Presented here is evidence of variations in solar irradiation as the Earth follows it’s elliptical orbit around the sun. It is proposed that these variations are due to changes in the density of dust clouds lying between the Earth and the Sun as the orbit moves from perihelion to aphelion. These variations become evident when compared to a calculation of the expected irradiation based on the Earth’s orbital parameters and a measured average solar constant of 1361 watts/m2. The change in irradiation between perihelion and aphelion is about 2 watt/m2 for the current eccentricity of 0.0167. This supports the hypothesis that the primary cause of recent Ice Ages has been increases in interplanetary dust for lower eccentricity of the Earth (“resonant” clouds). If the difference between an expected 1368 watts/m2 average solar irradiation and the measured value of 1361 watts/m2 is assumed to be all due to absorption and scattering of dust lying between Earth and the Sun then current absorption varies between a maximum of 8 watts/m2 at perihelion(closest approach) and a miniumum of 6 watts/m2 at aphelion (largest distance). During long glacial periods average global temperatures fall to about 2 degrees below current values which infer a further drop in solar irradiation of about 7 watts/m2. Therefore in low eccentric orbits the solar constant would then fall to ~1354 watts/m2. The hypothesis is that for the last million years interplanetary dust resonates to the same same gravitational cycles as Earth in the ecliptic plane leading to higher densities at lower eccentricities. This is described in the previous post
The data is taken from the SORCE Total Irradiance Monitor (TIM)  whose long-term point to point uncertainty is estimated to be < 0.014 W/m^2/yr (10 ppm/yr) , and has an absolute uncertainty of 0.48 watts/m2. The calculation of the solar intensity uses a solar constant of 1361 watts/m2, an eccentricity of 0.0167 and tracks the orbit for each day applying conservation of angular momentum and a year of length 365.25 days. The comparisons are shown in figure 1. Also plotted is the difference beween calculated and observed irradiance (first y-axis). A clear regular discrepancy is observed with some high frequency substructure evident as well.
The amplitude of the effect is about 2 watts/m2. At perihelion irradiation is attenuation greater than expected while at aphelion irradiation is greater than expected. This can be understood assuming a constant average attenuation of X watts/m2 with X+1 and X-1 representing net changes in density. Stefan Boltzman’s law predicts S0=1368 watts/m2 which all else being equal implies X=7 watts/m2.
A detail of a single orbit is shown in figure 2.
If we assume that the 2 watts/m2 discrepancy is due only to absorption by intermediate dust, then the density between the Earth and the Sun varies by about 30%. For comparison the total estimated radiative forcing caused by all CO2 emissions since the industrial revolution is also about 2 watts/m2.