CHAPTER I 

 Introduction 



The Heat Budget of the Earth 



The importance of the oceans to the circulation of the atmosphere is 

 best understood by considering briefly the heat budgets of the earth as a 

 whole and of the atmosphere. The earth as a whole receives and loses 

 energy by processes of radiation. Radiation is described, in general, as 

 a wave motion which, when absorbed in a medium, is transformed into 

 some other form of energy, such as heat. The wave length of radiation 

 varies within very wide limits, but the radiation that is of importance to 

 the energy balance of the earth all falls within a relatively narrow range. 

 The wave lengths wdll here be given in the unit fi, which is equal to 

 10~^ mm. In this unit the wave lengths of the visible Ught fall approxi- 

 mately within 0.38 /x and 0.7 /z, and the radiation that is of importance 

 to the heat budget of the earth falls within the hmits 0.15 ju and about 

 120 m. 



The energy which the earth receives by radiation from the sun is in 

 part reflected from the earth's surface or from clouds and is in part 

 absorbed in the atmosphere or at the earth's surface. Only the absorbed 

 amount is of importance to the heat budget of the earth. The earth 

 loses energy by radiation to space, partly directly from the earth's 

 surface and partly from the atmosphere. On an average, the amounts of 

 incoming and outgoing energy are at balance, because otherwise the 

 temperature of the earth would change, and no evidence exists for 

 measurable changes of this kind. In order to study this balance and to 

 examine the heat budget of the atmosphere, it is necessary to enter 

 briefly upon certain characteristics of the radiation from different bodies. 



Black-body Radiation. A body of a given temperature emits 

 radiation of different wave lengths, the amount of radiation from a unit 

 surface depending upon the temperature and the character of the radi- 

 ating body. According to experience, at every temperature there is an 

 upper Hmit to the amount of radiation that is emitted. A body which 

 at any given temperature emits the maximum amount of radiation at 

 every wave length is called a ''black body." For a black body the total 

 amount of energy radiated per unit time from a unit area equals aT,"^ 



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