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.


CYCLE/ 1234567891011
1 1878S1889190119131923M193319441954 19641976M1986M
2187918901902M1914M1924193419451955 1965M1977M1987M
31880M1891S190319151925S193519461956 1966M19781988
418811892190419161926S19361947*1957*S 19671979*1989*
51882189319051917*S19271937*19481958S 196819801990
61883*1894*190619181928*193819491959 1969*19811991M
71884S18951907*M191919291939M19501960 19701982S1992M
818851896M1908192019301940S19511961 19711983S1993
918861897M1909192119311941S19521962 1972S19841994
1018871898191019221932S19421953M1963 1973S19851995
1118881899S1911S1943M 1974
121900S1912S 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