Cloud Halos and their Roles in the Atmospheric Radiation Balance and Climate

最近的观测表明，不断增长的积云周围的空气有时几乎被水蒸气饱和。计算表明，云周围的这些蒸汽罩或“光晕”可以解释太阳辐射吸收的显著增加。该项目的目的是高精度和高分辨率地测量积云周围的蒸汽场，并利用这些信息计算辐射传输和评估云-环境相互作用对云微物理的影响。具体目标如下：-测量对流云内部和周围的蒸汽场，并获得足够的细节，以表征相对于云边缘的三维蒸汽结构；-同时测量云晕内气溶胶的大小分布、组成和光学性质；-分析由此产生的测量结果，以便提供几个完整记录的案例，用于辐射转移计算；-进行辐射传输分析，包括计算水汽、气溶胶和云的吸收和升温速率；-确定辐射分析对气候模式的影响。测量将由CIRPAS双水獭飞机进行，该飞机配备了Aerodyne研究公司开发的一种名为“快速水蒸气监测器”的新仪器，以及测量气溶胶、CCN、云滴和液态水含量的仪器。不同复杂程度的计算机代码将用于辐射传递计算。这些结果涉及到反常云吸收问题，反常云吸收是指云对太阳的吸收与用Mie散射理论计算的云滴总体的吸收之间的差异。这是加州理工学院和Aerodyne研究公司的合作研究项目。此次合作的Aerodyne组件由ATM-9910744， John T. Jayne博士，PI提供支持。

Recent observations indicate that the air surrounding growing cumulus clouds is sometimes nearly saturated with water vapor. Calculations show that these vapor shrouds or "halos" around clouds can account for a significant increase in the absorption of solar radiation. The purpose of this project is to measure the vapor field around cumulus clouds with high accuracy and resolution and to use the information in calculations of radiative transfer and in assessing the consequences of cloud-environment interactions on cloud microphysics. The specific objectives are as follows:- To measure the vapor field in and around convective clouds with sufficient detail to characterize the 3-dimensional vapor structure relative to cloud edges;- To measure concurrently the size distribution, composition, and optical properties of aerosols within the cloud halo;- To analyze the resulting measurements in order to provide several completely documented cases for use in radiative transfer calculations;- To carry out radiative transfer analyses including absorption and heating rate calculations for the observed distributions of water vapor, aerosols, and cloud;- To determine the implications of the radiation analysis for climate modeling.The measurements will be conducted with the CIRPAS Twin Otter aircraft, equipped with a new instrument called the Fast Water Vapor Monitor developed by Aerodyne Research along with instruments for measuring aerosols, CCN, cloud droplets, and liquid water content. Computer codes with different degrees of complexity will be used for the radiative transfer calculations. The results bear on the question of anomalous cloud absorption, which refers to the discrepancies that have been observed between the observed solar absorption by clouds and the absorption calculated using Mie scattering theory applied to populations of cloud drops. This is a collaborative research project between Cal Tech and Aerodyne Research, Inc. The Aerodyne component of the collaboration is supported by ATM-9910744, Dr. John T. Jayne, PI.