Characteristics of cloud cover and its radiative impacts over the high elevations of the Greenland ice sheet

Understanding the effects of clouds on the surface energy balance is a necessary part of understanding the controls on the mass balance of the Greenland ice sheet. Clouds have an enhanced role in governing the surface energy balance in dry polar atmospheres, yet their frequency, thermodynamic properties and radiative properties are poorly quantified over Greenland. In response to this important data gap, this research quantifies cloud occurrence and cloud radiative effects over the high plateau of Greenland using a unique new cloud data set. This data set is comprised of ground-based, high frequency cloud sky fraction and height measurements and high accuracy surface radiation measurements. Combined, they permit an unprecedented level of detail in the evaluation of the net radiative effect of cloud cover at the surface. This research also employs the MODIS cloud mask data set (MOD35) to quantify cloud frequency for a four-year period (March 2000--2004) over the high plateau of the Greenland ice sheet. This research contributes to our understanding the cloud climate of the high plateau of the Greenland ice sheet and the role of clouds in the surface energy balance in this environment. Both are useful contributions for improving regional climate modeling of Greenland.; The results of this research demonstrated that MOD35 is a useful tool for assessing cloud cover frequency over Greenland. During daylight hours, the accuracy of the cloud mask ranged from -7 to +12%. Using MOD35, this research showed that May is the most cloud free month of the year (27%) while August, excluding the winter range of errors, is the cloudiest (55%). Using high resolution radiation and cloud measurements, this research found that the radiative impact of clouds is positive for all hours of the day and all months of the year at Summit. Comparing hourly GC-Net radiation data and MOD35 cloud data, this research showed that the net radiative effect of clouds ranges from -20 W/m2 to 35 W/m2 over the high elevations of the Greenland ice sheet at midday during JJA. The strongest negative impact is found over South Dome; the strongest positive impact is found over NE Greenland.