Response of moist convection to multi‐scale surface flux heterogeneity

Abstract

We investigate the response of moist convection to the spatial variation of surface sensible heat flux (SHF) in a mesoscale domain during the evolution of the afternoon convective boundary layer (CBL), using large-eddy simulation. The surface SHF heterogeneity in the domain is analytically created as a function of the spectral slope in the wavelength range from a few tens of kilometres to a few hundreds of metres in the SHF spectrum on a log-log scale. Assuming surface energy balance and spatially uniform available energy, the prescribed SHF has a phase lag of 180• with respect to the latent heat flux (LHF) in the domain. Two sets of three simulations are forced by heterogeneous surface SHF fields, which are characterized by similar statistics. One set, however, is created with a spectral slope of k −3 (where k is wave number) and the other with a slope of k −2 . All of the simulations are integrated with the same observation-based initial sounding favourable for moist convection.In all of the k

Regional Bowen ratio controls on afternoon moist convection: A large eddy simulation study

“…Considering that the intensity of surface heterogeneity on scales of tens of kilometers has a pronounced impact on the CBL and moist convection [e.g., Raupach and Finnigan , ; Mahrt , ; Baidya Roy et al ., ; Taylor et al ., , ; Kang and Bryan , ; Kang and Ryu , ], we prescribe the surface flux fields of multiscale heterogeneity to be composed of the sinusoidal harmonics from a mesoscale wavelength of 28 km to a microscale wavelength of 0.1 km. The 28 km wavelength is somewhat shorter than the longest, 32 km, wavelength the LES horizontal domain permits, and the 0.1 km wavelength is the Nyquist wavelength of the LES grid spacing of 50 m. With the κ − 3 spectrum, a longer wavelength has higher amplitude than a shorter wavelength in the range, allowing us to create mesoscale heterogeneity‐enhanced, realistic multiscale surface flux fields.…”

“…In Figures and , one can compare the cospectra of κ Co rθ ( κ ), κ Co wθ ( κ ), and κ Co wr ( κ ) between 1200 and 1400 LT in the heterogeneous surface cases (B18K3 and B06K3) specifically on wavelengths >10 km at heights <0.8 ⟨ z i ⟩. First, it is evident that the significant cospectral densities mainly come from the turbulent vertical transports of mesoscale θ and r fluctuations, given the dominant w perturbations on scales of several kilometers or smaller (Figures a and b), as suggested by some previous studies [e.g., Kang and Davis , , ; Kang and Bryan , ; Kang and Ryu , ].…”

Response of Convective Boundary Layer and Shallow Cumulus to Soil Moisture Heterogeneity: A Large‐Eddy Simulation Study

“…Figure depicts the domain‐ and time‐averaged vertical profiles of the variance of horizontal wind velocity, vertical wind velocity, potential temperature, specific humidity, and cloud liquid water. We apply the scale decomposition scheme commonly used to isolate mesoscale circulation impacts (Hussain & Reynolds, ; Kang & Ryu, ; Patton et al, ; Sullivan et al, ), to inspect if the given two‐dimensional soil moisture heterogeneity induces any mesoscale circulation related processes that are strong enough to influence the boundary layer characteristics.…”

“…Large‐eddy simulation (LES) has been used to study land‐atmosphere interactions and the impact of the land surface heterogeneity on atmospheric boundary characteristic (Avissar & Schmidt, ; Hadfield et al, , ; Han et al, ; Patton et al, ; Raasch & Harbusch, ; Shen & Leclerc, ; Sühring et al, ; van Heerwaarden et al, ), on the shallow convection development (H. Y. Huang & Margulis, ; Kang & Ryu, ; Raasch & Harbusch, ; van Heerwaarden & de Arellano, ) and on the transition from shallow to deep convection (Kang & Bryan, ; Lee et al, ; Rieck et al, ; Rochetin et al, ) for the past two decades. One main concern of these studies has been the optimal heterogeneity scale to induce a mesoscale circulation, which is commonly suggested to be at a mesoscale but varies considerably.…”

“…In addition to the heterogeneity length scale, the heterogeneity amplitude can modify the mesoscale circulation (Avissar & Schmidt, ; van Heerwaarden et al, ; van Heerwaarden & de Arellano, ), which in turn triggers an earlier onset of convection (Kang & Bryan, ) and even a transition from shallow to deep convection (Kang & Ryu, ). Several studies have reported that the mesoscale circulation intensity increases with increasing heterogeneity amplitude (Avissar & Schmidt, ; Patton et al, ; van Heerwaarden & de Arellano, ).…”