Hurricane Frequency
Published:January 2, 2011, 12:00 am
Updated: January 29, 2011, 5:49 pmAuthor: C. Michael Hogan
Hurricane frequency (or typhoon frequency in the Southern Hemisphere) is the measure of how many hurricanes make landfall in a given season. Analysis of historical records in both Northern and Southern Hemispheres indicate there is no clear trend of hurricane frequency change in the last five centuries; however there is a slight trend that hurricane and typhoon frequencies have decreased over the last 200 to 500 years. In any case there is no factual evidence that the present slight increase in global surface temperature or greenhouse gas increase since the Industrial Revolution are having any adverse effect on hurricane or typhoon frequency.
Contents
Definition of Hurricane and Typhoon
A Hurricane or typhoon is a tropical cyclone in which the maximum sustained surface wind (using the U.S. one minute average) is 64 knots (74 mph or 119 km/hr) or more. Tropical cyclones originate over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. The direction of twisting is governed by the coriolis force. In the northern hemisphere a hurricane moves counter-clockwise as viewed from space; in the southern hemisphere, a typhoon moves clockwise.
The term hurricane is used for Northern Hemisphere tropical cyclones east of the International Dateline to the Greenwich Meridian. The term typhoon is used for Pacific tropical cyclones north of the Equator west of the International Dateline.
Historical Data on Hurricane Frequency
In North America records of hurricane frequency and intensity have been kept since about 1870. These records indicate wide variations in hurricane events from year to year; however, there is no evidence of increase in frequency or severity of the actual physical events. In fact, NOAA records indicate a gradual decline in hurricane frequency and intensity of hurricanes from 1850 to present. In particular there is no correlation between industrialization, greenhouse gases or fossil fuel combustion with hurricane frequency. Sometimes damage claims from insurance companies are used as a surrogate for the physical hurricane events; however, that provides great inaccuracy, because of increased numbers of people using property insurance and considerable inflation in real estate values in the last century.
Historical Data on Cyclone Frequency
In China, there is copious historical documentary records in the form of Fang Zhi (semiofficial local gazettes), providing an excellent way for providing a high-resolution historical data for the frequency of typhoon landfalls. Examining the millennium long time series of typhoon landfalls in the Guangdong Province of south China since 975 AD from Fang Zhi data. Although the 571 typhoon landfalls from historical documents may underrepresent the total number of typhoon landfalls in Guangdong, calibration of the historical data against the observations during the instrument period 1884-1909 suggests that the trends of the two datasets are significantly correlated (r = 0.71), confirming that the time series reconstructed from historical documentary evidence contains a reliable record of variability in typhoon landfalls.
On a decadal average, the twenty-year interval from 1660 to 1680 AD is the most intense typhoon period of record, with 28 to 37 typhoon landfalls per decade. The variability in typhoon landfalls in Guangdong parallels observations in other Asian paleoclimatic proxies (such as tree rings, ice cores). Notably, the two periods of highest typhoon landfalls in Guangdong (AD 1660-1680, 1850-1880) coincide with two of the coldest periods in China during the Little Ice Age. Thus, as in the case of hurricanes, there is no correlation of typhoon activity with industrialization, combustion of fossil fuels, global warming or greenhouse gases. In fact, highest typhoon frequency occurred in the coldest century of the last millennium.
References
- K. R. Briffa, P. D. Jones, T. S. Bartholin, D. Eckstein, F. H. Schweingruber, W. Karlén, P. Zetterberg, M. Eronen, Fennoscandian summers from A.D. 500: Temperature changes on short and long timescales. Clim. Dyn. 7, 111–119 (1992).
- Kam-biu Liu, Caiming Shen and Kin-sheun Louie (2001) A 1,000-Year History of Typhoon Landfalls in Guangdong, Southern China, Reconstructed from Chinese Historical Documentary Records. Annals of the Association of American Geographers. Vol. 91, No. 3 (Sep., 2001), pp. 453-464 (12 pages). Published By: Taylor & Francis, Ltd.
Citation
U.S. National Oceanic and Atmospheric Administration, C. Michael Hogan (2011). Hurricane Frequency. Encyclopedia of Earth. National Council for Science and Environment. Washington DC. Retrieved from http://editors.eol.org/eoearth/wiki/typhoon_(Hurricane)
