Recent Changes in Tropospheric Water Vapour of the Arctic

We examine recent changes in tropospheric water vapor over the Arctic for the period 1979 to 2009. The past decade has seen pronounced rises in surface and lower tropospheric air temperatures over the Arctic in autumn and winter that are larger than the warming for the northern hemisphere as a whole. Assessment of the satellite record of Arctic sea ice extent reveals downward trends in all months with the largest trends at the end of the melt season in September (11% per decade through 2009). Since 2002, each September has seen extreme minima, with a record low set in September 2007. A recent synthesis of the observational record for the pan-Arctic terrestrial drainage points to increases in annual precipitation, evapo-transpiration, and river discharge to the Arctic Ocean. While this apparent intensification of the Arctic hydrologic cycle is broadly consistent with expectations from simulations with coupled global climate models, the intrinsic variability and lack of consistency in observed trends limits confidence in the robustness of the changes. Our study makes use of humidity and temperature data from radiosondes and from the NASA MERRA and JRA-25 reanalyses. We emphasize anomalies in precipitable water and specific humidity at various atmospheric levels for the most recent decade (2000-2009) compared to a baseline period 1979-2009, and evaluate seasonal and interannual variability over the entire 30 year time period.