Surface Cyclogenesis from Convectively Driven Amplification of Midlevel Mesoscale Convective Vortices

Abstract

Mesoscale convective vortices (MCVs) are midtropospheric warm-core cyclonic circulations that often develop in the stratiform region of mesoscale convective systems. Typically, divergent, anticyclonically circulating, mesoscale cold anomalies appear both above and below the MCV. The upper-level cold anomaly is usually found near the tropopause while the low-level anomaly is surface based and exhibits locally higher pressure. One aspect of MCVs that has received much attention recently is the role that they may play in tropical cyclogenesis. Of special interest is how an MCV amplifies when deep convection redevelops within the borders of its midlevel cyclonic circulation and how the amplified MCV transforms the divergent surface-based cold pool with anomalously high surface pressure into a convergent cyclonic circulation with anomalously low pressure. The Pennsylvania State University?National Center for Atmospheric Research fifth-generation Mesoscale Model is used to simulate an MCV that was instrumental in initiating, within the borders of the midlevel vortex?s circulation, several successive cycles of convective development and decay over a 2-day period. After each cycle of convection, both the horizontal size of the cyclonic circulation and the magnitude of the potential vorticity associated with the vortex were observed to increase. The simulation reproduces the development and evolution of the MCV and associated convective cycles. Mesoscale features responsible for the initiation of convection within the circulation of the vortex and the impact of this convection on the structure and evolution of the vortex are investigated. A conceptual model is presented to explain how convective redevelopment within the MCV causes low-level heights to fall and cyclonic vorticity to grow downward to the surface. Applying this conceptual model to a tropical marine environment is also considered.