Ice crystal shape effects on solar radiative properties of Arctic mixed-phase clouds—Dependence on microphysical properties

Based on 1-year cloud measurements with radar and microwave radiometer broadband solar radiative transfer simulations were performed to quantify the impact of different ice crystal shapes of Arctic mixed-phase clouds on their radiative properties (reflectance, transmittance and absorptance). The ice crystal shape effects were investigated as a function of microphysical cloud properties (ice volume fraction f_i, ice and liquid water content IWC and LWC, mean particle diameter D_m^I and D_m^W of ice/water particle number size distributions, NSDs).The required NSDs were statistically derived from radar data. The NSD was composed of a liquid and a solid mode defined by LWC, D_m^W (water mode) and IWC, D_m^I (ice mode). It was found that the ratio of D_m^I and D_m^W determines the magnitude of the shape effect. For mixed-phase clouds with D_m^I ≤ 27 μm a significant shape effect was obtained. The shape effect was almost insensitive with regard to the solar zenith angle, but highly sensitive to the ice volume fraction of the mixed-phase cloud. For mixed-phase clouds containing small ice crystals (D_m^I ≤ 27 μm) and high ice volume fractions (f_i > 0.5) crystal shape is crucial. The largest shape effects were observed assuming aggregates and columns. If the IWC was conserved the shape effect reaches values up to 0.23 in cloud reflectance and transmittance. If the ice mode NSD was kept constant only a small shape effect was quantified (≤ 0.04).     

对云滴凝结增长方程的质疑

基于多元体系化学势和相平衡原理,分析认为“水蒸气凝结释放的潜热既升高了云滴表面温度,又向外传导热量”的观点违反了热力学第二定律,指出这样热传导过程是不可能进行的,分析认为大气中水蒸气凝结只能以辐射形式释放潜热。     

博州地区196 1—2006年太阳能资源的分析评估

根据太阳总辐射估算模型Q=Q0（a＋bS1）按月确定了博州地区邻近站伊宁的a、b系数,将其对应于博州地区4个站点1961～2006年逐月太阳辐射的计算,据此分析了全地区太阳总辐射的时空分布状况,并对太阳能资源按行业标准进行了评估。结果表明,46a来博州地区的太阳总辐射呈明显下降趋势,整体上冬季减少的贡献率最大;太阳总辐射与总、低云量、相对湿度、雨雪日数具有较好的相关性;造成博州地区太阳总辐射呈下降趋势的重要气候原因是：平均总、低云量,相对湿度,雨雪日数增加的综合作用;博州地区的太阳能资源较丰富,其开发利用的．综合条件较好。     

当前对流参数化研究存在问题的讨论

基于对流参数化的发展过程,讨论了当前对流参数化方案中存在的问题,着重分析了大尺度水汽辐合型和质量通量型方案的缺陷,同时对东亚季风区和我国的研究现状进行了分析,提出了通用对流参数化方案的设计思想和应该考虑的原则,具有重要的参考借鉴意义。     

机载微波辐射计反演云液水含量的云物理方法

用一维层状云模式产生云样本,通过统计回归求得机载对空微波辐射计测云中路径积分液态水含量的反演系数,与用历史探空统计资料作相对湿度诊断产生云样本的反演方法进行了比较,并通过因素分析、数值模拟检验等方法对机载微波辐射计的探测误差进行估计。对2001年7月8日的个例分析表明,用云模式得到的统计样本,由于加入了对层状云物理过程的考虑,较为符合当天的实际天气情况,在一定程度上减小了由于背景大气条件、云温、云内含水量的垂直分布等的不确定性所引起的反演误差。对反演精度的数值模拟检验表明,各高度层的均方根相对误差在9.5%～12.7%之间,反演精度在所有高度上都高于原方法。对探测误差的因素分析表明,与仪器漂移及背景场引起的误差相比,由云液水垂直分布的不确定所引起的误差是不可忽略的。因此为进一步提高反演精度,根据实际宏观观测资料,对云模式产生的大量样本进行筛选,从中选取与实际云况较为符合的云样本进行拟合,结果表明,采用这一措施可以使反演精度得到进一步改善。     

上海市郊林带附近晴天地表热量平衡特征的分析

林带附近的热量平衡各分量的变化体现了林带对周围近地大气环境的影响.本文根据上海市郊林带附近温、湿、风梯度及净辐射观测资料,分析了林带附近冬夏晴天热量平衡各分量的特征,结果表明:夏季林带附近的净辐射比非林带小,冬季则比非林带大;林带对风速有减弱作用,林带附近的湍流输送较弱,因而林带附近热量和水汽量输送较小;林带附近有植物蒸腾,蒸散耗热量较大,为热量平衡中主要支出项;土壤热通量变化与近地面地温变化有关;林带附近较大的蒸散耗热和较弱的湍流输送有利于有利林带附近土壤水分的储存,并使周围湿润,但高温或低温时,湿度增加会引起人体不适,在林带规划上要充分考虑以上特点.     

Detecting Aerosols over Land from Satellites by Measuring Far IR Radiation from the Earth-Atmospheric System

In this study, a special method is proposed for detecting aerosols over land by analyzing satellite-measured far IR radiation at three channels, 8.7, 11.5, and 12.5 um. Sensitivity tests revealed that the behavioral features of radiative brightness temperatures (BTs) at these three channels with increasing optical depth are different among different types of aerosols. Analyzing how BTs and their differences, xBT (BT11.5-BT12.5) and yBT (BT8.7-BT11.5), behave with varying optical depth can help to qualitatively distinguish among aerosols and semi-quantitatively estimate their optical thicknesses. In addition, the authors found that the vertical density profile of aerosols has little impact on this method.     

Correlation analysis of persistent heavy rainfall events in the vicinity of the Yangtze River valley and global outgoing longwave radiation in the preceding month

Based on the National Oceanic and Atmospheric Administration (NOAA) daily satellite dataset of global outgoing longwave radiation (OLR) for the period of 1974--2004 and the NCEP-NCAR reanalysis for 1971--2004, the linkage between persistent heavy rainfall (PHR) events in the vicinity of the Yangtze River valley and global OLR leading up to those events (with 1- to 30-day lag) was investigated. The results reveal that there is a significant connection between the initiation of PHR events over the study area and anomalous convective activity over the tropical Indian Ocean, maritime continent, and tropical western Pacific Ocean. During the 30-day period prior to the onset of PHR events, the major significantly anomalous convective centers have an apparent dipole structure, always with enhanced convection in the west and suppressed convection in the east. This dipole structure continuously shifts eastward with time during the 30-day lead period. The influence of the anomalous convective activity over the tropical oceans on the initiation of PHR events over the study area is achieved via an interaction between tropical and extratropical latitudes. More specifically, anomalous convective activity weakens the Walker circulation cell over the tropical Indian Ocean first. This is followed by a weakening of the Indian summer monsoon background state and the excitation and dispersion of Rossby wave activity over Eurasia. Finally, a major modulation of the large scale background circulation occurs. As a result, the condition of a phase-lock among major large scale circulation features favoring PHR events is established over the study area.     

台风“云娜”在近海强度变化及结构特征的数值研究Ⅰ:云微物理参数化对云结构及降水特征的影响

首先对AREM模式模拟的台风基本结构和云结构进行验证,检验了模拟结果的可靠性.在此基础上,设计了5组试验来研究云微物理参数化方案对台风"云娜"云结构及降水特征的影响.试验设计主要突出冰相云微物理过程、云微物理特征引发的冷却效应以及霰下落速度的重要性.结果表明:云微物理参数化过程对云的发展和降水特征的影响更为显著.各试验的水凝物分布和强度不同,降水类型和强度存在较大差异,由此引起的云中热力结构也有较大区别;在所有试验方案中,24 h降水率最大差异为52.5 mm/h.云微物理过程对云和降水特征的具体影响表现在:(1)如果不考虑雨水蒸发冷却效应,此时台风内核上升运动强度最强(达到-19 Pa/s),雨水和霰粒子增长最明显,相对于对照试验增量分别为1.8和2.5 g/kg.(2)霰和雪的融化对于螺旋雨带中雨滴的增长十分重要,但他们可能不是云墙中雨水形成的主导因子.(3)不同方案的降水模拟特征也存在较大差别,采用暖云参数化后,降水区域最小,但其中对流降水比例最大(63.19%);霰落速减半后,降水区域最大,其中非对流降水比例也最大(51.15%).     

辐射方案对GRAPES全球模式的影响

辐射过程是中期数值天气预报模式和气候模式中一个重要的物理过程。本文针对GRAPES (Global/Regional Assimilation and PrEdiction System) 全球模式非静力半隐式半拉格朗日的特点, 进行了不同辐射方案的敏感性比较试验, 以期找到一个适合于GRAPES全球模式的辐射方案。用到的方案包括WRF模式中的RRTM长波辐射方案、 NASA的Goddard短波辐射方案以及ECMWF的长短波辐射方案。试验结果表明, ECMWF的辐射方案更适合于GRAPES模式, 30天平均的北半球500 hPa高度场距平相关系数较WRF的辐射方案提高了近2%。另外, 针对实际运行中存在的辐射计算不稳定问题, 对辐射方案进行了气压订正和温度订正, 并对2005年7月影响我国的海棠台风进行了模拟试验, 气压订正后的120小时模式预报在对副热带高压和台风的描述上更接近于分析, 可用预报时效也有了明显提高。