Attribution of Future Changes in Atmospheric Poleward Energy Transport

We explore annual and seasonal changes in moist static energy transport (MSE) into the Arctic over the 21st century as projected by the National Center for Atmospheric Research Community Climate System Model, version 3 (CCSM3). Self-Organizing Maps (SOMs) are used to assess changes in MSE and its components, the latent heat flux (LH) and dry static energy flux (DSE) across 70N. These are computed from multi-level fields of specific humidity, meridional wind, geopotential, and temperature spanning periods in the 20th century (1960 to 1999) and the 21st century (2070 to 2089). The 21st century simulation incorporates the Special Report on Emission Scenarios A2 scenario. A strong decrease in tropospheric DSE of about 9% by the end of 21st century offsets an increase in LH of about 20% from its 20th century average. The combined changes result in a total annual decrease in tropospheric MSE of about 3% by the late 21st century, thus acting as a negative feedback on Arctic amplification. SOMs also allow an attribution of changes in MSE to factors related to varying atmospheric dynamics and/or thermodynamics. A positive contribution to the MSE related to more frequent low pressure systems in high latitudes (dynamic factor) occurs in all seasons, particularly in the summer. The decrease in DSE is mainly due to a weakened poleward temperature gradient (thermodynamic factor) during all seasons except summer, which in turn is caused by amplified warming at high latitudes as a result of increased greenhouse gases.