Aircraft Observation of the Specific Humidity and Process of the Water Vapor Transfer in the Upper Mixed Boundary Layer

摘要

The structure of the upper part of mixed layer and the exchange mechanism between mixed layer and upper stable layer are investigated using the humidity (Q) and potential temperature (θ) data observed on an airplane. It was found that Q was nearly constant with height in the mixed layer and decreased sharply at some upper height. This height is coincident in almost all the cases with the mixed layer height determined from the vertical profile of θ. During the developing process of the mixed layer, the humid air-mass is brought to the upper layer by thermal convections, and these convections penetrate into the upper stable layer as humid and cold plumes.At the top of the mixed layer, a wave-like surface is formed due to the influence of the wave-motion in the upper stable layer and intake-flows are induced in the vicinity of the upper boundary of the mixed layer. The dry and warm air in the upper layer is taken into the mixed layer by these intake-flows. During the decay of the thermal convections, the thickness of the mixed layer decreases with time due to these descending flows. The boundary surface between the mixed and upper stable layers has periodic undulations and their wavelength is about 2000-3000m and the amplitude is 100-200m.