TC Worlds in a Three-Level Model

Abstract

Abstract Three-level and thee-layer models of tropical cyclones (TCs) have provided a more conceptual view of TC dynamics than conventional numerical models. They have been purpose-built, with special treatments of boundary layers and/or convection. We show that a further simplification with minimal parameterization and a seamless connection to higher resolution captures TCs about as well. The framework of radiative–convective equilibrium avoids ambiguities from temporal and spatial boundaries. For the TCs, the minimal grid provides one level for outflow and one level for most of the inflow. A version with 10 levels is used for comparison. For the same average pressure intensity, the wind field is slightly broader around the three-level vortices, with stronger subsidence in the core and 25% more mass and moisture flux. However, thermodynamic efficiency, mechanical efficiency, and TC counts are about the same. Across runs with different surface temperatures and cooling rates, global energy scaling makes reasonable predictions of the maximum velocity allowing for variations in the effective forcing/dissipation area and surface humidity. TC count is inconsistent with theories for size as a function of Coriolis parameter. An overturning circuit is isolated within a composite vortex and analyzed using energy and entropy budgets to mirror analytical models. Effective radiation and dissipation temperatures are less extreme than often assumed in such models, yielding a smaller thermodynamic efficiency near the global value of ∼0.1. The pressure deficit arises mostly from inflow enthalpy increase, as expected, but dissipation reduces the contribution from an outflow pressure increase. The influence of ambient CAPE makes up most of the difference.