层状云微物理参数反演及其辐射效应的个例研究

A case study on the microphysical parameter retrieval and radiative effects of stratus clouds

利用毫米波云雷达、微波辐射计联合反演方法,对2015年11月11日安徽寿县的一次层状云过程的云参数进行了反演,将所得云参数加入到SBDART辐射传输模式中,进行辐射通量计算,并将计算的地面辐射通量与观测的地面辐射通量进行了对比分析。研究表明:1)利用毫米波雷达和微波辐射计数据联合反演的云参数比较可靠;2)利用SBDART模式并结合反演的云参数,可以准确实时地计算地面及其他高度层的长短波辐射通量;3)在反演的云参数中,光学厚度对地面各种辐射通量的影响是最大的,云层的光学厚度越大,到达地面的太阳短波辐射越小,地面反射短波辐射也越小。另外云底温度越高,云体向下发射的红外长波辐射越大。地面向上的长波辐射是地面温度的普朗克函数,随地面温度而变;4)云对地面的短波辐射强迫为负值,对地面有降温的作用。云对地面的长波辐射强迫是一个正值,对地面有一个增温的作用;5)云对地面的净辐射强迫随时间变化很大,它的正负与太阳高度角和云参数有关。

Clouds typically cover about 60%of the Earth s atmosphere,and this has an important influence on the radiation balance of the Earth s atmosphere system.At the same time,clouds are also one of the most important factors affecting climate change.The net radiation obtained by the ground system and the different heating distributions caused by radiation are strongly affected by cloud.It is important to understand the cloud macro and micro-physical properties in order to study the cloud radiation effects and improve the numerical model parameterization scheme.This paper aims to study the microphysical parameter retrieval of stratus cloud and its radiation effects.The microphysical parameters of the layered cloud mainly include the effective radius,number concentration,liquid water content and optical thickness.Synergetic measurements from mm-wavelength cloud radar and microwave radiometer were used to retrieve the cloud microphysical parameters of stratus case at Shou Country,Anhui Province,China on November 11,2015.The retrievals were coupled into a radiative transfer model,known as SBDART,for cloud radiative effect simulation.SBDART is a software tool that computes plane-parallel radiative transfer under clear and cloudy conditions,both within the Earth s atmosphere and at the surface.All important processes affecting the ultraviolet,visible,and infrared radiation fields are included.The code is a combination of a sophisticated discrete ordinate radiative transfer module,low-resolution atmospheric transmission models,and Mie scattering results for light scattering by water droplets and ice crystals.Shortwave radiation flux and longwave radiation flux comparisons were carried out between the simulations and observations one at the ground surface.The results show the following:1)The retrievals of stratus cloud from the synergetic measurements were reliable.2)The ground-surface shortwave and longwave radiative fluxes can be simulated in real-time with the SBDART radiative transfer model.3)In the cloud parameters of the inversion,the influence of the optical thickness on the radiation fluxes on the ground is the largest.The greater the optical thickness of the cloud is,the smaller the solar shortwave radiation reaching the ground will be,and the smaller the ground reflection shortwave radiation will be.In addition,the higher the cloud temperature is,the greater the infrared long-wave radiation emitted by the cloud will be.The long-wave radiation from the ground is the Planck s function of the ground temperature,which varies with the ground temperature.4)The cloud shortwave radiative forcing is negative with cooling effect on the surface,while the longwave radiative forcing is positive with warming effect on the surface.5)The cloud net radiative forcing at the ground surface changes significantly with time,depending on the solar zenith angle and cloud parameters.