**Characteristics of Convective Development in Simulated Squall Lines

Using a two-dimensional nested spectral model (NSM-2D) with classical thermodynamics and parameterized microphysics (CTPM) which has been developed by K.V. Ooyama of NOAA's Hurricane Research Division, tropical squall line systems have been simulated with various strengths of the initial low-level vertical shear of the horizontal wind. The resulting systems are found to produce cold surface outflow layers which propagate against the low-level flow with some finite ground-relative velocity. This propagation velocity may be related to several other aspects of the squall line system and its environment, specifically, the velocity profile of the low-level environmental inflow, the maximum updraft in the vicinity of the surface outflow head (gust front), and the rear-to-front flow through the convective region of the squall line system. This portion of the work represents an update and refinement of the theories presented earlier by Rotunno et al. (1988) and Weisman (1992). Additionally, the production of new convective cells near the gust front of a multicellular squall line system is commonly found to occur in either simple- or complex-periodic cycles, as examined by Fovell and Ogura (1989) and Fovell and Dailey (1995). The character of these cycles may also be related to aspects of the squall line system and its environment, including the propagation speed of the gust front and the influence of gravity waves generated on the surface of the cold outflow layer.