Comparison of Orographic and Thermal Forcings on Mesoscale Convective Systems

Hazardous squall lines are mesoscale meteorological phenomena that are commonly seen across the US; this mesoscale feature is the result of severe thunderstorms that make up part of mesoscale convective systems (MCSs). The development of MCSs and an increased understanding of how they react to different types of parameters and forcings is becoming an actively pursued research topic. Thunderstorms within the structure of the MCS vary in size and intensity and the difference in their attributes are often due to the thermodynamics of the vertical profile of the atmosphere. This project will seek to understand how these mesoscale convective systems (MCSs) react to different forms of convective forcings. The two forcings, orographic forcing and thermal forcing, demonstrate two very different ways in which thunderstorm development occurs. Using the Cloud Model 1 (CM1), two sets of simulations were run on each of the different forcings. The orographic forcing will place a mountain in the simulation with a known height and half-width to investigate how the thunderstorm develops over the terrain. The thermal forcings will affect the thunderstorm by initializing a warm bubble at some known location with a known vertical radius, horizontal radius, and perturbation. These simulations were run for ten hours each with a ten second time step. The orographic parameters were set up as a 2 km height and a 30 km half-width. The default parameters for the thermal forcings were a 1.4 km vertical radius, 10 km horizontal radius and a 2 Kelvin perturbation. Each of these simulations were set up using the default settings, including a Morrison double-moment Microphysics Scheme. The Planetary Boundary Layer and Radiation parameterizations were deactivated and the same initial atmospheric sounding was used throughout the simulation. The thermal forcing simulation caused higher reflectivity readings and a higher accumulated rainfall. The results showed that the orographic forcing caused higher wind speed at an earlier time than the thermal forcing simulations. Further research can be done to with the addition of the Coriolis parameter and meridional wind in an additional simulation to see how it affects the development and rotation within the MCS.