A New Paradigm for Intensity Modification of Tropical Cyclones: Thermodynamic Impact of Vertical Wind Shear on the Inflow Layer : Volume 9, Issue 3 (04/05/2009)

By Riemer, M.

Book Id: WPLBN0003987044
Format Type: PDF Article :
File Size: Pages 65
Reproduction Date: 2015

Title:	A New Paradigm for Intensity Modification of Tropical Cyclones: Thermodynamic Impact of Vertical Wind Shear on the Inflow Layer : Volume 9, Issue 3 (04/05/2009)
Author:	Riemer, M.
Volume:	Vol. 9, Issue 3
Language:	English
Subject:	Science, Atmospheric, Chemistry
Collections:	Periodicals: Journal and Magazine Collection (Contemporary), Copernicus GmbH
Historic Publication Date:	2009
Publisher:	Copernicus Gmbh, Göttingen, Germany

Member Page:	Copernicus Publications
Citation APA MLA Chicago Nicholls, M. E., Montgomery, M. T., & Riemer, M. (2009). A New Paradigm for Intensity Modification of Tropical Cyclones: Thermodynamic Impact of Vertical Wind Shear on the Inflow Layer : Volume 9, Issue 3 (04/05/2009). Retrieved from http://gutenberg.cc/

Description
Description: Department of Meteorology, Naval Postgraduate School, Monterey, CA, USA. An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the classical idealised numerical experiment of tropical cyclones (TCs) in vertical wind shear on an f-plane. We employ a set of simplified model physics – a simple bulk aerodynamic boundary layer scheme and warm rain microphysics – to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. A suite of experiments is performed with intense TCs in moderate to strong vertical shear. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur.

The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower Θ_e) air – anti-fuel for the TC power machine – can enter the core region of the TC. Strong and persistent downdrafts flux low Θ_e air from the lower and middle troposphere into the boundary layer, significantly depressing the Θ_e values in the storm's inflow layer. Air with lower Θ_e values enters the eyewall updrafts, considerably reducing eyewall Θ_e values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is – if at all – only valid for stationary and axisymmetric TCs, a strong correlation between the downward transport of low Θ_e into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis.

The downdrafts that flush the inflow layer with low Θ_e air are associated with a quasi-stationary region of convective activity outside the TC's eyewall. We show evidence that, to zero order, the formation of the convective asymmetry is driven by the balanced dynamical response of the TC vortex to the vertical shear forcing. Thus a close link is provided between the thermodynamic impact in the near-core boundary layer and the balanced dynamics governing the TC vortex evolution.

Summary
A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer

Excerpt
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