SRERROR4X3.TXT                                            2004/10/20
4X3 Model ERRORs in calculating Solar Radiation at top of Atmosphere

     Calculation for insolation in the 4x3 Atmosphere-Ocean Model has
inaccuracies that should be kept in mind.  These are roughly ordered
according to importance.

 1. We calculate the Earth in its orbit only once a day.
 2. Instead of integrating insolation over a GCM grid box, we integrate
    insolation over a single latitude line within the box.  That line
    is the area weighted latitude of the box.  This error causes global
    insolation to increase by .0001? and is accentuated at the poles.
 3. We keep the orbital parameters fixed during long runs.
 4. We keep the meridion where the sun is overhead on noon Greenwich
    mean time as the Greenwich meridion.  (That meridion is calculated
    but not used.  The Equation of Time is not used.)
 5. We treat the Sun as a point; its radius does not affect our
    distance to the sun.
 6. We treat the Earth as a point; its radius does not affect the
    distance to the sun.
 7. We ignore the existence of the Moon, and assume that the center of
    the Earth-Moon system is the center of the Earth.
 8. We assume that the Earth is spherical.
 9. We assume that the orbit is a perfect ellipse; other heavenly
    bodies do not affect it.
10. We use Berger's orbital parameters.