from Part II - The meteorological background
Published online by Cambridge University Press: 05 November 2011
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.
To save this book to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.