Tropical Intraseasonal Variability in Models and Observations

Colorado State University, Fort Collins CO

Investigators

Abstract

Understanding tropical intraseasonal variability is an important problem in climate dynamics. The goal of this project is to enhance understanding of the basic dynamics of the Madden-Julian oscillation (MJO). The broader impacts of this effort are very high. In collaboration with NCAR, the PI will incorporate newly developed process-oriented diagnostics into a diagnostics package that will be applied to different versions of NCAR's Community Earth System Model (CESM) to evaluate--and eventually improve--the representation of the MJO. In addition, there will graduate student and postdoc training as well as the development of diagnostic capabilities that could be used by the climate science community to potentially improve model simulations. The leading hypothesis that will be examined in this project is that wind-evaporation and radiative feedbacks are required to destabilize the MJO, in conjunction with weakly positive vertical gross moist stability. It is also hypothesized that horizontal advection is critical to eastward MJO propagation. Specific questions that the proposed work will address include: 1) What combination of processes is responsible for destabilization of the MJO, including vertical advection, surface fluxes, and/or radiative feedbacks? 2) What are the contributions of moisture advection by the mean flow, anomalous flow, and higher frequency disturbances to eastward propagation of the MJO? 3) How do selected process-based metrics inspired by the column-integrated MSE budget relate to model MJO performance, and what do these relationships tell us about MJO dynamics? 4) How does the partitioning of destabilization and propagation factors in the column-integrated MSE budget compare between models and observations, and how do differences in this partitioning relate to model mean state bias?