Synergistic Effect of Surface Thermal Heterogeneity in Phase With Topography on Deep Moist Convection.

Using large eddy simulation, we investigate the combined effect of terrain and surface sensible heat flux (SHF) heterogeneity on the development of afternoon deep moist convection (DMC). We implement an analytically derived, two‐dimensional terrain and SHF variations transformed from a κ−3 (where κ is the wavenumber) spectrum spanning wavelengths from 32 to 0.2 km. By separately coupling multiscale terrain with a homogeneous SHF field and the multiscale SHF field with flat terrain, we discern the individual impacts of these κ−3‐spectrum forcings on DMC. Our specific forcing configuration demonstrates that the multiscale terrain had a greater influence on DMC development compared to the multiscale SHF field. While the solely surface SHF heterogeneity forcing results in a wider pool of high relative humidity above the boundary layer, its significance is relatively lower in the mountainous terrain cases due to the shorter interaction time between highly buoyant thermals and the surrounding environment. However, when the multiscale terrain and SHF field are synchronized, DMC develops rapidly within a time frame of 4.5 hr, which is facilitated by enhanced surface buoyancy fluxes, the presence of highly buoyant thermals, and the persistence of mesoscale structures such as near‐surface convergence and mesoscale updrafts. Our study highlights the importance of the synergistic effects between multiscale terrain and surface SHF heterogeneity in DMC development. Additionally, our multiscale analyses of atmospheric variables reveal distinct atmospheric regimes between the pre‐storm and DMC periods. These findings contribute to a better understanding of the complex dynamics involved in the formation of afternoon DMC. Plain Language Summary: Our research used a high‐resolution model to explore how clouds and precipitation form in the afternoon in response to spatial variations in surface thermal properties and terrain height. Specifically, we analyze the effects of multiscale terrain height variation and surface thermal variation that is warmer and drier over higher terrain and cooler and moister over lower terrain. This is a realistic representation of how summits and valleys are differently heated in a mountainous area. Air flow moving up toward higher terrain is caused by both the difference in pressure between the summit and valley, as well as the varying thermal properties across the surface. To see the effects of each factor, we ran two additional simulations with a flat surface and homogeneous thermal properties. On the surface with thermal properties covarying with terrain height, a storm with rain quickly formed by 1500 local time. This study suggests that the contrasting thermal properties of warm summits and cool valleys greatly increase the chances of severe thunderstroms forming. Key Points: Multiscale surface‐thermal variation in phase with terrain has a stronger impact on moist convection than any single variationAn air pool of high humidity above the boundary layer has a lesser effect over mountainous terrain compared to surface thermal variationMesoscale variance of atmospheric variables significantly rises post onset of deep moist convection [ABSTRACT FROM AUTHOR]