气溶胶对不同气象条件下的层积云云量及含水量的影响

Stratocumulus cloud mainly occurs over the ocean and imposes a cooling effect on earth’s climate by reflecting solar radiation. With the increasing human activities, more aerosols are emitted to the atmosphere to act as cloud condensation nuclei. Therefore stratocumulus cloud has an enhanced reflectance of solar radiation. The increased aerosol can also suppress precipitation in stratocumulus cloud, and affect cloud amount and liquid water path, which would further affect the radiative properties of stratocumulus cloud. However, previous studies have shown that the effect of aerosols on cloud amount and liquid water path have a lot of uncertainties. Cloud amount and liquid water path does not necessarily increase when aerosol concentration increases. This is because the aerosol effect on stratocumulus cloud involves complicated feedbacks between cloud microphysics, precipitation, dynamics, and radiation. This project uses a cloud resolving model coupled with bin microphysics to investigate the effects of aerosols on cloud fraction and liquid water path in several stratocumulus cases under different meteorological conditions. The project will focus on the microphysics-precipitation-dynamics-radiation feedbacks, and investigate whether the feedbacks are different under different meteorological conditions. The mechanisms under which aerosols affect stratocumulus cloud will be elucidated. The results from this study will provide the physical basis for the modeling of stratocumulus cloud and its climate effect in climate models.

层积云主要出现在海洋上，通过对太阳光的反射而对全球气候系统具有冷却效应。随着人类活动的加剧，大气中的气溶胶粒子增多，导致层积云对太阳光的反射率增强；气溶胶增多还可以导致层积云降水被抑制，影响云量及含水量,从而进一步影响层积云对太阳光的反射。但是，已有的研究表明气溶胶对层积云云量及含水量的影响具有极大的不确定性，云量及含水量并不一定随着气溶胶的增加而增加。这主要是因为其中包含了复杂的微物理-降水-动力-辐射之间的反馈。本项目针对几个不同气象条件下的层积云个例，利用云分辨模式及云滴分档的微物理模块，研究气溶胶在不同气象条件下对层积云云量和含水量的影响。本项目重点关注层积云中的微物理-降水-动力-辐射过程的反馈，比较不同气象条件下上述反馈机制有何不同，从而揭示气溶胶影响层积云云量及含水量的物理机制，为更好地在气候模式中模拟层积云及其气候效应提供物理基础。

本项目主要研究层积云的云量和含水量受哪些因素影响，以及层积云的垂直结构有什么特点。这些特性决定了层积云的短波反照率以及长波吸收率和放射率。在不同的气象条件下，层积云中的微物理过程，湍流混合过程，降水过程，辐射过程，以及云与下垫面的能量和水汽交换过程，都有所不同，从而在不同程度上影响层积云的云量，含水量，以及垂直结构。本项目对不同气象条件下的层积云进行了研究，包括：副热带及热带海洋上的层积云，中纬度西北太平洋上的层积云，北极地区的混合相态层积云。对各个地区的层积云，本项目采用云分辨模式进行模拟，深入分析了各个物理过程在层积云中的反馈机制。项目的多项研究成果已发表在SCI期刊上，对深入理解层积云的形成机制和气候影响有重要意义。