Second-order Taylor expansion boundary element method for the second-order wave radiation problem

A novel Boundary Element Method (BEM) named the second-order Taylor Expansion Boundary Element Method (the 2nd order TEBEM) is developed for the solution of the second-order wave radiation velocity potential and sum-frequency wave loads for floating bodies. The radiation condition is enforced by a hybrid method of the multi-transmitting formula and damping zone. For the interior domain problem of a cube and a sphere, numerical results demonstrate that the 2nd order TEBEM can accurately solve the first and second-order gradients of velocity potential on the no-smoothed and smoothed boundary compared to the low-order BEM. The double frequency forces acting on the truncated cylinder are calculated under finite water depth. The agreement between the 2nd order TEBEM and others' numerical results is good. Moreover, all of the singular integrals in the 2nd order TEBEM can be solved analytically, so its implementation is much easier compared to the high-order BEM.     

地球大气纬向风系、副热带高压和太阳较差自转的形成机制

利用N S(Navier Stokes)方程和一个基本假设推导出星体大气平均纬向风和平均气压公式,根据公式讨论了地球大气纬向风系和平均气压以及副热带高压的成因并进行了数值模拟。结果发现,地球大气纬向风是大气微团密度与基准大气密度存在差异而形成的,大气微团的密度大于（小于）基准密度,则为西风（东风）;密度的差距越大,风速越强。在中高纬度地区大气微团吸收的太阳辐射少而向空间辐射多,导致其密度变大,因此在中高纬度盛行西风;而在低纬度地区,因为吸收的太阳辐射多使大气微团密度变小而盛行东风。夏季（冬季）太阳辐射增强（减弱）使得大气微团密度变小（增大）,进而导致中高纬度地区西风减弱（增强）和低纬度地区的东风加强（减弱）。风速的大小还与纬度的余弦成正比,这就使得最大西风带位于中纬度地区而不是大气微团密度最大的极地附近;也使得最大的东风不是发生在太阳直射点附近而是靠近赤道一侧。根据气压公式和大气密度的经向差异可以得出中高纬度区域气压随纬度的升高而减小的分布特征,而太阳辐射所造成低纬地区密度的减小是该区域气压大于中高纬度的主要原因;在赤道上纬度的正弦为零,使得气压在赤道上存在极小值,导致了赤道槽和副热带高压的形成,且太阳辐射越强、副热带高压越强。因为纬度正弦因子的存在,使得副高脊线总是位于太阳直射点的向极一侧。在假定太阳大气为理想气体的情况下,由N S方程推导出太阳大气自转角速度随纬度的变化公式,由此解释了太阳较差自转的成因在于低纬地区的大气微团密度大于高纬度,并且在赤道上大气微团的密度最大。该公式与观测得到的经验公式在略去高阶小项后一致。由此认为,太阳大气的运动在形成机制上与地球大气没有区别,不同的是在太阳表面没有象地球表面那样受太阳辐射的影响,N S方程是所有星体（包括恒星、行星）大气共同遵守的动力方程。     

长波区间太阳辐射对气候模拟的影响

长波区间的太阳辐射在气候模式中往往被忽略。利用国家气候中心BCC_AGCM2.0.1大气环流模式,采用矩阵算子辐射传输算法,研究了长波区间太阳辐射对气候模式辐射通量和温度模拟结果的影响。结果表明,以ISCCP和CERES辐射资料为标准,考虑长波区间太阳辐射后,长波区间晴空大气地表向下辐射通量平均误差减小2.05 W/m2,均方根误差减少1.29 W/m2;长波区间晴空大气模式顶向上辐射通量平均误差减小0.70 W/m2,均方根误差减小0.21 W/m2;长波区间有云大气地表向下辐射通量平均误差减小1.38 W/m2,均方根误差减小1.03 W/m2;长波区间有云大气模式顶向上辐射通量平均误差减小0.99 W/m2,均方根误差减小0.30 W/m2。以ECMWF再分析资料为标准,考虑长波区间太阳辐射后,赤道地区上对流层—下平流层区域温度的冷偏差得到改善,对流层顶温度平均误差减小0.27 K,均方根误差减小0.25 K。     

夏季东亚地区AOD与地面太阳辐射变化的联系及季风环流异常:季节趋势影响

利用2000—2013年MODIS-Terra卫星产品提供的气溶胶光学厚度(aerosol optical depth,AOD)资料及NCEP/NCAR再分析资料集,使用奇异值分解(singular value decomposition,SVD)方法,分析了夏季东亚地区AOD与到达地面太阳辐射(downward solar radiation flux,DSRF)相联系的主要模态,并分析了其与夏季风变化的关系。夏季多年平均的AOD分布显示,在东亚地区存在两个AOD大值区(0.9),分别位于山东、河南、河北交界处附近以及苏中部分地区。而在福建、台湾及其附近洋面上,夏季AOD的值小于0.4。地面太阳辐射总体上呈现出由南往北递增的分布。比较发现,AOD与地面太阳辐射的气候分布较为相似。在保留季节趋势的情况下,运用SVD方法对两者进行分解,结果表明东亚地区AOD与地面太阳辐射表现出较好的正相关关系。由于相对于年际变化而言,季节趋势是更为主要的部分,因而这种同相关系可归因于季风活动的季节性进程。利用SVD1左场时间系数进行相关分析发现:6月(2013年除外),当中国东部气溶胶AOD大而地面太阳辐射亦大时,在中国东南部以及日本岛南部地区,由于气流辐合增强和存在较强的上升运动,降水偏多,而由于副高位置偏南,使得中国中东部偏北地区水汽供应偏弱,降水偏少。由于地面净太阳辐射增强,华北部分地区异常增暖。8月,大陆上空AOD为负(时间系数为负),地面太阳辐射减少,北方降水增多而南方降水减少,华北地区有一小范围的异常降温。上述结果表明北方气溶胶明显偏少时,云量增加,降水将增多,且辐射明显减弱;说明夏季风的季节进程对气溶胶、到达地面的太阳辐射变化等具有重要影响。     

国家级太阳辐射测量标准及其质量控制

太阳辐射测量标准仅采取定期参加国际比对的溯源方法不能完全满足质量保证的要求。只有联合国际比对和期间核查的控制方法,才能确保测量标准的测量不确定度持续控制在误差允许范围之内。我国太阳辐射测量标准与世界辐射测量基准 (WRR) 比对结果的不确定度为0.17%,满足世界气象组织 (WMO) 要求,并达到世界先进水平。为了保证在两次国际周期比对间隔之间的准确可靠,并保证其处于良好置信度的校准状态,定期对测量标准的重复性和稳定性进行期间核查, 以图形记忆方式对太阳辐射测量标准的测量过程进行连续和长期的统计控制。通过期间核查,保证了太阳辐射测量标准的重复性不大于0.1%,年稳定性小于0.25%,未超出控制界限且分布呈随机状态,保证了测量过程处于稳定受控状态,满足建标要求。     

Comment on “Comparative study of beta-decay data for eight nuclides measured at the Physikalisch-Technische Bundesanstalt” [Astropart. Phys. 59 (2014) 47–58]

We would like to comment on a recent paper by Sturrock et al. (2014) in which the authors analyze decay data acquired by an ionization chamber in our institute. They interpret the variations in the data as solar-driven changes in the decay rates of the radionuclides under study. In brief we would like to discuss and elucidate the properties and the origin of the data used by the authors and explain why these data are not a sound basis for claiming evidence for new physics.     

TM65 m射电望远镜低频段系统噪声温度测试和分析

首先介绍了天马65 m射电望远镜(简称TM65 m)接收系统,包括L、S、C、X 4个频段各部分的噪声指标.然后对系统噪声温度的几种测试方法进行了讨论;对影响系统噪声温度测量的若干关键因素进行了分析,包括非线性误差、馈源网络插入损耗和失配误差等.采用Y因子法对试验室的噪声源定标值进行了校核,校核后偏差达到0.2 K左右.最后给出了TM65 m 4个低频段系统噪声温度的实测结果,并进行了分析.     

Further considerations of cosmic ray modulation of infra-red radiation in the atmosphere

Understanding effects of ionisation in the lower atmosphere is a new interdisciplinary area, crossing the traditionally distinct scientific boundaries between astro-particle and atmospheric physics and also requiring understanding of both heliospheric and magnetospheric influences on cosmic rays. Following the paper of Erlykin et al. (2014) we develop further the interpretation of our observed changes in long-wave (LW) radiation, Aplin and Lockwood (2013) by taking account of both cosmic ray ionisation yields and atmospheric radiative transfer. To demonstrate this, we show that the thermal structure of the whole atmosphere needs to be considered along with the vertical profile of ionisation. Allowing for, in particular, ionisation by all components of a cosmic ray shower and not just by the muons, reveals that the effect we have detected is certainly not inconsistent with laboratory observations of the LW absorption cross section. The analysis presented here, although very different from that of Erlykin et al., does come to the same conclusion that the events detected by AL were not caused by individual cosmic ray primaries – not because it is impossible on energetic grounds, but because events of the required energy are too infrequent for the 12 h⁻¹ rate at which they were seen by the AL experiment. The present paper numerically models the effect of three different scenario changes to the primary GCR spectrum which all reproduce the required magnitude of the effect observed by AL. However, they cannot solely explain the observed delay in the peak effect which, if confirmed, would appear to open up a whole new and interesting area in the study of water oligomers and their effects on LW radiation. We argue that a technical artefact in the AL experiment is highly unlikely and that our initial observations merit both a wide-ranging follow-up experiment and more rigorous, self-consistent, three-dimensional radiative transfer modelling.