The link between extreme precipitation and convective organization in a warming climate

The rate of increase of extreme precipitation in response to global warming varies dramatically across climate model simulations, particularly over the tropics, for reasons that have yet to be established. In this paper, we illustrate one candidate mechanism: changing organization of convection with climate. We analyze a set of idealized climate model simulations in which both convective organization and extreme precipitation vary. Twelve simulations with the Community Atmosphere Model version 5 (CAM5) are run in an idealized global radiative-convective equilibrium configuration. These simulations are forced by fixed sea surface temperature (SST) varying in two-degree increments from 285 to 307 K. In these simulations, convective organization varies from semi-organized in cold simulations, disorganized in warm simulations, and abruptly becomes highly organized at just over 300 K. The change in extreme precipitation with warming varies across these simulations, including a large increase at the transition from disorganized to organized convection. We develop an extreme-precipitation-focused metric to quantify convective organization, and use it to explore the connection between extreme precipitation and convective organization. We also perform a sensitivity analysis on the extreme precipitation change to isolate the influences of circulation, temperature structure, and SST. This sensitivity analysis shows that circulation change is needed to recover the large increase in extreme precipitation from disorganized to organized states.

Pendergrass, A. G., K. A. Reed, and B. Medeiros (2016), The link between extreme precipitation and convective organization in a warming climate: Global radiative-convective equilibrium simulations, Geophys. Res. Lett., 43, 11,445–11,452, doi:10.1002/2016GL071285