تشميس

Solar radiation map of Africa and Middle East

A مقياس الإشعاع السماوي, a component of a temporary remote meteorological station, measures insolation on Skagit Bay, واشنطن (ولاية).

Spherical triangle for application of the spherical law of cosines for the calculation the solar zenith angle Θ for observer at latitude φ and longitude λ from knowledge of the hour angle h and solar declination δ. (δ is latitude of subsolar point, and h is relative longitude of subsolar point).

${\displaystyle {\overline {Q}}^{\mathrm {day} }}$, the theoretical daily-average insolation at the top of the atmosphere, where θ is the polar angle of the Earth's orbit, and θ = 0 at the vernal equinox, and θ = 90° at the summer solstice; φ is the latitude of the Earth. The calculation assumed conditions appropriate for 2000 A.D.: a solar constant of S₀ = 1367 W m⁻², obliquity of ε = 23.4398°, longitude of perihelion of ϖ = 282.895°, eccentricity e = 0.016704. Contour labels (green) are in units of W m⁻².

Past and future of daily average insolation at top of the atmosphere on the day of the summer solstice, at 65 N latitude. The green curve is with eccentricity e hypothetically set to 0. The red curve uses the actual (predicted) value of e. Blue dot is current conditions, at 2 ky A.D.

Insolation variation by month; 1984-1993 averages for January (top) and April (bottom)