Evidence of variations in solar irradiance with Earth’s orbit

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) [1] 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.

Fig 1: Comparison of Measured Solar Irradiance from SORCE TIM Total Solar Irradiance instrument with calculated

Fig 1: Comparison of Measured Solar Irradiance from SORCE TIM Total Solar Irradiance instrument with calculated

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.

Fig 2: Detail of one orbit showing higher irradiance at aphelion and lower irradiance at perihelion as compared to vacuum values. Note the slight offset of the signal.

Fig 2: Detail of one orbit showing regular small variations compared to vacuum values. Note the slight offset of the signal.

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.

[1] http://lasp.colorado.edu/sorce/index.htm

About Clive Best

PhD High Energy Physics Worked at CERN, Rutherford Lab, JET, JRC, OSVision
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4 Responses to Evidence of variations in solar irradiance with Earth’s orbit

  1. P. Solar says:

    Interesting stuff.

    One thing that stands out to me about figure 1 and confirmed by the close up in figure 2, is that the residual DS seems to be related to the differential of your proposed cycle. Probably modulated by the intensity variation of the solar cycle.

    I’ll let you figure out what that means 😉

  2. P. Solar says:

    PS. you may also wish to consider that such dust as you describe should probably coalesce around the Legangian points.

  3. Clive Best says:

    I am convinced now that the signal is an artifact. My orbital model for the Earth is too simplistic since it does not take into account the gravitational pull of the other planets – especially Jupiter. I had some email correspondence with the SORCE-TIM lead Greg Kopp and learned that they use JPL ephemeris VSOP87 which includes everything. So when they measure TSI they correct all data to exactly 1 AU – then there is no effect. So it looks like my idea for the cause of Ice Ages being due to interplanetary dust change will not work

    However if you look at the next post you will see a beautiful lunar signal. Each month the Earth warms slightly as the Earth and Moon orbit around their centre of gravity. This varies on an 18 year cycle and presumably is greatest near a solar eclipse. The net effect on global temperature could be about 0.02 degrees C. Add in moonshine at night ant we can add another 0.01 degres C. Presumably in the Arctic/Antarctic winter moonshine is the only source of direct radiative heating !

  4. Cecil says:

    Thank you for this great article. I’ve been hunting for data on wavelengths at aphelion and perihelion. I believe this proves my theory http://cecilpickard.com/physics/forces/gravity/theory/cecils-unified-theory-of-gravity-and-space-expansion/

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