Simulating planetary wave propagation to the upper atmosphere during stratospheric warming events at different mountain wave scenarios

Parameterization schemes of atmospheric normal modes (NMs) and orographic gravity waves (OGWs) have been implemented into the mechanistic Middle and Upper Atmosphere Model (MUAM) simulating atmospheric general circulation. Based on the 12-members ensemble of runs with the MUAM, a composite of the stratospheric warming (SW) has been constructed using the UK Met Office data as the lower boundary conditions. The simulation results show that OGW amplitudes increase at altitudes above 30 km in the Northern Hemisphere after the SW event. At altitudes of about 50 km, OGWs have largest amplitudes over North American and European mountain systems before and during the composite SW, and over Himalayas after the SW. Simulations demonstrate substantial (up to 50–70%) variations of amplitudes of stationary planetary waves (PWs) during and after the SW in the mesosphere-lower thermosphere of the Northern Hemisphere. Westward travelling NMs have amplitude maxima not only in the Northern, but also in the Southern Hemisphere, where these modes have waveguides in the middle and upper atmosphere. Simulated variations of PW and NM amplitudes correspond to changes in the mean zonal wind, EP-fluxes and wave refractive index at different phases of the composite SW events. Inclusion of the parameterization of OGW effects leads to decreases in amplitudes (up to 15%) of almost all SPWs before and after the SW event and their increase (up to 40–60%) after the SW in the stratosphere and mesosphere at middle and high northern latitudes. It is suggested that observed changes in NM amplitudes in the Southern Hemisphere during SW could be caused by divergence of increased southward EP-flux. This EP-flux increases due to OGW drag before SW and extends into the Southern Hemisphere.     

Equatorial anomaly according to the Interkosmos-19 data and IRI model: A comparison

The comparison of the IRI model with the foF2 distribution in the equatorial anomaly region obtained by topside sounding onboard the Interkosmos-19 satellite has been carried out. The global distribution of foF2 in terms of LT-maps was constructed by averaging Intercosmos-19 data for summer, winter, and equinox. These maps, in fact, represent an empirical model of the equatorial anomaly for high solar activity F10.7 ~ 200. The comparison is carried out for the latitudinal foF2 profiles in the characteristic longitudinal sectors of 30, 90, 210, 270, and 330°, as well as for the longitudinal variations in foF2 over the equator. The largest difference between the models (up to 60%) for any season was found in the Pacific longitudinal sector of 210°, where there are a few ground-based sounding stations. Considerable discrepancies, however, are sometimes observed in the longitudinal sectors, where there are many ground-based stations, for example, in the European or Indian sector. The discrepancies reach their maximum at 00 LT, since a decay of the equatorial anomaly begins before midnight in the IRI model and after midnight according to the Interkosmos-19 data. The discrepancies are also large in the morning at 06 LT, since in the IRI model, the foF2 growth begins long before sunrise. In the longitudinal variations in foF2 over the equator at noon, according to the satellite data, four harmonics are distinguished in the June solstice and at the equinox, and three harmonics in the December solstice, while in the IRI model only two and one harmonics respectively are revealed. In diurnal variations in foF2 and, accordingly, in the equatorial anomaly intensity, the IRI model does not adequately reproduce even the main, evening extremum.     

Case study of inclined sporadic E layers in the Earth’s ionosphere observed by CHAMP/GPS radio occultations: Coupling between the tilted plasma layers and internal waves

We have used the radio occultation (RO) satellite data CHAMP/GPS (Challenging Minisatellite Payload/Global Positioning System) for studying the ionosphere of the Earth. A method for deriving the parameters of ionospheric structures is based upon an analysis of the RO signal variations in the phase path and intensity. This method allows one to estimate the spatial displacement of a plasma layer with respect to the ray perigee, and to determine the layer inclination and height correction values. In this paper, we focus on the case study of inclined sporadic E (E_s) layers in the high-latitude ionosphere based on available CHAMP RO data. Assuming that the internal gravity waves (IGWs) with the phase-fronts parallel to the ionization layer surfaces are responsible for the tilt angles of sporadic plasma layers, we have developed a new technique for determining the parameters of IGWs linked with the inclined E_s structures. A small-scale internal wave may be modulating initially horizontal E_s layer in height and causing a direction of the plasma density gradient to be rotated and aligned with that of the wave propagation vector k. The results of determination of the intrinsic wave frequency and period, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase speeds, and other characteristics of IGWs under study are presented and discussed.     

基于波段选择的RX改进算法

针对高光谱检测亚像元飞机的问题,提出基于大气吸收谱段的改进RX异常检测算法,实现亚像元检测能力和检测效率的提升.阐述了改进算法的基本原理,对比了10 km高度和地面大气吸收系数的曲线差异,建立了改进算法的检测模型,采用仿真的客用飞机可见-短波高光谱数据和海水背景高光谱数据,获得了信噪比10 dB的高光谱仿真图像.采用经...     

Dayside ionospheric uplift during strong geomagnetic storms as detected by the CHAMP,SAC-C,TOPEX and Jason-1 satellites

Ionosphere response to severe geomagnetic storms that occurred in 2001–2003 was analyzed using data of global ionosphere maps (GIM), altimeter data from the Jason-1 and TOPEX satellites, and data of GPS receivers on-board CHAMP and SAC-C satellites. This allowed us to study in detail ionosphere redistribution due to geomagnetic storms, dayside ionospheric uplift and overall dayside TEC increase. It is shown that after the interplanetary magnetic field turns southward and intensifies, the crests of the equatorial ionization anomaly (EIA) travel poleward and the TEC value within the EIA area increases significantly (up to ∼50%). GPS data from the SAC-C satellite show that during the main phase of geomagnetic storms TEC values above the altitude of 715 km are 2–3 times higher than during undisturbed conditions. These effects of dayside ionospheric uplift occur owing to the “super-fountain effect” and last few hours while the enhanced interplanetary electric field impinged on the magnetopause.     

从日地系统L2出发借力月球飞越近地小行星

对于停留在日地系统L2的“嫦娥2号”探测器,其后续飞行方案有多个选项,例如主动撞月或重返月球轨道、返回地球轨道或再入大气、飞往地月系统L1/L2或日地系统L1、进入深空飞越近地小行星(最终,“嫦娥2号”于2012年12月13日成功地实现了对Toutatis小行星的近距离飞越)。探讨上述的飞行方案需要对飞行轨道进行初步设计,总的速度脉冲限制在100 m/s以内并且需要考虑探测器同时受到太阳、地球、月球的引力作用。本研究设计了探测器从日地系统L2出发借力月球实现Toutatis小行星飞越的飞行方案,与直接飞越方案相比,借力月球可以进一步节省探测器的燃料消耗,其等效速度脉冲设计值为58.47 m/s。     

CHAMP卫星加速度计标校参数序列的谱分析

给出了利用能量守恒方法求定CHAMP卫星加速度计标校参数的基本原理和算法．对2001年8月-2003年12月共约两年半的CHAMP卫星加速度计数据进行了标校,导出了尺度、偏差和偏差漂移参数的时间序列,分别采用最小二乘谱分析和抗差谱分析对这些时间序列进行了分析．结果表明,尺度、偏差和偏差漂移参数都有明显的周期变化,但各主周期项略有差异．尺度的主周期是441d、220d、126d和13．4d的周期变化,其中220d和441d的周期变化的贡献相对较大．偏差中有明显的220d、126d和13．4d周期变化,各周期变化的贡献几乎相当;偏差漂移的主周期是220d、13．4d和9d的周期变化,其中13．4d的周期变化最为显著,几乎比其他周期项变化高出一个数量级．另外尺度和偏差参数还有明显的长期变化,而偏差漂移参数的长期变化不明显．     

基于慢特征密度聚类的气路异常检测方法

在结合核技巧、慢特征分析算法与密度聚类方法的基础上,提出了基于混合核慢特征分析和密度聚类的慢特征密度聚类算法,实现了基于民航发动机气路参数原始值的异常检测。核技巧的引入克服了慢特征分析法处理复杂数据时可能存在的维度爆炸问题,充分利用不同核函数的特点和慢特征分析的优势从气路参数原始值中提取出随时间变化最缓慢的特征作为密度聚类算法的输入,最终筛选出异常值。经实验对比发现,该方法针对某些异常拥有最好的聚类效果和最低的虚警率,尤其是检测可调放气活门系统异常时虚警数量不到样本总数量的0.5%,是一种有效的方法。      

基于天基光学探测图像初析南大西洋异常区影响

文章针对目前在轨运行的高灵敏度探测类可见光遥感器经过南大西洋异常区（SouthAtlanticAnomaly,SAA）时出现的探测能力降低、目标无法识别等现象,通过卫星在轨获取的SAA天基探测图像研究图像中出现的异常现象机理;提出了基于CCD探测器固有暗像元区的图像特征变化开展SAA影响评估的方法,根据在轨图像暗像元区的均值和标准差、图像区的热像素及活像元等特征参数的统计分析,判断经过SAA过程中连续获取的图像中出现显著影响时的拐点,通过曲线拟合估算出该轨道高度的SAA空间分布特征和边界,依此进一步提出利用在轨天基探测图像给出测量影响该轨道高度卫星SAA区域边界的简单方法;最后,基于SAA对天基探测器件的影响分析结果和认识,给出了高灵敏度探测类卫星避免或消除SAA影响的改进措施和建议。文章采用的数据分析和评估方法为提升SAA对天基探测影响的认识,以及下一步有效开展空间碎片探测工作提供参考。