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Journal Article

Impact of duration thresholds on Atlantic tropical cyclone counts

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Bengtsson,  Lennart
External Organizations;
Emeritus Scientific Members, MPI for Meteorology, Max Planck Society;

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1520-0442-2009jcli3034.1.pdf
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Citation

Landsea, C. W., Vecchi, G. A., Bengtsson, L., & Knutson, T. R. (2010). Impact of duration thresholds on Atlantic tropical cyclone counts. Journal of Climate, 23, 2508-2519. doi:10.1175/2009JCLI3034.1.


Cite as: https://hdl.handle.net/21.11116/0000-000D-055B-8
Abstract
Records of Atlantic basin tropical cyclones (TCs) since the late
nineteenth century indicate a very large upward trend in storm
frequency. This increase in documented TCs has been previously
interpreted as resulting from anthropogenic climate change. However,
improvements in observing and recording practices provide an alternative
interpretation for these changes: recent studies suggest that the number
of potentially missed TCs is sufficient to explain a large part of the
recorded increase in TC counts. This study explores the influence of
another factor-TC duration-on observed changes in TC frequency, using a
widely used Atlantic hurricane database (HURDAT). It is found that the
occurrence of short-lived storms (duration of 2 days or less) in the
database has increased dramatically, from less than one per year in the
late nineteenth-early twentieth century to about five per year since
about 2000, while medium-to long-lived storms have increased little, if
at all. Thus, the previously documented increase in total TC frequency
since the late nineteenth century in the database is primarily due to an
increase in very short-lived TCs.
The authors also undertake a sampling study based upon the distribution
of ship observations, which provides quantitative estimates of the
frequency of missed TCs, focusing just on the moderate to long-lived
systems with durations exceeding 2 days in the raw HURDAT. Upon adding
the estimated numbers of missed TCs, the time series of moderate to
long-lived Atlantic TCs show substantial multidecadal variability, but
neither time series exhibits a significant trend since the late
nineteenth century, with a nominal decrease in the adjusted time series.
Thus, to understand the source of the century-scale increase in Atlantic
TC counts in HURDAT, one must explain the relatively monotonic increase
in very short-duration storms since the late nineteenth century. While
it is possible that the recorded increase in short-duration TCs
represents a real climate signal, the authors consider that it is more
plausible that the increase arises primarily from improvements in the
quantity and quality of observations, along with enhanced interpretation
techniques. These have allowed National Hurricane Center forecasters to
better monitor and detect initial TC formation, and thus incorporate
increasing numbers of very short-lived systems into the TC database.