4A.8 Dynamic Amplification of Extreme Precipitation Sensitivity

Monday, 16 April 2018: 12:00 AM
Masters E (Sawgrass Marriott)
Ji Nie, Peking Univ., Beijing, China; and A. H. Sobel, S. Wang, and D. Shaevitz

It is usually hypothesized that precipitation extremes increase at the same rate as atmospheric moisture increases, which is ∼ 7% per K following the Clausius–Clapeyron (CC) relation. However, due to potential feedbacks between diabatic heating and dynamics, increased precipitation may invigorate the atmospheric flow, leading to a super- CC scaling. This study investigates the sensitivity of precipitation extremes to climate change in the 2015 Texas extreme precipitation event using the Column Quasi-Geostrophic (CQG) method. This event is simulated in different climatic conditions with varying surface temperature (Ts) given the same adiabatic quasi-geostrophic forcing. Results show that the extreme precipitation sensitivity is above the CC scaling due to the positive contribution from the dynamic responses. While the thermodynamic contribution is nearly independent on Ts , the dynamic contribution increases with Ts , leading to an accelerating extreme precipitation sensitivity. We further argue that the dynamic contribution is mainly due to diabatic heating amplification of thermodynamic contribution. Besides, vertical structure changes of moisture and diabatic heating lead to negative but secondary contributions to the sensitivity. Our results suggest that the positive feedback between thermodynamics and dynamics enhances the responses of extreme precipitation to climate change, and better representation of this feedback in GCMs are needed in term of reducing their uncertainties in extreme precipitation sensitivity.
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