A Three-Dimensional Simulation of Collisional-Interchange-Instability in the Equatorial-Low-Latitude Ionosphere

We present a three-dimensional simulation of collisional-interchange-instability in the equatorial-low-latitude F region of ionosphere. The instability is responsible for the generation of large plasma density depletion or bubble. General 3D potential and continuity equations are derived to simulate the phenomena. To understand the linear aspect of the instability, the general 3D linear growth rate is derived using 3D potential equation. The linear growth characteristics are compared with earlier field-aligned-integrated growth analyses. The numerical simulation of bubble in the 3D spherical polar geometry is finally presented. Distinct evolution characteristics of bubble in 3D and 2D simulation are further discussed.     

气象海洋卫星地面遥感站

气象海洋卫星地面遥感站主要是用于接收各类气象、海洋、环境卫星的遥感原始数据,并实现数据存储及相关数据处理,从中提取可用的空间环境资料。5.2m天线根据轨道预报捕获并跟踪目标,接收L/S/X三频段射频信号,将信号放大变频后送解调器,解调器从中频信号中恢复出原始遥感数据帧,由记录器对数据进行存储,快视设备实时对原始数据进行去格式处理后显示遥感图像,通过网络传输给各个用户。     

基于岭估计理论实现GPS快速定位研究

针对在短时间内 GPS观测方程的法方程容易形成病态的实际 ,探讨用岭估计理论消除其病态性的方法 ,然后用 LAMBDA方法确定其整周模糊度。实验证明 ,对于单频 GPS接收机 ,在 1 min左右 ,利用该技术即可正确确定整周模糊度 ,从而实现厘米级定位     

Tide variation monitoring based improved GNSS-MR by empirical mode decomposition

Global Navigation Satellite System multipath reflectometry (GNSS-MR) technology has great potential for monitoring tide level changes. GNSS-MR techniques usually extract signal-to-noise ratio (SNR) residual sequences using quadratic polynomials; however, such algorithms are affected considerably by satellite elevation angles. To improve the stability and accuracy of an SNR residual sequence, this study proposed an SNR signal decomposition method based on empirical mode decomposition (EMD). First, the SNR signal is decomposed by EMD, following which the SNR residual sequence is obtained by combining the corresponding intrinsic mode function with the frequency range of the coherent signal. Second, the Lomb–Scargle spectrum is analyzed to obtain the frequency of the SNR residual sequence. Finally, the SNR frequency is converted into the tide height. To verify the validity of the SNR residual sequence obtained by EMD, the algorithm performance was assessed using multigroup satellite elevation angle intervals with measured data from two station, SC02 in the United States and RSBY in Australia. Experimental results demonstrated that the accuracy of the improved algorithm was improved in the low-elevation range. The improved algorithm demonstrated high monitoring accuracy, and the effective number was not less than 80% of the total in SC02, which means it could effectively describe the trend of the tide with accuracy of approximately 10 cm, meanwhile, the RMS error of RSBY could be reduced by 30 cm, to the maximum extent. The EMD method effectively expands the range of available GNSS-MR elevations, avoids the loss of effective information, enhances considerably the utilization rate of GNSS data, and improves the accuracy of GNSS-MR tide level monitoring.     

Development of a coupled supersonic inlet-fan Navier–Stokes simulation method

A coupled supersonic inlet-fan Navier–Stokes simulation method was developed by using COMSOL-CFD code. The flow turning, pressure rise and loss effects across blade rows of the fan and the inlet-fan interactions were taken into account as source terms of the governing equations without a blade geometry by a body force model. In this model, viscous effects in blade passages can also be calculated directly, which include the exchange of momentum between fluids and detailed viscous flow close to walls. NASA Rotor 37 compressor test rig was used to validate the ability of the body force model to estimate the real performance of blade rows. Calculated pressure ratio characteristics and the distribution of the total pressure, total temperature, and swirl angle in the span direction agreed well with experimental and numerical data. It is shown that the body force model is a promising approach for predicting the flow field of the turbomachinery. Then, coupled axisymmetric mixed compression supersonic inlet-fan simulations were conducted at Mach number 2.8 operating conditions. The analysis includes coupled steady-state performance, and effects of the fan on the inlet. The results indicate that the coupled simulation method is capable of simulating behavior of the supersonic inlet-fan system.     

Effects of sector structure of the interplanetary magnetic field on the upper mesosphere–lower thermosphere dynamics

In this paper we study the influence of the interplanetary magnetic field (IMF) polarity changes caused by the Earth passing through the IMF sector boundary on the dynamic processes taking place in neutral atmosphere within the altitude interval of the upper mesosphere–lower thermosphere (83–101 km). The analysis has revealed the influence of the IMF sector structure on dynamics of the upper mesosphere–lower thermosphere. There has been a significant seasonal variation of the wind reaction to the IMF polarity changes observed. The influence of the IMF polarity changes on neutral atmosphere dynamics within the altitude range of 83–101 km is most pronounced in the zonal component of neural wind when the IMF polarity changes from negative to positive in all the seasons except for spring and when IMF polarity changes from positive to negative – in spring only.     

Dependence of the 27-day variation of cosmic rays on the global magnetic field of the Sun

We show that the higher range of the heliolongitudinal asymmetry of the solar wind speed in the positive polarity period (A > 0) than in the negative polarity period (A < 0) is one of the important reasons of the larger amplitudes of the 27-day variation of the galactic cosmic ray (GCR) intensity in the period of 1995–1997 (A > 0) than in 1985–1987 (A < 0). Subsequently, different ranges of the heliolongitudinal asymmetry of the solar wind speed jointly with equally important corresponding drift effect are general causes of the polarity dependence of the amplitudes of the 27-day variation of the GCR intensity. At the same time, we show that the polarity dependence is feeble for the last unusual minimum epoch of solar activity 2007–2009 (A < 0); the amplitude of the 27-day variation of the GCR intensity shows only a tendency of the polarity dependence. We present a three dimensional (3-D) model of the 27-day variation of GCR based on the Parker’s transport equation. In the 3-D model is implemented a longitudinal variation of the solar wind speed reproducing in situ measurements and corresponding divergence-free interplanetary magnetic field (IMF) derived from the Maxwell’s equations. We show that results of the proposed 3-D modeling of the 27-day variation of GCR intensity for different polarities of the solar magnetic cycle are in good agreement with the neutron monitors experimental data. To reach a compatibility of the theoretical modeling with observations for the last minimum epoch of solar activity 2007–2009 (A < 0) a parallel diffusion coefficient was increased by ∼40%.     

Study of the 27-day variations of the galactic cosmic ray intensity and anisotropy

We demonstrate that the general features of the radial and azimuthal components of the anisotropy of galactic cosmic rays can be studied by the harmonic analysis method using data from an individual neutron monitor with cut off rigidity <5 GV. In particular, we study the characteristics of the 27-day (solar rotation period) variations of the galactic cosmic ray intensity and anisotropy, solar wind velocity, interplanetary magnetic field strength and sunspot number. The amplitudes of the 27-day variations of the galactic cosmic ray anisotropy are greater, and the phases more clearly established, in A > 0 polarity periods than in A < 0 polarity periods at times of minimum solar activity. The phases of the 27-day variations of the galactic cosmic rays intensity and anisotropy are opposite with respect to the similar changes of the solar wind velocity in A > 0 polarity periods. No significant dependence of the amplitude of the 27-day variation of the galactic cosmic ray anisotropy on the tilt angle of the heliospheric neutral sheet is found. Daily epicyclegrams obtained by Chree’s method show that the 27-day variations of the galactic cosmic ray anisotropy during A > 0 polarity periods follow elliptical paths with the major axes oriented approximately along the interplanetary magnetic field. The paths are more irregular during A < 0 polarity periods.     

Characteristics of the seasonal variation of the global tropopause revealed by COSMIC/GPS data

Using the Global Navigation Satellite System (GNSS) radio occultation observations from Formosa Satellite mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) from 2007 to 2012, the climatological characteristics of the global tropopause was studied, with the following features identified. The overall results generally agree with previous studies. The tropopause has an obvious zonal structure, with more zonal characteristics in the Southern Hemisphere than the Northern Hemisphere. The vertical shape of the tropopause is sharp in the tropics and broad in the sub-tropical latitudes, with the sharpest latitudinal gradient in the mid-latitudes of both hemispheres. The global tropopause exists in a large range between 8 km and 17 km (or between 100 hPa and 340 hPa). The highest tropopause is over the South Asian monsoon regions for the entire year. The spatial structure of the tropopause in the polar region is of concentric structure, with an altitude between 7.5 km and 10 km. It is more symmetric in the Antarctic than the Arctic. Differing from other places, the height of the tropopause in the Antarctic is higher in winter as opposed to summer. The tropopause has distinct seasonal variability, especially in polar regions.     

Variations of geomagnetic cutoff rigidity in the southern hemisphere close to 70°W (South-Atlantic Anomaly and Antarctic zones) in the period 1975–2010

We report the existence of rapid variations in (effective) geomagnetic cutoff rigidity (Rc) between the equatorial and Antarctic zones adjacent to the Andes Mountains, revealed by the variation rate of geomagnetic cutoff rigidity (VRc) in the period 1975–2010. Our analysis is based on empirical records and theoretical models of the variations in cosmic rays and on the structure of geomagnetic fields. These have given us a different view of variations in Rc in time and space along the 70°W meridian, where secular variations in the geomagnetic field are strongly influenced by the proximity of the South Atlantic Magnetic Anomaly (SAMA), one of the most important characteristics of the terrestrial magnetic field that affects our planet, close from the equator to the 50°S parallel and from South America to South Africa. The VRc presents rapid changes in mid-latitudes where SAMA exerts its influence despite the existence of smooth changes in the geomagnetic field. This shows that these changes occur mainly in the spatial configuration, rather than in the temporal evolution of Rc. The analysis was performed using measurements from the Chilean Network of Cosmic Rays and Geomagnetism Observatories, equipped with BF-3 and latest generation He-3 neutron monitors, Fluxgate magnetometers, geomagnetic reference field (IGRF) and Tsyganenko 2001 model (just for completeness).