The Development and Assessment of a Model-, Grid-, and Basin-Independent Tropical Cyclone Detection Scheme

Abstract

A novel approach to tropical cyclone (TC) detection in coarse-resolution numerical model data is introduced and assessed. This approach differs from traditional detectors in two main ways. First, it was developed and tuned using 20 yr of ECMWF Interim Re-Analysis (ERA-Interim) data, rather than using climate model data. This ensures that the detector is independent of any climate models to which it will later be applied. Second, only relatively large-scale parameters resolvable in climate models are included, in order to minimize any grid-resolution dependence on parameter thresholds. This approach is taken in an attempt to construct a unified TC detection procedure applicable to all climate models without the need for any further tuning or adjustment.Unlike traditional detectors that seek to identify TCs directly, the authors' method seeks to identify conditions favorable for TC formation. Favorable TC formation regions at the center of closed circulations in the lower troposphere to the midtroposphere are identified using a low-deformation vorticity parameter. Additional relative and specific humidity thresholds are applied to ensure the thermodynamic environment is favorable, and a vertical wind shear threshold is applied to eliminate storms in a destructive shear environment. A further requirement is that thresholds for all parameters must be satisfied for at least 48 h before a TC is deemed to have developed.A thorough assessment of the detector performance is provided. It is demonstrated that the method reproduces realistic TC genesis frequency and spatial distributions in the ERA-Interim data. Application of the detector to four climate models is presented in a companion paper.

Skilful multiweek tropical cyclone prediction in ACCESS‐S1 and the role of the MJO

“…The thresholds are model‐ and grid‐resolution‐independent and are applied to all ocean basins. The algorithm reproduces realistic TC genesis frequency and spatial distribution when applied to reanalysis data and the mean annual TC frequency is statistically similar to observations at the 95% level (Tory et al ).…”

“…TCs are detected in ACCESS‐S1 using the Okubo–Weiss– Zeta parameter (OWZP) TC detection scheme (Tory et al ; ; ; ). The scheme identifies favourable conditions for TC formation using thresholds of a low‐deformation vorticity parameter.…”

Tropical cyclones and climate change

“…Ideally, there should be no uncertainty introduced by the method used to detect TCs in a climate model simulation. In practice, climate model studies use a wide range of TC tracking and detection schemes, but no detection technique is perfect . Traditional direct detection methods use (1) structural criteria to ensure a disturbance resembles a TC and (2) a wind speed threshold to determine if the disturbance is sufficiently intense to be considered a TC.…”

Objective identification of potentially damaging tropical cyclones over the Western North Pacific

“…This overcomes the need to use absolute thresholds for TC related windstorm detection and is one main difference to many TC detection algorithms (e.g. Sugi et al 2009, Tory et al 2013b, Camargo 2013, Walsh et al 2013, Horn et al 2014 which use different detection criteria/thresholds for e.g, wind speeds or relative vorticity (see table1 in Walsh et al 2007 &Zarzycki 2017 their appendix B).…”