The temporal variation of PM_2.5 concentration in Beijing, Shanghai and Lhasa in 2015 is investigated. Then, the analyses on their seasonal variation and comparison of the relative importance of diurnal variation and daily variation are conducted. Results show that the PM_2.5 concentration is generally higher in winter than that in summer from a long-term view. From a short-term view, the variation of PM_2.5 concentration in Beijing and Shanghai mainly demonstrates interdiurnal feature, and the synoptic systems exert profound impacts. The wintertime PM_2.5 concentration in Beijing also displays diurnal variation, but it is not evident in summer. In Shanghai, the diurnal cycle is not significant in both winter and summer. On the contrary, the synoptic system over Lhasa is stable. The daily variation is weak, while the diurnal variation is strong. The variation of PM_2.5 concentration is hence featured by two peaks.

Cloud occurrence frequency (COF, the ratio between the number of records with detected clouds with respect to the total available records) and the distribution of COF within one day below 8 kilometers in summer from 2007 to 2009 over Beijing is studied. Cloud base height (CBH) of one layer clouds, the characteristics of convective CBH and the relationship between convective CBH and relative humidity (RH) measured on the surface are further studied. Results show that cloud occurrence frequency is about 12% in summer over Beijing. Clouds are more likely to occur at night than in the afternoons. The distribution of CBH has one peak at 700 (±50) meters and low clouds (ranging up to 3000 meters) account for 82% of all clouds. Convective CBH ranges from 400 to 2000 meters for the cases studied, but do not vary much within each day. CBH can be conveniently derived from linear relationship between CBH and surface RH based on Adiabatic Parcel Model. Mean relative standard deviation of CBH is 0.321.

The authors use the detrended fluctuations analysis (DFA) to analyze the ISCCP cloud amount data at four locations: Beijing, Shanghai, Western Pacific, and Eastern Pacific. It is found that cloud amount indeed has power-law correlation in large time scales, which indicates that the cloud amount has strong long-term correlation in the locations studied. The crossover over the ocean appears later than that over the continent.The long-term correlation of the the cloud amount over the Western Pacific is stronger than the Eastern Pacific’s.

Large eddy simulations were used to get profiles of liquid water content and droplet effective radius in shallow cumulus clouds. Results show that both liquid water content and droplet effective radius increase with height (vertically inhomogeneous). Then the atmospheric radiative transfer model SBDART were used to study the effects of vertical distributions of microphysical properties on radiative transfer. The shortwave radiative forcings from a vertically inhomogeneous cloud and a vertically homogeneous cloud with the same liquid water path were compared. Results indicate that vertical distributions of microphysical properties have significant effects on radiative transfer. When droplet effective radius of the vertically homogeneous cloud is equal to 76% -90% of the cloud-top droplet effective radius in a vertically inhomogeneous cloud, the two clouds have similar radiatve forcing. This means that in global climate models, the assumption of vertical homogeneity of a cloud must be used carefully and the associated droplet effective radius must be about 76% -90% of the observed value at cloud top for shallow cumulus clouds. Results in this study are consistent with previous studies for stratified clouds.