Page 86 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

50 part I The energy–Atmosphere system
Surface area receiving insolation
More diffuse, larger area covered
Annually 2.5 times more energy than poles
More concentrated, smaller area covered
More diffuse
Sun’s rays arrive at oblique angles to Earth
Figure 2.9 illustrates daily variations throughout the year of en- ergy at the top of the atmo- sphere for four locations in watts per square metre (W·m−2). The graphs show the seasonal changes in insolation from the equato- rial regions northward and southward to the poles. In June, the North Pole re- ceives slightly more than 500 W·m−2 per day, which is more than is ever re- ceived at 40° N latitude or at the equator. Such high values result from long 24-hour daylengths at the poles in summer, com- pared with only 15 hours of daylight at 40° N lati- tude and 12 hours at the equator. However, at the poles the summertime Sun
Energy Receipts at
90° N, 50° N, 0°, and 90° S
North Pole (90° N)
the
Tropic of Cancer 23.5° N
Equator 0°
Tropic of Capricorn 23.5° S
Location of subsolar point moves between 23.5° N and 23.5° S during the year
Direct
Oblique
Sun’s rays arrive parallel to each other at Earth’s surface
600 Daily Receipt of Insolation (W/m2) 500
at Top of the Atmosphere
LatitudeJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 250
◀Figure 2.8 Insolation receipts and Earth’s curved surface. The angle at which insolation arrives from the sun determines the con­ centration of energy receipts by latitude. The subsolar point, where the sun’s rays arrive perpendicular to earth, moves between the trop­ ics during the year.
North Pole 90° 80°
Arctic Circle 70° 60°
Winnipeg 50° New York, 40°
Equator 0°
10°
0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
450
400 350
300
250
200 150 100
50
0
600 500
250
Winnipeg (50° N)
Rome Tropic of
30° Cancer 20°
0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
20° Capricorn 30°
40° New Zealand 50°
Antarctic 60° Circle 70°
80° South Pole 90°
600 500
250
0
600 500
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 250 0
Tropic of
10°
Equator (0°)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
South Pole (90° S)
at noon is low in the sky, so a daylength twice that of the equator yields only about a 100 W·m−2 difference.
In December, the pattern reverses, as shown on the graphs. Note that the top of the atmosphere at the South Pole receives even more insolation than the North Pole does in June (more than 550 W·m−2). This is a function of Earth’s closer location to the Sun at perihe- lion (January 3 in Figure 2.1d). Along the equator, two
▲Figure 2.9 Daily insolation received at the top of the atmosphere. The total daily insolation received at the top of the atmosphere is charted in watts per square metre per day by latitude and month
(1 W·m−2/day = 2.064 cal·cm−2/day). A profile of annual energy receipts is graphed to the right for the north pole, for Winnipeg at 50° n latitude, for the equator, and for the south pole. [reproduced by permis­ sion of the smithsonian Institution press from Smithsonian Miscellaneous Collec- tions: Smithsonian Meteorological Tables, vol. 114, 6th edition. report List, ed. (Washington, DC: smithsonian Institution, 1984), p. 419, Table 134.]
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Insolation (W/m2/day)
Insolation (W/m2/day)
Insolation (W/m2/day)
Insolation (W/m2/day)
Vernal equinox
Autumnal equinox
Summer solstice
Winter solstice
0
500
50
0
100
50
150
200
150
250
300
250
i
t
a
n
i
l
c
e
o
n
D
o
f
350
S
u
200 300
n
100
350
400
400
500 450
450
500
550
550