Thermodynamic characteristics of downdrafts in tropical cyclones as seen in idealized simulations of different intensities

Joshua B. Wadler, David S. Nolan, Jun A. Zhang, Lynn K. Shay

Research output: Contribution to journalArticlepeer-review

Abstract

The thermodynamic effect of downdrafts on the boundary layer and nearby updrafts are explored in idealized simulations of category-3 and category-5 tropical cyclones (TCs) (Ideal3 and Ideal5). In Ideal5, downdrafts underneath the eyewall pose no negative thermodynamic influence because of eye-eyewall mixing below 2-km altitude. Additionally, a layer of higher ue between 1- and 2-km altitude associated with low-level outflow that extends 40 km outward from the eyewall region creates a ''thermodynamic shield'' that prevents negative effects from downdrafts. In Ideal3, parcel trajectories from downdrafts directly underneath the eyewall reveal that low-ue air initially moves radially inward allowing for some recovery in the eye, but still enters eyewall updrafts with a mean ue deficit of 5.2 K. Parcels originating in low-level downdrafts often stay below 400 m for over an hour and increase their ue by 10-14 K, showing that air-sea enthalpy fluxes cause sufficient energetic recovery. The most thermodynamically unfavorable downdrafts occur;5 km radially outward from an updraft and transport low-ue midtropospheric air toward the inflow layer. Here, the low-ue air entrains into the updraft in less than 5 min with a mean ue deficit of 8.2 K. In general, ue recovery is a function of minimum parcel altitude such that downdrafts with the most negative influence are those entrained into the top of the inflow layer. With both simulated TCs exposed to environmental vertical wind shear, this study underscores that storm structure and individual downdraft characteristics must be considered when discussing paradigms for TC intensity evolution.

Original languageEnglish (US)
Pages (from-to)3503-3523
Number of pages21
JournalJournal of the Atmospheric Sciences
Volume78
Issue number11
DOIs
StatePublished - Nov 2021

Keywords

  • Air-sea interaction
  • Convection
  • Hurricanes
  • Thermodynamics
  • Tropical cyclones
  • Updrafts/downdrafts

ASJC Scopus subject areas

  • Atmospheric Science

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