A decentralized approach for modeling organized convection based on
thermal populations on a microgrid
Abstract
Recent insights into the spatial organization of atmospheric convection
have emphasized the importance of its correct representation in Earth
System Models (ESM). This study explores new opportunities created when
combining a thermal population model on a horizontal microgrid with a
decentralized vertical transport model. To this purpose the recently
proposed BiOMi population model (Binomials on Microgrids) is used. BiOMi
mimicks a population of independent but interacting convective thermals,
with their birth, movement and life cycle described as Bernoulli
processes. Simple rules of interaction are introduced to reflect
observed physical behavior in single cumulus clouds, such as pulsating
growth and environmental deformation. Under these rules, thermals can
congregate and form longer-lived coherent clusters or chains that
resemble cumulus clouds. The formation and evolution of these clusters
is a form of self-organization that retains convective memory. Through
an online clustering method the microgrid is coupled to a spectral EDMF
convection scheme, providing the cluster size distribution it needs as
input. This way, the inherently 3D structure of organized convection can
in principle be captured in reduced but efficient form. The system is
fully decentralized in that central top-down bulk closures are avoided.
The main science objective of this study is to provide proof of concept
of decentralized frameworks of this kind. To this purpose the BiOMi-EDMF
scheme as implemented in the DALES circulation model is tested for
various LASSO cases of shallow convection at the ARM SGP site. We find
that the scheme achieves stable and realistic diurnal quasi-equilibria
(as shown in the figure), and that the associated self-organizing
patterns on the microgrid are realistic. Impacts of spatial organization
and convective memory on the parameterized transport will be
investigated.