SLS - Tsung-Lin Hsieh (Princeton)
Using seeds and climatological indices to understand tropical cyclone frequency in a hierarchy of global atmospheric models
High-resolution global atmospheric models provide opportunities to investigate the statistics and dynamics of tropical cyclones (TCs) in a consistent framework. In this talk, I will introduce a quantitative relationship between TC frequency and the large-scale climate developed in Hsieh et al. (2020), and discuss its application to understand the diverse TC responses across three versions of GFDL atmospheric models.
Our TC-climate relationship models TC genesis as a multi-step process: first a non-rotating convective cluster and then a weakly rotating ``seed'', before developing into a TC. The distribution of convective clusters is constrained by the large-scale convective mass flux, verified in aquaplanet experiments with shifting ITCZ. The probability of transition to seeds is constrained by an analytical function of the large-scale vorticity, verified in aquaplanet experiments with uniform SST. In experiments with realistic boundary conditions, the relationship explains the TC and seed responses across a range of CO2 and SST perturbations.
Driven by identical radiative forcing and boundary conditions, we construct a suite of experiments using three models having different parameterization of convection. The models generate opposite responses of TC and seed frequency to various surface warming perturbations. The model inconsistency is attributed using our TC-climate relationship to the different climatological conditions, particularly the large-scale convective mass fluxes in the Northwest Pacific.
About this Series:
The Atmosphere, Ocean and Climate Sack Lunch Seminar Series is an informal seminar series within PAOC that focuses on more specialized topics than the PAOC Colloquium. Seminar topics include all research concerning the science of atmosphere, ocean and climate. The seminars usually take place on Wednesdays from 12-1pm. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.