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