Upper‐level trajectories in the prototype problem for tropical cyclone intensification

Shanghong Wang,Roger K Smith

doi:10.1002/qj.4110

Abstract

AbstractData from an idealized three‐dimensional numerical simulation of tropical cyclone intensification are used to calculate Lagrangian air parcel trajectories emanating from the inflow layer that develops beneath the upper‐tropospheric outflow layer. It is found that about half of these trajectories end up in the outflow layer itself. The other half slowly subside to the mid‐ to upper troposphere, below the outflow layer, and drift slowly outwards as a result of a relatively weak overturning circulation in that region. Calculations show that pseudo‐equivalent potential temperature is not approximately conserved along the air parcel trajectories, indicating that the turbulent diffusion of heat and moisture and/or the latent heat changes by freezing or melting along the trajectories is appreciable in the mid‐ and upper troposphere.

Highlights

The ability to make in situ observations of the upper-level outflow layer in tropical cyclones using dropsondes released from high-flying aircraft and unmanned drones has led to renewed efforts to understand the role of the outflow layer in tropical cyclone behaviour (e.g., Komaromi and Doyle, 2017, Doyle et al, 2017, Tao et al, 2019, Montgomery et al, 2020, Wang et al, 2020)
There are two main groups of trajectories in this set: 1. The air parcels starting at 70, 80 and 110 km radius spiral cyclonically inwards before entering the eyewall updraught
As in the previous set of trajectories, the air parcels which end up in the outflow layer take less than 12 hr to move more than 250 km in radius from the vortex centre, while those that descend to the middle layer remain within a radius of 150 km after 24 hr

Summary

Introduction

The ability to make in situ observations of the upper-level outflow layer in tropical cyclones using dropsondes released from high-flying aircraft and unmanned drones has led to renewed efforts to understand the role of the outflow layer in tropical cyclone behaviour (e.g., Komaromi and Doyle, 2017, Doyle et al, 2017, Tao et al, 2019, Montgomery et al, 2020, Wang et al, 2020) Two of these observational studies noted that, adjacent to the outflow layer, there are sometimes inflow layers as well (Komaromi and Doyle, 2017, Smith et al, 2019). They are not considered when treating the tropical cyclone as a type of thermodynamic Carnot heat engine (e.g., Emanuel, 1986; 1988; 1991; 2018 and references therein)

Methods

Results

Conclusion