Cabauw SF6 Dispersion Experiments 1977-1978
WHEN:
April 28, 1977 through October 31, 1978
LOCATION: The meteorological mast at Cabauw is located at 51.967 degrees North and 4.9333 degrees East in the centre of The Netherlands. The surroundings are topographically flat within a radius of 20 km or more and consist of meadows, with occasionally lines of trees, river dikes, and small villages. The surface roughness, which was determined by a method proposed by Wieringa (1976), is shown as a function of wind direction and season in Table 1 (Agterberg, et al., 1983). The general construction of the mast, which has a height of 213 m, is shown in Figure 1 (Agterberg, et al., 1983).
TRACER: Sulphur hexafluoride (SF6).
RELEASE:
In the cellar of the instrumentation room of the mast ten gas cylinders are installed, each cylinder containing 40 kg of liquid SF6 . The cylinders are connected via copper tubing to a reducing valve. After reducing the pressure to 0.8 MPa, the gas flows through a copper tube to points of release situated at heights of 80 and 200 m. At the point of release, which was 80 m or 200 m depending on the meteorological conditions, the pressure is reduced (twice) to about 0.15 MPa. Then the gas is emitted into the atmosphere via a fine metering valve and a dry gas meter. The gas meter reading is made every 10 minutes. The source strength is calculated taking into account temperature and pressure of the gas.
A full discussion of the release procedures and the determined release rates for each experiment are reported in Section 11 of the data volume report (Agterberg, et al., 1983).
SAMPLING:
Horizontal Sampling: Two consecutive 30-minute samples at a height of 1.5m above ground, along one arc, which depending on wind transport direction varied from 3150m to 4300m downwind of the release. The receptors were spaced at
Vertical Sampling: None.
A full discussion of the sampling procedures and the concentrations determined at each receptor post for each experiment are reported in Section 12 of the data volume report (Agterberg, et al., 1983).
METEOROLOGY
1. Profile Data. Along the 213m mast, platforms are installed at height intervals of 20 m starting at 20 m from ground level. The measuring platform, which is shown in Figure 2 (Agterberg, et al., 1983), consists of three booms, which extend 9.4 m beyond the mast. The instruments were mounted on the end of the upwind boom. Additional measurements were performed on an auxiliary 20 m mast in order to obtain surface layer characteristics.
30-minute average wind directions are reported for 9 levels (0.5, 5, 10, 20, 40, 80, 120, 160, and 200m). 30-minute average temperatures are reported for 6 levels (20, 40, 80, 120, 160, and 200m). 30-minute temperatures are reported for 11 levels (0.6, 2, 5, 10, 20, 40, 80, 120, 160, 200, and 213m).
These observations are reported in Section 4 of the data volume report (Agterberg, et al., 1983).
2. Turbulence measurements are reported for 6 levels (20, 40, 80, 120, 160 and 200m) for the standard deviation of the horizontal wind speed fluctuations, the horizontal wind direction fluctuations, the vertical wind elevation fluctuations, and the temperature fluctuations. At these same 6 levels are reported the absolute value of the horizontal turbulent stress, the direction of the horizontal turbulent stress, the vertical turbulent temperature flux, and the horizontal turbulent temperature flux.
These observations are reported in Section 5 of the data volume report (Agterberg, et al., 1983).
3. When visibility conditions were good, radiosondes were used to obtain meteorological data above the mast. During a dispersion release, two radiosondes were launched preferably before and after the 1-hour sampling period. These observations are reported in Section 6 of the data volume report (Agterberg, et al., 1983).
4. A monostatic acoustic sounder from Aerovironment Inc., was used to monitor the development of the atmospheric boundary layer. It primarily shows the boundary-layer height, when it is less than 500m. These observations are reported in Section 7 of the data volume report (Agterberg, et al., 1983).
5. Near the mast, radiation was observed at a height of 2m. The global radiation was measured with a Kipp (Moll-Gorzynski) and the net-radiation was measured with a Suomi. These observations are reported in Section 8 of the data volume report (Agterberg, et al., 1983).
6. During each dispersion release, synoptic observations were made primarily concerning the cloud cover. These observations together with a surface weather map are provided in Section 9 of the data volume report (Agterberg, et al., 1983).
7. The geostrophic wind was calculated each hour from synoptic pressure observations at 19 stations by a method based on principal component analysis (Cats, 1977). These observations are reported in Section 10 of the data volume report (Agterberg, et al., 1983).
DISCUSSION
Coordinates were not provided for the sampler positions. I enlarged Figure 3 (Agterberg, et al., 1983) to slightly twice its original size. I then drew a rectangular grid over the enlarged diagram, whose origin was centered on the 213m mast. Using this grid and the map scale reported in the figure, I determined coordinates for each of the sampling posts. These coordinates are listed with the concentration data in the digital data file.
In 1995, Frans Nieuwstadt and I exchanged emails. During this exchange, Frans Nieuwstadt provided his friction velocity, Monin-Obukhov length and mixing heights for some of the experiments. I have provided these values with those I determined in an Excel file. [MicrMetCabauw.xls, 22KB]
DIGITAL DATA FILES:
Tracer Observations
Horizontal sampling array concentration values. . There were 15 releases, but there are no concentration results for experiment 11 because of equipment failure. Along with the concentration valuies, I have listed the emission rate, my estimated values for the Monin-Obukhov length and friction velocity, and the sampling post positions relative to the 213m mast from which the releases were made. [CabauwConcentrationData.txt, 35 KB]
Meteorological Observations
I used the meteorological profile data for wind speed and temperature to estimate friction velocity and Monin-Obukhov length values for each of the experimental 30-minute periods. In 1995, Frans Nieuwstadt and and I exchanged emails. Dukring this exchange, Frans Nieuwstadt provided friction velocity, Monin-Obukhov length and mixing heights for some of the experiments. I have provided these values with those I determined in an Excel file. [MicrMetCabauw.xls, 22KB]
REFERENCES:
Agterberg, R., Nieuwstadt, F.T.M., Duuren, van H., Hasselton, A.J., and Krijt, G.D., (1983): Dispersion Experiments With Sulphur Hexafluoride From The 213m High Meteorological Mast At Cabauw In The Netherlands. Royal Netherlands Meteorological Institute, De Bilt, The Netherlands. 130 pages. [Cabauw1983JanuaryReport.pdf, 3.6MB]
van Duuren, H., and F.T.M. Nieuwstadt (1980): Dispersion experiments from the 213 m high meteorological mast at Cabauw in the Netherlands. Proceedings of the 14th International Colloquium, Paris, France May 5-8, 1980. Benarie (Ed.) Studies in Environmental Science, Volume 8, Elsevier Scientific Publishing Company, Amsterdam. Pages 77-90.
Nieuwstadt, F.T.M., and van Duuren, H., (1979): Dispersion experiments with SF6 from the 213 m high meteorological mast at Cabauw in the Netherlands. In Proceedings of the 4th Symposium on Turbulence, Diffusion and Air Pollution, Reno, Nevada, 15-18 January, pages 34-40, American Meteorological Society, Boston, MA.