Aquaplanet Simulations of Tropical Cyclones

Timothy M Merlis,Isaac M Held

doi:10.1007/s40641-019-00133-y

Abstract

Purpose of ReviewTropical cyclones (TCs) are strongly influenced by the large-scale environment of the tropics and will, therefore, be modified by climate changes. Numerical simulations designed to understand the sensitivities of TCs to environmental changes have typically followed one of two approaches: single-storm domain sizes with convection-permitting resolution and uniform thermal boundary conditions or comprehensive global high-resolution (about 50 km in the horizontal) atmospheric general circulation model (GCM) simulations. The approaches reviewed here rest between these two and are an important component of hierarchical modelling of the atmosphere: aquaplanet TC simulations.Recent FindingsIdealized model configurations have revealed controls on equilibrium TC size in large-domain simulations of rotating radiative-convective equilibrium. Simulations that include differential rotation (spherical geometry) but retain uniform thermal forcing have revealed a new mechanism of TC propagation change via storm-scale dynamics and show a poleward shift in genesis in response to warming. Simulations with Earth-like meridional thermal forcing gradients have isolated competing influences on TC genesis via shifts in the atmospheric general circulation and the temperature dependence of TC genesis in the absence of mean circulation changes.SummaryAquaplanet simulations of TCs with variants that include or inhibit certain processes have recently emerged as a research methodology that has advanced the understanding of the climatic controls on TC activity. Looking forward, idealized boundary condition model configurations can be used as a bridge between GCM resolution and convection-permitting resolution models and as a tool for identifying additional mechanisms through which climate changes influence TC activity.

Highlights

Tropical cyclones (TCs, known as hurricanes and typhoons) are a destructive component of the climate system
We review the choices of simulation domain and boundary conditions (BCs) that have been used for TC aquaplanet simulations (BSimulation Domain and Boundary Conditions^)
We focus on results performed across this hierarchy of simulation configurations performed with the Geophysical Fluid Dynamics Laboratory’s High-Resolution Atmospheric Model (HiRAM) general circulation model (GCM), which has a high-quality simulation of climatological, interannual, and interdecadal TC activity in comprehensive BC simulations with prescribed, interannually varying, observed sea surface temperature (SST) [9, public release available at https:// www.gfdl.noaa.gov/hiram-quickstart/]

Summary

Introduction

Tropical cyclones (TCs, known as hurricanes and typhoons) are a destructive component of the climate system. These simulations often use idealized boundary conditions (BCs) of doubly periodic f -plane geometry with a homogeneous thermal forcing (prescribed uniform SST, in particular), run at sufficiently high, Bcloud-resolving model^ (CRM) resolution (∼ 1km ) to capture storm intensity (Fig. 1a).

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