基于COSMIC掩星数据分析中低纬度地区电子密度分布变化

利用COSMIC掩星2009年电子密度剖面数据,筛选数据进行网格划分,网格内数据统计平均,基于球谐函数计算模型值,分析电离层中低纬度地区最大电子密度的地磁季节变化、昼夜测分布相对变化,及地磁活动对电子密度的分布影响.结果表明,最大电子密度昼测值明显高于夜测值,在中纬度部分区域增大明显.电子密度昼测值在地磁活动期间高度150-550 km中低纬度范围为正相扰动,随纬度变化存在区域差异,随高度增加,扰动加强.     

基于ZH-1卫星探测的太阳活动低年顶部电离层不规则结构的时空特征

利用ZH-1卫星2019、2020年的原位电子密度观测数据,对卫星观测范围,即地理纬度南北65°之间午夜后顶部电离层的不规则结构进行研究,得到如下结果.(1)午夜后顶部电离层不规则结构集中区主要分布在地磁赤道、中纬度以及较高纬度区,白天赤道异常峰值区为不规则结构的谷值区.(2)不同纬度区不规则结构随地理经度分布呈现出明...     

基于MF雷达观测的D区日食效应的研究

本文利用昆明站(25.6°N,103.8°E)MF雷达在2009年7月22日的观测数据,研究了这次日食期间D区电子密度的变化.结果表明,随着日食的开始,D区电子密度逐渐减小,在食甚后,电子密度开始恢复.但观测发现电子密度不与日食同步,而是存在一个大约9 min的时延.利用日食期间的观测数据,尝试建立了两个简单的模型来估...     

高纬电离层气候学特征研究--EISCAT雷达观测及与IRI模式的比较

利用1988～1999年欧洲非相干散射EISCAT（European Incoherent Scatter）雷达观测数据,对不同太阳活动周相、不同季节的极光椭圆区电离层F区电子密度进行统计分析,研究其气候学特征,并与IRI 2001模式比较.EISCAT观测到的电子密度显示出显著的太阳活动高年“冬季异常”和太阳活动低年半年变化等现象.EISCAT实测电子密度随时间和高度的平均二维分布和500 km高度以下总电子含量TEC,从总体来看与IRI 2001模式预测结果符合较好.但高年在TEC达到最大值前后,IRI 2001模式预测的电子密度高度剖面与EISCAT观测结果有显著差别：F2峰以上IRI 2001模式预测的电子密度过大,造成TEC明显高于雷达观测值.另外,在太阳活动下降相,EISCAT观测显示出明显的半年周期季节变化特征,但IRI 2001模式未能预测出此下降相季节变化.     

等离子体参量春夏季节背景变化特征研究

使用DEMETER卫星上Langmiur探针记录的电子密度（Ne）、离子密度（Ni）和电子温度（Te）资料,分析了2007年1～6月份地磁活动平静时段全球6个经度区（每60°一个区）,不同时间的电离层等离子体参量Ne、Ni和Te值在春夏季节的背景变化特征,发现Ne、Ni和Te随纬度空间变化比较大,且峰（谷）值纬度分布与地球的经度区也有一定的关系。对全球6个经区各个时段的Ne、Ni和Te值进行对比,发现不同时段,Ne、Ni和Te峰值的大小不等,可能与当地日变化有关。等离子体各参量与月份季节也存在一定的相关性。在一些相同的区域时段,1～3月的等离子参量数值明显高于4～6月的等离子参量数值。     

磁宁静期核心等离子体层电子密度分布的统计研究

等离子体层已有数十年研究历史,但对其核心等离子体区域却一直没有一个相对准确的界限和模型定义.基于范阿伦辐射带卫星RBSP-A在2012年9月18日至2014年10月13日约两年的观测,我们统计研究了磁宁静期间核心等离子体层电子密度随磁地方时(MLT)及磁壳指数(L-value)的分布特征.发现了核心等离子体层电子密度在不同MLT条件下随L值的变化趋势几乎一致,但与以前的等离子体层经验模式计算的电子密度存在较大的偏差.在不同L值下电子密度随MLT的变化趋势也相差不大,而且随MLT存在明显的逐日和半日变化.最后我们获得了等离子体层电子密度随L值和MLT变化的经验公式.研究结果对空间等离子体层建模及研究具有重要的意义.     

热带太平洋上层热力状况季节变化的正压特征——海表至深400m热储量的季节变化

使用斯克里普斯海洋研究所（SIO）整编的海洋上层（海表至400m）热储量资料，研究了热带太平洋上层热力状况季节变化的正压特征，指出与SST的分布不同，热储量在北纬5°N～10°N之间有一东西贯穿整个太平洋的带状热储量低值区，其季节变化率的分布特征分为两种，一是11月至2月为代表的“北半球冬季型”和5～8月的“北半球夏季型”，3月、4月和9月、10月为过渡阶段. 北半球10°N和2°N的季节变率的时间变化反位相，南半球的10°S、2°S?其季节变率随时间变化的位相则比较一致且与沿10°N位相大致相反. 东太平洋季节变化明显早于中、西太平洋，具有明显自东向西传播的特征. 10°S与10°N之间东、西太平洋的季节变率随时间的演变也基本上呈现反位相特征.     

NWC通信台在电离层中激发电磁响应的时变特征

本文利用DEMETER卫星VLF频段电场和磁场频谱数据对DEMETER卫星运行期间2005年至2009年澳大利亚甚低频(Very Low Frequency)通信台NWC发射的通信信号造成的电离层电磁响应的日变化、季节变化及年变化特征进行了统计分析,统计结果表明电磁响应日变化显著,夜间电场强度明显增强可达40dB,磁场变化略小也可为15dB左右,而季节变化不显著,年变化主要受太阳活动的影响,太阳活动越强,电磁响应越小.为解释数据分析结果,对地-电离层电磁波传播过程采用传递矩阵方法进行了模拟计算,模拟结果与数据分析的结果一致.我们认为这种随时间变化的特点可能由250km以下电离层电子密度分布特征导致,因此研究250km以下的电离层电子密度变化可能对寻找地震电离层电磁异常有重要意义.     

闽粤赣交界区地震震源位置及速度结构研究

采用震源位置及速度结果的联合反演方法确定闽粤赣交界区(24°~26.5°N,114°~117.8°E)地震的震源位置以及震源区速度结构。结果显示:1闽粤赣交界区地震震源平均深度随震级增大而加深的特征明显,即地震震级越大,震源深度越深,但平均深度不超过15 km;越靠近沿海,地震震源深度有加深的趋势。2通过对河源地区、邵武-河源断裂带中段(寻乌-瑞金)区域、政和-大浦断裂带中段(漳平附近)区域以及闽粤近海区域地震剖面研究,发现地震多发生于高低速异常结合部位。     

青藏块体东北缘平均波速比的测定及研究

利用兰州数字地震遥测台网观测报告,采用和达法计算出2001年1月-2007年6月发生在青藏块体东北缘2 953次地震的波速比值.将青藏块体东北缘按1°×1°、0.2°×0.2°分成小区,求出每个小区域内的平均波速比值.分析得出如下结论:(1)青藏块体东北缘平均波速比值在空间分布上有一定差异,甘东南(N34°以南)波速比值最高,祁连山地震带和西秦岭北缘断裂附近次之,甘肃中部最低;(2)青藏块体东北缘矿震分布区域和1°×1°的低波速比值区域一致,地震波速比值是判定矿震的可能依据之一;(3)地震波速比值随震级的增大而增大.所得的平均波速比值为研究青藏块体东北缘波速比值随时间变化有一定参考价值.     

Annual and seasonal variations in the low-latitude topside ionosphere

Annual and seasonal variations in the low-latitude topside ionosphere are investigated using observations made by the Hinotori satellite and the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The observed electron densities at 600 km altitude show a strong annual anomaly at all longitudes. The average electron densities of conjugate latitudes within the latitude range ±25° are higher at the December solstice than at the June solstice by about 100% during daytime and 30% during night-time. Model calculations show that the annual variations in the neutral gas densities play important roles. The model values obtained from calculations with inputs for the neutral densities obtained from MSIS86 reproduce the general behaviour of the observed annual anomaly. However, the differences in the modelled electron densities at the two solstices are only about 30% of that seen in the observed values. The model calculations suggest that while the differences between the solstice values of neutral wind, resulting from the coupling of the neutral gas and plasma, may also make a significant contribution to the daytime annual anomaly, the E × B drift velocity may slightly weaken the annual anomaly during daytime and strengthen the anomaly during the post-sunset period. It is suggested that energy sources, other than those arising from the 6% difference in the solar EUV fluxes at the two solstices due to the change in the Sun-Earth distance, may contribute to the annual anomaly. Observations show strong seasonal variations at the solstices, with the electron density at 600 km altitude being higher in the summer hemisphere than in the winter hemisphere, contrary to the behaviour in NmF2. Model calculations confirm that the seasonal behaviour results from effects caused by transequatorial component of the neutral wind in the direction summer hemisphere to winter hemisphere.     

Characterization of low latitude GPS-TEC during very low solar activity phase

We present the mean diurnal, seasonal and annual variations in TEC during the lowest solar activity phase from low latitude Indian zone recorded at Udaipur (Geog. Lat. 24.6°N, Geog. Long.73.7°E, Geomag. Lat. 15.6°N) using a GPS receiver. Seasonal variations in daytime TEC show a semiannual periodicity, with a minimum in winter. Results of seasonal variations have been compared with that of the IRI-2007 model. Model calculations reveal significant seasonal as well as longitudinal differences in TEC. Seasonal variations in the nighttime TEC reveal an annual periodicity. Near the crest of the EIA, TEC shows a very good correlation with the solar flux. The results also point to weakening of the anomaly crest as well as its spatial and temporal contraction with declining solar activity.     

北美地区夜间中尺度电离层行进式扰动的GPS台网监测研究

本文利用2007年6月～2008年5月期间北美GPS台站密集地区的TEC观测资料,对夜间中尺度电离层行进式扰动(MSTIDs)的传播特性进行了分析研究.结果表明:北美地区的夜间电离层行进式扰动一般发生在美国西部时间21:00～02:00LT(05:00～10:00UT)时段,表现在TEC中的最大扰动幅度为0.45～0....     

Yearly variations in the low-latitude topside ionosphere

Observations made by the Hinotori satellite have been analysed to determine the yearly variations of the electron density and electron temperature in the low-latitude topside ionosphere. The observations reveal the existence of an equinoctial asymmetry in the topside electron density at low latitudes, i.e. the density is higher at one equinox than at the other. The asymmetry is hemisphere-dependent with the higher electron density occurring at the March equinox in the Northern Hemisphere and at the September equinox in the Southern Hemisphere. The asymmetry becomes stronger with increasing latitude in both hemispheres. The behaviour of the asymmetry has no significant longitudinal and magnetic activity variations. A mechanism for the equinoctial asymmetry has been investigated using CTIP (coupled thermosphere ionosphere plasmasphere model). The model results reproduce the observed equinoctial asymmetry and suggest that the asymmetry is caused by the north-south imbalance of the thermosphere and ionosphere at the equinoxes due to the slow response of the thermosphere arising from the effects of the global thermospheric circulation. The observations also show that the relationship between the electron density and electron temperature is different for daytime and nighttime. During daytime the yearly variation of the electron temperature has negative correlation with the electron density, except at magnetic latitudes lower than 10°. At night, the correlation is positive.     

The equatorial ionospheric anomaly in electron content from solar minimum to solar maximum for South East Asia

Median hourly, electron content-latitude profiles obtained in South East Asia under solar minimum and maximum conditions have been used to establish seasonal and solar differences in the diurnal variations of the ionospheric equatorial anomaly (EIA). The seasonal changes have been mainly accounted for from a consideration of the daytime meridional wind, affecting the EIA diffusion of ionization from the magnetic equator down the magnetic field lines towards the crests. Depending upon the seasonal location of the subsolar point in relation to the magnetic equator diffusion rates were increased or decreased. This led to crest asymmetries at the solstices with (1) the winter crest enhanced in the morning (increased diffusion rate) and (2) the same crest decaying most rapidly in the late afternoon (faster recombination rate at lower ionospheric levels). Such asymmetries were also observed, to a lesser extent, at the equinoxes since the magnetic equator (located at about 9○N lat) does not coincide with the geographic equator. Another factor affecting the magnitude of a particular electron content crest was the proximity of the subsolar point, since this increased the local ionization production rate. Enhancements of the EIA took place around sunset, mainly during the equinoxes and more frequently at solar maximum, and also there was evidence of apparent EIA crest resurgences around 0300 LST for all seasons at solar maximum. The latter are thought to be associated with the commonly observed, post-midnight, ionization enhancements at midlatitudes, ionization being transported to low latitudes by an equatorward wind. The ratio increases in crest peak electron contents from solar minimum to maximum of 2.7 at the equinoxes, 2.0 at the northern summer solstice and 1.7 at northern winter solstice can be explained, only partly, by increases in the magnitude of the eastward electric field E overhead the magnetic equator affecting the [E×B] vertical drifts. The most important factor is the corresponding increase in ionization production rate due to the increase in solar radiation flux. The EIA crest asymmetries observed at solar maximum were less significant, and this is probably due to the corresponding increase in ionization densities leading to an increase of the retarding effect of ion-drag on the daytime meridional winds.     

The features and a possible mechanism of semiannual variation in the peak electron density of the low latitude F2 layer

Ionospheric data observed in 30 stations located in 3 longitude sectors (East Asia/Australia Sector, Europe/Africa Sector and America/East Pacific Ocean Sector) during 1974–1986 are used to analyse the characteristics of semiannual variation in the peak electron density of F2 layer (NmF2). The results indicate that the semiannual variation of NmF2 mainly presents in daytime. In nighttime, except in the region of geomagnetic equator between the two crests of ionospheric equatorial anomaly, NmF2 has no obvious semiannual variation. In the high latitude region, only in solar maxima years and in daytime, there are obvious semiannual variations of NmF2. The amplitude distribution of the semiannual variation of daytime NmF2 with latitude has a “double-humped structure”, which is very similar to the ionospheric equatorial anomaly. There is asymmetry between the Southern and the Northern Hemispheres of the profile of the amplitude of semiannual variation of NmF2 and longitudinal difference. A new possible mechanism of semiannual variation of NmF2 is put forward in this paper. The semiannual variation of the diurnal tide in the lower thermosphere induces the semiannual variation of the amplitude of the equatorial electrojet. This causes the semiannual variation of the amplitude of ionospheric equatorial anomaly through fountain effect. This process induces the semiannual variation of the low latitude NmF2.     

Ionospheric slab thickness and its seasonal variations observed by GPS

The ionospheric slab thickness, the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), is closely related to the shape of the ionospheric electron density profile Ne (h) and the TEC. Therefore, the ionospheric slab thickness is a significant parameter representative of the ionosphere. In this paper, the continuous GPS observations in South Korea are firstly used to study the equivalent slab thickness (EST) and its seasonal variability. The averaged diurnal medians of December–January–February (DJF), March–April–May (MAM), June–July–August (JJA) and September–October–November (SON) in 2003 have been considered to represent the winter, spring, summer and autumn seasons, respectively. The results show that the systematic diurnal changes of TEC, NmF2 and EST significantly appeared in each season and the higher values of TEC and NmF2 are observed during the equinoxes (semiannual anomaly) as well as in the mid-daytime of each season. The EST is significantly smaller in winter than in summer, but with a consistent variation pattern. During 14–16 LT in daytime, the larger EST values are observed in spring and autumn, while the smaller ones are in summer and winter. The peaks of EST diurnal variation are around 10–18 LT which are probably caused by the action of the thermospheric wind and the plasmapheric flow into the F2-region.     

Seasonal variation of the total electron content, maximum electron density and equivalent slab thickness at a South-American station

Total electron content (TEC) and foF2 ionosonde data obtained at Tucumán (26.9°S; 65.4°W) from April 1982 to March 1983 (high solar activity period) are analyzed to show the seasonal variation of TEC, NmF2 (proportional to square of foF2) and the equivalent slab thickness EST. Bimonthly averages of the monthly median for January–February, April–May, July–August and October–November have been considered to represent summer, autumn, winter and spring seasons, respectively. The results show that the higher values of TEC and maximum electron density of F2-layer NmF2 are observed during the equinoxes (semiannual anomaly). During daytime, both in TEC and in NmF2 the seasonal or winter anomaly can be seen. At nighttime, this effect is not observed. Also, the observed NmF2 values are used to check the validity of International Reference Ionosphere (IRI) to predict the seasonal variability of this parameter. In general, it is found that averaged monthly medians (obtained with the IRI model) overestimate averaged monthly median data for some hours of the day and underestimate for the other hours.     

2015年3月磁暴期间中国中低纬地区电离层变化分析

2015年3月17日爆发了本太阳活动周最大的地磁暴,Dst指数达到-233 nT.本文利用电离层测高仪f_。F_2和h_mF_2、北斗同步卫星(BDSGEO)TEC以及GPS电离层闪烁S4指数对此次磁暴期间中国中低纬地区(北京、武汉、邵阳和三亚)的电离层变化进行分析,并对此次磁暴所引发电离层暴的可能机制进行了探讨.磁暴期间,中低纬电离层暴整体表现为正相暴之后长时间强的负相暴.3月17日白天中纬正相暴为风场抬升电离层所致,而驼峰区及低纬地区正相暴由东向穿透电场所引起;3月18日白天长时间的强负相暴为西向扰动发电机电场和成分扰动所引起;3月17和18日夜间的负相暴可能是日落东向电场受到抑制以及赤道向风场对扩散的抑制导致驼峰向赤道压缩所致,同时被抑制的日落东向电场强度不足以触发产生赤道扩展F,导致低纬三亚和邵阳夜间电离层闪烁在磁暴期间受到完全抑制.这是我们首次基于北斗同步卫星TEC组网观测开展的电离层暴研究.