Characterization of Surface Heterogeneity‐Induced Convection Using Cluster Analysis

Abstract

Land-atmosphere interactions and boundary layer processes often control the formation of shallow clouds and subsequently deep convective precipitation over the U.S. Southern Great Plains. In this study, we examine the impacts of large-scale advection on the cloud populations and land-atmospheric coupling observed during the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems field campaign in 2016. We performed two large eddy simulations using the Weather Research and Forecasting Model for a day in which the transition from clear-sky to shallow precipitating clouds and isolated deep convection was observed. The control simulation reproduced the overall distribution of cloud populations by using realistic soil conditions with an interactive land model. In the sensitivity simulation where large-scale advection is removed, a strong relationship between the land and boundary layer is found. To study the timing, location, and intensity of convective initiation and the relationship of clouds with land surface properties, a cluster analysis of equivalent potential temperature is performed for the simulation without large-scale advection. That analysis shows that convective clouds first form over regions with higher surface sensible heat flux. Precipitation from those convective clouds likely triggers new updrafts nearby about 2 hr later through the lifting associated with cold pools. The cluster analysis also shows that in addition to the spatial pattern of soil moisture, land use and soil texture in western Oklahoma also influence the location of convective initiation. Plain Language Summary Accurately predicting the timing, location, and intensities of convection over midlatitude land is extremely important. Yet, complete answers to the related questions such as how the land properties impact the atmosphere and cloud properties remain lacking. Models that resolve boundary layer turbulence and clouds have been used extensively to understand processes controlling land-atmosphere interactions, but computational expense limits the employment of realistic land properties. In this study, we employ a more realistic modeling approach to study abovementioned question. First, we examined the relative role of large-scale advection and the local effects of land properties in convection and cloud formation. A comparison of two sensitivity studies shows that large-scale advection is vital in the characterization of land-atmosphere interactions not only in terms of the magnitude but also the types of relationships. Then, we analyzed the simulation with only local effects by cluster analysis. We found that convection initiates over the regions with high surface sensible heat flux. Precipitation from the earliest convection likely triggers new convection around about 2 hr later by forming a cold surface area due to evaporating cooling. Moreover, soil moisture, land use type, and soil texture play roles in determining the surface heat fluxes.

Determining Spatial Scales of Soil Moisture—Cloud Coupling Pathways Using Semi‐Idealized Simulations

“…We limit our analysis to the time period between 1000 and 1100 CST; specifically, we evaluate the average of 1000, 1015, 1030, and 1045 CST instantaneous outputs, referred to as the “1000 CST period” in the following. This is when the average z i already grows to be ∼1.5 km, an equilibrium height that remains the same in the afternoon, while clouds have not matured yet at this time to obscure the forcing from the surface to the atmosphere (Chen et al., 2020; Fast, Berg, Feng et al., 2019).…”

“…It is important to retain the same land cover as Fast, Berg, Feng et al (2019) because strong dependence of evaporative fraction on the vegetation cover has been suggested for the SGP site (Williams & Torn, 2015). Readers are also referred to Chen et al (2020) for the influence of land cover heterogeneity on the cloud development for the same HI-SCALE case. Surface topography is another important forcing, which we exclude from our main simulations to interpret atmospheric response to the imposed surface heterogeneities without other confounding effects.…”

Morning boundary layer conditions for shallow to deep convective cloud evolution during the dry season in the central Amazon

“…The median shows more intense radiative cooling during the ShCu regime than for ShDeep. For example, Edwards et al (2014), using large-eddy simulations, showed that radiative cooling has an important effect on the morning transition and in the development of the convective BL. The mechanical turbulence is seen in Fig.…”

Summertime Continental Shallow Cumulus Cloud Detection Using GOES-16 Satellite and Ground-Based Stereo Cameras at the DOE ARM Southern Great Plains Site

“…Continental shallow cumulus clouds (ShCu) are tightly coupled with the land surface and have strong impacts on the surface energy partition and the turbulent transport of momentum, heat, and moisture [1][2][3][4][5][6]. They are also important for their seeding role in transitioning into hot-tower deep convective clouds with heavy precipitation [7].…”

“…2021, 13, 2309 2 of 19 albedos, surface roughness, soil moisture content, and leaf area index. This is because: (1) ShCu strongly interact with the surface heating and moistening driven by the diurnally varying solar and infrared radiation; (2) observations of the initiation and continuous development of ShCu are needed to study the mechanisms controlling the transition from shallow to deep convection; (3) cloud size is important as larger clouds can grow deep and rain more easily [17]; and (4) ShCu may form preferentially over certain land surface properties or land cover types [18,19].…”