Wavelet Analysis of Thermocouple Measurements During CASES-99

In the stable nocturnal boundary layer, the turbulence can be very weak and intermittent. M-O similarity theory fails to describe intermittent turbulence. During CASES99, air temperature measured by thermocouples was recorded at 5 samples per second with the vertical spatial resolution of 1.8 m from the ground surface to 58.1 m height. In addition, there are 8 vertical levels of turbulence eddy-correlation measurements. Intermittent turbulence and strong vertical mixing events are commonly associated with a sharp drop of the air temperature at many vertical heights, and a gradual recover of the stratification. The thermocouple temperature and the turbulence during the period of intermittent turbulence and strong vertical mixing events are analyzed using statistical methods based on wavelet and Fourier analysis. The results from the two different analysis methods are compared. In addition, the structure of turbulence intermittency and strong vertical mixing events is investigated using classical statistical methods.