Sensitivity of Tropical Cyclone Formation to Resolution-Dependent and Independent Tracking Schemes in High-Resolution Climate Model Simulations

In the present study, global tropical cyclone (TC) formation characteristics are estimated using two fundamentally different Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Okubo-Weiss zeta parameter (OWZP) tracking schemes in the reanalysis data and in a high-resolution climate model with interannually varying sea surface temperatures. Both the schemes have a reasonable global geographical distribution of TC genesis locations with under simulation in the eastern North Atlantic and northwestern Australian regions. The mean annual TC frequency in the model is similar to observations using the CSIRO scheme but higher using the OWZP scheme, whereas the annual frequency in reanalysis using the OWZP scheme is similar to observations but halved using the CSIRO scheme. In the CSIRO scheme, both the resolution-dependent thresholds and large-scale climate may play a role for skilful TC formation statistics. In contrast, large-scale climate leads to changes in OWZP TC detections. This highlights the importance of the large-scale environment for TC detections in both the tracking schemes. The OWZP scheme can differentiate the monsoon lows from the actual TCs in the north Indian Ocean compared to the CSIRO scheme, which incorrectly detects them as TCs in the monsoon season. The distribution of TC lifetime in the model using the OWZP scheme is similar to observations. Conversely, the CSIRO scheme detected TCs have shorter lifetimes, perhaps due to intrinsic tracking scheme differences. Although the tracking schemes are fundamentally different, the study shows that there exist some similarities between them and for certain TC formation characteristics the OWZP scheme performs better compared to the CSIRO scheme. Plain Language Summary As the climate models act as the best tool to understand the relationship between the climate and TC formation, the TC research world is moving toward the high-resolution climate models with improved parameterization schemes to understand TC formation characteristics in the current climate better and improve the confidence in future projections. In the current study, a high-resolution atmospheric climate model is used to observe the performance of two different tracking schemes when compared with observations in simulating different TC characteristics like geographical distributions, mean annual numbers, the influence of El Nino (La Nina), and interannual and seasonal variability of TC frequency. Of the two schemes employed, one scheme is the traditional CSIRO tracking scheme that detects TC-like vorticities and the other scheme, using the Okubo-Weiss zeta parameter, a phenomena based scheme, detects the circulations that have the potential for TC formation. The Okubo-Weiss zeta parameter scheme has superior performance in simulating the TC frequency characteristics compared to the CSIRO scheme.