Attribution of Seasonal and Regional Changes in Arctic Moisture Convergence

Abstract

Spatial and temporal changes in high-latitude moisture convergence simulated by the National Center for Atmospheric Research Community Climate System Model, version 3 (CCSM3) are investigated. Moisture convergence is calculated using the aerological method with model fields of specific humidity and winds spanning the periods from 1960 to 1999 and 2070 to 2089. The twenty-first century incorporates the A2 scenario from the Special Report on Emissions Scenarios. The model?s realism in reproducing the twentieth-century moisture convergence is evaluated by comparison with values derived from the 40-yr ECMWF Re-Analysis (ERA-40). In the area north of 75°N, the simulated moisture convergence is similar to observations during summer, but it is larger in winter, spring, and autumn. The model also underestimates (overestimates) the mean annual moisture convergence in the eastern (western) Arctic. Late twenty-first century annual, seasonal, and regional changes are determined by applying a self-organizing map technique to the model?s sea level pressure fields to identify dominant atmospheric circulation regimes and their corresponding moisture convergence fields. Changes in moisture convergence from the twentieth to the twenty-first century result primarily from thermodynamic effects (?70%), albeit shifts in the frequency of dominant circulation patterns exert a relatively large influence on 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 increasing anthropogenic greenhouse gas emissions as prescribed by the A2 scenario.