Book Description

During the interval of 1818-1858, several curious decreases in the number of sunspot observing days per year are noted in the observing record of Samuel Heinrich Schwabe, the discoverer of the sunspot cycle, and in the reconstructed record of Rudolf Wolf, the founder of the now familiar relative sunspot number. These decreases appear to be nonrandom in nature and often extended for 13 yr (or more). Comparison of these decreases with equivalent annual mean temperature (both annual means and 4-yr moving averages). as recorded at Armagh Observatory (Northern Ireland), indicates that the temperature during the years of decreased number of observing days trended downward near the start of' each decrease and upward (suggesting some sort of recovery) just before the end of each decrease. The drop in equivalent annual mean temperature associated with each decrease, as determined from the moving averages, measured about 0.1-0.7 C. The decreases in number of observing days are found to be closely related to the occurrences of large, cataclysmic volcanic eruptions in the tropics or northern hemisphere. In particular, the interval of increasing number of observing days at the beginning of the record (i.e., 1818-1819) may be related to the improving atmospheric conditions in Europe following the 1815 eruption of Tambora (Indonesia; 8 deg. S), which previously, has been linked to "the year without a summer" (in 1816) and which is the strongest eruption in recent history, while the decreases associated with the years of 1824, 1837, and 1847 may, be linked, respectively, to the large, catacivsmic volcanic eruptions of Galunggung (Indonesia; 7 deg. S) in 1822, Cosiguina (Nicaragua) in 1835, and, perhaps, Hekla (Iceland; 64 deg. N) in 1845. Surprisingly, the number of observing days per year, as recorded specifically b), SchAabe (from Dessau, Germany), is found to be linearly correlated against the yearly mean temperature at Armagh Observatory (r = 0.5 at the 2 percent leve...