Connections between Potential Vorticity Intrusions and Convection in the Eastern Tropical Pacific

Abstract

Abstract The connections between intrusions of stratospheric air into the upper troposphere and deep convection in the tropical eastern Pacific are examined using a combination of data analysis, potential vorticity (PV) inversion, and numerical simulations. Analysis of NCEP–NCAR reanalyses and satellite measurements of outgoing longwave radiation during intrusion events shows increased cloudiness, lower static stability, upward motion, and a buildup of convective available potential energy (CAPE) at the leading edge of the intruding tongue of high PV. Potential inversion inversion calculations show that the upper-level PV makes the dominant contribution to the changes in the quantities that characterize convection. This supports the hypothesis that upper-level PV anomalies initiate and support convection by destabilizing the lower troposphere and causing upward motion ahead on the PV tongue. The dominant role of the upper-level PV is confirmed by simulations using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). Convection only occurs when the upper-level PV anomaly is present in the simulations, and the relative contribution of the upper-level PV to changes in the quantities that characterize convection is similar to that inferred from the PV inversion calculations.