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Solar eclipses


The University of Minnesota climatological observatory on the St. Paul campus has been in the path of four partial eclipses, ranging from 500/4 to 91 % of totality (the area of the covered sun) since operations began in 1960. Three of the four partial eclipses occurred while the atmosphere at St. Paul was essentially cloud-free. Measurements made during the three partial eclipses include incoming and reflected solar radiation, incoming and outgoing longwave radiation, air and soil temperatures, relative humidity, and wind speed and direction. Of the partial eclipses for which the effects could be measured, only the one of 30 May 1984 occurred in the absence of a snow cover. This partial eclipse, which attained a maximum coverage of 54% of totality, showed that the temperature of a soil surface devoid of vegetation was affected to a depth of at least 10 cm.

An interesting and seldom measured quantity is the difference between the reduction of the incoming and the outgoing terrestrial (longwave) radiation. For the 91% of totality 26 February 1979 eclipse the reduction of the terrestrial longwave radiation was three times greater than the incoming terrestrial radiation. This occurred because the earth temperature was reduced far more than that of the atmosphere. These and other responses of the meteorological variables to the partial eclipses are discussed and illustrated in this paper.

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