Recent changes in tropospheric water vapor over the Arctic

We examine recent changes in tropospheric water vapor over the Arctic for the period 1979 to 2009. Our study makes use of humidity and temperature profiles from 46 Arctic stations contained in the Integrated Global Rawinsonde Archive (IGRA), and humidity and temperature fields from the new NASA MERRA atmospheric reanalyses. Pentad mean atmospheric cross sections of anomalies in specific humidity from MERRA for autumn point to an emerging pattern of higher near surface humidity, strongest at about 70 degrees north latitude in the zonal mean. At longitudes surrounding the prime meridian, this increase corresponds to the northern end of the North Atlantic cyclone track. At longitudes surrounding the dateline, the increase corresponds to anomalous open water where downward trends in end-of-summer sea ice extent have been especially pronounced. Evidence of increasing humidity from the rawinsonde data is not as clear; precipitable water from the surface to the 850 hPa level has increased at some stations but few of the trends are statistically significant. Time series for many stations are quite noisy. Stations are necessarily land based and provide no information over the central Arctic Ocean.