Cooperative Institute for Research in Environmental Sciences

Attribution of projected changes in atmospheric moisture transport in the Arctic: A self-organizing map perspective

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

2009, Journal of Climate, 22, 4135-4153

We analyze meridonal moisture transport into the Arctic derived from one simulation of the National Center for Atmospheric Research Community Climate System Model (CCSM3) spanning the periods of 1960-1999, 2010-2030 and 2070-2089. The 21st century simulation incorporates the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 scenario for CO2 and sulfate emissions. Modeled and observed (from the European Centre for Medium-Range Weather Forecasting Reanalysis, ERA-40) sea level pressure (SLP) fields are classified using a neural-network technique called self-organizing maps to distill a set of characteristic atmospheric circulation patterns over the region north of 60?N. Model performance is validated for the 20th century by comparing the frequencies of occurrence of particular circulation regimes in the model to those from the ERA-40. The model successfully captures dominant SLP patterns, but differs from observations in the frequency with which certain patterns occur. The models 20th century vertical mean moisture transport profile across 70?N compares well in terms of structure but exceeds observations by about 12% overall. By relating moisture transport to a particular circulation regime, future changes in moisture transport across 70?N are assessed and attributed to changes in frequency with which the atmosphere resides in particular SLP patterns and/or to other factors, such as changes in the meridional moisture gradient. By the late 21st century, the transport is projected to increase by about 21% in this model realization, with the largest contribution (32%) to the total change occurring in summer. Only about a quarter of the annual increase is due to changes in pattern occupancy, suggesting that majority is related to mainly thermodynamic factors. A larger poleward moisture transport likely constitutes a positive feedback on the system through related increases in latent heat release and the emission of longwave radiation to the surface.