122 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. JO 



wards, and tends to lower the temperature of the coast waters, 

 " Skjargaard." By the land winds the ocean is relatively little 

 disturbed. 



When the zuinds blow toward the land the warmer surface water 

 is transported landwards. Since the sea winds on the west coast are 

 relatively warm and attended by increased cloudiness, the outgoing 

 radiation, and therefore the cooling-, is diminished. By the wave 

 actions the surface is warmed partly by mixing- with underlying 

 warmer water-layers and partly by the exchange of temperature with 

 the air. All these causes tend to increase the surface temperature. 



In the warmest season of the year we must, on the other hand, 

 expect exactly the opposite condition of affairs to that which we 

 have detailed. Then the light surface layer of the coast water will 

 be strongly heated and become considerably warmer than the under- 

 lying strata and also warmer than the surface water lying further 

 out in the open sea. Accordingly, one must expect with sea winds 

 that the surface temperature of the sea by the lighthouses along 

 the coast, as for example the Ona lighthouse, will fall and that 

 the surface temperatures will rise with land breezes, or when it 

 is calm, so that the surface layer of the coast water shall alone be 

 effective ."^ 



RELATION BETWEEN AIR PRESSURE GRADIENTS AND WATER 

 TEMPERATURES AT ONA AND TORUNGEN 



We shall first investigate the relation between the surface tem- 

 perature of the sea at Ona Lighthouse on the Norwegian west coast 

 (where we have a most complete series of observations.) and the 

 winds as determined by the direction of the isobars and the intensity 

 of the pressure gradients. We shall deal with the coldest time of 

 the year, in February, and with the warmest, in August. 



In the manner already described, we have determined the direc- 

 tion of the isobars and the intensity of the pressure gradients near 

 Stad at 62° 30' north, 5° east, and we give their mean direction 

 and intensity by progressive vector diagrams for the eleven-year 

 period 1889 to 1908. In those relating to the coldest time of the 



^However, land winds may at this time also produce cooling of the surface 

 temperature of the ocean near the coast, because the warmer surface water of 

 the land is driven off and the cooler underlying layers are brought up to the 

 surface, but this occurs generally only for the fjords and the sea nearest the 

 coast. It can for example scarcely occur at an island like Ona, which is much 

 further out to sea. 



