Aerosol direct radiative forcing (ADRF) has substantial impacts on regional and global climate changes, whereas it remains one of the largest uncertainties among various climate forcing factors. The 40-year detailed clear-sky ADRFs over China from 1981 to 2020 are systematically studied based on the MERRA-2 satellite reanalysis data, which hopefully benefit for the evaluation of the performances of aerosol-climate models. The clear-sky short-wave ADRFs show diverse spatial distributions with strong top of atmosphere (TOA) and surface cooling and atmospheric heating over the Taklamakan desert, eastern China, and southern China. A high clear-sky longwave surface ADRF reaching-6.5 W/m2 over dust source regions is found, and continuous increase of ADRFs over the Taklamakan desert during the past four decades may indicate that dust episodes therein are becoming severe. The mean clear-sky shortwave surface, TOA and atmospheric ADRFs, and longwave surface ADRF over China during 1981-2020 are found to be-12.3,-5.1, 7.2, and 1.0 W/m2, respectively. The seasonality of clear-sky ADRFs shows strongest mean values in spring, moderate forcings in summer and fall, and weakest levels in winter. The monthly average clear-sky surface and TOA ADRFs over China vary by approximately twofold, ranging the weakest values of-7.8 and-3.9 W/m2 in December to the strongest-17.6 and-7.1 W/m2 in April, respectively. Distinctive seasonal and monthly patterns of clear-sky ADRFs are generally seen among the Beijing -Tianjin-Hebei region, Yangtze River Delta, Pearl River Delta and Tarim Basin in China, while the monthly ADRF patterns over a typical area of these four regions are similar during four different decades. The clear-sky ADRFs over China are highly correlated with aerosol optical thickness, and dust has strong influences on clear-sky shortwave aerosol direct radiative forcing among column aerosol compositions. Our study indicates general underestimations of clear-sky atmospheric ADRF over China by aerosol-climate models and stronger impacts of aerosol scattering than absorption on the TOA radiation budgets in China.

The study examines the thermodynamic structure of the marine atmospheric boundary layer (MABL) and its effect on the aerosol dynamics in the Indian Ocean sector of Southern Ocean (ISSO) between 30 degrees S-67 degrees S and 57 degrees E-77 degrees E. It includes observations of aerosols and meteorology collected during the Xth Southern Ocean Expedition conducted in December 2017. The results revealed the effect of frontal-region-specific air-sea coupling on the thermodynamic structure of MABL and its role in regulating aerosols in ISSO. The MABL over the subtropical front was unstable and formed a well-evolved mixed layer ( 2400 m) capped by low-level inversions ( 660 m). Convective activities in the Sub-Antarctic Frontal region were associated with the Agulhas Retroflection Current, which supported the forma-tion of a well-developed mixed layer ( 1860 m). The mean estimates of aerosol optical depth (AOD) and black carbon (BC) mass concentrations were 0.095 +/- 0.006 and 50 +/- 14 ng m-3, respectively, and the resultant clear sky direct shortwave radiative forcing (DARF) and atmospheric heating rate (HR) were 1.32 +/- 0.11 W m-2 and 0.022 +/- 0.002 K day-1, respectively. In the polar front (PF) region, frequent mid-latitude cyclones led to highly stabilized MABL, supported low-level multi-layered clouds (>3-layers) and multiple high-level inversions (strength > 0.5 K m-1 > 3000 m). The clouds were mixed-phased with temperatures less than -12 degrees C at 3000 m altitude. Interestingly, there was higher loading of dust and BC aerosols (276 +/- 24 ng m-3), maximum AOD (0.109 +/- 0.009), clear sky DARF (1.73 +/- 0.02 W m-2), and HR (0.029 +/- 0.005 K day-1). This showed an accumulation of long-range advected anthro-pogenic aerosols within baroclinic-boundaries formed over the PF region. Specifically, in the region south of PF, weak convection caused weakly-unstable MABL with a single low-level inversion followed by no clouds/single-layer clouds. Predominant clean maritime air holding a small fraction of dust and BC accounted for lower estimates of AOD (0.071 +/- 0.004), BC concentrations (90 +/- 55 ng m-3) and associated clear sky DARF and HR were 1.16 +/- 0.06 W m-2 and 0.019 +/- 0.001 K day-1, respectively.