A Meso-β-Scale Kinetic Energy Analysis of a Midlatitude Squall System

Abstract

A meso-β-scale kinetic energy (KE) budget of a midlatitude mesoscale convective system (MCS) and its effects on larger-scale flow are investigated using a 21-h high-resolution real-data simulation of an intense squall system that occurred during 10-11 June 1985 PRE-STORM. It is found that the ageostrophic cross-contour generation in the front-to-rear (FTR) ascending flow provides a major source of KE to the squall system, whereas the horizontal flux divergence is a primary sink. The vertical flux divergence is a KE sink (source) in the FTR ascending flow below (above) an upper-level jet, but it is always a source in the rear-to-front (RTF) descending flow. Due to the downward KE transport in the RTF flow, the presence of the jet stream containing most of its KE along the line appears to affect the intensity of the squall system and surface gust fronts several hundreds kilometers away to the front and to the southwest of the system. The effects of moist convection on atmospheric motion of all resolvable scales are examined in a wavenumber space. With deep convection incorporated, the model produces little changes in the KE spectrum for smaller wavelengths but significant alterations in both the spectral magnitude and slope for longer wavelengths. The convectively generated alterations appear to be a consequence of the intermittent development of the MCS, rather than reverse KE cascade.