Peculiarities of entropy and magnetosonic waves in optically thin cosmic plasma

The stability problem for small magnetohydrodynamic (MHD) perturbations in an optically thin, perfectly conducting uniform plasma with a cosmic abundance of elements is solved in the linear approximation. The electron heat conduction along the magnetic field and the proton heat conduction across the field are taken into account. We have shown for the first time that the entropy waves can grow exponentially, while the magnetosonic waves are damped in a wide range of physical conditions closest to the conditions in stellar coronae with the proper allowance for radiative losses. Slow magnetosonic waves are damped particularly rapidly. For the solar corona, the calculated damping decrement of slow magnetosonic waves agrees well with the averaged one in 11 quasi-periodic events observed from the TRACE satellite in extreme ultraviolet radiation. Other possible astrophysical applications of the results obtained are briefly discussed.     

Heating of the intergalactic medium by primordial miniquasars

A simple analytical model is used to calculate the X-ray heating of the intergalactic medium (IGM) for a range of black hole masses. This process is efficient enough to decouple the spin temperature of the IGM from the cosmic microwave background (CMB) temperature and produce a differential brightness temperature of the order of ∼ 5–20 mK out to distances as large as a few comoving Mpc, depending on the redshift, black hole mass and lifetime. We explore the influence of two types of black holes, those with and without ionizing ultraviolet radiation. The results of the simple analytical model are compared to those of a full spherically symmetric radiative transfer code. Two simple scenarios are proposed for the formation and evolution of black hole mass density in the Universe. The first considers an intermediate mass black hole that form as an end-product of pop III stars, whereas the second considers supermassive black holes that form directly through the collapse of massive haloes with low spin parameter. These scenarios are shown not to violate any of the observational constraints, yet produce enough X-ray photons to decouple the spin temperature from that of the CMB. This is an important issue for future high-redshift 21-cm observations.     

A unified picture for the γ-ray and prompt optical emissions of GRB 990123

The prompt optical emission of GRB 990123 was uncorrelated to the γ-ray light curve and exhibited temporal properties similar to those of the steeply decaying, early X-ray emission observed by Swift at the end of many bursts. These facts suggest that the optical counterpart of GRB 990123 was the large-angle emission released during (the second pulse of) the burst. If the optical and γ-ray emissions of GRB 990123 have, indeed, the same origin then their properties require that (i) the optical counterpart was synchrotron emission and γ-rays arose from inverse-Compton scatterings (the 'synchrotron self-Compton model'), (ii) the peak energy of the optical-synchrotron component was at ∼20 eV and (iii) the burst emission was produced by a relativistic outflow moving at Lorentz factor  ≳450  and at a radius  ≳10¹⁵  cm, which is comparable to the outflow deceleration radius. Because the spectrum of GRB 990123 was optically thin above 2 keV, the magnetic field behind the shock must have decayed on a length-scale of  ≲1  per cent  of the thickness of the shocked gas, which corresponds to  10⁶–10⁷  plasma skin depths. Consistency of the optical counterpart decay rate and its spectral slope (or that of the burst, if they represent different spectral components) with the expectations for the large-angle burst emission represents the most direct test of the unifying picture proposed here for GRB 990123.     

用卫星资料计算我国东部地区晴空太阳辐射

根据光的多次散射理论的离散纵标法，利用我国东南沿海地区探空站的资料，计算出不同高度上分谱段的太阳直接辐射和向上，向下散射辐射，与相应时刻的卫星测值（可见光，红外通道S－VISSR计数值）进行逐步回归拟合，建立晴空状况下卫星测值与大气中各高度太阳直接辐射和攻射辐射的统计模式，并将拟合方法进行稳定性检验，据此可以利用卫星资料计算各高度分谱段的太阳直接辐射和散射辐射。     

MTCLIM模型（山地小气候模拟模型）的研究现状及其潜在应用

MTCLIM模型是许多生态、生理模型的分析工具。它能解释模型的结果，分析一些生态、水文过程在不同气候条件下的变化趋势，也是其它模型的辅助管理工具，辅助建立不同环境条件下的生态管理方案。本文介绍了该模型的基本原理及其各变量较详细的计算方法，概述其研究历史及发展现状，及模型应用的几个重要方面及其发展趋势。     

The influence of the interplanetary medium on SuperDARN radar scattering occurrence

The effects of the characteristics of the interplanetary medium on the radar scattering occurrence, related to the whole array of SuperDARN radars installed in the Northern Hemisphere, have been studied over a two-year period. Statistically significant correlations of the variation of the scattering occurrence are found with the merging electric field and with the negative B_z component of the interplanetary magnetic field, independent of the seasonal period considered. This result demonstrates that the merging rate (and in particular the reconnection process) between the interplanetary magnetic field and the magnetosphere is a relevant factor affecting the occurrence of scattering. For comparison, we note that no statistically significant correlations are obtained when the interplanetary ion density or the solar wind speed are considered, although also these variables affect to a small degree the scattering occurrence variation. The study of the latitudinal and magnetic local time dependence of the observations shows an association between the considered correlation and the location of the auroral oval and the cusp/cleft region.     

Relationship of surface heat flux to microscale temperature variations: Application to boreas

The surface heat flux is normally parameterized in terms of the difference between the air temperature and the surface radiative temperature, or equivalently, the temperature computed from the surface energy balance. In this note, the relationship between the heat flux and the air-surface temperature difference is shown to be sensitive to the microscale variability of the surface radiation temperature caused by differences between the well-ventilated tree tops and less ventilated ground surface. This conclusion is based on surface and aircraft data collected during the Boreal Ecosystem-Atmosphere Study (BOREAS). For this case, the heat flux cannot be predicted by adjusting the thermal roughness height. As an alternative, the aerodynamic temperature can be related to a weighted average of the surface radtation temperature analogous to application of a simple canopy model. Here, the total heat flux is the sum of the heat fluxes from each individual surface type weighted by the area-fractional coverage.Part of this work was carried out in the Dept. of Earth and Atmospheric Sciences, St. Louis University and the Mesoscale and Microscale Meteorology Division of the National Center for Atmospheric Research.Part of this work was carried out in the Mesoscale and Microscale Meteorology Division of the National Center for Atmospheric Research.     

CLIMATIC CHARACTERISTICS OF EARTH-ATMOSPHERE OUTGOING LONGWAVE RADIATION OVER CHINA

ERBE and ISCCP data are used to investigate the cloud forcing and latitude and atmospheric temperature effectson outgoing longwave radiation(OLR)in the earth-atmosphere system,and the similarity of OLR field to 500 hPa andsurface effective radiation fields.Also,discussion is taken up of the OLR distribution on a nationwide basis,indicatingthat the winter(summer)OLR pattern is roughly a zonal type(asymmetrical saddle)with the annual pattern analogousto the January one.In the end the yearly OLR variation features are addressed on a regional basis.     

自然光辐射各分量卫星遥感图像的计算机生成原理与方法

本文讨论了利用卫星遥感数据和与之匹配的数字地面模型以及它们和光辐射各分量之间的定量关系，使用计算逐点分解遥感数字图像以生成成像瞬间直、散射辐射光照射下相应的卫星遥感图像的原理、方法。最后，阐述了生成的辐射各分量遥感图像特点和应用前景。