冰雹与雷暴大风的云对地闪电特征

利用京津冀中尺度试验基地三站闪电定位资料，对１９８９—１９９２年２０个冰雹大风实例进行了分析。发现云对地闪电（简称地闪）活动表现为一次冰雹大风天气过程。且正的云对地闪电（简称正闪）占绝对优势，而负的云对地闪电（简称负闪）则与强降水相关。其开始发生时间与雷雨同步，比冰雹平均提前２５ｍｉｎ左右，出现在雹云前进方向右侧（下风方）１０—５０ｋｍ。当正闪发生在雹云后部时是冰雹发生与加强阶段，而闪电密集区与云体重叠时是冰雹过程强盛阶段，当位于云体的前方且散开时是冰雹减弱消亡阶段。这个特征对超短期预报具有指示意义。     

Modelling Boundary-Layer Clouds With a Statistical Cloud Scheme and a Second-Order Turbulence Closure

We present a second-order turbulence model for the cloudy planetary boundary layer (PBL), which includes a statistical scheme of the sub-grid scale condensation. The model contains prognostic equations for the turbulent kinetic energy, total water, and liquid water temperature, the latter two being assumed to be conservative variables. Using these conservative thermodynamic variables the condensation process is formulated as a function of the departure of the total water from saturation and its variance. The computation of the variance requires second moment correlations which are modelled through the parameterization of the third-order moments using a convective mass-flux formulation. The inclusion of these third moments and new assumptions on heat flux transport lead to a nonlocal turbulence scheme with counter-gradient effects. The final form for the heat flux turns out to be a linearized version of a previously established result. For the statistical cloud formulation, a linear combination of a Gaussian and a positively skewed distribution function is used with a modified liquid water flux expression to account fornon-Gaussian behaviour.The effect of the turbulence scheme on the boundary-layer cloud structure is discussed and the performance of the model is tested by comparing it against the large eddy simulation (LES) of the undisturbed period of the Atlantic Stratocumulus Transition Experiment (ASTEX). The model is able to produce both mean and turbulent quantities that are in reasonable agreement with the LES output of ASTEX.     

On the bulk parameterization of snow and its application to the quantitative studies of precipitation growth

Appropriate formulation of bulk parameterization of snow growth and evaporation based on observational characteristics of snow particles is presented. The parameterization is compared to that of S. A. Rutledge and P. V. Hobbs and to detailed treatment in which snow particles are assumed to grow or evaporate in each size bin separately. On the contrary to bulk parameterization of rain, snow diffusional growth or evaporation is accurately represented in the suggested bulk formulation, but growth by riming is overpredicted. Integrations of water budget equations in a one-dimensional updraft have shown that quantitative results, e.g., precipitation intensity, cloudwater content, supersaturation with respect to ice, depend on the parameterization scheme employed, which suggests that comparisons of field measurements with parameterized model outputs is usually not straightforward.     

中国东部暖季对流云与层状云的比例及与降水的对应关系

基于1985~2011年逐时地面台站观测云资料,分析了对流云和层状云及其比例关系的时空演变特征,结合逐日融合降水资料研究了对流云、层状云与季风雨带的对应关系。结果表明,中国东部暖季（5~9月）对流云发生频率平均为15.4%,层状云为30.0%。对流云与层状云发生频率的比例在广东、广西、海南省东部和贵州省大部分地区大于1,其它地区均小于1。伴随季风雨带的北进南退,层状云发生频率和云量中心均与降水中心对应,且层状云云带与季风雨带位置吻合,随时间的演变趋势也相同,说明季风雨带主要由层状降水构成,对流云发生频率和云量大值中心则位于季风雨带南侧。对流云和层状云发生频率/云量的变化在华南地区和江淮流域呈显著负相关,云的类型主要由大气稳定度决定。对流云和层状云发生频率在华北地区呈显著正相关,水汽是形成云的决定因素。就降水频率而言,华南地区层状云降水和对流云降水各占一定的比例,而江淮流域和华北地区层状云降水频率更大。     

W波段和Ka波段云雷达探测回波对比分析

通过分析W波段和Ka波段云雷达同时探测回波的差异,验证了W波段云雷达初样机的探测性能。结果表明：1）W波段云雷达初样机工作稳定,两个波段雷达都可以探测云层、云的边界、云厚等宏观参数,也可以反映出云的精细结构及云内微物理参数的变化,回波强、速度小、谱宽大的冰晶云含有上升气流及较多过冷水。2）增强模式的W波段云雷达在近地面探测雾、霾的能力比Ka波段云雷达强;两部云雷达对云层较薄的云探测能力基本相当,对多层云、云层较厚、含水量较多的云及降水的探测,由于强衰减的作用,W波段雷达所测云厚度小、云顶低、回波强度小,并且非瑞利散射也会造成W波段雷达的回波强度降低。     

利用三架飞机联合探测资料分析层积混合云催化物理效应

利用2009年4月18日三架飞机联合探测层积混合云资料,结合MICAPS再分析资料、雷达、卫星及地面台站资料等,在准确区分自然云区与催化响应区的基础上,对这次降水性层积混合云的微结构和催化物理响应进行了深入研究。结果表明:云上部(4 800 m层,距云顶1 700 m,距云底3 000 m)累积了云中大部分的过冷水,是云内发展强盛区;云上部嵌入式积云区温度低于周围层云区2℃,积云区含水量分布不均,最大值为1.5 g/m~3,标准差为0.4 g/m~3,而层云区含水量最大值和标准差分别为0.6 g/m~3和0.15 g/m~3,积云区和层云区的云滴谱峰值直径分别为25μm和15μm,云滴数浓度的量级分别为102cm-3和101cm-3。对催化云而言,此次联合探测在4 800 m层捕捉到嵌入式积云区的催化响应,人工播撒Ag I会促进该层云的消散过程,催化后1 h内云区占比由71%降至13%,云中液态含水量持续减少且趋于均匀分布,催化后10 min与20 min云中含水量的最大值分别为1.0 g/m~3和1.5 g/m~3,标准差为0.3 g/m~3和0.15 g/m~3,凇附与聚合增长为主要冰相微物理过程,云滴谱先变窄,后因H-M冰晶凇附繁生而拓宽;在云的中下层则受上层催化影响而产生旺盛云区,10 min内该层云区范围显著扩大,云滴及冰相粒子尺度均增加一倍,同时旺盛云区自上而下扩展。     

一次热带海洋对流云微物理过程的数值模拟

为了理解微物理过程以及次生对流云对热带对流云团发展演变过程的影响,利用二维云分辨模式对2006年1月20日靠近澳大利亚西北部的印度尼西亚暖池附近的一次对流云降水过程进行数值模拟,分析了对流云发展演变不同阶段各种微物理过程的特征,尤其对次生对流的形成以及并合过程进行了深入分析.结果表明:本个例所研究的热带对流云团具有发展...     

The formation of heavy hydrocarbons in molecular clouds

Laboratory data on the conversion of solid methane into large hydrocarbons by particle radiation are used to estimate the fraction of interstellar carbon converted by this process into refractory form. We find that the maximum fraction of carbon that can be converted into refractory form during the life of a dense core within an interstellar cloud is in the range of 1–5 per cent. The implication of this result is that the conversion of enough carbon into refractory form to contribute significantly to interstellar extinction requires the frequent passage of material into and out of dense cores. If so, then interstellar clouds must exist for at least 10 Myr. However, these conclusions should be regarded as preliminary until confirmed by further laboratory studies of the particle irradiation of complex ice mixtures.     

Very Long Baseline Array imaging of a periodic 12.2-GHz methanol maser flare in G9.62+0.20E

The class II methanol maser source G9.62+0.20E undergoes periodic flares at both 6.7 and 12.2 GHz. The flare starting in 2001 October was observed at seven epochs over three months using the Very Long Baseline Array (VLBA) at 12.2 GHz. High angular resolution images (beam size  ∼1.7 × 0.6 mas  ) were obtained, enabling us to observe changes in 16 individual maser components. It was found that while existing maser spots increased in flux density, no new spots developed and no changes in morphology were observed. This rules out any mechanism which disturbs the masing region itself, implying that the flares are caused by a change in either the seed or pump photon levels. A time delay of one to two weeks was observed between groups of maser features. These delays can be explained by light travel time between maser groups. The regularity of the flares can possibly be explained by a binary system.