Turbulence intermittency in the stable boundary layer

During CASES99, thermocouple temperatures were measured at 34 vertical levels on the main CASES tower and on adjacent mini towers. The temperature was recorded at 5 samples per second with a vertical resolution of 1.8 m on the main tower from the ground surface to 58.1 m height. Generally, the time series of the vertical temperature structure can be summarized into three categories: 1) large temperature oscillations, 2) strong vertical mixing events, and 3) quiet nights with little activity. Large temperature oscillations occur mostly when the air is strongly stratified. Strong vertical mixing events normally start at the top of the tower, propagate downward, and stop just above the ground surface where the stratification is strong. A strong vertical mixing event and a large oscillation event may occur sequentially during the same night. The phenomena of categories 1) and 2) occur 15 out 27 nights. The temporal variation of the vertical distribution of the bulk Richardson number will be examined. In addition, the turbulent transport of heat and momentum during the strong mixing event will be studied using sonic anemometer data from 8 observational heights.