D-region ionospheric disturbances associated with the Extremely Severe Cyclone Fani over North Indian Ocean as observed from two tropical VLF stations

The D-region ionospheric disturbances due to the tropical cyclone Fani over the Indian Ocean have been analysed using Very Low Frequency (VLF) radio communication signals from three transmitters (VTX, NWC and JJI) received at two low latitude stations (Kolkata-CUB and Cooch Behar-CHB). The cyclone Fani formed from a depression on 26th April, 2019 over the Bay of Bengal (Northeastern part of the Indian Ocean) and turned into an extremely severe cyclone with maximum 1-min sustained winds of 250 km/h on 2 May, 2019 which made landfall on 3 May, 2019. Out of six propagation paths, five propagation paths, except the JJI-CHB which was far away from the cyclone track, showed strong perturbations beyond $3\sigma$ level compared to unperturbed signals. Consistent good correlations of VLF signal perturbations with the wind speed and cyclone pressure have been seen for both the receiving stations. Computations of radio signal perturbations at CUB and CHB using the Long Wave Propagation Capability (LWPC) code revealed a Gaussian perturbation in the D-region ionosphere. Analysis of atmospheric temperature at different layers from the NASA’s TIMED satellite revealed a cooling effect near the tropopause and warming effects near the stratopause and upper mesosphere regions on 3 May, 2019. This study shows that the cyclone Fani perturbed the whole atmosphere, from troposphere to ionosphere and the VLF waves responded to the disturbances in the conductivity profiles of the lower ionosphere.     

E region electric fields at the dip equator and anomalous conductivity effects

Zonal and vertical electric fields were estimated at E region heights in the Brazilian sector. Zonal electric fields are obtained from the vertical electric fields based on their relation through the Hall-to-Pedersen ionospheric conductivities ratio. The technique for obtaining the vertical electric field is based on its proportionality to the Doppler velocities of type 2 irregularities as detected by coherent radars. The 50 MHz backscatter coherent (RESCO) radar was used to estimate the Doppler velocities of the type 2 irregularities embedded in the equatorial electrojet. A magnetic field-line integrated conductivity model was developed to provide the conductivities. It considers a multi-species ionosphere and a multi-species neutral atmosphere, and uses the IRI 2007, the MISIS 2000 and the IGRF 10 models as input parameters for ionosphere, neutral atmosphere and Earth’s magnetic field, respectively. The ion-neutral collision frequencies of all the species are combined through the momentum transfer collision frequency equation, and different percentages of electron-neutral collisions were artificially included for studying the implication of such increase in the zonal electric field, which resulted ranging from 0.13 to 0.49 mV/m between the 8 and 18 h (LT), under quiet magnetic conditions.     

全球电离层发电机方程的一种数值解法

为了将建立在赤道为对称面假设基础上的二维半球域对称）电离层发电机理论扩展到全球,本文在解发电机方程时,去掉赤道对称面这一假设条件和两极附加的边界条件,使通常的边值问题变成一种“无边界’问题．它更合理地描述了电离层发电机过程,而且可以给出半球发电机理论所不能给出的特征,例如,可以对Ｓｑ电流体系的ＵＴ变化、季节变化、非偶极子地磁场部分的发电机效应等南北半球不对称的情况进行数值计算．计算实例表示,在简单的赤道对称情况下,它可以复现二维半球（对称）发电机模型的结果．在不对称情况下,电流体系的强度、焦点位置、电流方向等显示出较为复杂的变化,而半球发电机理论则无法解释这些特征．     

大功率无线电波对高电离层的加热

根据动量方程、能量方程和电子的连续性方程，在偶极扩散的假设下，建立了地面入射的大功率无线电波加热高电离层的理论模型．作为应用，对以上方程组数值求解，计算了高电离层(150-400km)电子温度和电子密度随时间的变化．计算结果表明，对于一定参数的发射机，一定的吸收模型，电离层电子温度和密度均有明显的变化．我们发现，应用本文选取的加热参数，在电波反射点附近，电子温度有10％-25％的增加，电子密度有1％-2％左右的减少．电子温度达到稳态的时间要快于电子密度达到稳态的时间．最后，用本文的结果解释了电离层加热实验中的一些观测现象。     

高频电波在背景备向异性和不均匀的随机起伏电离层中的传播

运用波动理论,讨论背景为各向异性、不均匀的随机起伏电离层中高频电波的传播和散射问题,给出了电离层不均匀体散射引起的反射回波波场的起伏,并在垂测条件下计算了接收波场的相位与振幅起伏的谱分布。      

大功率高频无线电波对赤道E区双流不稳定性的影响--PIC静电粒子模拟研究

地面入射的大功率高频无线电波(泵波)和电离层等离子体之间的参数相互作用，能够引起静电波的激发，在一定条件下，产生不稳定性．本文用PIC静电粒子模拟方法，研究泵波与赤道电离层E区等离子体的相互作用．研究结果表明，泵波能够控制双流不稳定性的发生，在不同条件下，泵波对双流不稳定性起着稳定与不稳作用，模拟结果定性地与理论研究结果相符合，这为我们对不规则体产生的地面人工控制提供了依据．     

对10V直流电压参考标准校准方法的探讨

介绍３种校准１０Ｖ直流电压参考标准的方法，并对３种校准方法进行了详细的误差分析。第１种方法是由美国ＦＬＵＫＥ公司生产的３３５Ａ型直流标准电压源，７２０Ａ型Ｋ－Ｖ分压器，８４５ＡＲ型零值检测器和０．０００２级控温标准电池构成校准系统，其传递误差小于１×１０￣（－６）。在该方法中用英国ＤＡＴＲＯＮ公司的４０００Ａ型直流标准电压源取代３３５Ａ，其传递误差可降低到０．４×１０￣（－６）。第２种方法是由７２０Ａ型Ｋ－Ｖ分压器，８４５ＡＲ型零值检测器和０．０００２级控温电池构成校准系统，其传递误差小于０．３×１０￣（－６）。第３种方法是由３３５Ａ型直流标准电压源，７２０Ａ型Ｋ－Ｖ分压器、８４５ＡＲ型零值检测器，１５５型零值检测器和０．０００２级控温电池构成校准系统，其传递误差小于０．２×１０￣（－６）。在同样的条件下，对上述３种方法进行了比对（３种方法所用的标准电池为同一１０只组电池），比对结果表明，３种方法之间的误差小于０．３×１０￣（－６）。     

电离层对普通GPS和位置差分GPS定位误差的影响

在没有选择可用性条件下，差分ＧＰＳ定位精度完全取决于电离层的空间不相关性，为了改进差分ＧＰＳ的校正算法，本文在月平均电离层时延等值图的基础上，建立了一个简单而又逼真的电离层模型，并分析了普通ＧＰＳ和位置差分ＧＰＳ仅电离层单一因素引入的定位误差。     

高超声速乘波飞行器气动特性研究

用计算流体力学和风洞试验的方法对以锥导乘波体为基础生成的高超声速乘波飞行器的气动性能进行了研究。结果表明，以马赫数6，攻角4度为设计状态的乘波体，在马赫数5～7，攻角4～6度的范围内，都具有良好的气动特性，升阻比接近4。最后，提出了一个简单的以参考温度方法为基础的粘性阻力分析方法。该方法配合使用风洞试验和计算流体的结果，可以用来验证计算流体中难以计算准确的粘性阻力，也可以用来分析在风洞试验难以直接得到的粘性阻力。对于工程上的粘性阻力分析是一个有用的办法。     

Statistical description of low-latitude plasma blobs as observed by DMSP F15 and KOMPSAT-1

The global distribution of low-latitude plasma blobs was investigated by in-situ plasma density measurements from the Korea Multi-Purpose Satellite-1 (KOMPSAT-1) and Defense Meteorological Satellite Program (DMSP) F15. In the observations, blobs occurred in the longitude sector where the activity of the equatorial plasma bubble (EPB) was appreciable, and additional blobs were found at the lower (KOMPSAT-1) altitude as in the EPBs. However, several notable differences exist between the distributions of EPBs and blobs. First, KOMPSAT-1 found few blobs around 0°E in March and June, as did DMSP F15 from 30°W to 120°E for every season. Second, the overall occurrences in December and March at the DMSP F15 (840 km) altitude were somewhat lower than expected from those of the EBPs. Third, at the DMSP F15 altitude, the occurrence probability of plasma blobs was less controlled by yearly variations in the solar activity. These results imply that topside ionospheric conditions as well as the existence of EPBs control further development of blobs. Additionally, it was found that the blob latitudes became higher as the yearly solar activity increased. Moreover, most of the blobs were encountered in the winter hemisphere, possibly due to the low ambient density.