MASS Seminar – Olivier Pauluis (Courant) – Circulation On Moist Isentropes And The Extra-tropical Tropopause

Monday October 15, 2012 8:00 am

Title: Circulation on moist isentropes and the extra-tropical tropopause

Abstract: The global atmospheric circulation acts to transport energy from the equatorial regions to the higher latitudes. Such an energy transport requires an actual mass transport, which can be further characterized by analyzing the circulation in isentropic coordinates. However, due to the treatment of water vapor in the definition of entropy, one can obtained distinct sets of isentropic surfaces and their corresponding circulation. Here, I compare the circulation averaged on 'dry' isentropes, defined as surfaces of constant potential temperature, and the circulation averaged on 'moist' isentropes defined as surface of constant equivalent potential temperature. In the midlatitudes, the mass transport on moist isentropes is twice as large as that on dry isentropes. This additional mass transport corresponds to a poleward flow of warm moist air near the surface that rises in the upper troposphere. I will also argue this ascent of moist air within the stormtracks determine the potential temperature of the extra-tropical tropopause.