Momentum and scalar transport during the decay of CBL turbulence

Channeling in the Hudson Valley on fair weather days often leads to a convective boundary layer with a deep along-valley flow that shears to cross-valley flow in the upper mixed layer and above. After the early evening transition the wind at 150-300 m often exhibits the wind direction that was previously above zi. This directional shear at the beginning of the night strongly affects scalar characteristics in the stable boundary layer. Our research tests the idea that decaying turbulence in the CBL, while weak, is still sufficient to mix momentum as well as other scalar quantities down to the 200 m level. During the Hudson Valley Ambient Meteorology Study (HVAMS), 26 flights of the Wyoming King Air were completed, with most flight tracks confined to a 100-km stretch of the Hudson River just south of Albany NY. Thirteen flights occurred during the late afternoon. We use turbulence measurements from the aircraft as well as mean wind measurements from surface stations, sodars, and profilers to form a composite picture of scalar and momentum transport in the decaying CBL in this situation.