Weather Research Center Hurricane Outlook Description, December 12, 1996

HISTORY OF THE SOLAR CYCLONE STRIKE INDEX
BY: Jill F. Hasling and Dr. John C. Freeman
Weather Research Center - Houston, Texas

The Solar Cyclone Strike Index was developed in late 1985 as a tool to predict trends in tropical cyclone tracks in the North Atlantic. The researchers based the index on the premise that the same phenomenon or phenomena that cause the solar cycle on the sun might have a similar effect on the large scale circulations of the earth which would be reflected in the tracks of cyclones. This idea of a relationship between the sunspot cycle and cyclones is not new. Willet (1951) predicted correctly in the early 50's that the period 1959 to 1990 would have a relatively small number of hurricanes in the North Atlantic ocean. His later research found the 11 year sunspot cycle appeared to be related to the climate in the tropics. Recently Labitzke and Van Loon (1987) have showed that the solar cycle correlated highly with the general circulation depending on the phase of the quasibiennial-oscillation (QBO). The QBO is the oscillation of equatorial east-west winds which vary with a period of 26 to 30 months.

The sun has a year that varies from 10 to 12 earth years. For this research this sun year is referred to as the "sol-year" and begins with the earth year that the sunspot minimum occurs. The Sun orbits around the center of rotation of the solar system. This orbit takes 10 to 12 earth years to complete. During this orbit the sun goes through the solar cycle where the sunspots are at their minimum to the maximum and back again to the minimum. While the sun makes its orbit the earth is orbiting around the sun and the large scale circulation patterns of the earth experience some of the same influences as the sun.

The Solar Cyclone Strike Index is made up of cycles and phases. The cycles are the sol-years and range from 10 to 13 earth years. Phase 1 of the index is each earth year when the sunspot minimum occurred and Phase 2 is each earth year one year past the minimum etc. The tracks of North Atlantic tropical storms and hurricanes where then grouped into the Solar Cyclone Strike Index (SCSI).

Each phase of the index is then summarized and landfall along the United States coastlines then compared. The highest two probabilities for each section of the coast were considered to have the highest risk of a storm strike.

TABLE 1: SOLAR CYCLES('SOL-YEARS') AND PHASES OF SOLAR CYCLONE STRIKE INDEX

'SOL-YEARS'

CYCLE/	1	2	3	4	5	6	7	8	9	10	11
PHASE
1	1878S	1889	1901	1913	1923M	1933	1944	1954	1964	1976M	1986M
2	1879	1890	1902M	1914M	1924	1934	1945	1955	1965M	1977M	1987M
3	1880M	1891S	1903	1915	1925S	1935	1946	1956	1966M	1978	1988
4	1881	1892	1904	1916	1926S	1936	1947*	1957*S	1967	1979*	1989*
5	1882	1893	1905	1917*S	1927	1937*	1948	1958S	1968	1980	1990
6	1883*	1894*	1906	1918	1928*	1938	1949	1959	1969*	1981	1991M
7	1884S	1895	1907*M	1919	1929	1939M	1950	1960	1970	1982S	1992M
8	1885	1896M	1908	1920	1930	1940S	1951	1961	1971	1983S	1993
9	1886	1897M	1909	1921	1931	1941S	1952	1962	1972S	1984	1994
10	1887	1898	1910	1922	1932S	1942	1953M	1963	1973S	1985	1995
11	1888	1899S	1911S			1943M			1974
12		1900S	1912S						1975

* indicates the sunspot maximum
S or M indicates the severe and moderate El Nino's
Average "sol-year" 11.1 earth years.
Cycles start with the year of the sunspot mimimum which marks beginning of the "sol-year". Phase 1 is
made up of all the years in which the sunspot minimum occurred. Phase 2 is made up of all the
years 1 year after the sunspot minimum etc.

Weather Research Center
5104 Caroline St. Houston, Texas 77004
(713) 529-3076