Weather station
Geographical coordinates: 6°24'34'' East 50°54'36'' North, 91 m a. s. l.
The meteorological station is located in a clearing in the Stetternich forest. In addition to the meteorological tower, which can be seen from afar, there is an office and operations building as well as a climate garden.
The tasks of the station include the continuous recording of the current weather situation and atmospheric dispersion conditions. This meets the requirements of the guideline for emission and immission monitoring of nuclear facilities (REI) necessary for research with radioactive substances. The meteorological data is freely available for research and teaching purposes.
The meteorological tower was built in 1963 and 1964 based on international models such as Brookhaven (USA) and Risö (Denmark). Inside the 124 m high lattice tower with its triangular cross-section is an elevator for quick access to the platforms. The tower is braced in three directions at heights of 40 m and 100 m. It is also marked as an obstacle for aircraft at night by red signal lamps.
A total of seven accessible platforms are located at heights of 10 m, 20 m, 30 m, 50 m, 80 m, 100 m and 120 m. Each platform has a swivel arm on which the measuring devices are mounted, as well as power and telephone connections. An eighth measuring point is located at a height of 2 m in the clearing. The following picture shows the platform with the boom at a height of 120 m. Wind vanes and cup anemometers can be seen at the outer end of the arm.
Measurements for determining dispersion conditions
To determine the dispersion conditions, it is important to record the wind speed and wind direction. The wind speed at all eight measurement heights are measured using cup anemometers to precisely record the speed profile. Wind direction measurements are carried out at heights of 30 m, 50 m and 120 m by using wind vanes. In accordance with international agreements, wind measurements are taken 6-10 m above the mean disturbance level in order to ensure the comparability of measurements at different locations. The 30 m platform is located around 10 m above the average vegetation canopy surrounding the tower and thus satisfies this criterion.
Another important parameter for characterizing the dispersion situation is the vertical temperature gradient. Together with the mean wind speed, it is needed to determine the diffusion category (a division of the various turbulence states of the lower atmosphere into classes). To determine the temperature gradient, the difference between the temperatures at 20 m and 120 m is calculated. As this is often only a few tenths of a degree Celsius, the demands on the accuracy of the measurements are very high. This is why platinum wire temperature sensors (type PT-100) are used, with which the absolute temperatures can be determined to an error of a maximum of 0.1 °C. To ensure that the measurements are not falsified by heating due to solar radiation (radiation error), the sensors are located in chrome-plated double-walled pipes. A fan continuously draws in outside air through the pipes so that the sensors are constantly surrounded by air at the current temperature.
Redundancy measurements of wind speed, wind direction and temperature are carried out in parallel to the measurements described. This means that the most important measured values are available even if a sensor used in routine operation fails. The redundancy measurements are carried out with separate sensors on separate measuring lines. They are recorded graphically on line recorders and archived in a machine-readable format.
In order to ensure and document the quality of the measurements, regular periodic inspections are carried out in the presence of a TÜV expert. The sensors and the associated measurement technology are checked once a year. The test is carried out in accordance with safety regulation KTA-1508 for all sensors and measuring devices used for routine measurements to determine dispersion conditions.
Additional measurements and data use
Along with the measurements required for safety reasons, the tower is also used to determine other meteorological parameters. These include recording air humidity using hair hygrometers, measuring the duration of sunshine, global radiation and the radiation balance. The tower data is also complemented by measurements in the clearing, which include recording the amount of precipitation and ground temperatures down to a depth of 0.6 meters.
Most of the data is recorded electronically. Only the redundancy measurements are recorded on line recorders. For electronic data recording, data are recorded and stored as 10-minute averages or 10-minute sums, as in the case of precipitation and sunshine duration.
The 10-minute data is archived without changes so that the raw data can still be accessed for later purpose. The raw data is also converted into hourly values. A plausibility check is carried out, corrections are applied and downtimes are marked if, for example, a measuring device has been serviced. This data is archived as well. They form the basis for all further evaluations, such as the frequency distribution of wind directions or the determination of the diffusion category.
In addition to evaluating the data to determine the dispersion conditions, measured values from the meteorological station are also used by other institutes at the research center - in some cases as part of collaborations. They are used in modeling chemical reactions of trace substances in the atmosphere, as well as in the interpretation of measurement results from laboratory and field studies, the project planning of solar and wind energy plants and in the calibration of measuring instruments. Universities and research institutes are supported in their scientific work by providing meteorological data free of charge. For people outside the education and research sector, weather data can be provided for a fee.
Since March 1999, selected current measurements and climate values have been made available on a web weather page. The update takes place automatically shortly after every full tenth minute. This page provides information on air pressure, temperature, relative humidity, wind speed and wind direction. Climatological data of the previous day are also published here, such as extreme values of air temperature, the wind speed maximum, the amount of precipitation and the duration of sunshine. The web page also contains a table with the sunrise and sunset times for each day.
Climatological measurements
In addition to the meteorological measurements, climatological observations are regularly carried out at the weather station. They provide valuable additional information for the evaluation of the tower data. The observations take place on three fixed dates each day. These mainly involve determining variables that are not recorded by the automatic measuring system on the meteorological tower. These include the degree of cloud cover and cloud classification, type of precipitation and intensity, visibility and snow depth, as well as the recording of dew, frost and the condition of the ground. As the climate station is integrated into the climate measurement network of the German Weather Service (DWD), the data is sent to the weather office in Essen once a month.