Heterogeneities in Convective Parameters and Convection Initiation in Coastal Regions

The influence that large bodies of water have on the evolution of the near-shore convective environment and convection initiation (CI) is highly complex due to the variability of large-scale parameters that control relevant processes. In coastal regions during the warm season, CI is strongly influenced by the development of the sea-breeze front (SBF), which modulates the near-shore thermodynamic and kinematic environment and acts as a potential focal point for convection. Previous research has placed a substantial focus on interactions between the SBF and other mesoscale boundaries or organized boundary layer circulations and related implications on CI, however, less research has focused on heterogeneities in convective parameters caused by different large-scale environments and how those affect the coverage, timing, and location convection.

Using the PSU/NCAR Cloud Model 1, this presentation will analyze the heterogeneities of convective parameters across SBFs using a subset of 60 large-eddy simulations, with the parameter space varying the cross-shore wind component (-5 to 5 m s^-1 in 2.5 m s^-1 intervals), radiative forcing (15 June, 15 July, 15 August), and water surface temperature (25th, 50th, 75th, and 90th percentiles for Lake Michigan corresponding to the radiative forcing dates). In all simulations, the initial shore-parallel wind component was equal to 0 m s^-1. The model domain was 200 × 20 × 18 km in the W-E, N-S and vertical dimensions, with a surface type of water in the western 50 km and land in the eastern 150 km. Inclusion of radiative parameterization, friction, and surface heat fluxes enabled development of realistic boundary layer structure and CI. SBFs developed in every simulation with varying degrees of strength (temperature gradient, convergence, etc.), inland penetration, and thermodynamic and kinematic structure across the parameter space. In all simulations, greater surface-based CAPE (SBCAPE) occurred on the cool side of the SBF than on the warm side. These areas of enhanced SBCAPE were larger in both the amount of SBCAPE and spatial coverage in calm environments, June, and warmer water surface temperatures and coincided with lower LFC and LCL heights than those further inland. These environments also resulted in the earliest time of CI as well as the most widespread and intense convection.