Tracking Scheme Dependence of Simulated Tropical Cyclone Response to Idealized Climate Simulations

Abstract

Future tropical cyclone activity is a topic of great scientific and societal interest. In the absence of a climate theory of tropical cyclogenesis, general circulation models are the primary tool available for investigating the issue. However, the identification of tropical cyclones in model data at moderate resolution is complex, and numerous schemes have been developed for their detection.The influence of different tracking schemes on detected tropical cyclone activity and responses in the Hurricane Working Group experiments is examined herein. These are idealized atmospheric general circulation model experiments aimed at determining and distinguishing the effects of increased sea surface temperature and other increased CO 2 effects on tropical cyclone activity. Two tracking schemes are applied to these data and the tracks provided by each modeling group are analyzed.The results herein indicate moderate agreement between the different tracking methods, with some models and experiments showing better agreement across schemes than others. When comparing responses between experiments, it is found that much of the disagreement between schemes is due to differences in duration, wind speed, and formation-latitude thresholds. After homogenization in these thresholds, agreement between different tracking methods is improved. However, much disagreement remains, accountable for by more fundamental differences between the tracking schemes. The results indicate that sensitivity testing and selection of objective thresholds are the key factors in obtaining meaningful, reproducible results when tracking tropical cyclones in climate model data at these resolutions, but that more fundamental differences between tracking methods can also have a significant impact on the responses in activity detected.

Dynamical downscaling of tropical cyclones from CCSM4 simulations of the Last Glacial Maximum

“…Because the differences in storm counts between the two storm tracking schemes were not statistically significant, we proceed in the remainder of the study with an analysis of the results using the CZ02-generated track data set only. Despite the fact the differences are not statistically significant, it is noteworthy that the two algorithms yield different signs for the change in NTC between LGM and 20C; this highlights some of the variability inherent in different tracking algorithms, which can be especially large in their treatment of the weakest systems [Horn et al, 2014].…”

“…Different storm tracking methods use different criteria and variables to detect and define features [e.g., see Horn et al, 2014]. To identify and follow coherent warm-cored cyclonic systems, we set minimum thresholds for the CZ02 detection criteria to be 30 3 10 25 s 21 of 850 hPa vorticity, a 0.51 K temperature anomaly, 15 m s 21 of 10 m wind speed, a minimum of 2 days of duration for the storm (nonconsecutive), and a tracking threshold for of 7 3 10 25 for the vorticity.…”

Stride Search: a general algorithm for storm detection in high-resolution climate data

“…The particular variables and their appropriate threshold values vary greatly by application, and many studies have proposed and compared different sets of criteria; see Raible et al (2008) and Neu et al (2013) for a discussion of extratropical cyclone criteria. Walsh et al (2007) and Horn et al (2014) provide similar analyses for tropical cyclones.…”

“…In practice, however, we find that just as a change to the identification criteria of a particular storm type can change the statistics found in a particular data set Horn et al, 2014), the way that data set is divided and searched -independently of the identification criteriacan also affect the statistics.…”

The influence of model resolution on the simulated sensitivity of North Atlantic tropical cyclone maximum intensity to sea surface temperature

“…Additionally, the algorithms used to detect and track TCs in the model fields vary among the models. As demonstrated in Horn et al [2014], model simulation results are often sensitive to differences in the duration threshold, which ranges from 36 to 72 h for the models used in this study. It is possible that we filtered out this tracker effect by considering only the strongest TCs (i.e., those that are most likely to be detected regardless of the selected tracking algorithm).…”