Thickness distribution and extent of sea ice and snow in Prydz Bay and surrounding waters observed in 2012/2013 austral summer

Three ship-based observational campaigns were conducted to survey sea ice and snow in Prydz Bay and the surrounding waters(64.40°S–69.40°S, 76.11°E–81.29°E) from 28 November 2012 to 3 February 2013. In this paper, we present the sea ice extent and its variation, and the ice and snow thickness distributions and their variations with time in the observed zone. In the pack ice zone, the southern edge of the pack ice changed little, whereas the northern edge retreated significantly during the two earlier observation periods. Compared with the pack ice, the fast ice exhibited a significantly slower variation in extent with its northernmost edge retreating southwards by 6.7 km at a rate of 0.37 km?d-1. Generally, ice showed an increment in thickness with increasing latitude from the end of November to the middle of December. Ice and snow thickness followed an approximate normal distribution during the two earlier observations(79.7±28.9 cm, 79.1±19.1 cm for ice thickness, and 11.6±6.1 cm, 9.6±3.4 cm for snow thickness, respectively), and the distribution tended to be more concentrated in mid-December than in late November. The expected value of ice thickness decreased by 0.6 cm, whereas that of snow thickness decreased by 2 cm from 28 November to 18 December 2012. Ice thickness distribution showed no obvious regularity between 31 January and 3 February, 2013.     

磁层亚暴期间同步高度电子通量突增的理论计算

本文在给定的电场和磁场模式下,利用引导中心的动力学方程,计算了在磁层亚暴期间同步高度处电子通量突增的过程。结果表明:在增长相期间,电子通量并不增长,甚而有下降的趋势,电子通量的突增,大约是在膨胀相的开始。突增事件是发生在地方时半夜到黎明,10点到18点这一时间内没有突增现象,18点以后又发现有突增现象。这些主要特征与卫星的观测结果相符合。     

大地测量学科发展现状与趋势

近50年,由于大地测量观测手段的不断进步和应用领域的不断拓展,大地测量学科不断进化,并与其他学科不断交叉与融合。本文首先简述了大地测量学发展的背景和在历史上发挥的主要作用,梳理了大地测量传统学科的形成。进一步,分析了大地测量发展现状,侧重从观测手段的进步描述学科的发展;从应用领域的拓展描述交叉学科的形成;从国家需求和科学发展出发,描述了大地测量学科未来的发展趋势。最后,综合各方面因素,提出了大地测量现阶段学科分类建议,试图为大地测量工作者的科研选题、基金申请提供借鉴。     

不稳定性和频谱演化──再论等离子体辐射与其它辐射机制的关系

本文力图阐明的一个基本观点是:由等离子体不稳定性所激发的电磁波幅度的增长从本质上揭示了辐射过程内部的波粒相互作用对辐射频谱演化的贡献。因此,等离子体辐射理论是建立在经典电动力学的辐射理论的基础之上,并以各种基本辐射过程(如轫致辐射、回旋及同步辐射等)的平衡态为初始条件,从而发展起来的动态辐射理论。     

HITRAN数据库对卫星1.6 μm通道CO2辐射传输特性计算的影响

卫星遥感器中的CO21.6μm弱吸收带通道测量信号可以反映CO2的近地层浓度分布,是温室气体卫星反演的重要通道之一。HITRAN数据库是建立卫星遥感CO2浓度算法依赖的重要分子光谱参数数据库,目前已经更新到了2012版,不同版本中大气分子谱线参数存在差异。本文利用逐线积分模式LBLRTM,研究了最近3个版本HITRAN数据库(04、08、12版)在CO2的弱吸收带通道上大气光学厚度、透过率的差异,发现04版计算的气体光学厚度普遍偏高,可对CO2造成约38 ppm的低估;08版本得到的气体光学厚度与12版本接近,反演相差2 ppm以内。在此基础上,分析了不同HITRAN数据库对整层CO2变化和近地层CO2变化的敏感性,结果表明:04版对整层和近地面大气的变化敏感性最强,并且放大了近地层信号;08版与12版对整层或近地层CO2的敏感度接近,两者经过卷积后得到的信号无差异。     

动态破裂远场辐射的单力偶分量

重新审核了地震学文献中的两条基本原理,即远场弹性位移与动态断层面上的滑动速度成正比,以及地震断层上的平面动态滑动与双力偶体力等效等两条基本原理。我们指出,如果断裂发生于具有一定厚度的断层上,并且向前扩展的裂纹端部附近存在强度弱化区的话,则在与其等效的体力中会有一个附加的单力偶项,且在远场位移中也会有一个与向前扩展的强度弱化区内的应力降随时间增加的变化率成正比的附加项。我们还指出,与单力偶等效的体力并不违背牛顿力学原理,因为单力偶转矩为断层区内的旋转所平衡;于是,裂纹便辐射出扭转波与旋转形变场。     

Scintillation Dynamic Spectra and Transverse Velocities ofSeven Pulsars

Using a pulsar timing system developed at Urumqi Astronomical Observatory‘s 25-m telescope, we observed scintillation dynamic spectra for seven pulsars at the relatively high frequency of 1540 MHz over a wide frequency band of 320 MHz. Averaging observations at different epochs, we obtain time scales and decorrelation bandwidths for diffractive scintillation and show that these imply a power-law index for the electron density fluctuation close to 4.0. Assuming this value and that the scattering disk is approximately midway between the pulsar and the earth, we compute transverse velocities for the seven pulsars. These values are generally in good agreement with the proper motion velocities.