Recent increases in surface temperature and snow melt acceleration in the Himalayan region are influenced by many factors. Here we investigate the influence of absorbing aerosols, including black carbon and dust, on surface temperature and snow melt in western, central, and eastern parts of the India-Nepal Himalayan region (INHR). We compare 40-y simulations (1971-2010) one with all evolving forcing agents representative of a present-day aerosol scenario, compared to a low aerosol forcing scenario. The difference between these scenarios shows a significant increase in surface air temperature, with higher warming in parts of Western and Central Himalaya (-0.2-2 degrees C) in the months of April and May. Higher absorbing aerosol (BC and dust abundance) both at the surface and in the atmospheric column, in the present-day aerosol simulations, led to increases in atmospheric radiative forcing and surface shortwave heating rate forcing (SWHRF), compared to the low aerosol forcing case. Therefore, the absorbing aerosols cause anomalous atmospheric heat energy transfer to land due to high surface SWHRF and changes in surface energy flux, leading to snow melt. The present model version did not parameterize snow albedo feedback, which would increase the magnitudes of the changes simulated here. (C) 2021 Elsevier B.V. All rights reserved.

We use Aerosol Robotic Network (AERONET) observation data to empirically determine how natural and anthropogenic aerosol categories (i.e. mineral dust, biomass burning, and urban-industrial aerosols) affect light extinction, showing that their radiative forcing varies strongly with the surface albedo. Generally, the radiative forcing depends on the aerosol loading, but the efficiency varies with the aerosol type and aerosol-radiation-surface interactions. Desert dust, biomass burning and urban-industrial aerosols can exhibit dramatic shifts in radiative forcing at the top of the atmosphere, from cooling to warming, at surface albedos from below 0.5 to above 0.75. Based on the linear relationship between the radiative forcing efficiency and surface albedo for aeolian aerosols, using Moderate Resolution Imaging Spectroradiometer (MODIS) AOT (Aerosol Optical Thickness) and surface albedo data, we characterized a large Asian dust event during the spring of 2001, and demonstrate its immense spatially varying radiative forcing, ranging from about -84.0 to +69.3 W/m(2). For extensive Russian wildfires during the summer of 2010, strong radiative cooling forcing variability of biomass combustion aerosols is found, ranging from about -86.3 to +3.1 W/m(2). For a thick urban-industrial aerosol haze over northern India during the winter of 2017, a large range of about -85.0 to -0.3 W/m(2) is found. These wide ranges underscore the need to accurately define aerosol-radiation-surface interactions.

In order to describe the means, variability and trends of the aerosol radiative effects on the southwest Atlantic coast of Europe, 11 years of aerosol light scattering (sigma(sp)) and 4 years of aerosol light absorption (sigma(sp)) are analyzed. A 2006-2016 trend analysis of sigma(sp) for D < 10 mu m indicates statistically significant trends for March, May-June and September-November, with a decreasing trend ranging from -1.5 to - 2.8 Mm(-1)/year. In the 2009-2016 period, the decreasing trend is only observed for the months of June and September. For scattering Angstrom exponent (SAE) there is an increasing trend during June with a rate of 0.059/year and a decreasing trend during October with - 0.060/year. The trends observed may be caused by a reduction of Saharan dust aerosol or a drop in particle loading in anthropogenic influenced air masses. The relationship between SAE and absorption Angstrom exponent is used to assess the aerosol typing. Based on this typing, the sub-micron particles are dominated by black carbon, mixed black and brown carbon or marine with anthropogenic influences, while the super-micrometer particles are desert dust and sea spray aerosol. The mean and standard deviation of the dry aerosol direct radiative effect at the top of the atmosphere (DRETOA) are -4.7 +/- 4.2 W m(-2). DRETOA for marine aerosol shows all observations more negative than - 4 W m(-2 )and for anthropogenic aerosol type, DRETOA ranges from -5.0 to -13.0 W m(-2). DRETOA of regional marine aerosol ranges from -3 to -7 W m(-2), as it consists of a mixture of sea salt and anthropogenic aerosol. The variability in DRETOA is mainly dependent on AOD, given that variations in backscatter fraction and the single scattering albedo tend to counteract each other in the radiative forcing efficiency equation. The results shown here may help in interpretation of satellite retrieval products and provide context for model evaluation.