Solar radiation as climate factor
Climate is the total state of the atmosphere at a certain place on earth. Climate is allways a
long dated state, short term differences and changes doesn't contribute to climate.
Sun distributes radiation and so energy to us. Without our atmosphere we would have temperatures
around -15°C on earth. The reason why we have greater temperatures is the natural greenhouse effect.
Visual light arrives undisturbed the earth surface. There it gets absorbed heats the surface and
gets reemitted in infra red region. But now it cannot arrive space undisturbed. A fraction of infra red
radiation gets absorbed and reflected. This process cumulates in an higher surface temperature.
The figure shows the progression of the solar constant. The huge fluctuations are caused by the 11
years cycle of solar activity. Also some little fluctuations happen. These are mainly caused by solar
activity fluctuations.(C. Fröhlich, PMOD)
Energytransport throught the Earth atmosphere,
But how does the solar activity contribute to the earth climate? At times with less solar activity,
signalized by less sun spots, sun radiates less energy. The figure above shows the solar constant.
The solar constant is a number which indicates the amount of radiation earth gets from sun measured outside
atmosphere. The mean value for the solat constant is 1367 W/m2. Because of the spherical earth body and the
earth atmosphere only about 1/6 th of the value from above arrive at earth surface. That's about 240 W/m2.
In the figure you can see cleary fluctuations of the value of the solar constant which indicates the
11 years cycle of sun. During maunder minimum (1645-1715) the number of sun spots observed was very low
and as a historical fact also the climate was very rough. Namenly we had a little ice age. But this wasn┬┤t
a single event. In the earlier earth history we had some such periods.
- Dalton Minimum (1800-1820)
- Spörer Minimum (1420-1540)
- Wolf Mimimum (1280-1320)
Spörer- and Wolf minimum wasn't determined by sunspot numbers because the first person (in europe, in china
people knew about sunspots earlier) who has seen sunspots was Galileo Galilei 1610. But scientists have discovered
some other methods to calculate the sunspot numbers backwards. We are shielded from cosmic radiation by the solar
magnetic field. If sun is more activ also the shielding is better. Cosmic radiation causes Be10 in earth atmosphere.
This element is built in glaciers. So if sun activity is high less Be10 is built in. If it is low, more Be10 is built in.