scholarly journals Influence of Tropical Tropopause Layer Cooling on Atlantic Hurricane Activity

2013 ◽  
Vol 26 (7) ◽  
pp. 2288-2301 ◽  
Author(s):  
Kerry Emanuel ◽  
Susan Solomon ◽  
Doris Folini ◽  
Sean Davis ◽  
Chiara Cagnazzo
Keyword(s):  
Tropical Cyclone ◽  
General Circulation ◽  
General Circulation Models ◽  
Tropical Cyclone Activity ◽  
Sea Surface ◽  
Cyclone Activity ◽  
Tropical Tropopause Layer ◽  
The Past ◽  
Tropical Tropopause ◽  
Atlantic Tropical Cyclone

Abstract Virtually all metrics of Atlantic tropical cyclone activity show substantial increases over the past two decades. It is argued here that cooling near the tropical tropopause and the associated decrease in tropical cyclone outflow temperature contributed to the observed increase in tropical cyclone potential intensity over this period. Quantitative uncertainties in the magnitude of the cooling are important, but a broad range of observations supports some cooling. Downscalings of the output of atmospheric general circulation models (AGCMs) that are driven by observed sea surface temperatures and sea ice cover produce little if any increase in Atlantic tropical cyclone metrics over the past two decades, even though observed variability before roughly 1970 is well simulated by some of the models. Part of this shortcoming is traced to the failure of the AGCMs examined to reproduce the observed cooling of the lower stratosphere and tropical tropopause layer (TTL) over the past few decades. The authors caution against using sea surface temperature or proxies based on it to make projections of tropical cyclone activity as there can be significant contributions from other variables such as the outflow temperature. The proposed mechanisms of TTL cooling (e.g., ozone depletion and stratospheric circulation changes) are reviewed, and the need for improved representations of these processes in global models in order to improve projections of future tropical cyclone activity is emphasized.

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

2014 ◽  
Vol 27 (24) ◽  
pp. 9197-9213 ◽  
Author(s):  
Michael Horn ◽  
Kevin Walsh ◽  
Ming Zhao ◽  
Suzana J. Camargo ◽  
Enrico Scoccimarro ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
General Circulation ◽  
Climate Model ◽  
Circulation Model ◽  
General Circulation Models ◽  
Tropical Cyclone Activity ◽  
Model Data ◽  
Cyclone Activity ◽  
Sensitivity Testing

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 CO2 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.

scholarly journals The Roles of Wind Shear and Thermal Stratification in Past and Projected Changes of Atlantic Tropical Cyclone Activity

2009 ◽  
Vol 22 (17) ◽  
pp. 4723-4734 ◽  
Author(s):  
Stephen T. Garner ◽  
Isaac M. Held ◽  
Thomas Knutson ◽  
Joseph Sirutis
Keyword(s):  
Tropical Cyclone ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Tropical Cyclone Activity ◽  
Sea Surface ◽  
Vertical Shear ◽  
Cyclone Activity ◽  
Western Atlantic ◽  
Environmental Indices ◽  
Atlantic Tropical Cyclone

Abstract Atlantic tropical cyclone activity has trended upward in recent decades. The increase coincides with favorable changes in local sea surface temperature and other environmental indices, principally associated with vertical shear and the thermodynamic profile. The relative importance of these environmental factors has not been firmly established. A recent study using a high-resolution dynamical downscaling model has captured both the trend and interannual variations in Atlantic storm frequency with considerable fidelity. In the present work, this downscaling framework is used to assess the importance of the large-scale thermodynamic environment relative to other factors influencing Atlantic tropical storms. Separate assessments are done for the recent multidecadal trend (1980–2006) and a model-projected global warming environment for the late 21st century. For the multidecadal trend, changes in the seasonal-mean thermodynamic environment (sea surface temperature and atmospheric temperature profile at fixed relative humidity) account for more than half of the observed increase in tropical cyclone frequency, with other seasonal-mean changes (including vertical shear) having a somewhat smaller combined effect. In contrast, the model’s projected reduction in Atlantic tropical cyclone activity in the warm climate scenario appears to be driven mostly by increased seasonal-mean vertical shear in the western Atlantic and Caribbean rather than by changes in the SST and thermodynamic profile.

scholarly journals New evidence for a relationship between Atlantic tropical cyclone activity and African dust outbreaks

2006 ◽  
Vol 33 (19) ◽  
Author(s):  
Amato T. Evan ◽  
Jason Dunion ◽  
Jonathan A. Foley ◽  
Andrew K. Heidinger ◽  
Christopher S. Velden
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclone Activity ◽  
Cyclone Activity ◽  
African Dust ◽  
New Evidence ◽  
Atlantic Tropical Cyclone

scholarly journals Dynamical Simulations of North Atlantic Tropical Cyclone Activity Using Observed Low-Frequency SST Oscillation Imposed on CMIP5 Model RCP4.5 SST Projections

2014 ◽  
Vol 27 (21) ◽  
pp. 8055-8069 ◽  
Author(s):  
Timothy E. LaRow ◽  
Lydia Stefanova ◽  
Chana Seitz
Keyword(s):  
Tropical Cyclone ◽  
North Atlantic ◽  
Climate Models ◽  
The United States ◽  
Tropical Cyclone Activity ◽  
First Century ◽  
Cyclone Activity ◽  
The Mean ◽  
Twenty First Century ◽  
Atlantic Tropical Cyclone

Abstract The effects on early and late twenty-first-century North Atlantic tropical cyclone statistics resulting from imposing the patterns of maximum/minimum phases of the observed Atlantic multidecadal oscillation (AMO) onto projected sea surface temperatures (SSTs) from two climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are examined using a 100-km resolution global atmospheric model. By imposing the observed maximum positive and negative phases of the AMO onto two CMIP5 SST projections from the representative concentration pathway (RCP) 4.5 scenario, this study places bounds on future North Atlantic tropical cyclone activity during the early (2020–39) and late (2080–99) twenty-first century. Averaging over both time periods and both AMO phases, the mean named tropical cyclones (NTCs) count increases by 35% when compared to simulations using observed SSTs from 1982 to 2009. The positive AMO simulations produce approximately a 68% increase in mean NTC count, while the negative AMO simulations are statistically indistinguishable from the mean NTC count determined from the 1995–2009 simulations—a period of observed positive AMO phase. Examination of the tropical cyclone track densities shows a statistically significant increase in the tracks along the East Coast of the United States in the future simulations compared to the models’ 1982–2009 climate simulations. The increase occurs regardless of AMO phase, although the negative phase produces higher track densities. The maximum wind speeds increase by 6%, in agreement with other climate change studies. Finally, the NTC-related precipitation is found to increase (approximately by 13%) compared to the 1982–2009 simulations.

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