Low-frequency waves in asymmetric magnetized relativistic pair plasma

The properties of waves in a pulsar magnetosphere are considered in the most general case of a non-neutral, current-carrying pair plasma with arbitrary distribution functions for electrons and positrons. General dispersion relations are derived for a strong but finite magnetic field, including gyrotropic terms caused by the deviations from quasi-neutrality and the relative streaming of electrons and positrons. It is shown how the ellipticity of the wave polarization depends on the plasma parameters and angle of propagation. Two examples of plasma distributions are analysed numerically: a waterbag distribution and a piecewise distribution that models the numerical result for pair cascades. A possible application to the interpretation of the observed circular polarization of some pulsars is discussed.     

Glacier ice mass fluctuations and fault instability in tectonically active Southern Alaska

Across the plate boundary zone in south central Alaska, tectonic strain rates are high in a region that includes large glaciers undergoing wastage (glacier retreat and thinning) and surges. For the coastal region between the Bering and Malaspina Glaciers, the average ice mass thickness changes between 1995 and 2000 range from 1 to 5 m/year. These ice changes caused solid Earth displacements in our study region with predicted values of −10 to 50 mm in the vertical and predicted horizontal displacements of 0–10 mm at variable orientations. Relative to stable North America, observed horizontal rates of tectonic deformation range from 10 to 40 mm/year to the north–northwest and the predicted tectonic uplift rates range from approximately 0 mm/year near the Gulf of Alaska coast to 12 mm/year further inland. The ice mass changes between 1995 and 2000 resulted in discernible changes in the Global Positioning System (GPS) measured station positions of one site (ISLE) located adjacent to the Bagley Ice Valley and at one site, DON, located south of the Bering Glacier terminus. In addition to modifying the surface displacements rates, we evaluated the influence ice changes during the Bering glacier surge cycle had on the background seismic rate. We found an increase in the number of earthquakes (M_L≥2.5) and seismic rate associated with ice thinning and a decrease in the number of earthquakes and seismic rate associated with ice thickening. These results support the hypothesis that ice mass changes can modulate the background seismic rate.During the last century, wastage of the coastal glaciers in the Icy Bay and Malaspina region indicates thinning of hundreds of meters and in areas of major retreat, maximum losses of ice thickness approaching 1 km. Between the 1899 Yakataga and Yakutat earthquakes (M_w=8.1, 8.1) and prior to the 1979 St. Elias earthquake (M_s=7.2), the plate interface below Icy Bay was locked and tectonic strain accumulated. We used estimated ice mass change during the 1899–1979 time period to calculate the change in the fault stability margin (FSM) prior to the 1979 St. Elias earthquake. Our results suggest that a cumulative decrease in the fault stability margin at seismogenic depths, due to ice wastage over 80 years, was large, up to 2 MPa. Ice wastage would promote thrust faulting in events such as the 1979 earthquake and subsequent aftershocks.     

论静电场与静磁场场方程的微分形式

本文从库仑定律和比沙定律出发,直接用del算符对场量进行运算得出场方程的微分形式,以此表示场的基本方程是从实验规律出发对场的本质更为普遍化的概括,并指出在两种不同媒质的交界面处场方程的微分形式不再适用。     

Derivation of flare magnetic field and density from two simultaneous frequency observations

We developed a simple model for a flare loop, which was used to fit the emission in the microwave (17 GHz) and millimetre-wave (80 GHz) ranges for the giant flare of 1991 June 4. The simplicity of the model enabled the exploration of a wide range of parameters in a reasonable time. It was possible, using the simple model, to derive from the 17- and 80-GHz data the magnetic field and the number density for every measurement point in the time range we chose to fit.     

Mapping travelling convection vortex events with respect to energetic particle boundaries

Thirteen events of high-latitude ionospheric travelling convection vortices during very quiet conditions were identified in the Greenland magnetometer data during 1990 and 1991. The latitudes of the vortex centres for these events are compared to the energetic electron trapping boundaries as identified by the particle measurements of the NOAA 10 satellite. In addition, for all events at least one close DMSP overpass was available. All but one of the 13 cases agree to an exceptional degree that: the TCV centres are located within the region of trapped, high energy electrons close to the trapping boundary for the population of electrons with energy greater than > 100 keV. Correspondingly, from the DMSP data they are located within the region of plasmasheet-type precipitation close to the CPS/BPS precipitation boundary. That is, the TCV centres map to deep inside the magnetosphere and not to the magnetopause.     

大气电场异常作为地震短临预报标志研究进展

通过对华北地地区进行震前大气电场异常观测研究的较为全面分析和总结,验证和论述了震前大气电场异常的基本特征,用大量的震例证实了在每次较大的近场地震发生前都能观测到该类异常现象,以及当较长一段时间内观测不到该类异常时,近场近期也不会有较大地震发生的可能。     

“97-11-24”和“97-11-27”大暴雨过程T106物理量预报场分析

对1997年11月24日和1997年11月27日两次江西大暴雨过程的T106物理量预报场进行了分析,得到T106物理量场对稳定切变的暴雨形势有较好的预报能力等一些有意义的结果。     

Scaling Law for Galactic Magnetic Fields

A nonlinear mean field dynamo in turbulent disks and spherical shells is discussed. We use a nonlinearity in the dynamo which includes the effect of delayed back-reaction of the mean magnetic field on the magnetic part of the — effect. This effect is determined by an evolutionary equation. The axisymmetric case is considered. An analytical expression (in a single-mode approximation) is derived which gives the magnitude of the mean magnetic field as a function of rotation and the parameters for turbulent disks. The value obtained for the mean magnetic field is in agreement with observations for galaxies.