The Dynamics of Westerly Wind Bursts

Westerly Wind Bursts (WWBs) are short-term reversals of the prevailing easterlies in the equatorial pacific. WWBs have a zonal scale of thousands of kilometers, last 5-20 days, and occur a few times per year; they are known to both occur more frequently during developing warm (El Nino) events, as well as to amplify such developing warm events through the excitation of equatorial Kelvin waves. It has been suggested yet debated (Chiodi et al. 2014) that WWBs tend to happen more frequently during the active phase of the MJO. We investigate the genesis and dynamics of WWBs by analyzing their connection to atmospheric convection and self-aggregation in a zonally symmetric aquaplanet model. Composited WWBs time series indicate that WWBs are coupled with a strong eastward propagating convection signal. By modifying entrainment, long wave cooling, and moisture advection, we analyze the importance of these processes and of self-aggregation to the WWB formation and dissipation mechanism. Then, to better understand the mutual interaction between WWB and ENSO, we perform experiments forced with an El-Nino like zonally asymmetric SST anomaly. Improved understanding of the dynamics of WWBs and their dependence on the SST is important to our understanding of the dynamics of ENSO in the past, present, and future.