Objectively Determined Resolution-Dependent Threshold Criteria for the Detection of Tropical Cyclones in Climate Models and Reanalyses

Abstract

Objectively derived resolution-dependent criteria are defined for the detection of tropical cyclones in model simulations and observationally based analyses. These criteria are derived from the wind profiles of observed tropical cyclones, averaged at various resolutions. Both an analytical wind profile model and two-dimensional observed wind analyses are used. The results show that the threshold wind speed of an observed tropical cyclone varies roughly linearly with resolution. The criteria derived here are compared to the numerous different criteria previously employed in climate model simulations. The resulting method provides a simple means of comparing climate model simulations and reanalyses.

Simulation of medicanes over the Mediterranean Sea in a regional climate model ensemble: impact of ocean–atmosphere coupling and increased resolution

“…As we are dealing with tropical-like cyclones, we will use the criteria presented by Walsh et al (2007) for obtaining a resolution-dependent threshold for tropical storms, which have maximum surface winds above 17.5 m/s. Winds in tropical cyclones reach a maximum at a relatively small distance from the cyclone center, decreasing rapidly with increasing distance.…”

“…Therefore, if we sample the winds using a larger grid spacing (coarser resolution), a smaller wind maximum will be simulated. Following Walsh et al (2007), for the resolutions used in the present study, the threshold values for tropical storm intensity are 16.5 m/s Figure 4 (upper panel) shows the yearly frequency of medicanes for the different low/high resolution pairs of simulations using the same model (most of them have 50/12.5 km grid spacings). There is a clear frequency increase with resolution, which is systematic (all models show it) and generally strong (in six out of ten models, the frequency increases nearly two times or more).…”

Bias corrections of global models for regional climate simulations of high-impact weather

“…One approach is to apply combined bias-correction and downscaling methods directly to the GCM data in the form of empirical relationships between the large scales and high impact weather (Camargo et al 2007;Walsh et al 2007;Bruyère et al 2012). An obvious shortcoming of this method is that this bias correction is applied independently across time, space and variable, without taking into account feedback mechanisms between atmospheric processes.…”

Future changes in tropical cyclone activity projected by multi-physics and multi-SST ensemble experiments using the 60-km-mesh MRI-AGCM

“…Both theory (Emanuel 1987) and modelling studies (Knutson et al 2010) suggest that the TC intensity could increase with global warming (IPCC 2007); however, projected changes in the TC genesis number have varied considerably, especially at the ocean-basin scale (IPCC 2007;Emanuel 2008;Zhao et al 2009;Knutson et al 2010). This inconsistency among projections arises from a number of factors, including differences in assumed spatial patterns of future changes in sea surface temperature (SST; Sugi et al 2009;Zhao et al 2009), differences in model physical parameterisations (Walsh et al 2010), differences in the chosen global warming scenario (Stowasser et al 2007), and differences in the methods used to detect TCs (Walsh et al 2007).…”