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The Influence of Meteorology and Clouds Properties on Downwelling Shortwave and Longwave Irradiance at Ross Island, Antarctica


Understanding the effect of clouds on atmospheric radiative processes affecting downwelling radiation is critical in discerning the causal nature of large-scale melt events in Antarctica. The influence of varying cloud types on solar and terrestrial radiation presents itself as a multifarious problem interwoven within many hierarchical orders of physical interactions across a range of spatial scales. In this work we show how large-scale meteorology leads to advection of moisture over varying terrain, influencing the microphysical properties of clouds and their effect on shortwave and longwave radiation at the Antarctic surface.

Synoptic circulation patterns over West Antarctica (WA) were grouped and categorized by Scott et al. 2018 into four recurring meteorological regimes using k-means cluster analysis of daily 700 hPa geopotential height fields. Regime 1 is representative of warm surface air temperature, and moist marine air advection over WA with liquid-bearing and classical liquid-dominated mixed-phase clouds. Regime 2 is characterized by large-scale subsidence, outflow of continental polar air, and anomalously clear skies. Regime 3 is of smaller sample size, and produces similar surface radiative flux levels to those of Regime 1. Regime 4 is distinguished by an orographic influence upstream of Ross Island, resulting in the formation of geometrically thick, mixed-phase clouds.

This study focuses on the radiative differences in downwelling shortwave and longwave irradiance by comparing prevailing meteorological regimes and cloud properties therein. The influence of supplemental ice absorption on downwelling shortwave flux is highlighted when comparing cloud optical depth properties of Regime 4 to that of Regime 1 and 2. The influence of cloud base temperature on downwelling longwave flux is noted when comparing cloud optical depth properties of Regime 2 to that of Regime 1.

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