5:15 PM - 6:30 PM
[ACG06-P01] The lack of westerly wind bursts in 2014 and its relation to background wind states
Keywords:El Niño, westerly wind bursts, Madden Julian Oscillation
The successive WWBs from January to March 2014 excited strong oceanic Kelvin waves, resulting in a large increase in the eastern Pacific sea surface temperature (SST). However, there are no successive WWBs or the Kelvin waves after April, resulting in a decrease in the SST.
Our previous studies have shown that WWBs occur frequently when tropical intraseasonal convection, so-called the Madden-Julian Oscillation (MJO), propagates over the Pacific under the equatorial westerly background states, which contribute to develop eddy disturbances via background zonal wind convergence near the equator. In 2014, there were several MJO events throughout the year. However, few WWBs accompanied the MJO convection.
Focusing on the background states after the WWB occurrences in early 2014, zonal wind convergence was retracted and did not reach the equatorial central Pacific. In boreal summer, climatologically, convectively active and westerly regions shift north of the equator. Because this environmental condition is not favorable for the WWB occurrences, the WWB frequency in boreal summer is statistically low. In 2014, unchanged background states can be a reason for the lack of WWBs even with several MJO events.