Impacts of Greenland Block Location on Clouds and Surface Energy Fluxes over the Greenland Ice Sheet

Abstract:

Clouds and blocking activity have both been cited as drivers of Greenland Ice Sheet surface melt (e.g., Bennartz et al., 2013; Tedesco et al., 2013). Blocks, or quasi-stationary anticyclones that persist for days to weeks at a time, affect Greenland’s climate by importing warm, moist air from lower latitudes and reducing cloud cover. However, block-induced cloud formation, circulation, and energy fluxes are complicated by the elevated Greenland Ice Sheet. In this study, we combine daily MODIS cloud data and MERRA-2 meteorological and surface energy flux reanalysis data to better understand the impacts of Greenland block location on summertime (i.e., June, July, and August) clouds and surface energy fluxes in 2002-2018. We define block location using four equal-area block quadrants over Greenland. Northern quadrant block days produce cloud fraction and cloud water path reductions four times greater than southern quadrant blocking. Similarly, cloud-induced radiative forcing is more negative for northern quadrant block days. Overall, Greenland-average net surface energy flux changes resulting from blocking range between and for each block quadrant location. Net shortwave energy and sensible heat anomalies are the largest contributors to net surface energy flux changes produced by blocking for all quadrants. Specifically, net shortwave anomalies comprise 50%-60% of total surface energy change during western quadrant block days while sensible heating contributes roughly 50% of total surface energy change during eastern Greenland block days.