Cloud optical and microphysical properties derived from ground-based and satellite sensors over a site in the Yangtze Delta region

Jianjun Liu,^1,2,3 Zhanqing Li,^1,2 Youfei Zheng,³ J. Christine Chiu,⁴ Fengsheng Zhao,² Maria Cadeddu,⁵ Fuzhong Weng,⁶ and Maureen Cribb²

¹ State Laboratory of Earth Surface Process and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing, China;

² Department of Atmospheric and Oceanic Science and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, USA;

³ Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Nanjing University of Information Science and Technology, Nanjing, China;

⁴ Department of Meteorology, University of Reading, Reading, UK;

⁵ Argonne National Laboratory, Lemont, Illinois, USA;

⁶ NOAA/Center for Satellite Applications and Research, College Park, Maryland, USA.

Abstract: Comprehensive surface-based retrievals of cloud optical and microphysical properties were made at Taihu, a highly polluted site in the central Yangtze Delta region, during a research campaign from May 2008 to December 2009. Cloud optical depth (COD), effective radius (R_e), and liquid water path (LWP) were retrieved from measurements made with a suite of ground-based and spaceborne instruments, including an Analytical Spectral Devices spectroradiometer, a multifilter rotating shadowband radiometer, a multichannel microwave radiometer profiler, and the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua satellites. Retrievals from zenith radiance measurements capture better the temporal variation of cloud properties than do retrievals from hemispherical fluxes. Annual mean LWP, COD, and Re are 115.8 ± 90.8 g/m², 28.5 ± 19.2, and 6.9 ± 4.2 μm. Over 90% of LWP values are less than 250 g/m².Most of the COD values (>90%) fall between 5 and 60, and ~80% of R_e values are less than 10 μm. Maximum (minimum) values of LWP and R_e occur in summer (winter); COD is highest in winter and spring. Raining and nonraining clouds have significant differences in LWP, COD, and R_e. Rainfall frequency is best correlated with LWP, followed by COD and R_e. Cloud properties retrieved from multiple ground-based instruments are also compared with those from satellite retrievals. On average, relative to surface retrievals, mean differences of satellite retrievals in cloud LWP, COD, and R_e were -33.6 g/m² (-26.4%), -5.8 (-31.4%), and 2.9 μm (29.3%) for 11 MODIS-Terra overpasses and -43.3 g/m² (-22.3%), -3.0 (-10.0%), and -1.3 μm (-12.0%) for 8 MODIS-Aqua overpasses, respectively. These discrepancies indicate that MODIS cloud products still suffer from large uncertainties in this region.