Publication Date:
2023-01-17
Description:
In this study, a spectral model for convective transport is coupled to a thermal population model on a two‐dimensional horizontal “microgrid,” covering the typical gridbox size of general circulation models. The goal is to explore new ways of representing impacts of spatial organization in cumulus cloud fields. The thermals are considered the smallest building block of convection, with thermal life cycle and movement represented through binomial functions. Thermals interact through two simple rules, reflecting pulsating growth and environmental deformation. Long‐lived thermal clusters thus form on the microgrid, exhibiting scale growth and spacing that represent simple forms of spatial organization and memory. Size distributions of cluster number are diagnosed from the microgrid through an online clustering algorithm, and provided as input to a spectral multiplume eddy‐diffusivity mass flux scheme. This yields a decentralized transport system, in that the thermal clusters acting as independent but interacting nodes that carry information about spatial structure. The main objectives of this study are (a) to seek proof of concept of this approach, and (b) to gain insight into impacts of spatial organization on convective transport. Single‐column model experiments demonstrate satisfactory skill in reproducing two observed cases of continental shallow convection. Metrics expressing self‐organization and spatial organization match well with large‐eddy simulation results. We find that in this coupled system, spatial organization impacts convective transport primarily through the scale break in the size distribution of cluster number. The rooting of saturated plumes in the subcloud mixed layer plays a key role in this process.
Description:
Plain Language Summary:
Recent studies have emphasized the importance of the spatial structure of convective cloud fields in Earth's climate, yet this phenomenon is not yet represented well in Earth System Models (ESMs). This study explores a new way to achieve this goal, by considering spatial organization at the scale of small bubbles of rising air called thermals that together make up convective clouds. Populations of interacting thermals are modeled in a computationally efficient way on a small two‐dimensional grid. This microgrid is then coupled to a convection scheme, which stands for the set of equations used to statistically represent the impact of convective transport at scales that remain unresolved in ESMs. The coupling makes the scheme decentralized, in that the transport becomes dependent on a population of longer‐lived convective structures that slowly develop and evolve on the microgrid. The new scheme is tested for observed conditions at a meteorological site in the Southern Great Plains area of the United States, making use of a combination of high‐resolution simulations and measurements to evaluate performance. Apart from proof of concept for the new modeling approach, the results provide new insights into how the spatial structure of convective cloud populations can affect its vertical transport.
Description:
Key Points:
A multiplume spectral convection scheme is coupled to a binomial thermal population model on a horizontal microgrid.
Observed diurnal cycles of continental shallow convection are reproduced, including good agreement on scale growth and spatial organization.
Spatial organization impacts convective transport through the scale break in the cluster number density, with a key role played by plume rooting.
Description:
U.S. Department of Energy
http://dx.doi.org/10.13039/100000015
Description:
https://doi.org/10.5281/zenodo.6044338
Keywords:
ddc:551.5
;
convective parameterization
;
spatial organization
;
population dynamics
;
thermals
;
microgrid modeling
;
shallow cumulus
Language:
English
Type:
doc-type:article
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