Special ClimaTea Lecture


Tuesday, May 3, 2016, 12:00pm


Hoffman Faculty Lounge

This Tuesday, Lei Wang will speak on Intra-seasonal periodicity behavior of finite-amplitude wave activity in the mid-latitude troposphere. Lei says the following about his talk:

"Intra-seasonal atmospheric variability is a prediction gap between weather and climate predictions, and is important for skillfully predict high-impact extreme events such as blocking. Variations in jet stream are primarily driven by atmospheric synoptic eddies that cannot be easily quantified by traditional linear theory. Using theory of finite-amplitude wave activity (FAWA), we develop a new zonal momentum-wave activity cycle, as a counterpart of global energy cycle (Lorenz 1955), but with several advantages for climate diagnostics such as providing quantitative assessment of eddy forcing.

In midlatitude austral summer, the zonal momentum-wave activity cycle reveals a largely adiabatic, antiphase covariation of FAWA and the mean flow. A marked periodicity is found for FAWA around 20–30 days, consistent with the recently discovered Baroclinic Annular Mode by Thompson and collaborators. Analysis of the ERA-Interim product reveals that the 20-30 day periodicity in FAWA and eddy heat flux is robust only during the warm season. A series of idealized AGCM are shown to reproduce qualitatively a BAM-like eddy heat flux spectrum only if the zonal-mean state resembles that of the austral summer, which points to an important consequence of the basic state bias in climate simulations. A two-layer quasi-geostrophic model is adopted to illustrate a theory of this periodicity.  I will also discuss the implications of the framework for atmospheric finite-amplitude wave variability in a changing climate."