Combined Effects of Earth Orbit Perturbations and Solar Activity on Terrestrial Insolation. Part I: Sample Days and Annual Mean Values

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  • 1 Main Geophysical Observatory, Leningrad, USSR
  • | 2 High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307
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Abstract

We combine calculated effects of short- and long-period orbital perturbations with modeled effects of recorded sunspot and facular activity to examine patterns of terrestrial insulation at selected latitudes in the Northern Hemisphere for the period 1874–1981. Here we consider systematic insulation effects 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 insulation at the period of the solar activity cycle with a maximum depletion, in years of maximum sunspot area, of about 0.1%. At high latitudes, where their effect is greatest, long-period orbital perturbations have driven annual mean insulation downward at a rate of about 0.05%/century. At middle and low latitudes this orbitally-induced, Milankovitch trend in annual mean insulation 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 product secular trends in combined insulation patterns that vary in amplitude, phase, and sign with latitude and time of year.

Abstract

We combine calculated effects of short- and long-period orbital perturbations with modeled effects of recorded sunspot and facular activity to examine patterns of terrestrial insulation at selected latitudes in the Northern Hemisphere for the period 1874–1981. Here we consider systematic insulation effects 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 insulation at the period of the solar activity cycle with a maximum depletion, in years of maximum sunspot area, of about 0.1%. At high latitudes, where their effect is greatest, long-period orbital perturbations have driven annual mean insulation downward at a rate of about 0.05%/century. At middle and low latitudes this orbitally-induced, Milankovitch trend in annual mean insulation 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 product secular trends in combined insulation patterns that vary in amplitude, phase, and sign with latitude and time of year.

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