料,分析东亚扇区赤道异常北峰的移动规律,得到北峰位置随季节、太阳活动不同周相的移动规律。并且发现赤道异常的两日振荡将引起北峰位置作相应的波动。     

赤道电离异常特征参量地方时梯度的日变化特征——Swarm卫星观测

Swarm A/C卫星在460 km左右高度伴飞,地方时差异5.6 min,为赤道电离异常（Equatorial Ionization Anomaly,EIA）研究提供了一个绝好的观测机会.本文利用Swarm A/C卫星2014-2017年期间的电子密度观测数据,研究了地磁活动相对平静期EIA特征参量地方时梯度的日变化特征.分析发现：（1）EIA驼峰强度和位置的地方时梯度,ΔNe和Δβ,在正午前随地方时线性减小,午后达到极小值;傍晚前后,二者先增大后减小.该日变化特征在各季节具有普适性.（2）ΔNe和Δβ的日变化表现出紧密的相关性,且在白天和日落后两个时段内遵从明显不同的线性关系.（3）ΔNe和Δβ对赤道等离子体抬升通量地方时梯度,Δflux,的响应非常迅速,滞后时间约为1 h.

     

东亚扇区赤道异常北峰的移动规律

本文利用冲绳、台北、广州、海南四个电离层垂测站的f₀F₂月报表资料,分析东亚扇区赤道异常北峰的移动规律,得到北峰位置随季节、太阳活动不同周相的移动规律。并且发现赤道异常的两日振荡将引起北峰位置作相应的波动。     

基于GNSS观测的全球赤道等离子体泡对太阳和地磁活动及季节依赖特征

赤道等离子体泡是在磁赤道和低纬地区一种通常发生在夜间的大尺度电离层不规则结构.本文利用2010—2021年全球低纬地区GNSS TEC监测仪长期观测数据,分析了赤道等离子体泡对太阳和地磁活动及季节的依赖特征.结果表明,全球每个经度区赤道等离子体泡发生率与太阳活动都显著正相关,赤道等离子体泡的日发生率与F₁₀₇指数相关系数接近0.70.经度-60°~-30°在赤道等离子体泡高发月份的日落后发生率与F₁₀₇的相关关系有明显的饱和效应.在季节变化方面,经度-60°~-30°赤道等离子体泡主要发生在1—3月和10—12月,其他经度主要发生在分季.不同经度区赤道等离子体泡日落后发生率季节不对称性存在显著区别,在太阳活动上升期,经度-60°~-30°的10—12月发生率明显高于1—3月;在太阳活动下降期,0°~180°经度区3月分季高于9月分季.此外,地磁扰动对产生赤道等离子体泡主要是抑制作用,特别是在太阳活动高年、分季.

     

北赤道暖流

北赤道暖流,在赤道北侧,由于该暖流是受东北信风的影响而形成的自东向西推进的洋流,因而属于风海流．与由于受东南信风影响形成的南赤道暖流合称“信风流”。其基本特点是从东向西流动,横贯大洋．水温高,盐度低。     

赤道电射流的影响范围

本文收集了１９８２年３月印度、中国、菲律宾低纬地区９个地磁台的静日月均值资料。经分析对比后绘出了Ｓｑ（Ｈ），Ｓｑ（Ｚ）变幅与离磁赤道距离的关系图。结果显示赤道电射流对Ｓｑ（Ｚ）的影响可达５００ｋｍ，对Ｓｑ（Ｈ）的影响范围小于４００ｋｍ。这个结果与ＰＡＲＫＩＮＳＯＮ（１９８３）书中的论述基本一致。离磁赤道远达１０００ｋｍ的琼中台资料没受赤道电射流的影响，广州台资料则更不可能受影响。     

太平洋北赤道流表层的分叉

利用1993～2006年间的网格化高度计数据,通过经验正交函数（EOF）方法研究了北赤道流在表层分叉的变化规律．包括过去研究的季节和年际变化,研究结果发现一些较短周期的信号（6个月,4个月,3个月和2个月）．除在年际时间尺度上,局地的风应力旋度可能是控制分叉纬度变化的重要原因．计算的年平均分叉纬度约为13．3°N,1月份最北在14．0°N,7月份最南在12．5°N．分叉纬度的变化幅度为1．5°,这主要是来自年信号的贡献（1．2°）和半年信号的贡献（0．3°）．     

A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

A global coupled thermosphere-ionosphere-plasmasphere model is used to simulate a family of large-scale imperfectly ducted atmospheric gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) originating at conjugate magnetic latitudes in the north and south auroral zones and subsequently propagating meridionally to equatorial latitudes. A fast dominant mode and two slower modes are identified. We find that, at the magnetic equator, all the clearly identified modes of AGW interfere constructively and pass through to the opposite hemisphere with unchanged velocity. At F-region altitudes the fast AGW has the largest amplitude, and when northward propagating and southward propagating modes interfere at the equator, the TID (as parameterised by the fractional change in the electron density at the F2 peak) increases in magnitude at the equator. The amplitude of the TID at the magnetic equator is increased compared to mid-latitudes in both upper and lower F-regions with a larger increase in the upper F-region. The ionospheric disturbance at the equator persists in the upper F-region for about 1 hour and in the lower F-region for 2.5 hours after the AGWs first interfere, and it is suggested that this is due to enhancements of the TID by slower AGW modes arriving later at the magnetic equator. The complex effects of the interplays of the TIDs generated in the equatorial plasmasphere are analysed by examining neutral and ion winds predicted by the model, and are demonstrated to be consequences of the forcing of the plasmasphere along the magnetic field lines by the neutral air pressure wave.     

A climatological study of nocturnal equatorial F-region irregularities at the west Pacific longitudes by using phase fluctuations of the global positioning system

This study investigated a long-term climatology of nocturnal equatorial F-region irregularities by using phase fluctuations of the global positioning system during the solar cycle of 1996–2006 at the west Pacific longitudes. The results showed that the distribution of the occurrence of irregularities is a two-peak pattern, which peaks in equinoxes with a shallow/deep dip in June/December solstice during high solar activity but with two about the same dips in magnitude in both June and December solstices during low solar activity. Moreover, the most interesting longitudinal effect in the area is in solstice occurrences of irregularities during high solar activity that the irregularities in December solstice months develop easier in the west area but those in June solstice months develop easier in the east area.     

A review of atmospheric gravity waves and travelling ionospheric disturbances: 1982-1995

Recent investigations of atmospheric gravity waves (AGW) and travelling ionospheric disturbances (TID) in the Earth’s thermosphere and ionosphere are reviewed. In the past decade, the generation of gravity waves at high latitudes and their subsequent propagation to low latitudes have been studied by several global model simulations and coordinated observation campaigns such as the Worldwide Atmospheric Gravity-wave Study (WAGS), the results are presented in the first part of the review. The second part describes the progress towards understanding the AGW/TID characteristics. It points to the AGW/TID relationship which has been recently revealed with the aid of model-data comparisons and by the application of new inversion techniques. We describe the morphology and climatology of gravity waves and their ionospheric manifestations, TIDs, from numerous new observations.     

Topographic and atmospheric effects on goce gradiometric data in a local north-oriented frame: A case study in Fennoscandia and Iran

Satellite gradiometry is an observation technique providing data that allow for evaluation of Stokes’ (geopotential) coefficients. This technique is capable of determining higher degrees/orders of the geopotential coefficients than can be achieved by traditional dynamic satellite geodesy. The satellite gradiometry data include topographic and atmospheric effects. By removing those effects, the satellite data becomes smoother and harmonic outside sea level and therefore more suitable for downward continuation to the Earth’s surface. For example, in this way one may determine a set of spherical harmonics of the gravity field that is harmonic in the exterior to sea level. This article deals with the above effects on the satellite gravity gradients in the local north-oriented frame. The conventional expressions of the gradients in this frame have a rather complicated form, depending on the first-and second-order derivatives of the associated Legendre functions, which contain singular factors when approaching the poles. On the contrary, we express the harmonic series of atmospheric and topographic effects as non-singular expressions. The theory is applied to the regions of Fennoscandia and Iran, where maps of such effects and their statistics are presented and discussed.     

火星磁鞘区反射拾起氧离子事件分析

火星逃逸层中性成分经光致电离、电荷交换和电子碰撞产生新生离子,新生离子随即被太阳风和火星磁鞘电磁场拾起,称为"拾起"离子.已有观测表明拾起氧离子（O+）在朝向火星沉降途中会被反射,但发生反射的空间位置和反射机制尚不十分明确.若反射离子持续进入探测器,将为我们追踪反射发生的空间位置提供重要机遇.本文将报道这样一个观测实例,2016年9月25日04：18：30—04：24：54 UT期间,火星大气和挥发物演化任务（Mars Atmosphere and Volatile EvolutioN,MAVEN）运行在-E半球（对流电场E指向火星）的磁鞘区,轨道高度逐渐降低,持续观测到背离火星运动的O+（103~104 eV）束流,即正在反射的拾起O+.反射拾起O+大致可分为两部分：相空间密度较高、能量较低的部分是由磁鞘拾起O+被反射后形成;相空间密度较低、能量较高的部分则源于太阳风拾起O+发生反射后形成.我们推断反射发生在感应磁层边界附近的强磁场区域.     

A study on three-dimensional structures of the ionospheric dynamo currents induced by the neutral winds simulated by the Kyushu-GCM

Three-dimensional structures of the ionospheric dynamo currents are examined using the neutral winds in a general circulation model of the middle atmosphere at Kyushu University. A quasi-three-dimensional ionospheric dynamo model is constructed assuming an infinite parallel conductivity in the ionosphere. This model is able to simulate both the equatorial electrojet and the global Sq current system successfully. The simulated results reveal that the equatorial electrojet is confined in quite narrow latitudes around the equator accompanied with meridional current circulations and satisfies a non-divergent structure mainly within the E region. A vertically stratified double layered structure is seen in the east–west current density near the focus latitude of the global Sq current system. It is shown that the stratified structure mainly consists of the east–west Hall current associated with the eastward wind of zonal wavenumbers 1 and 2 in the lower altitudes and the westward wind of zonal wavenumber 2 in the upper altitudes. The day-to-day variation of the neutral winds can significantly vary the induced ionospheric dynamo current system, which is recognized as changes of the focus latitude and/or the maximum value of the equatorial electrojet.     

Hydroclimate variability and long-lead forecasting of rainfall over Thailand by large-scale atmospheric variables

Abstract

The development of statistical relationships between local hydroclimates and large-scale atmospheric variables enhances the understanding of hydroclimate variability. The rainfall in the study basin (the Upper Chao Phraya River Basin, Thailand) is influenced by the Indian Ocean and tropical Pacific Ocean atmospheric circulation. Using correlation analysis and cross-validated multiple regression, the large-scale atmospheric variables, such as temperature, pressure and wind, over given regions are identified. The forecasting models using atmospheric predictors show the capability of long-lead forecasting. The modified k-nearest neighbour (k-nn) model, which is developed using the identified predictors to forecast rainfall, and evaluated by likelihood function, shows a long-lead forecast of monsoon rainfall at 7–9 months. The decreasing performance in forecasting dry-season rainfall is found for both short and long lead times. The developed model also presents better performance in forecasting pre-monsoon season rainfall in dry years compared to wet years, and vice versa for monsoon season rainfall.

Editor Z.W. Kundzewicz

Citation Singhrattna, N., Babel, M.S. and Perret, S.R., 2012. Hydroclimate variability and long-lead forecasting of rainfall over Thailand by large-scale atmospheric variables. Hydrological Sciences Journal, 57 (1), 26–41.     

利用中国GPS站网对地震波引发的大尺度电离层扰动的观测

地震瑞利波在沿地表传输时衰减很慢,其能量在远离震中的区域仍然能够激发大气和电离层扰动.本文利用中国境内的GPS接收机网络观测电离层总电子含量（total electron content,TEC）,分析了2011年日本地震后在中国区域上空产生的电离层扰动.研究发现,瑞利波的能量从地面经大气耦合传输到电离层高度,导致在中国区域上空电离层出现与瑞利波传播同步的TEC扰动.利用中东部的稠密接收机网络,还揭示了扰动的大尺度二维空间结构：瑞利波经过后产生的TEC扰动呈条带状,在中纬度地区沿西北-东南方向排列,而在低纬度大致为东西方向.条带的转向可能与地磁场作用下的中性-离子耦合过程有关,大气波动导致的等离子扰动倾向于沿磁力线方向（向南）传播,从而形成垂直磁力线方向（东西）的波前结构.这是首次在远离震中的区域使用GPS站网研究地震波耦合电离层扰动的大尺度二维空间结构.