Clear-sky thermodynamic and radiative anomalies over a sea ice sensitive region of the Arctic

Monthly clear-sky anomalies of atmospheric temperature and water vapor over the East Siberian Sea and Laptev Sea regions of the Arctic for 2003-2010 are examined. This region experiences significant inter-annual variations in sea ice concentration and is also where ice loss was most apparent in the record year 2007. Clear-sky thermodynamic profiles come from the Atmospheric Infrared Sounder (AIRS) sensor onboard the Aqua satellite. Associated longwave (LW) and shortwave (SW) radiation-flux anomalies are estimated through radiative transfer modeling. Anomalies of temperature (± 10 K) and water vapor (± 1 g kg-1) often positively co-vary, resulting in distinct signatures in the downwelling LW (LWD) anomalies, occasionally larger than ± 10 W m-2 above the 2003-2010 climatology. Estimates of mean greenhouse anomalies indicate a shift from negative to positive anomalies mid-way through the 8-year record. Sensitivity tests suggest that temperature anomalies are the strongest contributor to both LWD and greenhouse anomalies, relative to water-vapor anomalies; monthly averaging of column precipitable water yields relatively small anomalies (order 1 mm) that produce a linear response in greenhouse anomalies. Finally the clear-sky contribution to 2007 monthly ice thickness is estimated. Anomalous clear-sky radiation retards the total 2007 ice thickness by 0.3 m (15-30 % of ice-thickness climatology), and anomalous LW radiation is most important for preconditioning the ice during the months prior to, and after, the summer melt season. A highly-sensitive interaction between cloud fraction, surface albedo and LWD anomalies is found, and we develop a metric for determining clear-sky anomalous ice melt potential.