On the distribution of helicity in the tropical cyclone boundary layer from dropsonde composites

Nuo Chen, Jie Tang, Jun A. Zhang, Lei Ming Ma, Hui Yu

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

This study analyzes GPS dropsonde data in multiple tropical cyclones from 1997 to 2017 to investigate the boundary layer structure with a focus on helicity distribution. A helicity-based method for boundary layer height is developed and evaluated by comparing it to other boundary layer height scales including the inflow layer depth, height of the maximum tangential wind speed and thermodynamic mixed layer depth. Our dropsonde composites confirmed the radial variations of these boundary layer heights seen in previous studies. The results show that the boundary layer height defined by the maximum vertical gradient of helicity is closest to the height of the maximum tangential wind speed or jet height and is located between the inflow layer depth and thermodynamic mixed layer height in all intensity groups. All three kinematic height scales generally decrease with storm intensity at a given radius. These kinematic height scales converge in the major hurricane group, while the inflow layer depth is much larger than the other two height scales in the tropical storm group. The maximum normalized helicity is located at 100–200 m altitude which is close to the height of the maximum inflow. Both front-back and downshear-upshear asymmetries are observed in the 0–1 km layer integrated helicity in the inner core region of a storm, and the helicity on the front and downshear sides is larger in all intensity groups. The results also show that the helicity magnitude is generally larger in the boundary layer of stronger storms. Application of helicity to quantify turbulent characteristics in the boundary layer is discussed.

Original languageEnglish (US)
Article number105298
JournalAtmospheric Research
Volume249
DOIs
StatePublished - Feb 2021

Keywords

  • Boundary layer
  • Dropsonde composite
  • Helicity
  • Tropical cyclone

ASJC Scopus subject areas

  • Atmospheric Science

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