Numerical prediction of an intense convective system associated with the July 1987 montreal flood. part II: A trailing stratiform rainband

Stéphane Bélair, Da‐Lin Zhang, Jocelyn Mailhot
In this study, thé internai circulation structures of thé 14 July 1987 intense mesoscale convective System (MCS) are investigated using an improved high-resolution version of thé Canadian régional finite-element model. It is found that although thé MCS is characterized by a leading convective Une followed by a trailing stratiform rainband, thé associated circulation structures differ substantially from those in thé classical midlatitude squall System. Thèse include thé rapid propagation and
more » ... propagation and séparation of thé leading convection from thé trailing rainband, thé development of a surface-based instead of an elevated rear-to-front descending flow and a shallow front-to-rear ascendingflow associated with thé stratiform précipitation, thé génération oflow-and mid-level rather than mid-to upper-level stratiform cloudiness and thé development ofa strong anticyclonic vorticity band at thé back edge ofthe stratiform région. It is shown that thé trailing stratiform rainband is dynamically forced by frontogenetical processes, and aided by thé release of conditional symmetric instability and local orographical lifting. The intense leading and trailing circulations resuit from latent heat released by thé convective and explicit cloud schemes, respectively. Sensitivity experiments reveal that thé proper coupling of thèse two cloud schemes is instrumental in obtaining a realistic prédiction of thé above-mentioned various mesoscale components. Vorticity budget calculations show that tilting of horizontal vorticity contributes thé most to thé amplification ofthe anticyclonic vorticity band, particularly during thé squall's incipient stage. The sensitivity of thé simulated squall System to other model physical parameters is also examined. (3) 1995, 475-500 0705-5900/95/0000-0475SO 1.25/0
doi:10.1080/07055900.1995.9649541 fatcat:ajgfggva25ealnrst4o35lmdpa