Agriculture Reference
In-Depth Information
Equator
Parallel 37°N
A
A
A
Summer
21 June
Winter
22 December
Spring 21 March
Autumn 23 September
In summer horizontal surface A receives
more radiation than in winter
In spring and autumn the
situation is intermediate
At the equator radiation is high throughout the year
Fig. 2.9.
The incidence of direct solar radiation at noon in the south of Spain (37°N) in the winter and
summer solstices and in the spring and autumn equinoxes.
Sun trajectory
Sunset
Noon
O
S
N
Sun trajectory
Noon
Sunset
O
Sunrise
E
S
N
Spring and autumn equinoxes
Sun trajectory
Sunrise
E
Noon
Sunset
O
S
N
Summer solstice
Sunrise
E
Fig. 2.10.
Apparent trajectory of the Sun with respect to the horizontal plane in mid-latitudes of the
northern hemisphere, in the winter solstice (top left), in the spring and autumn equinoxes (centre right)
and the summer solstice (bottom left) (adapted from Fuentes, 1999).
5000 nm, with a maximum of emission at
470 nm (Fig. 2.11). During the crossing of
our atmosphere, even with good weather
conditions (clear sky), this radiation is
mitigated and modified, due to the pres-
ence of water vapour, nitrous oxides,
ozone, oxygen and other gases, which
means that a large part of this radiation is
scattered.
The majority of the global solar energy
flux at the Earth's surface level (99%) is
found between 300 and 2500 nm, made up
of three categories of radiation as a function
of the wavelength intervals they represent
(spectral composition):
•
Ultraviolet radiation
(UV), below 380 nm.
