Atmosphere Ocean Science Friday Seminar

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Radiation Impacts on Hurricane-Like Vortices in the Conditionally Unstable Layer

Speaker: Mu-Hua Chien, CAOS

Location: Warren Weaver Hall 1314

Date: Friday, October 1, 2021, 4 p.m.

Notes:

The present work investigates how radiative cooling affects hurricane-like vortices in rotating moist Rayleigh–Bénard convection(RMRBC). In RMRBC, a rotating Boussinesq atmosphere with simplified thermodynamics for phase transition is destabilized by imposing a warm, moist lower boundary and a colder, dryer upper boundary. These boundary conditions are chosen such that the atmosphere is relaxed toward a conditionally unstable state in which saturated air parcels experience a stable stratification and unsaturated parcels experience an unstable one. Hurricane-like vortices appear in rotating conditionally unstable moist Rayleigh–Bénard convection in the absence of radiative transfer.

Radiative cooling affects moist Rayleigh-Bénard convection in two significant ways. First, as the cooling must be compensated for by an upward energy transport, it leads to an intensification of the atmospheric overturning. Second, radiative cooling acts to destabilize the lower part of the atmospheric layer and stabilize it near the upper boundary. This significantly enhances convective activity near the lower boundary in a way that is reminiscent of the planetary boundary layer in the Earth’s atmosphere.

As the intensity of radiative cooling increases, the dry convective transport increases through the entire layer, leading to a significant enhancement of the upward transport of energy and water. This heat transport performs a better efficiency than the heat transport in the conditionally unstable layers. As a result, the organized hurricane-like vortices are replaced by small and aligned vortices found in standard Rayleigh-Bénard convection. Sufficiently strong radiative cooling can eliminate the vortices.