SOLAR RADIATION BUDGET

Author: Bernard Yves BONNET

The sun is the main energy source for our planet. The emitting temperature in the photosphere (6000 K) places its radiation within the range of visible and near infrared wavelengths. The Earth's surface atmosphere system absorbs part of this radiation and re-emits energy in the medium and far infrared. The radiation budget is determined by the difference between the absorbed solar energy flux and the outgoing longwave radiation at the top of the atmosphere. These two components interact in a very complex way with most of the atmospheric processes. Throughout long periods and for the whole planet, they tend to balance each other, thereby maintaining on average constant climatic conditions. On a smaller temporal and spatial scale, this balance is disrupted, and the regional results of the radiation budget then contribute to atmospheric and oceanic circulations. In the context of climate perturbations, modifications in vegetation or in the extension of ice on the Earth's surface, increases in greenhouse gases such as carbon dioxide can introduce more or less direct perturbations in the components of the radiation budget. As for inter-annual variations, climatic anomalies such as the El Niņo / Southern Oscillation event change strongly the distribution of the convective cloud cover along the Peruvian coasts and in Indonesia, thus resulting in perturbations of the system's radiative budget.

This last point highlights the role of cloudiness in the radiation balance and explains why understanding of the interactions between clouds and radiation is a major goal of climate research.

By means of satellites, the thermal outgoing radiation at the top of the atmosphere can be observed fairly directly. However, the vertical structure of the thermal radiation inside the atmosphere cannot be observed directly. It can be calculated from the thermodynamic structure, the cloud distribution and the composition of the atmosphere by radiative transfer models.

Knowledge of the 3D thermodynamic structure and cloud parameters provided by the 3I algorithm along with use of a radiative transfer model (in this case, the model of the European Center for Medium-range Weather Forecasting) allow us to calculate the longwave radiation balance on a planetary scale.

a : Outgoing thermal radiation (W/m2) at the top of the atmosphere in January 1988 (7:30), calculated without clouds. The distribution of the radiation is essentially zonal : low flux on the poles and higher flux in the tropical regions.

b: Outgoing thermal radiation (W/m2) at the top of the atmosphere in January 1988 (7:30), with cloud cover. The cloud cover radically changes this zonal distribution by preventing a part of the thermal radiation, up to 60 W/m2, from escaping into space over a belt including Indonesia, Central Africa, Brazil, and Peru.

AVAILABLE SOLAR ENERGY TO THE PLANET

by: Luis Klemas

Earth Diameter: 12,733 km

Earth Projected Area: 1.27 108   km2

W/m2 kW/km2 kW GW-year
100 100,000 1.27 1013 1.11 1011
200 200,000 2.54 1013 2.22 1011
250 250,000 3.18 1013 2.78 1011
300 300,000 3.81 1013 3.34 1011

At a conservative average of only 200 W/m2, the net yearly solar energy input to the planet corresponds to 2.22 1011 GW-year, equivalent to 7.577 1020 btu, or, 757,700 quads, or, 1.29 1014 petroleum barrels/year: this amount is equivalent 353,000 million barrels per day. The actual petroleum world consumption is around 70 million barrels per day. Therefore, the solar available energy power is 5,000 times the total energy power derived from actual world oil produced combustion (counted at 100% efficiency).

Even at an energy transformation efficiency of only10% and covering with energy collectors only 1% of land surface, solar energy would provide about 6 times the actual oil used equivalent.

The solar energy is plentiful  for human civilization sustainability purposes. It is non exhaustible, and non polluting to the earth, to the ecosystem and to the biosphere. What are we waiting for?

If you wish to explore the timeout limits of world oil reserves for various projected scenarios of increase or decrease of world oil consumption, consult our page on World Energy Projections. You may also download OILEND software. It is free ! use it and share it !


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