Please use this identifier to cite or link to this item:
Aggregation or No Aggregation and Beyond: from a Cloud-Resolving Model Perspective
aggregation,convective organization,slab ocean,radiative-convective equilibrium,cloud-resolving model,
|Publication Year :||2018|
In this study, a slab ocean is employed to a vector vorticity equation cloud-resolving model (VVM) to investigate the development of convective aggregation in radiative-convective equilibrium. The model is initialized by a weak sea surface temperature gradient to generate a thermal-direct circulation. From the perspective of the atmosphere, the radiative heating, surface enthalpy fluxes and moist static energy (MSE) convergence induce positive feedback in the early stage of convective aggregation. In particular, the interactive sea surface temperature (SST) intensifies surface enthalpy flux variance by enhanced heating at high MSE region and suppressed flux at low MSE area. As the difference of dry and moist area enlarges, wind convergence homogenizes MSE variance by pumping out MSE from the wet to dry, while the convective heating terms are strong enough to sustain the convective aggregation. All of the above processes exhibit the strongest signal in the dry zone during the convective aggregation stage.
From the view of the ocean-atmosphere coupling system, the longwave radiative cooling is particularly important for the convective aggregation. Although the simulation is conducted with the uneven surface boundary condition, the spatial inhomogeneity becomes less important within 5 days of integration and the result suggests that the radiative-convection-SST coupling is very strong after the convective aggregation is triggered.
The key mechanism for convective aggregation is the low-level MSE up-gradient transport. As the low-level moisture gradient is established, resulting in the development of virtual temperature gradient near surface which drives the low-level wind and promotes the convective aggregation. We found that the estimated inversion strength (EIS) appears to be related to wind stress and better indicates the low-level stability that further decides the direction of MSE transport.
For the non-aggregation simulation, the climate falls into a runaway state in which the domain average SST increases from initial 300K to 306K in 100 days. The mixed layer budget shows that the air-sea interaction evolves to an equilibrium state that the net flux in the mixed layer is close to zero whether there is aggregation or not. Even so, the convective aggregation is a much more efficient adjustment that promptly saves the climate from a runaway state.
|Appears in Collections:||大氣科學系|
Files in This Item:
|22.11 MB||Adobe PDF|
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.