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Melbourne University
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- PublicationRestrictedCluster analysis of downscaled and explicitly simulated North Atlantic tropical cyclone tracks(2015-02)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Daloz, A. S.; University of Wisconsin-Madison ;Camargo, S.; Columbia University ;Kossin, J. P.; NOAA/NCDC ;Emanuel, K.; MIT ;Horn, M.; University of Melbourne ;Jonas, J. A.; Columbia Univrsity ;Kim, D.; Columbia /university ;Larow, T.; Florida State university ;Lim, Y-K.; NASA ;Patricola, C. M.; Texas University ;Roberts, M. J.; Met Office ;Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Shaevitz, D.; Columbia UNiversity ;Vidale, P. L.; University of Reading ;Wehner, M.; University of California ;Zhao, M.; GFDL; ; ; ; ; ; ; ; ; ; ; ; ; ; ; A realistic representation of the North Atlantic tropical cyclone tracks is crucial as it allows, for example, explaining potential changes in U.S. landfalling systems. Here, the authors present a tentative study that examines the ability of recent climate models to represent North Atlantic tropical cyclone tracks. Tracks from two types of climate models are evaluated: explicit tracks are obtained from tropical cyclones simulated in regional or global climate models with moderate to high horizontal resolution (1°–0.25°), and downscaled tracks are obtained using a downscaling technique with large-scale environmental fields from a subset of these models. For both configurations, tracks are objectively separated into four groups using a cluster technique, leading to a zonal and a meridional separation of the tracks. The meridional separation largely captures the separation between deep tropical and subtropical, hybrid or baroclinic cyclones, while the zonal separation segregates Gulf of Mexico and Cape Verde storms. The properties of the tracks’ seasonality, intensity, and power dissipation index in each cluster are documented for both configurations. The authors’ results show that, except for the seasonality, the downscaled tracks better capture the observed characteristics of the clusters. The authors also use three different idealized scenarios to examine the possible future changes of tropical cyclone tracks under 1) warming sea surface temperature, 2) increasing carbon dioxide, and 3) a combination of the two. The response to each scenario is highly variable depending on the simulation considered. Finally, the authors examine the role of each cluster in these future changes and find no preponderant contribution of any single cluster over the others.140 16 - PublicationRestrictedHurricanes and climate: the U.S. CLIVAR working group on hurricanes(2015)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Walsh, K. J. E.; University of Melbourne ;Camargo, S. J.; Columbia University ;Vecchi, G. A.; GFDL ;Daloz, A. S.; University of Wisconsin-Madison ;Elsner, J.; Florida State University ;Emanuel, K.; MIT ;Horn, M.; University of Melbourne ;Lim, Y. K.; NASA ;Roberts, M.; Met-Office ;Patricola, C.; Texas A&M University ;Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Sobel, A.; Columbia University ;Strazzo, S.; Florida State University ;Villarini, G.; IOWA University ;Wehner, M.; Lawrence Berkeley National Laboratory, ;Zhao, M.; GFDL ;Kossin, J. P.; NOAA/NCDC ;Larow, T.; Florida State University ;Oouchi, K.; JAMSTEC ;Shubert, S.; NASA ;Wang, H.; NOAA/NCEP ;Bacmeister, J.; NCAR ;Chang, P.; Texas A&M University ;Chauvin, F.; Meteo-France ;Jablonowski, C.; University of Michigan ;Kumar, A.; NOAA ;Murakami, H.; GFDL ;Ose, T.; MRI/JMA ;Reed, K.; NCAR ;Saravanan, R.; Texas A&M University ;Yamada, Y.; JAMSTEC ;Zarzycki, C. M.; University of Michigan ;Vidale, P. L.; University of Reading ;Jonas, J. A.; Columbia Univeristy ;Henderson, N.; Lamont-Doherty Earth Observatory,; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and understand the relationship between climate and tropical cyclone formation. Climate models are now able to simulate a realistic rate of global tropical cyclone formation, although simulation of the Atlantic tropical cyclone climatology remains challenging unless horizontal resolutions finer than 50 km are employed. This article summarizes published research from the idealized experiments of the Hurricane Working Group of U.S. CLIVAR (CLImate VARiability and predictability of the ocean-atmosphere system). This work, combined with results from other model simulations, has strengthened relationships between tropical cyclone formation rates and climate variables such as mid-tropospheric vertical velocity, with decreased climatological vertical velocities leading to decreased tropical cyclone formation. Systematic differences are shown between experiments in which only sea surface temperature is increased versus experiments where only atmospheric carbon dioxide is increased, with the carbon dioxide experiments more likely to demonstrate the decrease in tropical cyclone numbers previously shown to be a common response of climate models in a warmer climate. Experiments where the two effects are combined also show decreases in numbers, but these tend to be less for models that demonstrate a strong tropical cyclone response to increased sea surface temperatures. Further experiments are proposed that may improve our understanding of the relationship between climate and tropical cyclone formation, including experiments with two-way interaction between the ocean and the atmosphere and variations in atmospheric aerosols.246 57 - PublicationRestrictedTracking Scheme Dependence of Simulated Tropical Cyclone Response to Idealized Climate Simulations(2014)
; ; ; ; ; ; ; ; ; ; ; ; ;Horn, M.; Melbourne University ;Walsh, K.; Melbourne University ;Zhao, M.; GFDL ;Camargo, S.; Columbia University NY ;Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Murakami, H.; GFDL ;Ballinger, A.; Princeton University ;Wang, H.; NOAA ;Kumar, A.; NOAA ;Shaewitz, D.; Columbia University NY ;Jonas, J. A.; NASA ;Oouchi, K.; IPRC/MRI; ; ; ; ; ; ; ; ; ; ; 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. We here examine the influence of different tracking schemes on detected tropical cyclone activity and responses in the Hurricane Working Group experiments. These are idealized atmospheric general circulation model experiments aimed at determining and distinguishing the effects of increased sea-surface temperature and other increased CO2 effects on tropical cyclone activity. We apply two tracking schemes to these data and also analyze the tracks provided by each modelling group. Our results 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, we find that much of the disagreement between schemes is due to differences in duration, wind speed, and formation-latitude thresholds. After homogenisation in these thresholds, agreement between different tracking methods is improved. However, much disagreement remains, accountable for by more fundamental differences between the tracking schemes. Our 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.210 45