632 



GROEN AND GROVES 



[chap. 17 



(29), (6) a current "caused" by Vh, according to the second term of the right- 

 hand member of (29), and (c) a current "caused" by the leak, according to (34). 

 Following Weenink and Groen (1958), these component current fields may be 

 called "curl t current", (f>a, "bottom slope current", ^^ and "leak current", (f)c, 

 respectively, and may be formally defined by splitting up the right-hand 

 member of (29) and the boundary conditions (30), (34) and (3o) as follows : 



'^{cf>a) = p-^h curl T, 

 <^a(DEA) = <f>a{BC) = 0, 



f^ + rh-^^ = along CD; 



dx 



^{<t^t 



— n-l 



dh 



dx 



dh 



dy 



Tx 



<^,(DEA) = </.,(BC) = 0, 



'' dx dy ^ 



Wz = along CD ; 



(29a) 

 (30a) 



(35a) 



(29b) 



(30b) 



(35b) 



(29c) 

 (30c) 

 (34c) 



(35c) 



0c(DEA) = 0, 



c/.c(BC) = xa*AB-^**), 



/^V,A-i^ = along CD; 



"^ 8x dy & ' 



where =^(^) means the left-hand member of (29) and 



^*AB = UAB) + ^a(AB) + ^,(AB), 



l,a and ^ft being the two parts of the current effect ^r/ determined by cjia and </>{,, 

 respectively, while the remaining j^art l,c is brought about by ^c and may, 

 therefore, be called the "leak effect" : 



^U = ^a + ^&+^c- 



The physical mechanisms underlying the idea of these different sorts of 

 currents are immediately clear for the "curl t current" and the "leak current". 

 The idea of the "bottom slope current" may be explained in the following way. 

 Suppose the depth of the sea represented in Fig. 9 decreases from west (left) 

 to east (right) and a uniform wind blows from the north. Then the static wind 

 effect t,T will increase from A to E, so that, since no wind stress is working in 

 that direction, a current will run in the opposite direction, giving rise to an 

 anticyclonic circulation in the sea area. This is the bottom slope current. 



We shall not enter into details of various mathematical techniques of com- 

 puting the wind-induced current field from the above equations. Weenink 

 (1958) has worked out various examples of such current fields for the North 

 Sea. Weenink, with a view to the practice of forecasting wind-surge heights of 



