Electron--positron outflows from gamma-ray emitting accretion discs     

A. M. Beloborodov 《Monthly notices of the Royal Astronomical Society》1999,305(1):181-189

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Erratum: Self-similarity and scaling behaviour of infrared emission from radiatively heated dust -- I. Theory     

《Monthly notices of the Royal Astronomical Society》1999,303(4):864-864

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Solar Stokes Spectrum Observation at Yunnan Astronomical Observatory     

Qu Z.Q.    Chen X.K.  Zhang X.Y.  Gu X.M.  Feng Y.M.  Zhong S.H. 《天文研究与技术》1999,(Z1)

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On the line formation process in stellar atmospheres – I. Unpolarized light     

Z. Q.  Qu  X. Y.  Zhang  X. M.  Gu 《Monthly notices of the Royal Astronomical Society》1999,305(4):737-745

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The effect of angle-dependent non-coherent electron scattering and partial redistribution on the polarization of resonance lines     

K. E. Rangarajan 《Monthly notices of the Royal Astronomical Society》1999,308(4):1053-1060

The polarized radiative transfer equation is solved when angle-dependent partial redistribution and non-coherent electron scattering are included as line-scattering mechanisms. A static atmosphere with plane parallel symmetry is assumed. Test calculations are used to illustrate the effects of the electron-scattering coefficient, the thermalization parameter and the continuous absorption coefficient on the line polarization. Results of angle-averaged and angle-dependent redistribution functions are compared and it is shown that angle-dependent functions should be used to model the wing polarization of optically thin lines. The lower the continuous absorption compared with the electron scattering, the higher the wing polarization.  相似文献   

An irradiation effect in Nova DN Gem 1912 and the significance of the period gap for classical novae   总被引：1，自引：0，他引：1  

A. Retter  E. M. Leibowitz  T. Naylor 《Monthly notices of the Royal Astronomical Society》1999,308(1):140-146

Continuous CCD photometry of the classical nova DN Gem during 52 nights in the years 1992–1998 reveals a modulation with a period of 0.127844 d. The semi-amplitude is about 0.03 mag. The stability of the variation suggests that it is the orbital period of the binary system. This interpretation makes DN Gem the fourth nova inside the cataclysmic variable (CV) period gap, as defined by Diaz & Bruch, and it bolsters the idea that there is no period gap for classical novae. However, the number of known nova periods is still too small to establish this idea statistically. We eliminate several possible mechanisms for the variation, and propose that the modulation is driven by an irradiation effect. We find that model light curves of an irradiated secondary star fit the data well. The inclination angle of the system is restricted by this model to 10°≲ i ≲65°. We also refine a previous estimate of the distance to the binary system, and find d =1.6±0.6 kpc.  相似文献   

Correction of atmospheric effect on ADEOS/OCTS ocean color data: Algorithm description and evaluation of its performance     

Hajime Fukushima  Akiko Higurashi  Yasushi Mitomi  Teruyuki Nakajima  Toshimitsu Noguchi  Toshio Tanaka  Mitsuhiro Toratani 《Journal of Oceanography》1998,54(5):417-430

This paper first describes the atmospheric correction algorithm for OCTS visible band data used at NASDA/EOC. Sharing a basic structure with Gordon and Wang’s Sea WiFS algorithm, it uses 10 candidate aerosol models including the “Asian dust model” introduced in consideration of the unique feature of aerosols over the east Asian waters. Based on the observations at 670 and 865 nm bands, the algorithm selects a pair of aerosol models that account best for the observed spectral reflectances, and synthesizes the aerosol reflectance used for the atmospheric correction. Two different schemes for determining the value of the parameter for the aerosol model selection are presented and their anticipated estimation error is analyzed in terms of retrieved water reflectance at 443 nm. The results of our numerical simulation show that the standard deviation of the estimation error of the “weighted average” scheme is mostly within the permissible level of ±0.002, reducing the error by 18% on average compared to the “simple average” scheme. The paper further discusses the expected error under the old CZCS-type atmospheric correction, which assumes constant aerosol optical properties throughout the given image. Although our algorithm has a better performance than the CZCS algorithm, further analysis shows that the error induced by the assumption taken in the algorithm that the water-leaving radiance at 670 nm band is negligibly small may be large in high pigment concentration waters, indicating the necessity for future improvements.  相似文献   

黑河地区大气沙尘对地面辐射能收支的影响   总被引：29，自引：16，他引：13  

沈志宝  魏丽 《高原气象》1999,18(1):1-8

利用１９９１年２月下旬至５月中旬ＨＥＩＦＥ张掖绿洲和沙漠站大气浑浊度观测和地面辐射平衡各个分量观测资料,分析和估算了大气沙尘对地面辐射能收支的影响,晴天大气透过率和达地面的短波辐射与大气浑浊度系数有产好的负相关,大气军浊系数增大时透过率和地面总辐射减少,大气浑浊度系数增大０．１,地面总辐射减少１．３％～１．９％,４月大气浑浊度由０．１增大到０．６,正午时刻地面总辐射减少６７．６～８５．８Ｗ／ｍ＾２  相似文献   

相对湿度对大气气溶胶粒子短波辐射特性的影响   总被引：25，自引：2，他引：23  

杨军  李子华  黄世鸿 《大气科学》1999,23(2):239-247

利用Mie散射原理和重庆实测气溶胶资料,详细计算了边界层内单个气溶胶粒子的光学特性参量,气溶胶粒子群体的散射、吸收、消光系数及不对称因子、散射比、光学厚度;进而采用二流近似和累加法计算了边界层内太阳短波辐射增温率。目的在于研究相对湿度对以上各特性参量的影响。结果表明,相对湿度在65%～95%之间变化时,对气溶胶粒子群体光学特性参数和太阳增温率的影响在量级上可与气溶胶粒子浓度成倍变化的影响相比拟。  相似文献   

Radiative forcing by contrails     

R. Meerkötter  U. Schumann  D. R. Doelling  P. Minnis  T. Nakajima  Y. Tsushima 《Annales Geophysicae》1999,17(8):1080-1094

A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm⁻² daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.  相似文献