An Empirical Study of the Planetary Boundary Layer in the Vicinity of the Intertropical Convergence Zone.
AIR FORCE ENVIRONMENTAL TECHNICAL APPLICATIONS CENTER SCOTT AFB ILL
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Marshall Islands data for May 1956 are used to evaluate the balance of forces in the equatorial tropics. Flow is balanced north of the ITC, while south to the equator various inertial and Reynolds stress terms are important. Friction is important in the first 2km at all latitudes. Composite profiles of wind, humidity and temperature in the boundary layer near the ITC are derived from the Line Islands Experiment and BOMEX Fourth Phase as well as the Marshalls data. On the average, an Ekman layer north of the ITC accounts for the equatoward flux. The layer is 2-3km deep but 50 percent of the transport is below 750m. The poleward flux south of the ITC is much deeper and winds back with height above a shallow veering layer below the clouds. The boundary layer on the equator is on the order of 2km deep and winds either turn very little or back with height. Daily case studies from BOMEX using aircraft and satellite-derived winds reveal excellent correlation between ITC cloud bands and meso-scale patterns of cyclonic vorticity and convergence in the boundary layer. These data support the hypothesis that CISK maintains the ITC.