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Summertime stationary waves integrate tropical and extratropical impacts on tropical cyclone activity
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2020
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Source: Proceedings of the National Academy of Sciences, 117(37)
[PDF-5.55 MB]
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Journal Title:Proceedings of the National Academy of Sciences
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Description:Skillful seasonal prediction of tropical cyclone (TC) activity helps hurricane preparedness and mitigation, especially when the storm impacts are expected to worsen with increasing sea level and water vapor capacity in a warming climate. Slowly varying tropical oceanic conditions have been regarded as a primary source of predictability for TC activity, but recent studies suggest that TC activity is also subject to some long-range impacts of extratropical processes. We show that summertime stationary waves in the Northern Hemisphere, including tropical upper-tropospheric troughs, integrate tropical and extratropical impacts into a unified framework and provide a hemispheric perspective that helps in understanding the variability and predictability of TC activity over the North Atlantic and North Pacific.Tropical cyclones (TC) are one of the most severe storm systems on Earth and cause significant loss of life and property upon landfall in coastal areas. A better understanding of their variability mechanisms will help improve the TC seasonal prediction skill and mitigate the destructive impacts of the storms. Early studies focused primarily on tropical processes in regulating the variability of TC activity, while recent studies suggest also some long-range impacts of extratropical processes, such as lateral transport of dry air and potential vorticity by large-scale waves. Here we show that stationary waves in the Northern Hemisphere integrate tropical and extratropical impacts on TC activity in July through October. In particular, tropical upper-tropospheric troughs (TUTTs), as part of the summertime stationary waves, are associated with the variability of large-scale environmental conditions in the tropical North Atlantic and North Pacific and significantly correlated to the variability of TC activity in these basins. TUTTs are subject to the modulation of diabatic heating in various regions and are the preferred locations for extratropical Rossby wave breaking (RWB). A strong TUTT in a basin is associated with enhanced RWB and tropical−extratropical stirring in that basin, and the resultant changes in the tropical atmospheric conditions modulate TC activity. In addition, the anticorrelation of TUTTs between the North Atlantic and North Pacific makes the TC activity indices over the two basins compensate each other, rendering the global TC activity less variable than otherwise would be the case if TUTTs were independent.
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Source:Proceedings of the National Academy of Sciences, 117(37)
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