Cooperative Institute for Research in Environmental Sciences

Attribution of seasonal and regional changes in Arctic moisture convergence

Skific, N., J.A. Francis, and J.J. Cassano

2009, Journal of Climate, 22, 5115-5134

We investigate spatial and temporalchanges in high-latitude moisture convergence simulated by the National Center for Atmospheric Research Community Climate System Model, version 3 (CCSM3). Moisture convergence is calculated using the aerological method with model fields of specific humidity, zonal and meridional winds spanning the periods from 1960 to 1999 and from 2070 to 2089 (the 21st centuryincorporates the Special Report on Emissions Scenarios A2 scenario for carbon and sulfate emissions). The models realism in reproducing the 20thcentury moisture convergence isevaluated by comparison with values derived from the European Centre for Medium Range Weather Forecastsreanalysis (ERA-40). In the area north of 75?N we find that summer moisture convergence is similar to observations, but the model generally overestimates it in winter, spring and autumn. The model also underestimates (overestimates) long-termmean annual moisture convergence in the eastern (western) Arctic. Late 21st century regional, annual, and seasonal changes are determined by applying a self-organizing map technique to the models sea-level pressure fields to identify dominant atmospheric circulation regimes and their corresponding moisture convergence fields. Changes in moisture convergence from the 20th to the 21st centuryprimarily result from thermodynamic effects (~70%), albeit shifts in the frequency of dominant circulation patterns drive future changes in the Eastern Arctic. Increased moisture convergence in the central Arctic (North Atlantic) stems mainly from thermodynamic changes in summer (winter). Changes in the strength and location of poleward moisture gradients are most likely responsible for projected variations in moisture transport, which are in turn a consequence of anthropogenic climate change.