Samples of Persistent Elevated Winter Inversion

The Doppler SODAR 24 with the RASS extension was used to take samples of persistent elevated winter inversion at the Metek facility in Elmshorn northern Germany in January 2001.

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General
With a high pressure system a foggy period of about 2.5 days duration occurred over most of the northern part of Germany. The fog layer was observed within the lowest 200-400 m height agl which was determined by a strong inversion of about 4-5 K/50m within the height range of 200 – 300 m. Beneath the inversions very low wind speeds were measured for most of the time showing significant wind shear compared to the heights above the inversion. From ultrasonic measurements the turbulent heat flux was measured as low as 20-30 W/m2 at that time. With the arrival of a warmer air mass the elevated inversion vanished and the visibility returned to normal conditions.

Site Conditions
The SODAR-RASS system was installed on Metek’s test ground in Elmshorn which is located northwest of the metropole region of Hamburg. As a part of the final acceptance test the system was operated continuously for a 3 day period in routine operation scheme without outer access. The background noise varied between 50 and 61 dB during daytime, occasional noise measurements at night showed intensities of about 45 – 61 dB. Within a distance of less than 50 m buildings, trees and electrical masts are located.

Shown Samples
Wind speed and wind direction are given as vectors, temperature is given as contour plots as potential RASS temperature (this corresponds mainly to the meteorological virtual temperature).

Main Operation Parameters

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Fig. 1 above: Jan 2001, Time/Height Cross Section of RASS Temperature

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Fig. 3 above: Jan 2001, Cross/Height Section of Wind Vectors

E&OE