Researchers conclude that the reported upswing in short-duration North Atlantic hurricanes is due to better observing systems
Researchers at Princeton University have concluded that the prominent upswing in the detection of North Atlantic tropical storms beginning in the mid-20th century is attributable predominantly to changes in observing systems that enabled the detection of “shorties”: tropical cyclones with durations of less than 2 days. Their paper is published in the Journal of Geophysical Research.
The researchers note that their finding does not rule out the possibility of a climate-driven increase in shorties over the twentieth century. Rather, any existing trend will be imperceptible, as it is masked by data quality issues.
Using a database of hurricane observations stretching back to 1878, Villarini et al. try to tease out any detectable climate signal from the records. The authors note that between 1878 and 1943 there were 0.58 shorty detections per year, and between 1944 and 2008 there were 2.58 shorty detections per year. This increase in shorties, which the authors propose may be related to the end of World War II and the dawn of air-based reconnaissance and weather tracking, was not mirrored by an increase in tropical cyclone activity for storms longer than 2 days.
The authors compare the rate of shorty detections against a variety of climate parameters, including North Atlantic sea surface temperature, mean tropical sea surface temperature, the North Atlantic Oscillation, and the Southern Oscillation Index. The authors find that North Atlantic sea surface temperatures were related to tropical cyclones of longer than 2 days’ duration but were not related to the rate of short detections. Additionally, for every decade after 1950s the occurrence of shorties seems to be related to a different climate parameter.
Both of these findings are highly suggestive of data quality problems for the shorties record, they said.
By using statistical methods combined with the current understanding of the physical processes, we are unable to find support for the hypothesis that the century-scale record of short-lived tropical cyclones in the Atlantic contains a detectable real climate signal. Therefore, we interpret the long-term secular increase in short-duration North Atlantic tropical storms as likely to be substantially inflated by observing system changes over time.
These results strongly suggest that studies examining the frequency of North Atlantic tropical storms over the historical era (between the 19th century and present) should focus on storms of duration greater than about 2 days.—Villarini et al.
Villarini, G., G. A. Vecchi, T. R. Knutson, and J. A. Smith (2011), Is the recorded increase in short-duration North Atlantic tropical storms spurious?, J. Geophys. Res., 116, D10114, doi: 10.1029/2010JD015493