Global validation of IRI TEC for high and medium solar activity conditions

The IRI model offers a choice of options for the computation of the electron density profile and electron content (TEC). Recently new options for the topside electron density profile have been developed, which have a strong impact on TEC. Therefore it is important to test massively the IRI and the new options with experimental data. A large number of permanent stations record dual frequency GPS data from which it is possible to obtain TEC values. Thirty-one worldwide distributed stations have been selected to investigate the capabilities of the IRI to reproduce experimental TEC. Data for years 2000 (high solar activity) and 2004 (medium solar activity) have been analyzed computing modeled values with the IRI-2001 and the IRI-2007-NeQuick topside options. It is found that IRI-2007-NeQuick option generally improves the estimate of the slant TEC, especially in the case of high latitudes stations during high solar activity.     

Rapid ionospheric variations at high latitudes: Focusing on Greenland

The Helheim glacier, located in southeast Greenland, has more than ten campaign-type Global Positioning System (GPS) sites; data processing led to the observation of a very rapid change in the ionospheric delay. To identify the cause of these sporadic disturbances, we analyzed the slant total electron content (STEC), single-differenced STEC (SD-STEC) and scintillation proxy index called the delta phase rate (DPR). From this analysis, the abrupt change of those ionospheric indicators was attributed to the line-of-sight direction to the satellite and the temporal sequence of the event was found to be highly correlated with the geometry of the GPS sites. In addition, the disturbance based on the result of SD-STEC occurred mostly during the night, from 17 UTC through 7 UTC, and across a band spanning the east-west direction. Based on the DPR indices obtained from GPS stations distributed across all of Greenland, Iceland, and northeastern Canada, the rapid ionospheric variation was found to be correlated with the time of the day and the geomagnetic latitude of the station. The disturbance was larger at the relatively low geomagnetic latitudes at night but was more significant at higher latitudes in the daytime. These rapid ionospheric variations tended to appear in band shapes parallel to the geomagnetic field. These results allow us to attribute such disturbance observed at the Helheim glacier to aurora-related phenomena.     

Variations of total electron content over high latitude region during the ascending phase of 24th solar cycle

The solar cycle variation and seasonal changes significantly affects the ionization process of earth’s ionosphere and required to be monitored in real time basis for regional level refinement of existing models. In view of this, the present study has been carried out by using the ionospheric Total Electron Content (TEC) data observed with the help of Global Ionospheric Scintillation and TEC monitoring (GISTM) system installed at Indian Antarctic Research Station, “Maitri” [70°46′00″S 11°43′56″E] during the ascending phase of 24th solar cycle. The daily values of solar extreme ultraviolet (EUV) flux (0.1–50?nm wavelength), 10.7?cm radio flux F_10.7 and Sunspot number (SSN) has been taken as a proxy to represent the solar cycle variation to correlate with TEC. The linear regression results revels better correlation of TEC with EUV flux rather than F_10.7 and SSN. Also, the EUV and TEC show better agreement during summer as compared to winter and equinox period. Correlation between TEC and EUV appears significantly noticeable during ten internationally defined quiet days of each month (stable background geophysical condition) as compared to the overall days (2010–2014). Further, saturation effect has been observed on TEC values during the solar maxima year 2014. The saturation effects are more prominent during the night hours of winter and equinox season due to transportation losses manifested by the equator-ward direction of meridional wind.     

基于改进Gauss伪谱法的高超声速飞行器航迹规划

针对使用传统Gauss伪谱法(GPM)求解航迹规划问题时计算复杂的问题,提出了基于两点间经纬度坐标变换的改进GPM高超声速飞行器滑翔段航迹规划方法。对经纬度坐标进行处理,以经纬度变换代替时域变换改进GPM,规划两点间的航迹。仿真结果表明,改进后的算法能够准确、高效地规划出一条合理的航迹,满足飞行约束条件。     

单轴旋转惯导纬度误差和航向误差关联性分析

为实现舰船单轴旋转惯导航向误差海上动态评估,考虑单轴旋转惯导纬度误差和航向误差都是在相同误差源作用下的惯性导航解算输出结果,通过研究引起单轴旋转激光陀螺惯导航向误差和纬度误差的机理,建立了单轴旋转惯导纬度误差与航向误差之间的关联性模型。仿真分析验证了单轴旋转惯导纬度误差与航向误差之间关联性分析的正确性。基于二者之间的关联性,在无外界参考航向信息情况下,可实现海上舰船单轴旋转惯导航向误差实时动态评估与补偿,对提升舰船武器系统作战效能具有重要的实用价值。     

VLF Emissions observed at the low latitude Indian station Varanasi

VLF emissions such as hiss, chorus, pulsing hiss, triggered emissions observed at Varanasi (geom. lat. = 14° 55′ N, long. = 153° 55′ E) are reported. An attempt has been made to explain the dynamic spectra in terms of the generation mechanism and propagation through the inhomogeneous magnetoplasma. It is noted that the reported events have propagated along different L-values in the magnetosphere, although they have been recorded at the same station. The ULF waves propagating along geomagnetic field lines modulate the growth rate of VLF waves, which results in the pulsation of VLF hiss intensity. The pulsating growth rate has been computed.     

Observations of TEC depletions over Indian low latitudes

Results pertaining to the latitudinal extent of the ionospheric irregularities in terms of TEC depletions have been presented for the two nights namely; 28 October 2004 and 7 February 2005. This study has been carried out using the GPS–TEC over the Indian low latitude stations, at Udaipur, Hyderabad and Bengaluru. This is probably the first report of simultaneous GPS observation of TEC depletions over different latitudes from the Indian sector. The results show that the amplitude of TEC depletions due to the equatorial spread F may vary with time and the location of the observation. The maximum amplitude of the TEC depletion has been found to be about 30 TECU over Hyderabad. The depletions in TEC are found to be field aligned.     

Variability of the behavior of the bottomside (B0, B1) parameters obtained from the ground-based ionograms at China’s low latitude station

In this paper, data of (B0, B1) parameters deduced from the electron density profiles that are inverted from the ionograms recorded at Hainan (19.4°N, 109.0°E), China during a three year period from March 2002 to February 2005 are used to study the diurnal and seasonal variation of (B0, B1) parameters at low latitude. The observational results are compared with the IRI2001 model predictions. Variability study of (B0, B1) in terms of percentage ratio of the inter-quartiles to the median values and correlative analysis between (B0, B1) parameters and other ionospheric characteristics such as hmF2 and M(3000)F2 are also made. Our present study showed that: (1) for daytime hours, the IRI2001 model results with new table option (B0_Tab) is in a better agreement with the observational results (B0_Obs) than the IRI2001 model results with Gulyaeva option (B0_Gul) for summer season, whereas B0_Gul is in a better agreement with B0_Obs than B0_Tab for winter season. For nighttime, in general, B0_Gul is in a better agreement with B0_Obs than B0_Tab. For other occasions, both B0_Tab and B0_Gul showed some systematic deviations from the observational ones. Moreover, the deviations of B0_Tab and B0_Gul from B0_Obs showed opposite trends; (2) the monthly upper (lower) quartiles of (B0, B1) parameter showed a good linear relationship with the monthly median values, this makes it possible to do the regression analysis between the monthly upper (lower) quartiles and the monthly median values, which can give a measure of the variability of these parameters. In terms of the percentage ratio of the inter-quartiles to the median values, the variability of B0 showed a diurnal variation ranging between 22% and 36% with maximum value occurring at pre-sunrise hours, whereas the variability of B1 showed a diurnal variation ranging between 15% and 30% with higher value by daytime than at night; (3) B0 shows high linear correlative relationships with hmF2 and M(3000)F2 for most of the local time period of a day except for a few hours around midnight, whereas B1 showed high linear correlations with B0, hmF2 for daytime hours, but not for nighttime hours. This suggests that it maybe is possible to obtain the synthetic database of (B0, B1) parameter or to construct the model of (B0, B1) using database of hmF2 or M(3000)F2 which is much easier to obtain from experimental measurements.     

Formation and characteristics of low latitude boundary layer

Characteristics of low latitude boundary layer (LLBL) of the Earth’s magnetosphere are investigated using data of Interball/Tail probe observations. The role of different processes of LLBL formation is discussed. The high level of magnetosheath turbulence is taken into account. It is shown that the turbulent nature of magnetic field and plasma fluctuations in the magnetosheath is one of the main factors determining the structure of LLBL. The results of Interball/Tail probe observations of the event 9 March 1996 are analyzed. The thickness of LLBL is determined for the number of cases. The change of LLBL thickness under the influence of the changes of solar wind parameters is investigated. It is shown that variability of solar wind conditions can be the important factor controlling LLBL thickness. Results of observations are compared with the theory which explains the value of LLBL thickness as the result of plasma transport inside the magnetosphere. It is shown that the theory gives the qualitative explanation of the observed dependence of LLBL thickness on solar wind parameters.     

基于低空突防的空对舰攻击导引技术综述及研究思路

介绍了基于低空突防的空对舰攻击相关问题研究状况与发展趋势,为空对舰攻击导引研究提供了思路。