Environmental Engineering Reference
In-Depth Information
March 21
Earth
23.5°
Ecliptic
June 21
December 21
Sun
152 Mio. km
147 Mio. km
Aphelion
(July 2)
Perihelion
(January 2)
September 23
Fig. 2.2 Elliptical orbit of the earth around the sun (see /2-2/)
Thus, the solar constant reaches its maximum in January at almost 1,420 W/m 2 ,
due to reaching the shortest distance between the sun and the earth (Perihelion) on
January, 2 nd . The opposite takes place on June, 2 nd , when it reaches its minimum
with approximately 1,330 W/m 2 (Aphelion).
1,420
1,400
1,380
Annual mean
1,360
1,340
Monthly mean
1,320
Time in months
Fig. 2.3 Solar constant in the course of one year (see /2-2/, /2-3/, /2-5/)
In spite of the higher radiation intensity at the outer atmospheric rim, on aver-
age there are significantly lower temperatures on the Northern hemisphere during
the winter than during the summer. The reason for this is that the rotation axis of
the earth forms an angle of 66.5° with the orbital plane (Fig. 2.2). Thus during the
winter the Southern hemisphere is facing the sun more than the Northern hemi-
sphere. This leads to a higher solar altitude and longer periods of sunshine.
Search WWH ::




Custom Search