Optical Properties Of Single-phase Clouds Derived From Ground-based Remote Sensing In Taihu Area

Cloud plays a critical role in climate change and the energy budget of the plant. Under most conditions, to estimate its impact on radiative flux and climate change always need its optical properties.However, only few work about cloud optical properties in China especially in Taihu area where the aerosol content in a high value have been done yet and the results from satellite observation have to be verified by using ground-based sensing measurement.Therefore, it becomes much more important to retrieve cloud optical properties in such area. Based on the remote sensing measurement from Taihu mobile Site of Nanjing University of information Science and Technology and combined with SBDART model,1-year data of Multifilter Rotating Shadowband Radiometer(MFRSR), Micro-pulse Lidar(MPL), Total Sky Imager(TSI), Microwave Profiling Radiometer(MWR) have been used to derive thin (including ice cloud and water cloud) and thick cloud optical and microphysical properties using different approaches. The results indicated that (1) the cloud information can be distinguished from aerosol by giving the Angstrom exponetn a threshold which computed from the solar direct beam mearsured from MFRSR. After defining the cloud phase form MPL data, thin cloud optical depth can be retrieved using different parameter schemes.3 cases have been discussed in this paper and the results showed that the cloud optical depth(COD) increases from the edgy to the center of the cloud in both ice and water cloud case. However, the COD of water cloud case shows somewhat lager than the ice ones because of its better continuity. (2) Radiant energy budget under cloud situation can be simulated from SBDART model, then a Lookup Table of total solar radiance, COD, solar zenith angel and effective radius can be built based on the result, from this, the optical depth of thick cloud can be derived if the total solar radiance has already been measured from MFRSR.The results from thick cloud case in Taihu area indicates that the average of COD in that day is about 20.3 and can reach 40 when the cloud stage changes.(3)The results from SBDART model have been verified from Liquid water path(LWP) data which derived from MWRP measurement.The average of LWP in thick cloud case is about 0.35mm and can grow to 0.6mm while the optical depth shows the highest value.Based on the LWP and effective radius, COD of thick cloud has been retrieved and its average is about 24.3, same as whick simulated from SBDART.The differences occur at the period where the solar zenith angel are somewhat great.