Section 22. The Cooling of the Sea 



As we have seen, the cooling of the sea surface is brought about by three processes: radi- 

 ation, convection and evaporation. 



Other conditions being equal, the effective radiation is proportional to the difference of the 

 fourth powers of the water and air temperatures. Convection is proportional to the water-air 

 temperature difference and wind effect. Evaporation is proportional to the moisture deficit and 

 wind effect. The moisture deficit is, in turn, a direct function of the water-air temperature dif- 

 ference. Thus, all of the three processes that cool the sea surface are directly proportional to the 

 water-air temperature difference, but convection and evaporation are, in addition, proportional to 

 wind speed. 



On the whole it could be said that the cumulative speed of cooling of the sea and ice is di- 

 rectly proportional to the temperature difference and wind speed. 



In order to investigate the effect of temperature difference and wind on the rate of cooling of 

 water, Bodman carried out special observations during the Swedish Antarctic Expedition from 1901 

 to 1903. He measured the time needed for the cooling of water in an open container from 30° to 

 20° at various air temperatures and wind speeds, and presented the relationship by the following 

 empirical formula: 



C= (1—0.04/°) (1+0.271V), 

 where t = air temperature, 



10 = wind celerity in m/sec, 



c = coefficient of "severeness" of weather. 



In table 16 are listed the values of "severness" calculated by me for certain points of the 

 Soviet Arctic. 



In the marginal seas of the Soviet Arctic, especially in coastal areas, the air temperature is 

 higher in summer and lower in winter than the water temperature. The time moment when the air 

 and water temperatures become equal marks the beginning of winter cooling in the seas. However, 

 the determination of the moment of temperature equalization — as well as the moment when the air 

 temperature passes 0° for individual points on the etirth's surface, the significance of which is not 

 smaller for the cooling of the sea and the subsequent ice formation — is a very difficult task, which 

 can be accomplished with an accuracy that is sufficient for practical purposes only by means of a 

 multiannual cross section. 



If, however, the conditions of individual years are examined, repeated air temperature tran- 

 sitions across the sea-air temperature equalization point and 0° are observed at each individual 

 point of the sea, which is explained by continual shifts in synoptic processes. 



In the latter relationship we have to take into consideration, first, the shift of natural syn- 

 optic periods, which continues in the arctic for approximately 7 days and determines the general 

 character of the weather for this time period, and secondly, the passage of one or the other basic 

 system across the given point. 



48 



