The impacts of column water vapour variability on Atlantic basin tropical cyclone activity
Column water vapour (CWV) in the Tropics is well known to affect tropical deep convection. It has been established that the tropical deep convection required for tropical cyclone formation markedly increases after reaching a critical CWV threshold. Therefore, CWV values below this threshold represen...
| Published in: | Quarterly Journal of the Royal Meteorological Society |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Wiley
2016
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1002/qj.2886 https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fqj.2886 https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.2886 |
| Summary: | Column water vapour (CWV) in the Tropics is well known to affect tropical deep convection. It has been established that the tropical deep convection required for tropical cyclone formation markedly increases after reaching a critical CWV threshold. Therefore, CWV values below this threshold represent an atmosphere that is too dry for tropical cyclone formation. The interannual variability of the occurrence of this dry air and its impacts on tropical cyclone activity over the Atlantic are examined. CWV empirical orthogonal function (EOF) analysis reveals a dominant mode of interannual variability of dry air events over the tropical North Atlantic, with strong variations over the central and eastern Atlantic between 15°N and 30°N. In the positive (negative) phase of the EOF modes, tropical cyclone activity is reduced (increased) over the Atlantic basin, particularly over the main development region. On the origin of dry air, the Saharan Air Layer does not explain the CWV EOF pattern, but the pattern is shown to be related to large‐scale subsidence in association with enhanced anticyclonic vorticity. The leading mode shows significant correlations to several large‐scale climate oscillations, including the Atlantic Multi‐decadal Oscillation, Pacific Decadal Oscillation, Atlantic Meridional Mode, Pacific North American Pattern, and others. The EOF mode also indicates a relationship to the large‐scale circulation via the Hadley cell. An evaluation of the steering flow for tropical cyclones from the modulation of the subtropical high and the values of deep layer vertical wind shear is consistent with the distribution of tropical cyclone activity in only certain limited areas, suggesting that the impacts of the dry air patterns are required to provide a more complete explanation of the activity. |
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