Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- Part I The dryland environment
- Part II The meteorological background
- 4 The general atmospheric circulation
- 5 The global distribution of arid climates and rainfall
- 6 Radiation, heat, and surface exchange processes
- 7 Water balance
- 8 Evaporation
- Part III The climatic environment of drylands
- Part IV The earth’s drylands
- Part V Life and change in the dryland regions
- Index
- References
4 - The general atmospheric circulation
from Part II - The meteorological background
Published online by Cambridge University Press: 05 November 2011
Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- Part I The dryland environment
- Part II The meteorological background
- 4 The general atmospheric circulation
- 5 The global distribution of arid climates and rainfall
- 6 Radiation, heat, and surface exchange processes
- 7 Water balance
- 8 Evaporation
- Part III The climatic environment of drylands
- Part IV The earth’s drylands
- Part V Life and change in the dryland regions
- Index
- References
Summary
Receipt of solar radiation
The ultimate source of the earth’s energy is the sun. It provides energy in the form of electromagnetic radiation that is converted within the earth–atmosphere system to the mechanical motion of the winds and the thermal energy of the earth and atmosphere. The amount of solar radiation received at the top of the atmosphere at a given point on the earth depends on four factors: (1) the magnitude of solar output, (2) the distance from the sun, (3) the obliquity or tilt of the sun’s rays, and (4) the length of day. Thus, the insolation at the top of the atmosphere varies with season, time of day, and latitude.
However, the amount received at the top of the atmosphere on a surface perpendicular to the solar beam is relatively constant. This amount, which is 2 cal/cm2 per minute, is called the solar constant. The beam’s effectiveness is reduced when it hits the atmosphere or earth’s surface at an oblique angle, as is the case at higher latitudes. This is illustrated in Fig. 4.1. In both diagrams the beam is equally intense, but when it strikes obliquely, the radiation is distributed over a greater area. The obliquity affects the amount of radiation reaching the earth’s surface in another way; the path length of oblique rays through the atmosphere is greater than those striking perpendicularly. Therefore, the attenuation of the beam by scattering and absorption in the atmosphere is also greater.
- Type
- Chapter
- Information
- Dryland Climatology , pp. 67 - 82Publisher: Cambridge University PressPrint publication year: 2011
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