Surface-based Measurements on Aerosol First Indirect Effects over a Site in Southeastern China

Abstract:

The first comprehensive insights of the aerosol first indirect effects (FIE) in southeastern China were examined based on the ground-based measurements during the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) campaign in Shouxian (SX) from May to December 2008. During our study period, aerosol burden is larger in summer (JJA) and during the morning period (AM) than in autumn (SON) and during the afternoon period (PM). More clouds with the larger COD and LWP in SON and AM than those in JJA and PM, with the larger cloud droplet radius (DER) in SON and PM than those in JJA and AM. Generally, obviously opposite relationship between the mean aerosol loading proxies (aerosol scattering coefficient (σ_s), horizontal visibility), and DER were detected. High aerosol loading leads to a shift in the probability distribution functions of DER toward smaller values and results in the narrow distribution of DER. For whole period, the value of FIE is 0.15 and 0.09 for the clouds with LWP ranging from 75-100 g m^-2 and 125-150 g m^-2, respectively, which indicated that the disturbance of aerosol on cloud significantly weaken with the LWP increasing. There is no significant difference in FIE estimation between AM and PM, while the FIE is generally larger in SON than that in JJA. The FIE estimated based on the cloud condensation nuclei concentration is larger than that based on the optical-related aerosol properties, such as σ_s and scattering wavelength index. Use of the σ_s alone, without aerosol size information, tends to underestimate the magnitude of FIE than use of the combination of σ_s and size information. Compared with the result from surface measurements, the effects of aerosol on cloud microphysical properties estimated from MODIS are weaker and affected by much more noises, implying that the studies of aerosol indirect effect based on the satellite measurements may induce large uncertainties due to some inherent insufficient.