Physical understanding of the tropical cyclone wind-pressure relationship

Daniel R Chavas,John A Knaff,Kevin A Reed

doi:10.1038/s41467-017-01546-9

Daniel R Chavas, John A Knaff + Show 1 more

Open Access

https://doi.org/10.1038/s41467-017-01546-9

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Abstract

The relationship between the two common measures of tropical cyclone intensity, the central pressure deficit and the peak near-surface wind speed, is a long-standing problem in tropical meteorology that has been approximated empirically yet lacks physical understanding. Here we provide theoretical grounding for this relationship. We first demonstrate that the central pressure deficit is highly predictable from the low-level wind field via gradient wind balance. We then show that this relationship reduces to a dependence on two velocity scales: the maximum azimuthal-mean azimuthal wind speed and half the product of the Coriolis parameter and outer storm size. This simple theory is found to hold across a hierarchy of models spanning reduced-complexity and Earth-like global simulations and observations. Thus, the central pressure deficit is an intensity measure that combines maximum wind speed, storm size, and background rotation rate. This work has significant implications for both fundamental understanding and risk analysis, including why the central pressure better explains historical economic damages than does maximum wind speed.

Highlights

The relationship between the two common measures of tropical cyclone intensity, the central pressure deficit and the peak near-surface wind speed, is a long-standing problem in tropical meteorology that has been approximated empirically yet lacks physical understanding
The relationship between the central pressure deficit and peak near-surface wind speed in a tropical cyclone is a long-standing unsolved problem in tropical meteorology, one that has significant implications for both our physical understanding of the tropical cyclone as well as the communication and interpretation of hazard information for evaluating risk of damage and loss of life. Both metrics have been employed as essentially interchangeable measures of tropical cyclone intensity
General circulation models at resolutions of 50–100 km are capable of reproducing the range of central pressure deficit values found in observations despite their inability to reproduce the upper end of the range of peak wind speeds[14,16,17], perhaps due to variations in other relevant storm properties, such as storm size

Summary

Introduction

The relationship between the two common measures of tropical cyclone intensity, the central pressure deficit and the peak near-surface wind speed, is a long-standing problem in tropical meteorology that has been approximated empirically yet lacks physical understanding. Physical understanding is currently lacking, the prevailing empirical model[6,7] for this relationship trained on historical observations determined that the central pressure deficit depends principally on storm peak wind speed and secondarily on latitude and a normalized measure of storm size The choice of their parameters were broadly motivated by gradient wind balance, which directly relates the low-level radial distributions of pressure and wind. We find that the simple theory holds well across the hierarchy, indicating that this theory captures the fundamental dependence of the central pressure deficit for real storms in nature This understanding of the relationship between central pressure and maximum wind speed can be used to improve the interpretation of real-time tropical cyclone observations of storm intensity and size as well as to better understand variability in tropical cyclones and long-term hazard risk in both the historical record and in model simulations of present and future climate states

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