Ocean Temperatures along the West Coast of North America. 269 



greater than (2 D), the actual velocity at any point of the surface 

 current is the resultant of the velocity (U ) (problem 2, page 253) and 

 the velocity in a surface layer which the corresponding local wind would 

 produce in an ocean extending to a great distance from the point in 

 all directions, according to problem (1), page (251). 



But along the Pacific coast, the wind direction, except during a 

 few weeks in the winter is toward the south east, and makes an angle 

 of about (25) with the coast within about (300) kilometers from the 

 shore. Therefore the angle that the surface velocity (V) would make 

 with the coast would be (45) (25) = (20) if (U ) were zero, and it 

 can be shown the actual value of (U ) next to the coast reduces this 

 to (10). But the wind direction shifts to the west at points to the 

 south and west of Cape Mendocino, and makes an angle of about 

 (45) to the west of a north and south line at the latitude of (32) 

 and longitude (140) in the summer. Therefore, we would expect (U ) 

 to diminish and the surface velocity to be directed more and more to 

 the west as the distance from the coast increases and the latitude 

 diminishes. 



Therefore a stream-line (a line having at each point the direction 

 of the motion at that point) starting from the vicinity of Cape Men- 

 docino would be about parallel to the coast there, but would con- 

 tinually turn to the right as the latitude diminished. A series of such 

 stream-lines starting from points equidistant from each other along the 

 coast would divide the water area into a series of sections, such that 

 the water upwelling into each one would come from the ocean bottom 

 underneath the part next to the coast, and no surface water could 

 intrude from other regions. Observation shows that the cooling effect 

 of the upwelling water diminishes as the distance from the coast along 

 a stream-line increases, and in the following discussion, we will assume 

 for the outer boundary of any section a line parallel to that 

 part of the coast bounding the opposite end, and at such a distance 

 that the temperature is practically normal. Now the cooling effect in 

 an east and west area such as was considered on page (257) could be 

 determined by computing the amount of water upwelling into each 

 section that crosses it, and then calculating the temperature of the 

 part of each section included in this area. 



From the appearance of the isotherms, the actual as well as the 

 normal temperature of any section increases in proportion to the distance 

 from the coast along the corresponding stream lines, therefore the 

 assumptions stated on page (257) except as to direction of flow, corre- 



