电离层峰值变化特性及其影响因素分析

电离层延迟误差是影响GNSS高精度定位的重要误差来源之一,分析和掌握各因素对电离层变化规律的影响,有助于建立高精度电离层模型。为此,本文采用IGS中心提供的1999年~2015年电离层GIM数据计算南北半球不同经度圈的峰值不对称指数,分析其与太阳活动情况和地磁活动情况的相关性,并对单日电离层峰值变化情况进行分析。通过分析表明：(1)峰值不对称指数具有明显的年周期性和季节周期性;(2)西半球峰值不对称指数与太阳黑子数的相关性大于东半球,但东半球和西半球峰值不对称指数与地磁指数相关性几乎相同;(3)除08:00 LT ~ 10:00 LT(Local Time) 赤道两侧不存在明显峰值外,剩余时段均有明显的峰值,且通常在12:00 LT ~ 16:00 LT 取得极大值。     

电场对暴时低纬电离层foF2变化的影响

电场在低纬电离层的演化过程中扮演着重要角色. 以2003年10～11月的两次强磁暴事件为例, 分析105°E附近由赤道区域扰动电场引起的等离子体输运对低纬指定区域内电离层的影响, 并用电离层模型SAMI2进行数值模拟. 研究表明, 电场能引起电离层foF2的复杂变化. 在2003年11月19～24日孤立磁暴事件中, 扰动电场在电离层暴初期起主导作用, 向上和向极漂移的等离子体造成赤道异常峰南侧海口站电离层负暴和北侧重庆及兰州站正暴. 在2003年10月28日～11月2日连续磁暴事件中, 电离层暴初期以电场影响为主, 随后电场和中性扰动成分共同作用于电离层, 表现出复杂的暴时变化. 电场扰动能迅速引起电离层的响应, 只是后者能维持较长时间. 上述结果对区域电离层短期预报具有重要意义.     

热层大气赤道异常的研究进展

热层大气赤道异常是指热层大气存在类似电离层赤道异常的驼峰结构,但其南北驼峰出现于磁纬±20~30°区域.热层赤道现象早在40年前就被发现,然而其形成机制一直是电离层学界研究的热点问题.前人陆续提出了化学加热及纬向风场拖曳作用等假说来解释热层赤道异常的形成,但基于这些假说得到的低纬热层结构与观测不符.最近研究发现,热层赤道异常槽与电离层驼峰的形成原因不同,离子与中性大气的场向拖曳作用形成热层赤道槽,且离子与中性气体相互碰撞引起的能量交换是热层赤道异常驼峰的形成机制.本文简述热层大气赤道异常的研究进展以及存在的科学问题.     

磁暴对夜间中低电离层影响的数值模拟

从电子连续方程、电子运动方程以及离子运动方程出发,选用IRI-90电子浓度为磁暴初始时的浓度,并采用HEDIN-90剪切时变中性风模式,对中低纬电离层F层在磁暴期间的变化形态进行了数值模拟研究.模拟结果表明:磁暴会引起电离层产生不同程度的扰动,在磁暴时存在的东西方向电场的作用下,电离层F层峰产生垂直漂移.不同情况的模拟表明:不同强度的暴时电场会对电离层F层产生不同的影响,并且纬度越低F层受暴时电场的影响越大,这与磁暴期间观测到的电波实验现象一致.     

磁暴对低纬电离层和低纬哨声的影响

总结在低纬（包括赤道异常区）地区多年观测到的磁暴期间哨声的出现特征和其他有别于磁静日的特征，联系低纬液间Ｆ层在磁暴期间出电离层垂直漂移运动特征，用数值模拟计算在磁暴期间出增强的东西向电场时的低纬Ｆ层液间动力学特征，同时用全解计算夜间动力学特征，同时全波解计算液间怕波束在电离层底部的透射与反身特性。较好地解释了磁暴期间出的多跳扩展哨声现象。     

基于IGS的TEC赤道异常南-北不对称性分析

利用IGS提供的太阳活动第23-24周期间2000年1月1日至2011年12月31日的GPS TEC数据,分析了东南亚地区经度110°E区域在不同的太阳活动情况下白天电离层赤道异常(EIA)各参数的南-北不对称性变化,以及不对称性随太阳活动变化的关系。结果表明:太阳活动的强弱与赤道异常双峰强度和双峰差异大小的关系明显,赤道异常双峰在驼峰强度、纬度位置和出现的时间等都有明显的季节变化特征,且有比较明显的南-北不对称性。在太阳活动高时,EIA双峰强度差异明显比太阳活动低时要大,各季节的峰值强度均值表现为北驼峰比南驼峰强,6-8月份北驼峰峰值出现的时间平均比南驼峰出现时间晚约1 h。在太阳活动低时,夏季和秋季节时北驼峰比南驼峰强,秋冬季节南驼峰比北驼峰强,且冬季北驼峰出现的时间要比南驼峰早约1 h,在5-9月份期间北驼峰出现的时间要比南驼峰晚约2 h。随着太阳活动的逐渐升高,冬至期间不对称性指数Ia均值增大的趋势非常明显。     

利用IGS电离层格网产品分析电离层峰值变化特性

电离层延迟误差是影响GNSS高精度定位的重要误差来源之一,分析和掌握各因素对电离层变化规律的影响,有助于建立高精度电离层模型。为此,采用IGS中心提供的1999~2015年电离层GIM数据计算南北半球不同经度圈的峰值不对称指数,分析其与太阳活动情况和地磁活动情况的相关性;并对单日电离层峰值变化情况进行分析。通过分析表明:(1)峰值不对称指数具有明显的年周期性和季节周期性;(2)西半球峰值不对称指数与太阳黑子数的相关性大于东半球,但东半球和西半球峰值不对称指数与地磁指数相关性几乎相同;(3)除08:00 LT(local time)~10:00 LT赤道两侧不存在明显峰值外,剩余时段均有明显的峰值;且通常在12:00 LT~16:00 LT取得极大值。     

地磁太阴日变化L的M2潮变化特征

用M2潮引起的地磁太阳日变化L的谐波分析方法,计算了佘山地磁台的磁偏角、水平和垂直分量L的谐波系数。分离出海洋和电离层发电机对L的贡献,讨论了太阳活动对地磁太阳日变化的影响,并把结果与国外部分台站的结果进行了对比分析。     

基于COSMIC数据开展全球电离层foF2建模及变化特征研究

电离层foF2是短波通信、天波超视距雷达系统所需的关键环境参数,本文使用2006-2014年COMSIC掩星电离层数据和多项式方法,自主构建了高精度全球电离层foF2经验模型,并使用2015-2019年观测数据进行独立检验。本模型结果与建模及独立检验时段电离层foF2观测数据的相关系数分别为0.948和0.937,平均偏差分别为2.38%和3.08%,相对误差分别为11.72%和12.69%。利用该模型研究了电离层foF2时空变化特征,结果表明电离层foF2日夜变化幅度随纬度增加而变大,春秋分季期间南半球日夜变化幅度显著高于北半球,而夏季半球则远低于冬季半球。电离层foF2季节变化幅度随纬度增加而变大,夜间电离层foF2的季节变化以年特征为主,白天则包含了显著的年、半年特征,夜间季节变化幅度明显高于白天,南半球显著高于北半球。电离层foF2中纬槽现象主要出现在春秋分季夜间,经度方向四波结构主要出现在太阳活动低年和春秋分季期间。     

震前电离层扰动研究进展及汶川地震前电离层变化

介绍了近年来国内外对震前电离层异常扰动研究进展,大量新的观测证据显示,地震活动前的电离层扰动确实存在,而且在震级大于5级的地震发生前几天到几个小时内的孕震区上空会发生显著电离层扰动。针对2008年5月12日发生的里氏8.0级汶川大地震事件,通过利用漠河、北京、武汉和三亚的地基GPS测量获得的垂直电子总含量(VTEC)数据,北京地面测高仪测量的F_2层临界频率和Es临界频率等参量,考察中国上空电离层在地震前的变化情况,发现地震前1～6 d中,5月6-7,10-11日,白天电子浓度比5月1-5日的值偏低。但f_0E_s增强。5月9日日落后中低纬电子浓度出现异常增强,而这段时间地磁活动平静。探求这些异常变化的机制则需收集更多资料做进一步的研究。     

A theoretical model for mid-and low-latitude ionospheric electric fields in realistic geomagnetic fields

The geomagnetic fields, which play important roles in the ionospheric dynamo, can greatly affect the global distribution of ionospheric electric fields, currents and other ionospheric electrodynamics phenomena. In the study of ionospheric electrodynamics phenomena, such as the longitudinal variations of ionospheric electric fields, the non-dipolar component of the geomagnetic fields must be taken into account. In this paper, we deduce a theoretical electric field model for ionospheric dynamo at mid- and low-latitude which adopt a modified magnetic apex coordinates system. In the new electric field model, the geomagnetic fields can be calculated from either the IGRF model or the dipole field model, and the neutral winds and conductivities are calculated based on empirical models. Then the dynamo equation for the electric potential is finally solved in terms of the line-by-line iteration method, and the ionospheric electric fields and currents are derived from the calculated potential. Our model can reproduce the main features of the ionospheric electrodynamics processes, so it will be a useful tool for the investigation of the upper atmosphere and ionosphere.     

基于无线电掩星观测的火星电离层观测研究进展

火星电离层早期的观测数据非常少,除了Viking登陆器对火星电离层的在位测量外,火星电离层的主要物理信息是通过掩星观测方法得到的.近年来,Mars Global Surveyor和Mars Express轨道器通过掩星观测的方法对火星的上层大气和电离层进行了长期的观测,得到了大量的火星电离层电子密度廓线资料.火星电离层受到来自太阳EUV和X射线辐射、太阳风、太阳耀斑、中性大气、表面壳磁场、宇宙射线、流星等多种因素的影响,使其结构发生瞬态或季节性的变化.本文介绍了行星无线电掩星探测的基本原理和技术特点,回顾了国内外科学家们基于已有的火星掩星观测数据（主要是Mars GlobalSurveyor和Mars Express）在火星电离层研究中的一些最新科学成果,并详细介绍了火星电离层的结构和火星夜间电离层的主要特征.     

Plasma transport between the ionosphere and plasmasphere in response to solar wind dynamic pressure pulsation

The plasma transport between the plasmasphere and the ionosphere in response to the interplanetary conditions is still not fully understood until now.Simultaneous observations of the plasmasphere and ionosphere from the newly developed Chinese Meridian Project provide a new opportunity for understanding the characteristic of the plasma transport and the coupling mechanism between these two regions.We investigate the response of the plasmasphere(L≈2)and ionosphere to the solar wind dynamic pressure pulse during geomagnetically quiet period of 21–27 March 2011.The response of the plasmasphere shows a significant depletion.The plasmaspheric density nearly decreases by half in response to the solar wind dynamic pressure pulse,and subsequently recovers to the original level in 1–2 d.Meanwhile,the maximum electron density of the ionospheric F2 layer(NmF2)and the total electron content(TEC)increase by 13%and 21%,respectively,and then gradually recover,which is opposite to the behavior during magnetic storms.Preliminary analysis shows that the plasmaspheric depletion may be mainly caused by the southward interplanetary magnetic field and changing dawn-dusk electric field.The plasmaspheric density variations seem to be controlled by both the IMF and ionospheric conditions.     

老哈河流域水文要素变化研究

对老哈河流域近50a的水文要素进行了年际变化、年代际变化和线性变化趋势的研究,结果表明:(a)年降雨量的年际变化幅度最均匀、离散度最小,而年径流深和年径流系数的年际变化不均匀、离散度大.降雨量是影响径流的主要因素,但并不是唯一因素,在某些年份径流还受到其他因素的强烈干扰.另外,年径流深不仅受年降雨总量的影响,也受降雨的年内时空分布的影响.(b)从20世纪60年代到21世纪初,各要素的年代际变化不一致:年降雨量变化为少-多-少-多-少,年径流深和年径流系数变化为多-少-少-多-少.年降雨量年代际距平变化最小,变化幅度较平缓,而年径流深和年径流系数的年代际变化都比年降雨量的年代际变化大得多.(c)降雨量没有明显的增减变化,而径流却具有显著的减少趋势,其中年径流深通过了95%的置信度检验,年径流系数通过了99%的置信度检验.分析结果表明,径流的变化除了受降雨量的影响之外,还可能受气温变化和人类活动等其他因素的影响.     

Storm-time ionospheric disturbances monitored by GPS beacon measurements

The Total Electron Content (TEC) during three great storms, from April to August 2000, was collected by means of a GPS receiver located in Jingzhou (30.4° N, 112.2° E). The time-latitude-dependent features of ionospheric storms are identified using TEC difference images based on the deviations of TEC during storm relative to quiet time. The responses of ionospheric TEC to magnetic storms were analyzed. The results show that: 1) In middle and low latitude, ionospheric storms effects are more apparent in local day time than at night: 2) Ionospheric storm effects are more dominant near the hump of the equatorial anomaly region than in other regions of TEC measurements; 3) The positive effects during the main phase of ionospheric storm may be caused by electric fields in low latitude; 4) During the recovery period of ionospheric storm, the negative phase of storm may be due to the perturbation of the neutral gas composition. Foundation item: Supported by the National Natural Science Foundation of China (49984001) Biography: Pei Xiao-hong (1977-), male, Master candidate, research direction: studying ionosphere on GPS beacons.     

电离层F层动力学数值模拟

中、低纬电离层Ｆ层动力学的数值模拟通过研究等离子体的连续性方程和运动方程进行，等离子体的输运过程顺电磁漂移的运动坐标系中运算。计及双极扩散、温度、中性风、电磁漂等影响。     

Correlation between ionospheric longitudinal harmonic components and upper atmospheric tides

There is strong correlation among the ionospheric longitudinal structures of wavenumber-3 (WN3), wavenumber-4 (WN4), and eastward-propagating diurnal tides with zonal wave numbers s = 2 and 3 (DE2 and DE3) in the upper atmosphere. The total electron content derived from the Global Ionospheric Maps of the Jet Propulsion Laboratory is used to deduce the latitudinally total electron content (ITEC) in the low-latitude ionosphere, and TIDE/TIMED observations are employed to obtain zonal and meridian winds of the mesopause and lower thermosphere. Through Fourier transformation, various ionospheric longitudinal harmonic components and tidal patterns are derived from the ionospheric and upper-atmospheric observations, and we compare the annual/inter-annual variations in ionospheric harmonic components WN3 and WN4 with those in atmospheric tides (DE2 and DE3). It is found that the annual and inter-annual variations in WN3 and WN4 are consistent with those in DE2 and DE3 zonal wind components respectively, while they are inconsistent with those in the meridian components. We then decompose the harmonic components into “tidal patterns”, finding that the “DE2” and “DE3” patterns are the main parts of WN3 and WN4 respectively. Their annual and inter-annual variations are similar to those of atmospheric tidal patterns (DE2 and DE3). Complex correlation results show that correlation between the ionospheric “DE2” in WN3 and the atmospheric tidal DE2 zonal wind component is quite strong in the Northern Hemisphere, while that between the ionospheric “DE3” in WN4 and the atmospheric tidal DE3 zonal wind component is much stronger at low latitudes. At the same time, the contribution of the meridian wind component is very weak. Above all, the atmospheric tidal DE2 and DE3 patterns are important factors of the ionospheric WN3 and WN4 structures.     

Climatological analysis and modeling of the ionospheric global electron content

In this paper, we calculate the ionospheric global electron content （GEC） from the GPS TEC data along the geographic longitude 120°E during the period of 1996-2004, and investigate the relationship between GEC and 10.7 cm solar radio flux F10.7 and its seasonal dependence with partial correlation analysis. Our results show that GEC is closely correlated with solar activity index F10.7 and is also related with annual and semiannual variations. An empirical GEC model driven by those factors is then to examine the influences of different solar activity proxies for the model input. The results suggest that GEC mainly depends on solar activity and the seasonal variations; the latter is also modulated by solar activity. Furthermore, the magnitude of semiannual variation is a little greater than that of annual variation. Our empirical GEC model is proved to be better than the model proposed by Afraimovich et al.     

Interannual and interdecadal variabilities in SST anomaly over the eastern equatorial Pacific

The global sea surface temperature (SST) anomaly data from 1950 to 1996 were used to analyze spatial characters of interdecadal SST variations. A wavelet transform was made for the equatorial eastern Pacific SST anomaly time series. Results show that there are three remarkable timescale SST variations: 130-month interdecadal variation, 57-month interannual variation and 28-month quasi-2-a variation. Based on this result, an El Nino event was predicted in the early part of 1997.     

大气中尘埃层对电离层电场向下映射的影响

本文首先用分析解方法计算了高纬电离层对流电场向下映射,在平流层、对流层上的水平电场分布情况。地磁场作用使70km以上的电导率呈各向异性,但计算表明,这对极区对流电场向下映射的影响不大。最后,着重讨论了尘埃层使电导率大大下降对电场映射的作用。结果表明,高高度上的尘埃层能完全改变原有的映射图象,而30km以下的尘埃层影响很小。