Vertical Velocity Fluctuations in a Nocturnal Low-Level Jet

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Abstract
Sonic anemometers were installed at four levels on the Cedar Hill television tower and operated for selected periods during three weeks in August 1963. One of the runs covered the entire history of a nocturnal low-level jet. The vertical velocity fluctuations measured by the sonic anemometers are examined closely for their relationship to mean horizontal wind speed and temperature profiles obtained from existing meteorological instrumentation on the tower. In a qualitative sense the data confirm many of the current speculations on the role of turbulence in the development and dissipation of these jets. Statistical analysis of the fluctuation data provides some interesting results, particularly for the period following breakdown of the surface inversion. The constant of proportionality between standard deviation of the vertical velocity component at 150 ft and friction velocity is found to be 1.22. The limiting value of Richardson number for maintenance of an inversion at 450 ft appears to be 0.25. Abstract Sonic anemometers were installed at four levels on the Cedar Hill television tower and operated for selected periods during three weeks in August 1963. One of the runs covered the entire history of a nocturnal low-level jet. The vertical velocity fluctuations measured by the sonic anemometers are examined closely for their relationship to mean horizontal wind speed and temperature profiles obtained from existing meteorological instrumentation on the tower. In a qualitative sense the data confirm many of the current speculations on the role of turbulence in the development and dissipation of these jets. Statistical analysis of the fluctuation data provides some interesting results, particularly for the period following breakdown of the surface inversion. The constant of proportionality between standard deviation of the vertical velocity component at 150 ft and friction velocity is found to be 1.22. The limiting value of Richardson number for maintenance of an inversion at 450 ft appears to be 0.25.

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