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Seminar

Title : Interaction between water vapor, radiation and convection in the Tropics
Name of the speaker : Tom Beucler
Affiliation : étudiant en these au MIT avec Kerry Emanuel et Tim Cronin
Laboratory organizer : LMD
Date and time : 18-12-2018 14h00
Location : Salle Froidevaux-314, 3rd floor, 24 rue Lhomond, 75005 Paris
Summary :

The interaction between convection and large-scale dynamics is a primary source of uncertainty in numerical simulations of the atmosphere, impeding our understanding of the climate. In large-scale atmospheric models, this uncertainty can be attributed to improperly-simulated interactions between atmospheric heating and water vapor across scales. Water vapor has a central role in the atmosphere: it is the most abundant greenhouse gas in the atmosphere, the main absorber of solar radiation in the troposphere. Water vapor is also intimately connected to atmospheric convection which lifts it, leading it to condense into clouds. Once formed, these clouds have even larger radiative effects. However, we still lack a robust conceptual framework connecting water vapor and clouds to convection and radiation.
Using fluid dynamics, thermodynamics and spectral analysis tools, we investigate the interaction between water vapor, radiation and convection in observations of the tropical atmosphere and in high-resolution models of radiative-convective equilibrium. Radiative-convective equilibrium is the simplest model of the tropical atmosphere, in which convective heating balances radiative cooling in the absence of horizontal energy transport. We introduce a framework relating the evolution of the length scale at which convection organizes to the spatial spectra of radiative cooling, surface enthalpy fluxes, and horizontal energy transport. The cloud longwave radiative effect is most important, stretching humid and dry regions to scales of several thousand kilometers in the Tropics. These findings suggest that resolving the coherence between high, ice-cloud radiation and water vapor across the 1-10,000 km scale range is key to modeling tropical dynamics, and may considerably reduce our biases in modeling large-scale tropical precipitation patterns that are relevant for human activity.

Contact :

caroline.muller@lmd.ens.fr