Speaker: Andrew Williams, Princeton University

Title: A robust constraint on the response of convective mass fluxes to warming 

Abstract: Understanding how the tropical circulation responds to warming is crucial if we are to project future hydroclimate changes. An important quantity in this regard is the 'convective mass flux', which measures the net upwards mass flux in tropical convection. Previous work by Held and Soden (2006) proposed a scaling for changes in the convective mass flux at cloud base with warming, but previous literature has questioned its validity. Here we show, using a diverse ensemble of cloud-resolving simulations, that the Held and Soden scaling does not capture inter-model spread in cloud base mass flux changes under warming. We then introduce a new scaling for changes in convective mass flux under warming based on the clear-sky energy budget, which holds throughout the free-troposphere (as opposed to just at cloud base). We verify that this scaling works across a hierarchy of models, from idealized radiative-convective equilibrium simulations to global storm-resolving runs with GFDL's X-SHiELD model. This work provides, for the first time, a constraint on changes in convective mass flux throughout the troposphere which can be derived from first principles, and which is verified across a hierarchy of models. 

Bio:  Andrew Williams is a postdoctoral fellow working at Princeton University and NOAA's Geophysical Fluid Dynamics Laboratory. He studies the physics of clouds and radiation and how they shape atmospheric circulation and the hydrological cycle. He obtained a PhD in climate physics from the University of Oxford in 2023, where he studied the sensitivity of global and regional climate to changes in the spatial pattern of sea-surface temperature and anthropogenic aerosol. He currently lives in New York with his partner and their cat, Cleopatra.