160 Salinity of the Ocean, its Variation in Oceanic Space and in Time 



present before the disturbance produced by rainfall, so that 2-3 h after the rain had 

 ceased the salinity values did not differ from the value before the rain by more than 

 0-05-0-10%o. 



A quantitative treatment of these processes has been given by Defant and Ertel 

 (1939). The rain v/ater falling on the surface can be regarded physically as a salinity 

 sink at the surface (z = 0) that consumes a quantity of salt —S per unit time and unit 

 area; this corresponds to an intensity in the salinity flux —A^ids/dz) immediately at 

 the sea surface z = (^4^ is the vertical exchange coefficient, s is the amount of salt 

 in unit mass, z is counted positive downwards). This reduction in salinity extends 

 downwards into deeper layers by mixing during the precipitation period according to 

 the exchange equation 



ds A 8^s 

 'dt^ ~p 8z^' 



At the start of precipitation (/ = 0) the salinity should be uniform {s = ^o)- ^ will be 

 dependent on the intensity of precipitation and on the time t and therefore for a dura- 

 tion T of precipitation 



2J(t) > for ^ t ^ T 



while at the end of precipitation 



2:(t) = for t ^ T. 



At large depths the disturbance will vanish so that for z = oo and for any time s =s*. 

 Solution of the problem for the given boundary conditions will give a complete 

 answer for the entire process not only for the sea surface but also for all the layers 

 underneath the surface. The simplest case is that where for the total duration T of 

 precipitation 27 is constant for S t ^ T, while after the rainfall 27 = for / ^ T. 

 In this case the solution for the total precipitation time T is 



' = '*- (vSx)) ^' 



and when precipitation has ceased 



The maximum salinity disturbance q will reach by the end of the precipitation a value 



^ ~ VipTrA) • 



The salinity disturbance at the sea surface during the precipitation will follow the 

 equation 



s* - s = q hr for (0 ^ r ^ T). 



At the end of rain {t = T) q reaches a maximum value and then the disturbance 

 decreases according to the formula 



_\l T \]\t 



for (/ Z T). 



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