Weissfluhjoch test site ¶
Just below the former SLF main building on the Weissfluhjoch is the SLF's oldest test site with its many measuring instruments which have been providing serial measurements continuously.
In the autumn of 1936, the Expert Commission for Snow and Avalanche Research in Switzerland set up the first snow laboratory on the Weissfluhjoch. The accompanying test site is set on a flat area of the Dorftäli, approximately 150 metres below the Weissfluhjoch, at an altitude of 2536 metres. In view of its easy accessibility and the numerous avalanche-prone slopes in the vicinity, over the years countless major experiments and studies in the fields of snow mechanics, snow metamorphism, snow characterisation and measuring methodology have been conducted here, and this continues today. Prototypes of various instruments and remote sensing products are also tested and used on the site.
Daily weather and snow measurements have been carried out on the Weissfluhjoch test site ever since the SLF was established. The site is the only one at this altitude worldwide that has a continuous record of serial measurements dating back 80 years.
These long-term measurements tell us, for example, that:
- the average date for the first snow cover is 18 October (earliest: 6 September (in 1984); latest: 25 November (in 1983));
- the average onset date for snowmelt is 8 July (earliest: 3 June (in 1947); latest: 16 August (in 1980));
- annual precipitation comes to about 1200 mm, of which 75% falls as snow;
- the greatest snow depth ever measured here was 366 cm (on 9 March 1945);
- the snow depth on 1 January ranges from 38 cm (1949) to 222 cm (1975);
- at least one avalanche (whether naturally triggered or artificially released by explosive blasts) can be observed in the Weissfluhjoch's local area (100 km2) on 34% of all days, and no avalanches are observed on 46% of days; poor visibility prevents any observations on 20% of days (statistics covering the 15 winters from 1988 until 2002).
The facilities on the test site are being extended and expanded all the time. While we operate and use the sensors and experimental setups described below largely for our own purposes, some of the systems come from partner institutions and industry, who use the Weissfluhjoch site for calibration and testing purposes and for their experimental setups. Their activities facilitate a comparison with established measuring methods and sensors.
Various measuring systems ¶
Originally researchers performed almost all their test site measurements manually, but nowadays as many parameters as possible are measured automatically. A large number of different systems are used:
Operational systems
Both manual and automatic measurements are invaluable operational aids for avalanche forecasters. They also provide the basis for snow hydrology investigations; and supply observations covering many years which are very useful for mountain climatologists.
Manual measurements
Among other parameters, we have been measuring depth of fresh snow, snow depth in general and snow density on the test site every day for 80 years now. The Weissfluhjoch test site is part of the traditional nationwide network of measuring stations operated by the Swiss avalanche warning service. Detailed snow profiling also takes place here twice a month. This involves us collecting ram penetration resistance data, measuring snow temperatures and the snow water equivalent, and classifying the snow layers.
Automated measuring station (forming part of the IMIS network)
The automated measuring station at the centre of the test site forms part of the Intercantonal Measurement and Information System (IMIS) for avalanche forecasting. Like the other 'snow stations' scattered throughout the Swiss Alps, it records not only air temperature, humidity, wind, reflected radiation and precipitation but also specific snowpack parameters, such as total snow depth, the snow surface temperature, and the snow temperature at various depths. These parameters are also used to test and improve the SNOWPACK model developed by the SLF. In view of its status as the SLF's 'home station', the institute's employees also use it as a testing station for updating and further developing the automatic measuring network.
MeteoSwiss precipitation measurements
MeteoSwiss has been measuring the precipitation on the test site at 10-minute intervals since 2015, using a precipitation sensor installed at a fixed height (opening 3 m above the ground). This replaces the MeteoSwiss precipitation sensor according to Joss-Tognini which had been used since 1974 and which, unlike the equipment at most other SwissMetNet stations, was manually adjusted every 14 days based on the snow depth, so that it always measured the precipitation 1.5 to 2 m above the snow surface.
Experimental systems
Alongside the working systems described above, on the site we operate various measuring systems and sensors for testing purposes and as prototypes. Examples:
Double Fence Intercomparison Reference (DFIR) precipitation gauge
The DFIR precipitation gauge is part of a World Meteorological Organisation (WMO) project called SPICE (Solid Precipitation Intercomparison Experiment) covering solid-precipitation measurements. Operated by MeteoSwiss, it records round the clock with high temporal resolution whenever precipitation falls and how much. A double fence around the reference precipitation gauge (hence the name 'Double Fence Intercomparison Reference (DFIR) gauge') interrupts the wind field and ensures that the falling precipitation gets less blown by the wind. This means that snow in particular can be collected more efficiently. As part of the SPICE project, the WMO has installed in total 15 of these precipitation units around the world in, for example, the USA, Australia, Chile, Canada, Poland and Finland. The goal of this international project is to improve the methods for measuring solid precipitation. The Weissfluhjoch test site is an especially suitable location for making these measurements because of the 80 years of comparative data it can offer. Within the project, it serves as a benchmark measuring site for alpine conditions. As well as its many years of experience in data collection, the SLF also offers the project the benefit of the site's infrastructure. In return, we can use the measured data in our own research work.
Present weather sensors
A productive laser disdrometer classifies the type of precipitation (snow, hail, graupel, rain, etc.) and also supplies precipitation intensity data.
Snow pillow
A 3 by 3-metre pillow, filled with a mixture of water and glycol, uses a piezoelectric sensor to measure the hydrostatic pressure being exerted by the snowpack. The pressure value indicates the snow water equivalent. The large size of the pillow minimises the influence of bridging in the snowpack.
Snow scale (SWR)
The snow scale is a platform-weighing machine for snow. Like the snow pillow, it measures the snow water equivalent. This involves several electronic sensors directly recording the weight force exerted by the snowpack. The sensors are installed underneath the middle aluminium plate of seven covering an area of 2.4 by 2.8 metres.
