| Aerosol mainly influences the Earth’s climate through two pathways, namely aerosol-radiation interaction(ARI) and aerosol-cloud interaction(ACI). Atmospheric aerosol particles can act as cloud condensation nuclei(CCN) or ice nuclei(IN), thereofore variations in aerosol particles condensation, size or chemical composition will lead to changes in micro- and macro-properties of cloud. However, uncertainty in ACI estimate remains one of the large uncertainties in the IPCC AR5 report in term of radiative forcing of climate change. In addition, the difficulty in untangling relationships among the aerosol and clouds reflects the inadequacy of methodologies to account for processes that buffer cloud responses to aerosol perturbations. In the past decades, eastern China has become a hotspot for research related to the effects of aerosols on clouds due to the increasing emission of aerosols and the complexity of aerosol composition. This dissertation intends to extend understanding of the ACI buffering system through aerosol 3D temporal and spatial distribution, competitive role of meteorological conditions to aerosol and aerosol relative position to cloud.Seasonal variation in MODIS/Aqua derived AOD(Aerosol Optical Depth) are compared to aerosol vertical profiles and ground-based PM(Particulate Matter) measurements. AOD is high during spring and summer while the minimum PM2.5 and PM10 concentrations are observed during summertime. Since the satellite derived AOD can be obtained only under clear sky condition, and clouds are common in spring and summer, it results in a decrease in the valid AOD observations. In addition, aerosol vertical distribution has been recognized as one another key factor dictating the correlation between near surface PM concentration and AOD.The aerosol indirect effect has been proved climatically significant after decades of research, albeit still with large uncertainty. This is partially due to the frustrating difficulty in decoupling the aerosol effect from meteorology influences on cloud properties. Monthly AOD and cloud properties co-variability makes this point quite clear. The following statistical analysis reveals an “anti-Twomey” effect over eastern China, as opposed to the aerosol-cloud interaction mechanism that increase in AOD would lead to decreasing of cloud effective droplet radius(CDR) while liquid water path(LWP) held constantly.Further statistical analysis compared ACI over land to ocean with simultaneously observed aerosol and cloud properties from MODIS/Aqua Level 2/Level 3 datasets, and meteorological properties from NCEP Final Analyses Operational Global Analysis datasets. The results reveal the evidence of Twomey’s effect over land, and the response function of cloud properties to aerosol increasing is not monotone. It indicates possible existence of competitive mechanism that larger CDR, irrespective of over land and ocean, can be attributed to the rising motion favoring the growth of cloud droplet..Estimation of ACI is further conducted using near-simultaneous aerosol and warm cloud retrievals from MODIS/AQUA, CALIOP/CALIPSO, and CPR/CLOUDSAT over eastern China. Results indicate that aerosol and cloud layers are vertically separated(or uncertain) in 7.53% of all pixels comparable to 8.95% are vertically mixed. In addition, ACI under mixed condition is nearly four times larger than ACI under separated condition at moderated aerosol loading. However CDR decreased with increasing AOD became saturated at AOD of around 0.5, followed by an increase in CDR with increasing AOD, known as boomerang shape. By categorizing the cases into summer- and winter-season subsets, the results indicate the boomerang shape varied with season. The response of CDR to AOD in summer exhibited similar but much more deepened boomerang shape, as compared with the all year round case. In contrast, CDR in winter did not follow the boomerang shape, and cloud droplet size varies inconsistently after the saturation zone. |
PDF Full Text Request