2nd ICTP Summer School on Theory, Mechanisms and Hierarchical Modelling of Climate Dynamics: Convect
Updated: Jun 27
2nd ICTP Summer School on Theory, Mechanisms and Hierarchical Modelling of Climate Dynamics: Convective Organization and Climate Sensitivity | 1-12 July 2019 | (http://indico.ictp.it/event/8669/).
According to (Wing et al., 2017) RCE is an idealized climatic state by which the radiative cooling in the atmosphere is balanced by the heating that is due to latent heat release and surface heat fluxes. In RCE state lateral energy transport is neglected.
A common feature observed in idealized RCE numerical simulations is that convection organizes spatially into compact convective areas (self-aggregation), despite the fact that the same forcing is provided everywhere in the domain. Self-aggregation is observed in a plethora of domain geometries and sizes and under stable SST conditions (high SSTs favor aggregation) or under a Weak Temperature Gradient (WTG) and under the absence of vertical wind shear and absence of strong mean winds. In self-aggregated conditions, the dry equilibrium is identified as a dry region where no convection occurs, while the moist equilibrium corresponds to regions with convective activity and high moisture. The aforementioned conditions occur in non-rotating experiments. Under rotating conditions aggregation resembles tropical cyclogenesis (Wing et al., 2017).
Self-aggregation is caused by the synergetic effect of clouds, moisture and radiation and more specifically they are influenced by processes related to shortwave and longwave radiation, surface fluxes, moisture feedbacks and advective processes (Wing et al., 2017). In RCE state the convective areas of the domain have a random spatial distribution, but as the simulation time evolves, the dry regions expand and convection is aggregated in certain confined regions. In general, in RCE simulations dry regions are associated with strong radiative cooling, weaker surface enthalpy fluxes and subsidence.
An additional challenging step in the study of aggregation is to quantify its existence, across different SSTs, and various spatial and temporal scales. Towards this direction, the following metrics have been developed and used in the literature.
1. Quantification of how non-convective regions dry over the evolution of simulation time and how the variance of the precipitable water increases.
2. Increase of OLR over the spatial mean of the domain.
3. How the area of subsidence increases as the simulation time evolves.