Pacific Ocean Circulation — HiDAKA 
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from Ekman’s theory of the limit of the wind-driven currents. This implies that the mo- 
tion of water in most parts of the oceanic troposphere could be produced by the stresses 
of the permanent wind system prevailing over the oceans. In other words, the winds are 
responsible not only for the currents in the skin layer of the ocean, but also for most of 
the circulation in the oceanic troposphere. 
We have long considered that the winds are responsible only for the current motion in 
the surface layer of about 200 meters. This depth is nothing but the “depth of the frictional 
influence” defined by Ekman. To explain the circulation in deeper parts of the troposphere, 
we had to assume a very strong convection current and slope current. Still we had a dis- 
tinct difference in the circulation patterns between the troposphere and stratosphere. 
These circumstances have made several problems very complicated. Defant (1928) defined 
the troposphere as the part of the ocean in which we can expect strong currents due to 
violent turbulence and convection. Still we can have violent convection in the seas of 
higher latitudes beyond the polar fronts which are no longer defined as troposphere. The 
conclusion that the drift currents penetrate into much deeper layers than D z is much in 
favor of the definition of the troposphere as the upper layer of the ocean in which strong 
currents are present. 
The explanation of the result that we can have a strong ‘motion even in a layer several 
hundred meters deep might seem to be possible by assuming slope currents which would 
be produced as the effect of purely wind-driven water masses piled up against the land 
barriers. As a matter of fact, Ekman’s theory assumes no boundaries and a constant 
latitude. We can prove the existence of slope current in an ocean having boundaries partly 
or completely enclosing it. The slope current is uniform from the surface down to the 
bottom. This fact seems in favor of the theoretical result we have obtained. Still, we must 
give attention to the fact that the velocity of slope current is always inversely proportional 
to the depth of the sea. When the depth is large, as we see in the actual oceans, the slope 
current will not be strong enough to account for those large velocities we have obtained 
at the depth twice or three times as large as D z . 
We do not know an appropriate explanation of the theoretical result that the effect of 
winds can be felt at a depth several times as large as Ekman’s depth of frictional influence. 
It is to be hoped that someone may be able to solve this question satisfactorily in the near 
future. 
SUMMARY 
(1) A theory of the general circulation of water in the Pacific Ocean produced by the 
semipermanent wind system prevailing over this ocean is propounded. 
(2) The velocity is used to express the water motion which has formerly been explained 
by several authors in terms of mass transport. 
(3) The Pacific Ocean is considered to be a rectangular ocean extending from 60° S to 
60° N latitudes and from 0° to 120° longitude, and a zonal distribution of the wind system 
determined from actual observations has been assumed. 
(4) The effects of horizontal turbulence and the meridional variation of the Coriolis 
force have been taken into account. 
(5) The patterns of horizontal circulation are obtained in terms of streamlines for the 
sea surface and several deeper layers specified by the ratio z/D z where z is the geometrical 
depth below the surface and D z the depth of the frictional influence, a measure of vertical 
turbulence. 
