Core and margin in warm convective clouds – Part 1: Core types and evolution during a cloud's lifetime

Abstract

Abstract. The properties of a warm convective cloud are determined by the competition between the growth and dissipation processes occurring within it. One way to observe and follow this competition is by partitioning the cloud to core and margin regions. Here we look at three core definitions, namely positive vertical velocity (Wcore), supersaturation (RHcore), and positive buoyancy (Bcore), and follow their evolution throughout the lifetime of warm convective clouds. Using single cloud and cloud field simulations with bin-microphysics schemes, we show that the different core types tend to be subsets of one another in the following order: Bcore⊆RHcore⊆Wcore. This property is seen for several different thermodynamic profile initializations and is generally maintained during the growing and mature stages of a cloud's lifetime. This finding is in line with previous works and theoretical predictions showing that cumulus clouds may be dominated by negative buoyancy at certain stages of their lifetime. The RHcore–Wcore pair is most interchangeable, especially during the growing stages of the cloud. For all three definitions, the core–shell model of a core (positive values) at the center of the cloud surrounded by a shell (negative values) at the cloud periphery applies to over 80 % of a typical cloud's lifetime. The core–shell model is less appropriate in larger clouds with multiple cores displaced from the cloud center. Larger clouds may also exhibit buoyancy cores centered near the cloud edge. During dissipation the cores show less overlap, reduce in size, and may migrate from the cloud center.

The incorporation of the Tripleclouds concept into the <i>δ</i>-Eddington two-stream radiation scheme: solver characterization and its application to shallow cumulus clouds

“…In this model, the convective cloud "core" associated with updraft motion and increased condensate loading is located in the geometrical center of the cloud, surrounded by the cloud "shell" associated with downdrafts and condensate evaporation. The core-shell model is supported by multiple observational studies (e.g., Heus et al, 2009;Rodts et al, 2003;Wang et al, 2009) and numerical modeling investigations (e.g., Heus and Jonker, 2008;Jonker et al, 2008;Seigel, 2014) and hence represents the essence of several convection parameterizations. Heiblum et al (2019) showed that the core-shell model is valid for about 90 % of the typical cloud's lifetime, with the largest discrepancy from the assumed core-shell geometry occurring during the dissipation stage of the cloud.…”

“…This knowledge will be exploited later when constructing the Tripleclouds radiation scheme. Shallow cumulus clouds are convective clouds, which are often treated with the "coreshell model" (Heus and Jonker, 2008;Heiblum et al, 2019). In this model, the convective cloud "core" associated with updraft motion and increased condensate loading is located in the geometrical center of the cloud, surrounded by the cloud "shell" associated with downdrafts and condensate evaporation.…”

“…Whereas most of the clouds contain a single core, larger clouds can possess multiple cores. Similarly, clouds in a cloud field have multiple cores, whereby their aggregate effect can be modeled with a core-shell model (Heiblum et al, 2019).…”

The incorporation of the Tripleclouds concept into the <i>δ</i>-Eddington two-stream radiation scheme: solver characterization and its application to shallow cumulus clouds

“…This knowledge will be exploited later when constructing the Tripleclouds radiation scheme. Shallow cumulus clouds are convective clouds, which are often treated with the "core-shell model" (Heus and Jonker, 2008;Heiblum et al, 2019). In this model the convective "cloud core" associated with updraft motion and increased condensate loading is located in the geometrical centre of the cloud, surrounded by the "cloud shell" associated with downdrafts and condensate evaporation.…”

“…The core-shell model is supported by multiple observational studies (e.g., Heus et al, 2009;Rodts et al, 2003;Wang et al, 2009) and numerical modelling investigations (e.g., Heus and Jonker, 2008;Jonker et al, 2008;Seigel, 2014) and hence represents the essence of several convection parametrizations. Heiblum et al (2019) showed that the core-shell model is valid for about 90 % of the typical cloud's lifetime, with the largest discrepancy from the assumed core-shell geometry occurring during the dissipation stage of the cloud. Whereas most of the clouds contain a single core, larger clouds can possess multiple cores.…”