235 



increase about 10 m sec through the lowest 600 meters . As this situation 

 is one in which the Coriolis and pressure gradient terms of the equation 

 of motion are not balanced, the increase in wind with he i git probably does not 

 attain the full geostrophic value . The wind speed increase from 100 m to 

 1000 m on September 1, I96U, was about 12 m sec" which is in fair agreement 

 with the computed thermal wind increase . 



One additional bit of information is now presented that will aid in the 

 analysis of the generation of the low level jet. The magnitudes of the root- 

 mean-square turbulent vertical velocities of the air have been measured from 

 the aircraft's accelerometer according to the method of Bunker (1955) and 

 expressed in cm sec"-'-- Ths observations were made on September 1, 196U, 

 around 11° N, 57 E. Also plotted on the height- vertical velocity diagram, 

 Figure 6, are values of the turbulent velocities observed in other regions 

 of the world. Several features of these data are very unusual pnd significant. 

 First, it is noted that the turbulent velocities at the lowest level are about 

 the same as the turbulent velocities measured in the trade winds of the Morth 

 Atlantic Ocean by Bunker (1955) • From this observation of weak turbulence it 

 is concluded that the frictional drag of the water-, on the air is nearly the , 

 same as the drag found under the lighter (5 m sec ) trade wind situation and \/ 

 is therefore many times smaller than would be expected for high winds of 15 

 to 20 m sec' • 



The small frictional force coupled with the small Coriolis force, due to 

 the small Coriolis paramater near the equator, caimot balance the pressure 

 gradient force and hence the air particles are accelerated rapidly across the 

 isobars . In the region of the strongest winds , it appears that geostrophic 

 balance is never attained. Down wind of the jet the pressure gradient 

 decreases and the wind becomes geostrophic. To understand and prove these 

 relationships in this region a much more detailed and quantitative study of 

 the terms of the equation of motion must be made . 



The second noteworthy feature of Figure 6, is the high turbulent velocities 

 observed at the 600 meter level. For comparison, observations made at various 

 heights in a strong wind (20 m sec" ) situation over the North Atlantic Ocean 

 by Bunker (i960) are plotted on the diagram. It is seen that after a rapid 

 increase in turbulence in the lowest layers the turbulence decreases rapidly 

 with height. Such a turbulence-height curve is characteristic of a situation 

 in which the turbulence is generated by the flow of air over a surface and 

 decays aloft. In the present case it appears that only a small amount of 

 turbulence is generated by the flow of the stable air over the water and that •/ 

 a greater amount is generated at a higher level where the air is not- as stable. 

 It is concluded from this trace that the turbulence must be generated by high 

 wind shears and that the aircraft was flying below the level of the maximum 



probably extends to ll" N, 58"^ E, where it was observed at 1000 meters. 



winds. If this is true then the jet observed at 12 N, 53" E, at 500 m 

 r extends to 11° N, 58° E, where it was obsei 



