Can aerosol loading explain the solar dimming over the Tibetan Plateau?

Abstract

[1] Solar radiation over the Tibetan Plateau has declined over recent three decades, whereas total cloud cover has a decreasing trend. A likely explanation to this paradox is the increase in aerosols over this clean region. However, this study shows that the radiation extinction due to aerosol loading is of one order lower in magnitude than the observed dimming, and the solar dimming is also seen in a satellite product that was produced without considering temporal variations of aerosols. Instead, the inter-annual variability and decadal change in solar radiation is contrasting to that in water vapor amount and deep cloud cover (but not total cloud cover). Therefore, we suggest that the solar dimming over the Plateau is mainly due to the increase in water vapor amount and deep cloud cover, which in turn are related to the rapid warming and the increase in convective available potential energy.

Impacts of 3D Aerosol, Cloud, and Water Vapor Variations on the Recent Brightening during the South Asian Monsoon Season

“…The SSR in clear-sky conditions from CloudSat increased by approximately 4.8 W m −2 (p = 0.05). Except for the contribution of water vapor variations, this radiative change was possibly caused by the change in atmospheric conditions and the incoming solar radiation provided by ECMWF-AUX and CloudSat [52]. The spatial variation in SSR in the clear-sky conditions was highly negative and consistent with that of PW (Figures 6d and 7b), especially in the western and central regions of South Asia, which partly consists of deserts.…”

“…Furthermore, the indirect effects of water vapor occur in the all-sky conditions, and such effects are called water vapor-cloud interaction. Generally, a high concentration of water vapor favorably generates additional or robust convective clouds and results in decreased radiation at the surface, and vice versa [52]. Moreover, water vapor also regulates cloud amount by affecting the aerosol-cloud interaction, which generally shows a positive relationship under moist atmospheric conditions [53].…”

“…The SSR in clear-sky conditions from CloudSat increased by approximately 4.8 W m −2 (p = 0.05). Except for the contribution of water vapor variations, this radiative change was possibly caused by the change in atmospheric conditions and the incoming solar radiation provided by ECMWF-AUX and CloudSat [52]. Due to the intrinsically positive association of water vapor and clouds, we focus mainly on the effect of water vapor on solar radiation in clear-sky conditions to restrict the disturbance from clouds.…”

Reconstruction of the mass balance of Muztag Ata No. 15 glacier, eastern Pamir, and its climatic drivers

“…During the periods of 1998-2012, the intensified meridional flow transported more water vapor to the TP (Gao and others, 2013;Lu and others, 2015). The warming and moistening increased atmospheric instability, which triggered vertical mixing, thicker cloud cover and more precipitation (Yang and others, 2012).…”

“…In addition, it can be deduced that a change in the amount of snowfall for these regions was mainly the result of changes in the amount of precipitation based on the above statements. With increases in precipitation in the main precipitation seasons (Hewitt, 2005;Yao and others, 2012;Kapnick and others, 2014;Zhang and others, 2017), such as in winter in the Karakoram, and in the ablation season in the Muztag Ata region, this leads to increases in snowfall and further decreases in melt energy in the ablation season due to increasing albedo under warming and and others, 2016), the mean air temperature was higher during 2001-2012than 1970(Zhang and others, 2017. This means that a greater mass loss occurred during the period of 2001-2012 than during 1970-2000 for these regions, which was in contrast with the observed regional glacier changes.…”