requirement was that the year prior to the two-year event must be a non-El Nino year. The 
two-year events that met this criteria were: 1911-12, 1917-18, 1925-26, 1930-31, 1939- 
40, 1957-58, 1972-73, and 1982-83. The most significant anomalies were: below normal 
rainfall over the State during winter (December, January and February) and spring (March, 
April and May) of the year prior to an El Nino event; and above normal rainfall over the State 
during the winter and spring of the second year of an El Nino event. The largest rainfall 
anomalies occurred in the southern climatic divisions of Florida (the Everglades and southeast 
coast, lower east coast, and the Keys). 
5.3. Volcanic eruptions 
As early as 1913, the effect of volcanic eruptions on global climate was recognized, and the 
levels of solar radiation after a volcanic eruption measured (Abbot and Fowle, 1913). 
Scattering of sunlight by volcanic aerosols can change the Earth's albedo or reflectivity, 
thereby causing climatic changes (Wilson, 1989). It has been shown that direct volcanic 
injection of material into the stratospheric aerosol layer occasionally takes place, and 
historically, effects such as poor harvests due to cool summers related to volcanic activity 
have been documented (Newell and Deepak, 1982; Friend, 1991; Rampino, 1991a and 1991b; 
Robock, 1991; and others). Recently, atmospheric chemical and radioactive effects have been 
examined. The eruption of Mt. Pinatubo in June 1991 produced a stratospheric aerosol cloud 
which was observed at altitudes between 18 - 28 km (Kinnison et al., 1992). Although the 
latitudinal distribution of Pinatubo aerosol was initially equatorial, some of the material seemed 
to reach northern mid-latitudes, primarily in the lower stratosphere. Aerosol optical thickness 
was consistently observed to be twice the expected background values in a zone about 40° wide 
straddling the equator. This increased aerosol burden produced a strong cooling effect 
immediately after the eruption and the effect increased through September 1991 (Minnis et al., 
1993). The observed correlation of stratospheric plumes with climatic effects indicates that 
those plumes nearest the Equator have the largest impact on surface temperatures (Jakorsky, 
V)86). Injection of debris into the stratosphere is more important in determining the effect on 
climate than the volcanic explosivity of the eruption or the actual height reached within the 
stratosphere. Volcanic eruptions observed to reach the stratosphere since 1883 are listed in 
Table 12 (Jakorsky, 1986). 
5.4. Solar cycles 
Sunspots are dark (cool) areas on the Sun's surface that interrupt the regular pattern of solar 
emissions (NOAA, 1991a). Sunspots are accompanied by strong magnetic fields and have 
lifetimes ranging from days to a few months. Sunspot frequency rises and falls with the 11-yr 
solar cycle and provides an index of solar magnetic activity. In 1848, the Swiss astronomer 
Johann Rudolph Wolf introduced a daily measurement of sunspot number. His method, which is 
still used today, counts both the total number of spots visible on the face of the Sun and the 
number of groups into which they cluster because neither quantity alone satisfactorily 
measures sunspot activity. Results can vary greatly, however, since the measurement 
strongly depends on observer interpretation and experience and on the stability of the Earth's 
atmosphere above the observing site. To compensate for these limitations, each daily 
international number is computed as a weighted average of measurements made from a network 
of cooperating observatories. Monthly mean values are shown in Figure 4. The 27-day 
fluctuation that reflects the rotation period of the Sun has been smoothed. The highest daily 
counts on record occurred in December 1957. 
Wilson (1989) found that major tropical volcanic activity (those that can inject sufficient 
quantities of aerosols into the atmosphere that persist up to 3 yrs) can account for 70% of El 
Nino events, although major volcanic activity regardless of latitude can account for 85% of the 
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