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Aerosol-cloud-precipitation interactions in the trade wind boundary layer.

机译：商风边界层中的气溶胶-云-降水相互作用。

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摘要

This dissertation includes an overview of aerosol, cloud, and precipitation properties associated with shallow marine cumulus clouds observed during the Barbados Aerosol Cloud Experiment (BACEX, March-April 2010) and a discussion of their interactions. The principal observing platform for the experiment was the Cooperative Institute for Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter (TO) research aircraft that was equipped with aerosol, cloud, and precipitation probes, standard meteorological instruments, and a up-looking cloud radar.;The temporal variations and vertical distributions of aerosols observed on the 15 flights show a wide range of aerosol conditions that include the most intense African dust event observed at the Barbados surface site during all of 2010. An average CCN varied from 50 cm-3 to 800 cm -3 at super-saturation of 0.6 %, for example. The 10-day backward trajectories show that three distinctive air masses (originality of air mass as well as the vertical structure) dominate over the Eastern Caribbean (e.g., typical maritime air mass, Saharan Air Layer (SAL), Middle latitude dry air) with characteristic aerosol vertical structures.;Many clouds in various phases of growth during BACEX are sampled. The maximum cloud depth observed is about less than 3 km and in most of the clouds is less than 1 km. Two types of precipitation features were observed for the shallow marine cumulus clouds with different impacts on boundary layer. In one, precipitation shafts are observed to emanate from the cloud base with evaporation in the sub-cloud layer (stabilize the sub-cloud layer). In the other, precipitation shafts emanate mainly near the cloud top on the downshear side of the cloud and evaporate in the cloud layer, leading to destabilizing the cloud layer and providing moisture to the layer. Only 42-44 % of clouds sampled were purely non-precipitating throughout the clouds; the remainder of the clouds showed precipitation somewhere in the cloud, predominantly closer to the cloud top.;The relationship between aerosol (Na), cloud droplets (N d), and precipitation rates (R) is addressed to explore aerosol-cloud-precipitation interactions. A robust increase in Nd with increase in aerosol concentrations is documented. Further, a strong linear relation between sub-cloud CCN and cloud-base Nd is observed in updrafts. The sensitivity of Nd to changes in vertical velocity perturbations w' (i.e., dlnNd/dlnw'), is greater in the regimes of high aerosol concentrations, suggesting a slight increase in updrafts (or w') in polluted conditions can lead to greater increases in Nd. Suppression of precipitation with aerosol is a common feature during BACEX. To quantify this decrease of precipitation toward higher aerosol concentration, the sensitivity of precipitation to changes in aerosol (i.e., precipitation susceptibility S0) is examined. S0 exhibits three regimes and peaks at intermediate range of cloud thickness. Further, the removal of Nd , due to the rain (wet scavenging), makes susceptibility stronger overall.;In addition to the aerosol feeding clouds from the sub-cloud layer, small cumuli can alter the aerosol properties of their immediate environment through cloud and precipitation processes. In the warm cumuli studied, the depletion of aerosols near cloud field (so-called cloud halos/shell regimes) are notable, and the reduction of aerosols is more significant in precipitating clouds compared with non-and/or light-precipitating clouds.;The modification of boundary layer aerosol by cloud processes is also explored. The comparisons of the thermodynamic structures observed over Africa with those at Barbados indicate that layers below the SAL are moistened by surface fluxes and convective processes as the air masses are advected across the Atlantic over 7-10 days.
机译：本文概述了巴巴多斯气溶胶云实验（BACEX，2010年3月至4月）期间观测到的与浅海积云有关的气溶胶，云和降水特性，并讨论了它们之间的相互作用。该实验的主要观测平台是装有遥控飞机的合作研究所（CIRPAS）双水獭（TO）研究飞机，该飞机配备了气溶胶，云和降水探测器，标准气象仪器和一个向上看的云雷达。 ；在15次飞行中观测到的气溶胶的时间变化和垂直分布显示出广泛的气溶胶状况，其中包括2010年全年在巴巴多斯地表观测到的最强烈的非洲尘埃事件。平均CCN变化范围为50 cm -3 至800 cm -3 的饱和度为0.6％。向后10天的轨迹显示，东加勒比地区有3个独特的气团（气团的原始性和垂直结构）占主导地位（例如典型的海洋气团，撒哈拉气层（SAL），中纬度干燥空气），特征性气溶胶垂直结构。;在BACEX期间，对处于不同生长阶段的许多云进行了采样。观测到的最大云层深度约小于3 km，在大多数云层中，小于1 km。浅海积云对边界层影响有两种类型的降水特征。在一种方法中，观察到降水轴从云层中散发出来，并在亚云层中蒸发（稳定了亚云层）。另一方面，降水轴主要发散在云层下剪切面的云层顶部附近，并在云层中蒸发，从而导致云层不稳定并向该层提供水分。仅有42-44％的采样云在整个云中完全没有降水；其余的云显示在云中的某处降水，主要是靠近云顶。；气溶胶（N a ），云滴（N d ），降水率（R）用于探讨气溶胶-云-降水相互作用。 N d 随气溶胶浓度的增加而强劲增加。此外，在上升气流中观察到亚云CCN与云基N d 之间的强线性关系。 N d 对垂直速度扰动w'（即， dlnN d / dlnw '）的变化的敏感性在较高的气溶胶浓度，表明污染条件下的上升气流（或w'）略有增加，可能导致N d 的增加。在BACEX中，使用气溶胶抑制降水是一个普遍的特征。为了量化降水量向高浓度气溶胶浓度下降的趋势，研究了降水量对气溶胶浓度变化的敏感性（即降水敏感性S 0 ）。 S 0 在云层厚度的中间范围内表现出三种状态和峰值。此外，由于降雨（湿扫气）而去除了N d ，使整体敏感性更强。；除了从亚云层供气雾剂外，小的积云还可以改变气溶胶。通过云和降水过程获得其周围环境的特性。在研究的温暖积云中，值得注意的是云场附近的气溶胶耗竭（所谓的云晕/壳状态），与非和/或光降水云相比，在降水云中气溶胶的减少更为显着。还研究了云过程对边界层气溶胶的改性作用。在非洲和巴巴多斯所观察到的热力学结构的比较表明，随着空气团在大西洋上平流7-10天，SAL下方的各层被表面通量和对流过程弄湿了。

著录项

  • 作者

    Jung, Eunsil.;

  • 作者单位

    University of Miami.;

  • 授予单位 University of Miami.;
  • 学科 Atmospheric Sciences.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 212 p.
  • 总页数 212
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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