Combined effects of earth orbit perturbations and solar activity on terrestrial insolation. I: sample days and annual mean values

• Published in: Journal of the atmospheric sciences 1985-05, Vol.42 (9), p.933-940
• Main Authors: BORISENKOV, YE. P, TSVETKOV, A. V, EDDY, J. A
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology; Radiative transfer. Solar radiation
• ISSN: 0022-4928; 1520-0469

Calculated effects of short- and long-period orbital perturbations are combined with modeled effects of recorded sunspot and facular activity to examine patterns of terrestrial insolation at selected latitudes in the Northern Hemisphere for the period 1874-1981. Systematic insolation effects are considered at times of equinox and solstice and as annual means over the 108-year period. Solar activity is the more dominant term; it modulates global insolation at the period of the solar activity cycle with a maximum depletion, in years of maximum sunspot area, of about 0.1 percent. At high latitudes, where their effect is greatest, long-period orbital perturbations have driven annual mean insolation downward at a rate of about 0.05 percent/century. At middle and low latitudes this orbitally induced, Milankovich trend in annual mean insolation is positive and about 100 times smaller. Nutation of earth's rotational axis induced by the gravitational pull of the moon adds a distinct modulation of 18.6-year period that significantly influences insolation at polar latitudes. Orbital perturbations by Jupiter and the inner planets add weaker modulation at shorter periods. The influence of orbital effects is to produce secular trends in combined insolation patterns that vary in amplitude, phase, and sign with latitude and time of year.