Meteorologische Zeitschrift (Aug 2015)
Analysis of a 7-year low-level temperature inversion data set measured at the 280 m high Hamburg weather mast
Abstract
We use a 7-year set of temperature, humidity, wind vector, heat flux and momentum flux data recorded at 6 levels at the 280 m high Hamburg weather mast in order to analyse the frequency and vertical structure of 15 inversion types with different base and top. For each type we present the diurnal frequency cycle and the mean vertical profiles of the above-mentioned quantities. Due to the 1-hourly time resolution we are able to follow the night-time growth and the morning-time rise of the inversion. Inversions occur in 27 % of time, with surface-based inversions in 15 % and elevated inversions in 12 % of time. Surface-based inversions exist almost only during night. Most elevated inversions are transitions of surface inversions rising in the morning hours after sunrise. The heat flux in surface inversions vanishes at the surface but has a minimum (maximum downward heat flux) at the 50 m or 110 m level indicating the presence of turbulence in the inversion layer. Both, temperature difference and wind shear across the inversion increase in the course of the night. They act against each other concerning turbulence generation with the result that the Richardson number can temporarily decrease in spite of an increasing temperature difference. For elevated or rising inversions the temperature increase below the inversion is driven by surface and entrainment heat flux and radiation flux. Radiation flux divergence is the most important process for inversion formation and dissolution. We assume that the results from the Hamburg weather mast are also valid for the surrounding region in North Germany and also for other regions with similar topography and similar synoptic-climatologic conditions.
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