Dynamics and Energetics Associated With Two East Pacific Easterly Waves During the OTREC Campaign in August 2019

Abstract

This study investigates the vertical structure and related dynamical and energy conversion processes that aided the development of two east Pacific easterly waves (EWs) during the 2019 OTREC (Organization of Tropical East Pacific Convection) campaign period. The initial mesoscale convective systems (MCSs) that seeded both disturbances formed near the Panama Bight and developed into EWs near the Papagayo jet exit region. In the MCS stage, both disturbances were characterized by top-heavy vertical motions and midlevel vorticity near the maximum vorticity center. The deep convection caused strong latent heating and eddy available potential energy (EAPE) generation and conversion to eddy kinetic energy (EKE) in the upper levels. When the disturbances moved to the south of the Papagayo jet, they interacted with the low-level shear vorticity there, enhancing low-level stretching and vorticity. Subsequently, the top-heavy upward motion intensified and led to enhanced stretching and vorticity intensification at midlevels. The enhanced stretching on the southwest side also favored the formation of southwest-northeast tilted vorticity at midlevels that characterizes EWs. After the EWs formed near the jet exit, the vertical motion weakened and became more bottom-heavy, with the maximum vorticity shifting to lower levels. This change in the vertical motion profile near the jet exit region is likely modulated by the lower sea surface temperature, reduced moisture, and weaker convective instability. While EAPE-to-EKE conversion weakened during this period, the low-level barotropic conversion of EKE in the jet exit served as the primary energy source for the EWs.