Intraseasonal Variability of the West African Monsoon

Colorado State University, Fort Collins CO

Investigators

Abstract

The Madden-Julian Oscillation (MJO) modulates tropical cyclones and easterly waves in the Atlantic, providing the potential for prediction of enhanced Atlantic hurricane activity a couple of weeks in advance. This project will address several major outstanding questions: (i) the teleconnection pathway by which the MJO affects the Atlantic during boreal summer, (ii) how west African and Atlantic precipitation is actually initiated by the MJO once the teleconnection is established, (iii) the mechanism by which the MJO modulates African easterly waves, and (iv) how these easterly waves feed back to influence the MJO. A hierarchy of models will be used to understand the teleconnection pathways by which the MJO affects the Atlantic and west Africa, including the non-divergent barotropic vorticity equation, a filtered shallow water model on a sphere, and an atmospheric general circulation model. Because it is hypothesized that the MJO first initiates convection anomalies over the Darfur region of the Sudan, several observational products (e.g. Cloud Archive User Service (CLAUS) brightness temperature, Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Climatology Project (GPCP) precipitation) will be used to document the time evolution of precipitation in west Africa as a function of MJO phase. A primitive equation model will be used to test the hypothesis that strong heating variations over the Darfur region forced by the MJO modulate the amplitude of easterly wave activity in west Africa and the Atlantic, and test the hypothesis that MJO-related structural changes in the African easterly jet significantly affect easterly wave growth. Further, the impact of MJO-related easterly wave variability on the column-integrated intraseasonal moisture budget in west Africa and the Atlantic will be examined in satellite and reanalysis datasets. The broader impacts of this work are educational and in the potential to improve our prospects for medium range prediction of periods of enhanced Atlantic tropical cyclone activity.