Séminaire
Our day-to-day experience with the weather could lead us to believe that wind is unpredictable and chaotic. However, when looked upon on larger scale, the atmosphere exhibits a well-defined global circulation. This circulation plays a key role in the climate system by transporting energy and water around the Earth, preventing the Poles from becoming too cold and the equatorial regions too warm. To describe the large-scale atmospheric, it is common to consider the zonal and time average circulation.
However, the mean circulation depends critically on how the averaging is done and, in particular, on the choice for the vertical coordinate system. For instance, when the circulation is averaged on surface of constant geopotential height, it exhibits a three-cell structure in each hemisphere, with a direct Hadley cell in the tropics, a reverse Ferrel cell in the midlatitudes, and a weak direct cell in the polar region. In contrast, when the circulation is averaged on isentropes -- defined as surfaces of constant potential temperature -- it exhibits a single equator-to-pole cell.
In this talk, I will review the circulation patterns that emerge from averaging the circulation in different coordinate system, show that these differences can provide new insights on the behavior of the atmosphere, and discuss a new mathematical framework to compute the averaged circulation in an arbitrary coordinate system.
Guillaume Lapeyre, LMD/IPSL