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Thursday, November 27, 2008

Estimated Number of Major Atlantic Hurricanes and Vertical Windshear

I’ve moved to WordPress.  This post can now be found at Estimated Number of Major Atlantic Hurricanes and Vertical Windshear
And to those of you who are not celebrating the holiday, Happy Thursday.

With the 2008 Hurricane Season coming to a close, it seemed appropriate to resurrect the paleoclimatological reconstruction of the estimated number of major Atlantic hurricanes created by Nyberg et al in 2007. The data source is here:
I wrote resurrect above because I know I’d read this abstract before, but googling the title in quotes revealed only 6 references, all of them NASA or NCDC websites. Regardless, here’s the graph of the Estimated Number of Hurricanes. I haven’t graphed the windshear. The data was smoothed by the authors, not by me. The graph is created by the raw data.

Nyberg, J., et al. 2007.Estimated Number of Major Atlantic Hurricanes and Vertical Windshear.IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2007-056.NOAA/NCDC Paleoclimatology Program, Boulder CO, USA.

This file contains estimated number of major hurricanes and vertical windshear (five-year running averages). Back propagation artificial neural networks were used to estimate past number of major hurricanes and vertical windshear. The relationships between combined input (independent) proxy records and the two output (dependent) instrumental records of number of major hurricanes and vertical windshear were determined unconnectedly.

Hurricane activity in the North Atlantic Ocean has increased significantly since 1995. This trend has been attributed to both anthropogenically induced climate change and natural variability, but the primary cause remains uncertain. Changes in the frequency and intensity of hurricanes in the past can provide insights into the factors that influence hurricane activity, but reliable observations of hurricane activity in the North Atlantic only cover the past few decades. Here we construct a record of the frequency of major Atlantic hurricanes over the past 270 years using proxy records of vertical wind shear and sea surface temperature (the main controls on the formation of major hurricanes in this region) from corals and a marine sediment core. The record indicates that the average frequency of major hurricanes decreased gradually from the 1760s until the early 1990s, reaching anomalously low values during the 1970s and 1980s. Furthermore, the phase of enhanced hurricane activity since 1995 is not unusual compared to other periods of high hurricane activity in the record and thus appears to represent a recovery to normal hurricane activity, rather than a direct response to increasing sea surface temperature. Comparison of the record with a reconstruction of vertical wind shear indicates that variability in this parameter primarily controlled the frequency of major hurricanes in the Atlantic over the past 270 years, suggesting that changes in the magnitude of vertical wind shear will have a significant influence on future hurricane activity.

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