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The detail of EQINOX_FRACTION in module_model_constants.F and how to calculate it

dovahk1n111

New member
I am conducting a simulation representing conditions 8,500 years before present (8.5 ka BP), and need to adjust certain Earth orbital parameters accordingly. In particular, I came across the variable EQINOX_FRACTION which is in WRFV4.0/share/module_model_constants.F, defined as "the fraction of the tropical year, measured from perihelion, at which the Northern Hemisphere vernal equinox occurs." I'm uncertain how to compute this value for 8.5 ka BP. Could it be parameterized as a function of years before present?
 
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