It contains the description of the Solar radiation relation with the astronomical movements of both Earth and sun. Used in the class of Hydrology at the University of Trento

1. Riccardo Rigon
IlSole,F.Lelong,2008,ValdiSella
Solar Radiation
From Sun to Earth

2. R. Rigon
The energy irradiated by the Sun passes through an imaginary disc with diameter
the same as the Earth’s. The energy flow is maximum at that point on the Earth
where the radiation is perpendicular.
From Sun to Earth
18
2
From Sun To Earth

3. R. Rigon
T h e S u n i r r a d i a t e s
approximately at the solar
constant rate, which is, on
the average, on the top of
the atmosphere,
Solar radiation
http://en.wikipedia.org/wiki/Solar_constant
Frolich,1985
19
3
From Sun To Earth

4. R. Rigon
In its orbit around the Sun, the Earth keeps its north-south rotational axis
unvaried, causing a different angle between the Sun’s rays and the surface of the
Earth.
Astronomical variability of radiation
4
Copying with Earth surface

5. R. Rigon
Seasons
The Earth is 5 million kilometers closer to the Sun during the northern
winter: a clear indication that temperature is controlled more by orientation
than by distance.
Figure 3.1
5
From Sun To Earth

6. R. Rigon
The Earth’s orbit around the Sun is an ellipse. The shape of the ellipse is
determined by its eccentricity, which varies in time, changing the distances of
the aphelion and perihelion
Corrections to the solar constant
http://www.ascensionrecta.com/
20
6
From Sun To Earth

7. R. Rigon
Precession of the polar axis
The axis of rotation moves with a slow period, executing
a complete precession every 26,000 years.
Polar stars behave like this for only a very short period
7
From Sun To Earth

8. R. Rigon
Astronomical influences
Orbit angle
Orbit change
Orbit shape
8
From Sun To Earth

9. R. Rigon
Therefore the solar contant must be corrected
(e.g. Corripio, 2002):
Solar radiation in
hydrological models
9
S
From Sun To Earth

10. R. Rigon
N is the day of the year (in 1, ..., 365)
where:
Solar radiation in
hydrological models
10
Therefore the solar contant must be corrected
(e.g. Corripio, 2002):S
From Sun To Earth