Isentropic constraints by midlatitude surface warming on the Arctic midtroposphere

Abstract

AbstractIn simulations of 21st century climate, it is argued that changes in midlatitude near‐surface moisture and temperature could explain the autumn midtropospheric Arctic warming. The argument is based on a comparison between the Arctic midtropospheric warming and theoretical estimates in which synoptic scale transient eddies propagate near‐surface warming anomalies along either dry potential temperature surfaces or equivalent (moist) potential temperature surfaces. In most models, it is observed that the Arctic midtropospheric warming can be obtained from the propagation of midlatitude near‐surface warming anomalies according to a dynamic that is intermediate between the dry and moist theories. While many models follow more closely the moist theory, few follow more closely the dry theory. This finding suggests that, as for the tropical atmosphere, theories of high‐latitude midtropospheric warming based on changes in poleward heat fluxes should include a moist component.