Need for RDC

First uploaded on 2022/08/21
Last updated on 2023/02/13
Copyright(C)2022 jos <jos@kaleidoscheme.com> All rights reserved.

Without Radiatively Driven Circulation (RDC), the atmosphere would transition to a state out of the current thermodynamical equilibrium, so RDC must be present regardless of whether it is in a cumulus-resolving model or a non-resolving model. Existing non-cumulus-resolving models may ambiguously resolve the deviation from the thermal equilibrium in calculations of large-scale fields u_L and dynamical detrainment u_D, and may not correctly represent the RDC transport processes that should occur as a result of the resolution. In the non-cumulus-resolving models, it is important to extract the RDC process and treat its transport explicitly.

More specifically, only the RDC can maintain a perfect radiative-convective equilibrium in the troposphere. If any parameterization is introduced that creates a flow in the troposphere different from the RDC that transports mass and heat, the current equilibrium state is destroyed. This leads to the very strong conclusion that any parameterization that creates a flow field (including dynamical detrainment) other than the RDC is not allowed.

At the same time, however, RDC does not prohibit physically meaningful transitions from the current equilibrium state. The RDC calculation F_R is only for the motion that maintains the current equilibrium state. The predictive calculations given explicitly in the model are made using the remaining radiative cooling, excluding the portion eliminated by RDC. In situations where no RDC is possible (no supplying source domains), for example, the modelled flow field u includes zero RDC flow field u_R=0 and the entire radiative cooling is used for the predictive equation for temperature. (In this case, the modelled troposphere will be cooled and become unstable to generate new cumulus domains.) If they change the current equilibrium state, resulting in a new equilibrium state, the next RDC calculation will try to maintain the new equilibrium state (if possible). In other words, RDC does not place any restrictions on physically meaningful equilibrium state transitions.