Vertical structure of the tropical boundary layer.

Observations presented show that the undisturbed subcloud layer near the ITCZ resembles that of the trades. Mixed and transition layers are also seen between cloud drafts during disturbed periods when shallow mixed layers (c200m) can persist for several hours. Modification of the lower atmosphere during disturbed periods is most marked in the lowest 1200m. Mixed layers are observed during prolonged disturbed periods; disturbed mixed layers are shallower and cooler than undisturbed ones. Light and moderate rainfall events moisten the mixed layer, but mixed layers in the environment around strong rainfall are drier. It is hypothesized that the effect of a number of downdrafts spreading laterally produces the mixed layer cooling and drying. Observed changes of mixed layer structure with stability, measured by the ratio of mixed layer height to the Monin-Obukhov length, are presented.-Authors