Initiation and Maintenance of Long-lived Summertime Mesoscale Vortices over Central and East China: Composite Analysis and Semi-idealized Simulations

We first perform composite analysis of 11 long-lived (≥ 42 hours) heavily-precipitative mesoscale convective vortices (MCVs) that generated around the Dabie Mountain Ranges over the middle reaches of the Yangtze River Basin in Central East China during the summers of 2000-2013. Based on the composite initial and boundary conditions of these events, we then conduct several semi-idealized convection-permitting experiments using the Weather Research and Forecasting (WRF) model to understand the impacts of large-scale monsoon environmental conditions, regional topography and diabatic heating in the initiation, intensification and maintenance of summertime MCVs over Central and East China. The control semi-idealized simulation initialized 12 hours before the composite MCV initiation successfully reproduced a long-lived mesoscale vortex that has all the salient characteristics and 3-dimensional evolution of the MCV composed of 11 long-lived heavy-precipitation-inducing events. Preliminary findings from the composite analysis, control and sensitivity experiments suggest that supposition of the north-south-oriented large-scale leeside trough with the east-west-oriented quasi-stationary Meiyu front is essential for the initiation of the mesoscale vortex in this region. Latent heat release is critical for enhancement and maintenance of the long-lived vortex in its eastward progression along the quasi-stationary frontal boundary. The detailed topography to the east of the step-2 mountain ranges including the Dabie Mountain terrains in the area of the MCV initiation likely play a secondary role. Preliminary vorticity budget analysis indicates that the convergence-related shrinking dominated the formation and rapid development of the MCV after initiation. More in-depth analysis of the life cycles of the composite and simulated MCVs is ongoing and will be presented during the conference.