Variations in Insolation, General Circulation and Climate

Two primary causes of variation in insolation—changes in solar output and in atmospheric transmission — are discussed, particularly with respect to basic changes in the mid- and high-latitude circulation pattern. Sunspot maxima in winter, on the average, are associated with greater tendency toward circulation blocks over the Northern Hemisphere and favorable conditions for heavy snow in regions known to have been glaciated in the past (Wisconsin) ice age. An explanation, based on an assumed greater insolation during sunspot maxima, is proposed. But summer weather conditions during sunspot maxima do not appear to favor preservation of the previous winter's accumulation of snow and ice. Hence an alternative explanation, based on decreased insolation accompanying periods of high atmospheric turbidity is proposed. The unequal response of continents and oceans to the decreased insolation causes heavy snow blankets to be deposited in areas known to have been glaciated and the lesser insolation in summer helps preserve a remnant of the snow until the next winter's contribution.