The Three-dimensional Temperature Distribution and its Variation in Time 1 1 1 



points and are then referred to "geographic" co-ordinates. These last changes are 

 more complicated, since they are a combination of thermal changes within an indi- 

 vidual water mass and of changes caused by the displacement of different water bodies 

 (ocean currents). t 



For most parts of the ocean the annual displacements of the currents are known and 

 most of the major annual changes in these areas can be ascribed to these. The seasonal 

 displacements of the Gulf Stream system and the Labrador Current in the region of 

 the Grand Banks of Newfoundland are well known. The large annual temperature 

 variations in this region of the sea are associated with these displacements Similar 

 conditions are found off the Norwegian coast where the seasonal displacements of the 

 coastal current and the Atlantic current cause pronounced seasonal variations in 

 temperature and salinity. 



For smaller areas the annual temperature variation at the sea surface can be derived 

 only from a statistical evaluation of ship's observations and for the deeper layers from 

 series observations made by oceanographic expeditions. Averaging the values that fall 

 for different parts of the year into one, two or more degree squares gives mean tem- 

 peratures for these subsections of the year with sufficient accuracy, provided there is a 

 reasonable number of observations available. This of course gives only values related 

 to "geographic" co-ordinates. Such a rough statistical method can only be used with 

 some reliability for the sea surface. 



All the available data on surface temperature in the Atlantic Ocean have been 

 collected and studied by Bohnecke (1936) and presented in a comprehensive form. 

 For the Indian and Pacific Oceans a less complete presentation has been given by 

 SCHOTT (1942). These show that there is an absolute minimum in the annual variation 

 of surface temperature of all oceans in the tropics where over extended areas, especially 

 in the Indian and Pacific Oceans, this variation is less than 1 °C. There is also a second- 

 ary minimum in the Southern Hemisphere everywhere in the water encircling the 

 Antarctic continent which also shows values less than 1 °C. In the Northern Hemi- 

 sphere there is a decrease in the annual temperature variation in the Norwegian Sea 

 and the variation becomes gradually smaller towards the north; this is true also for the 

 North Pacific, but the northward decrease is slower. The maximum annual tempera- 

 ture variation always occurs in the subtropical high-pressure belt where, near to the 

 Bermudas and near the Azores, the maximum value is greater than 8°C. This region 

 is connected with that showing the absolute maximum surface temperature variation 



t The individual change in temperature d?^ldt in a given unit mass is caused by the addition or 

 abstraction of a given quantity of heat Q. This quantity Q is due to the absorption of radiation, to 

 back-radiation, to thermal conductivity, to evaporation and to mixing and others. If the local distri- 

 bution and that with time of these properties is given along the path followed by the unit mass of 

 water then the "individual" variation in temperature d^ldt can be found. If the "local" temperature 

 change d^jdt is required for a fixed point occupied successively by different masses of water, then for 

 a given flow (velocity u) in the direction n the following equation is valid: 



db db db 1 



dt ct dn Cp 



The advection term u(8bl8x), which includes the effects of the transport and the displacement of 

 different masses of water at different temperatures in the direction n, thus plays an important role 

 for the assessment of the local temperature change d^ldt. 



