Tropical precipitation extremes: Response to SST‐induced warming in aquaplanet simulations

Abstract

Scaling of tropical precipitation extremes in response to warming is studied in aquaplanet experiments using the global Weather Research and Forecasting (WRF) model. We show how the scaling of precipitation extremes is highly sensitive to spatial and temporal averaging: while instantaneous grid point extreme precipitation scales more strongly than the percentage increase (∼7% K−1) predicted by the Clausius‐Clapeyron (CC) relationship, extremes for zonally and temporally averaged precipitation follow a slight sub‐CC scaling, in agreement with results from Climate Model Intercomparison Project (CMIP) models. The scaling depends crucially on the employed convection parameterization. This is particularly true when grid point instantaneous extremes are considered. These results highlight how understanding the response of precipitation extremes to warming requires consideration of dynamic changes in addition to the thermodynamic response. Changes in grid‐scale precipitation, unlike those in convective‐scale precipitation, scale linearly with the resolved flow. Hence, dynamic changes include changes in both large‐scale and convective‐scale motions.

Water Cycle Changes

“…This evidence continues to support a thermodynamic strengthening of monsoon precipitation that is partly offset by slowing of the tropical circulation but with weak evidence and low agreement for regional aspects of circulation changes. Disagreement between paleoclimate and modern observations, physical theory and numerical simulations of global monsoons have been partly reconciled (Section 3.3.3.2) through improved understanding of regional processes (Harrison et al, 2015;R. Bhattacharya et al, 2017;Bhattacharya et al, 2018;Biasutti et al, 2018;D'Agostino et al, 2019;Jalihal et al, 2019;Seth et al, 2019), although interpreting past changes in the context of future projections requires careful account of differing forcings and feedbacks (D'Agostino et al, 2019).…”

On the Dependence of Cloud Feedbacks on Physical Parameterizations in WRF Aquaplanet Simulations

“…Following the Aqua‐Planet Experiment project (APE, Williamson et al, ), we perform two sets of eight simulations each, using WRF version 3.5.1 of the Advanced Research WRF core: a control experiment with zonally symmetric prescribed sea surface temperature (SST) referred to as Control, as in APE, and a warmer experiment with uniformly +4K increased SST simulations referred to as 4K. WRF model is run on 1° × 1° regular latitude‐longitude projection with a 40‐level stretched vertical grid and a time step of 200 s. Our setup closely follows the one described in Bhattacharya et al (). Orbital parameters are set to perpetual equinox conditions with a fixed solar constant, but the diurnal cycle is retained.…”

Parameterization Interactions in Global Aquaplanet Simulations

“…We perform simulations using the global WRF model (ARW, Version 3) (Skamarock et al, 2008) in aquaplanet setup (Hoskins et al, 1999). This setup has also been utilized in Bhattacharya et al (2017), as well as in Cesana et al (2017). The horizontal resolution is 1 31 and we use a stretched vertical mesh with 40 levels up to the top of the atmosphere.…”

“…The prescribed insolation is held at its constant equinox distribution, that is, there is no seasonal cycle. Six simulations are performed using widely varying BL schemes (EDMF and MYNN, described below) for a range of modeled convective activity starting from no cumulus scheme to moderate (Tiedtke scheme) to highly active (GFS scheme) (Bhattacharya et al, 2017). Dudhia et al (2012) and Biswas et al (2014) show that the Tiedtke and GFS (simplified Arakawa Schubert scheme designed for the Global Forecasting System of the National Centers for Environmental Prediction (Han & Pan, 2011)) lie at opposite extremes in terms of the ratio of convective to stratiform precipitation in WRF, with the former and the latter having the smallest and largest ratio, respectively (and other convection schemes lying in between).…”