基于COSMIC的平流层重力波参数分析

基于COSMIC卫星观测的2006年12月29日到2008年1月3日30°-40°N纬度内的温度剖面,分别利用垂直滑动窗、双滤波器和单滤波器三种方法计算低平流层重力波的扰动和势能,获得重力波扰动和势能随高度、经度的分布以及多时间尺度变化特性,分析重力波扰动势能与背景温度及风场的变化趋势和特点.比较三种方法得到的结果发现:垂直滑动窗方法只能去除大垂直尺度的背景,无法抑制小尺度的扰动,其得到的结果误差较大;双滤波器法对温度剖面中的大尺度背景和小尺度扰动都能很好地抑制;单滤波器法得到的重力波扰动中基本不包含垂直方向的大尺度背景,但是包含一些小垂直尺度的扰动.因此,对于垂直波长为10km左右的重力波,采用双滤波器法合适;如果需要得到小尺度重力波的变化特性,采用单滤波器法合适.采用双滤波器法无法得到势能随高度的变化,而采用单滤波器法能够给出每月势能随高度的分布.对30°-40°N纬度内的重力波参数进行统计分析得到重力波扰动、势能与背景温度和水平风场的关系.      

基于COSMIC掩星精密定轨数据的等离子体层电子含量研究

等离子体层是日地环境重要的组成部分.本文利用COSMIC掩星精密定轨数据经处理后得到的podTec文件获取等离子体层电子含量（PEC）对等离子体层进行研究.将podTec数据进行处理后获得的PEC（pod-PEC）和IRI-Plas经验模型提供的PEC （IRI-PEC）进行对比,发现pod-PEC与IRI-PEC符合得较好.在低（0°—20°）、中（20°—50°）、高（50°—90°）修正地磁纬度带下,分析了COSMIC在太阳活动极大年（2014年）3,6,9和12月的pod-PEC,得到如下结论:PEC随着纬度升高而逐渐减少,且3,9月PEC在中低纬关于磁赤道的南北对称性较好,6月北半球各纬度带的PEC明显高于南半球同一纬度带的值,而12月情况则完全相反,南半球中纬的PEC甚至会等于北半球低纬的PEC值;PEC在白天高而晚上低,高纬地区的PEC昼夜变化不明显;PEC具有明显的季节性.对于北半球,一年中PEC最大值出现在春季,冬秋季次之,夏季最低,具有明显的年度异常现象.      

AIRS观测资料研究全球平流层重力波特性

利用2012—2014年1月和7月AIRS（Atmospheric Infrared Sounder）第79通道的观测数据,分析了平流层重力波活动强弱的全球分布以及重力波发生频率的全球分布;分析了重力波活动随纬度和经度的变化特征,给出了重力波活动在全球范围内的热点区域及其活动强度;对比了白天与夜间的重力波活动强度及发生频率.研究表明重力波活动强度呈现出随纬度变化的特征,在低纬度地区（0°—30°）,冬季半球重力波活动强度低,夏季半球重力波活动高;在中高纬度地区,冬季半球重力波活动强度高而夏季半球重力波活动强度低.在1月,全球重力波活动有4个突出的热点区域,分别为50°N附近欧洲大陆与大西洋交接地带、北美洲与大西洋交接地,20°S附近南美洲与大西洋交接地区、非洲与印度洋交接地区.在7月,重力波活动突出的地方为巴塔哥尼亚至南极半岛地区,以及50°S和75°E附近的印度洋区域.重力波活动强度在夜间大于白天,但是夜间的强重力波活动区域小于白天.      

基于陆态网的区域电离层TEC空间变化特性分析

为研究中国陆态网区域电离层TEC在空间小尺度、高分辨率情况下的变化特性及适用精度范围,利用陆态网260个GNSS连续运行观测站数据,解算并生成2016-2017年731天陆态网区域电离层RIM格网,并进行精度验证.在同一RIM格网中,分别在经度和纬度方向上对间隔不同经纬度的TEC格网点作差分析.结果表明:陆态网区域内经度方向上TEC最大变化率和平均变化率分别为0.30TECU·（°）-1和0.11TECU·（°）-1;经度间隔1°时,TEC差值小于2TECU,且随着经度间隔的增大,其TEC差值也随之增大,并表现出一定的半年和周年变化规律;纬度方向上TEC最大变化率和平均变化率分别为1.7TECU·（°）-1和0.46TECU·（°）-1;陆态网区域内电离层TEC随纬度减小而增大,纬度间隔1°时,99.4%的TEC差值小于4TECU,且随着纬度间隔的增大,其TEC差值也随之增大,并表现出一定的半年和周年变化规律;间隔相同情况下,纬度方向上TEC的变化比经度方向上大.      

极区中层惯性重力波VHF雷达观测的统计特征

本文采用ＳＯＵＳＹＶＨＦ雷达１９８７年６月２２日至６月２９日在挪威Ａｎｄφｙａ（６９°Ｎ，１０°Ｅ）的观测数据，研究中层惯性重力波传播的统计特征．２１个周期为数小时的准单色波例子，在垂直方向上有确定的相位移动，表明它们是惯性内重力波．通过分析波相关水平扰动速度的矢端曲线，获得了水平传播矢量的大小和方向的分布，大多数（７６％）波具有西向传播的波矢分量，似乎与中层顶具有强的西向背景风有关；水平传播速度的大小与中层高度上典型的观测值一致．本文分析结果还表明在极区中不仅存在向上的能量传输，也存在强烈的向下的能量传输．     

极区中层惯性重力波VFH雷达观测的统计特征

本文采用ＳＯＵＳＹ ＶＨＦ雷达１９８７年６月２２日至６月２９日在挪威ＡｎｄΦｙａ（６９°Ｎ，１０°Ｅ）的观测数据，研究中层惯性重力波传播的统计特征，２１个周期为数小时的准单色波例子，在垂直方向上有确定的相位移动，表明它们是惯性内重力波，通过分析波相关水平扰动速度的矢端曲线，获得了水平传播矢量的大小和方向的分布，大多数（７６％）波具有西向传播的波矢分量，似乎与中层顶具有强的西向背景风有关；水平传播速     

极区中层惯性重力波临界层的VHF雷达观测

本文采用移动式ＳＯＵＳＹＶＨＦ雷达１９８７年６月在挪威Ａｎｄφｙａ（６９°Ｎ，１０°Ｅ）的观测数据，研究中层惯性重力波在临界层的传播特征．数据分析结果表明，在临界层附近波动会突然衰减，波能量被背景风所吸收，惯性重力波的水平传播方向和垂直传播方向在通过临界层后会迅速发生改变，说明临界层附近会产生向下传播的能量源．并且在临界层，回波强度达到峰值，表明临界层对产生雷达回波起着重要作用．     

极区中层惯性重力波的VHF雷达观测

本文采用ＳＯＵＳＹＶＨＦ雷达１９８７年６月在挪威Ａｎｄｏｐｖａ（６９°Ｎ，１０°Ｅ）的观测数据，研究中层惯性重力波的传播特征．几个周期为数小时的准单色波例子，在垂直方向上有确定的相位移动，表明它们是惯性内重力波．通过分析波相关的流体速度东向和北向分量的变化，获得水平传播矢量的大小和方向，它们与中层高度上典型的观测值一致．同时还观察到三个等相面上行的惯性重力波，其速度偏振椭圆是逆时针旋转的．波相关的扰动速度为１５－４０ｍ／ｓ，说明在中层存在强烈的向下的能量传输．估算出它的运动学参量，周期为数小时，垂直相速度在０．ｌ—０．６ｍ／ｓ之间，垂直波长约为６．０ｋｍ．     

重力波非线性传播过程中的饱和与破碎

采用水平方向的显式算法与垂直方向的隐式算法相结合的时间分裂法,建立了二维可压缩大气中重力波非线性传播的数值模式.用本模式对小振幅重力波传播过程的模拟结果与线性重力波理论预测的结果吻合很好,从而验证了本模式的正确性.我们用此模式模拟了有限振幅重力波在非线性传播过程中的饱和与破碎,结果表明,(1)翻转出现在饱和之前,但向破碎演化仍需要一段时间,由于非线性波-波和波-流相互作用使得非线性数值模拟的饱和高度(出现时间)高(早)于线性饱和理论预测的结果;(2)重力波在不稳定之前已经有能量向背景场中转移,破碎直接导致非线性波-波相互作用,造成能量向小尺度短波上转移;(3)背景风场的加速方向,形成射流的方向与重力波的水平传播方向一致,表明重力波与背景流的非线性相互作用加剧了背景风剪切和不稳定性的发展.      

2009年冬季平流层爆发性增温期间行星波活动特征

利用2008年12月至2009年4月的MERRA再分析数据资料,对2009年1月下旬北半球高纬平流层发生的强增温事件以及与之相关的行星波活动进行了研究.谱分析发现,SSW发生前后极区平流层内准16天行星波活动显著.利用二维谐波拟合法分别拟合温度场准16天波4个波模（W1,W2,E1,E2）的振幅和相位,结果表明:背景西风减弱时四个波模的振幅均有不同程度的增大,且都在50°-80°N范围内的平流层中上层达到最大值;准16天W2波的增幅最大且辐合最强烈,其引起的背景流最大西风减速超过4m·-1·d-1,说明准16天W2波在该次增温事件中占主导地位;行星波传播与零风线移动关系密切,准16天W2波在中高纬地区垂直向上传播并近似呈现经向驻波结构,然后分别向极点和赤道两个方向传播,这表明中高纬地区可能是行星波的一个源区.      

Indication of convectively generated gravity waves observed by CLAES

Cryogenic Limb Array Etalon Spectrometer temperature data are analyzed for gravity waves (GWs) using the same methods previously employed for CRISTA data. We obtain nearly 1.5 years of continuous GW data between 34°S and 34°N and good coverage at higher latitudes depending on UARS yaw maneuvers. Correlations of GW variances with sea surface temperature indicate strong convective forcing above the Gulf of Mexico and the Kuro-Shio stream as well as above source regions in the southern subtropics during the summer months of the respective hemisphere. However, it appears difficult to clearly separate between convective forcing and the effects of the background winds, for which similar correlations are found. Further progress in accessing GW sources therefore can be expected mainly from improved measurements, which could provide also information about the GW horizontal wavelength as well as from quantitative comparisons to model predictions.     

子午工程首次火箭探空数据准单色惯性重力波特性分析

利用2010年6月3日子午工程首次气象火箭探测的温度和风场数据,采用矢端曲线法分别从平流层（20~50km）和对流层（0~15km）廓线提取了海南火箭发射场上空准单色惯性重力波参数.火箭探测的平流层和对流层两个准单色惯性重力波分别向上和向下逆风传播,固有周期为20.1h和22.4h,垂直波长为9.5km和4.0km,水平波长为2900km和753km,垂直群速度c_gz为0.0887m·-1和0.0298m·-1,水平群速度c_gh为12.7m·-1和3.65m·-1,λ_h/λ_z为305:1和188:1,c_gh/c_gz为143:1和122:1.      

Observation of a 27-day solar signature in noctilucent cloud altitude

Previous studies have identified solar 27-day signatures in several parameters in the Mesosphere/Lower thermosphere region, including temperature and Noctilucent cloud (NLC) occurrence frequency. In this study we report on a solar 27-day signature in NLC altitude with peak-to-peak variations of about 400?m. We use SCIAMACHY limb-scatter observations from 2002 to 2012 to detect NLCs. The superposed epoch analysis method is applied to extract solar 27-day signatures. A 27-day signature in NLC altitude can be identified in both hemispheres in the SCIAMACHY dataset, but the signature is more pronounced in the northern hemisphere. The solar signature in NLC altitude is found to be in phase with solar activity and temperature for latitudes $?70°$N. We provide a qualitative explanation for the positive correlation between solar activity and NLC altitude based on published model simulations.     

Hemispheric differences in the earth radiation budget derived from Nimbus-7 related to climate studies

Earth Radiation Budget (ERB) data from Nimbus-7 over the period November 1978 – June 1980 has consistently shown strong hemispheric differences when analyzed over different temporal and spatial scales. Hemispheric variations in time latitude cross sections of net and emitted radiation were found to be caused by changes in the Earth-Sun distance and continental effects.Maps of annual range for the entire Earth calculated from monthly averages showed areas of high and low variability of the different ERB parameters. The ERB of these regional areas were examined and most of the variability was found to lay in the large amplitude of the annual solar cycle. Variations in the global annual cycle of albedo /1/ are studied with respect to differences in latitudinal averaged albedo. The anomaly in the annual cycle of global averaged albedo was found to be caused by tropical albedo changes.     

Tilts and polarity separation in the sunspot groups and active regions at the ascending and descending phases of the cycle 23

The Solar Feature Catalogues for sunspots and active regions measured with SOHO/MDI instrument and Ca II K3 spectroheliograph of the Paris-Meudon Observatory are analyzed with the automated classification technique for sunspot groups and active region polarities. We report the first classification results for daily variations of tilt angles (normal and trigonometric ones) in sunspot groups (SG) and active (AR) regions in the cycle 23. The average normal tilts are presented for every year at the ascending and descending phases of the cycle 23 which are similar to those deduced by other authors for the cycles 19–22. The normal tilts of both the sunspot groups and active regions are shown to increase in the ascending phase and a decrease in the descending phase. Similar to SG and AR areas, the trigonometric tilts are shown to have the noticeable North–South asymmetry with the Southern hemisphere dominant in the selected ascending and descending periods. The normal tilt variations with latitude follow Joy’s law revealing a periodicity along the meridian of about 10° and reaching the maximum of 14° at the latitude of about 32° corresponding to the top of the ‘royal zone’ where the sunspots appear. The variations of polarity separation with a latitude are in an anti-phase with those of the tilts reaching a maximum at the latitude of 35° and showing a small positive separation for the groups/active regions in a vicinity of the average tilts ±40°. The ratio R of the polarity separation to the trigonometric tilt fits the linear function of a latitude φ as R = −0.0213φ − 0.1245 confirming positive separation for the polarities of active regions with the average tilts, or the dominance of activity in the Southern hemisphere activity, for the selected period of observations.     

Remote sounding of atmospheric gravity waves with satellite limb and nadir techniques

Recent advances in satellite techniques hold great potential for mapping global gravity wave (GW) processes at various altitudes. Poor understanding of small-scale GWs has been a major limitation to numerical climate and weather models for making reliable forecasts. Observations of short-scale features have important implication for validating and improving future high-resolution numerical models. This paper summarizes recent GW observations and sensitivities from several satellite instruments, including MLS, AMSU-A, AIRS, GPS, and CLAES. It is shown in an example that mountain waves with horizontal wavelengths as short as 30 km now can be observed by AIRS, reflecting the superior horizontal resolution in these modern satellite instruments. Our studies show that MLS, AMSU-A and AIRS observations reveal similar GW characteristics, with the observed variances correlated well with background winds. As a complementary technique, limb sounding instruments like CRISTA, CLAES, and GPS can detect GWs with better vertical but poorer horizontal resolutions. To resolve different parts of the broad GW spectrum, both satellite limb and nadir observing techniques are needed, and a better understanding of GW complexities requires joint analyses of these data and dedicated high-resolution model simulations.     

Negative VTEC with spherical harmonic expansion model under different solar activity conditions

The Earth’s ionosphere can be described by a spherical harmonic (SH) expansion up to a specific degree. However, there exist negative vertical total electron content (VTEC) values in the global ionosphere map (GIM) with the SH expansion model. In this contribution, we specifically investigated the negative VTEC values that are induced by the SH expansion model and validated the performance of the inequality-constrained least squares (ICLS) method in eliminating the negative VTEC values. The GPS data from 2004 to 2017 was selected to cover one solar cycle and the experiments under different solar activity conditions were analyzed. The results in our work show that the occurrence of the negative VTEC values is attributed to the deficiency of the SH expansion model when the VTEC itself is small instead of the unevenly distribution of the GNSS stations. The negative VTEC values appear periodically in the temporal domain, showing apparently one year and half year periods. During one year, two peaks in June and December can be observed in the time series of the negative VTEC values. The number of negative VTEC values in June is obvious larger than that in December. During one solar cycle, the number of negative VTEC values under quiet solar activity condition is obvious larger than that under strong solar activity condition. In the spatial domain, the appearance of the negative VTEC values is strongly related with the movement of the subsolar point. In the latitude of the subsolar point has the largest magnitude, the negative values will appear on the opposite hemisphere and the further from the subsolar point the more negative values. The maximum number of the negative VTEC values in the southern hemisphere appears in June, while the peak value in the northern hemisphere appears in December. The maximum number of negative VTEC values in the southern hemisphere is generally larger than that in the northern hemisphere. In addition, the negative VTEC values are distributed both at middle latitude and high latitude in the southern hemisphere, while they are mainly distributed at high latitude in the northern hemisphere. When the ICLS method is used, the negative VTEC values can be eliminated efficiently and it has nearly no influence on the positive VTEC values. The ICLS method can also improve the receiver’s differential code bias (DCB) and significantly decrease the unreasonable negative slant TEC (STEC) values along the lines of sight. Using the final GIM product of the Jet Propulsion Laboratory (JPLG) as a reference, the root mean square (RMS) of the ICLS solution shows maximum 25%, 20% and 45% improvement relative to the least squares (LS) solution at northern high latitude, southern middle latitude and southern high latitude, respectively.     

2008—2009年电离层对重现型地磁活动的响应

利用2008—2009年的GPS TEC数据,分析了电离层对冕洞引起的重现型地磁活动的响应. 结果表明,在太阳活动低年,电离层TEC表现出与地磁 ap指数（采用全球3h等效幅度指数ap来表征）和太阳风速度相似的9天和13.5天短周期变化,表明TEC的这种短周期特性主要与重现型地磁活动相关. 地磁纬度和地方时分析表明,夜间高纬地区正负相扰动明显,中低纬地区则以正相扰动为主,较大的TEC变幅主要发生在南北半球高纬地区,夜间南半球高纬地区TEC变化相对ap指数变化有相位延迟. 白天中低纬地区正负相扰动明显,TEC短周期变化与ap指数变化相位基本一致. 2008年TEC的9天和13.5天周期变化幅度大于2009年.      

Longitudinal variations of the ionospheric trough position

For the first time a comprehensive pattern of the longitudinal effect of the ionospheric trough position was obtained. We present new results with longitudinal variations of the winter trough position as a function of geomagnetic latitude for both hemispheres and conditions of high and low solar activity and all local time hours. We used a large observational data set obtained onboard the Kosmos-900, Interkosmos-19 and CHAMP satellites for quiet geomagnetic conditions. We found that a magnitude of the trough position longitudinal effect averaged for a fixed local time is greater in the daytime (6–8°) than in the nighttime (3–5°). The longitudinal effect magnitude reaches its maximum (16°) in the morning (at 08 LT) in the Southern hemisphere at high solar activity. But on certain days at any solar activity the longitudinal effect magnitude can reach 9–10° even at night. The shape of the longitudinal effect was found to differ significantly in two hemispheres. In the Northern hemisphere the trough is usually closest to the pole in the eastern (American) longitudinal sector, and in the Southern hemisphere the trough is closest in the western (Eurasian) longitudinal sector. The magnitude and shape of the longitudinal effect is also different during low and high solar activity. The Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) simulations demonstrate that during low solar activity, the longitudinal variations of the daytime trough position is mainly determined by longitudinal variations of the ionization function, formed due to the longitudinal variations in the solar zenith angle and the atomic oxygen density distribution. The longitudinal variations of the nighttime trough position is formed by the longitudinal variations in ionization of precipitating auroral particles, neutral atmosphere composition, and electric field.