Snow depth
The snow depth is the indication of the absolute height of the snow cover at a certain location.
Information: snow cover thickness, new snow depth, new snow total
The snow depth (and precipitation intensity ) is generally in contrast to precipitation (mm per hour) usually in centimeters given
A precise distinction is therefore made between the thickness of the snow cover as the total height and the amount of new snow as the increase in the last measurement period - whereby in today's meteorology and avalanche science, 24 hours are taken as a basis and measurements are taken at 7:30 a.m. The total of new snow is then determined over longer periods of time (e.g. 3-day total of new snow as the increase in snow height over the last 72 hours).
| Snow type | Weight per m 3 | Snow depth of 100 kg per m 2 |
|---|---|---|
| Dry, loose fresh snow | 30-50 kg | approx. 2-3 m |
| Bound fresh snow | 50-100 kg | approx. 1–2 m |
| Heavily bound fresh snow | 100-200 kg | approx. 0.5–1 m |
| Dry old snow | 200-400 kg | approx. 25-50 cm |
| Moist old snow | 300-500 kg | approx. 20-35 cm |
| Perennial firn | 500-800 kg | approx. 12-20 cm |
| ice | 800-900 kg | approx. 11–12 cm thick |
| Source: Lower Austrian Civil Protection Association | ||
One also speaks of the amount of snow , which then denotes a cumulative increase in height of a certain period of snowfall, more precisely the corresponding volume , either based on a standard area (one square meter), or as the total cubature or mass , for example in the case of snow peaks or an avalanche . Structurally, this is related to the snow load as weight (or snow pressure as force), which depends on whether the snow is powdery or wet: Due to the large specific volume of snow (the low specific weight ), even relatively unspectacular amounts of water can cause considerable snow depths : For snow, the density is between 30 kg \ m³ (dry, loose fresh snow) and 200 kg \ m³ (heavily bound fresh snow). Fresh snow has about 1 ⁄ 10 (up to 1 ⁄ 15 - 1 ⁄ 30 ) the density of water, but settles quite quickly (within hours, especially due to the weight of the layers that have snowed over it) to roughly half, so that 1 meter of fresh snow and 1 ⁄ 2 meters of freshly set snow corresponds to about 100 mm of rain. 100 millimeters (or liters per square meter) in a heavy but not extraordinary rain.
Since the snow can stay or, depending on the temperature, also melt, snow cover does not have to rise despite fresh snow. The mere indication of the snow depth does not necessarily mean that snow has recently fallen. The volume of the snow shrinks due to its own weight and the other weather values (humidity, temperature gradients): Even regardless of melting and sublimation , the total of new snow and the entire thickness of the snow cover are not the total of the new snow depths. Depending on the cold, it is typically one to two thirds of the total amount of new snow in the immediately preceding snowfall period. The most precise description of the amount of snow as a term is a difference in the total snow depth at two points in time, including interim settlement and melt.
Ultimately, the total amount of fresh snow in a season in the glacier's depletion area is reduced to layers of compressed ice that are often only a few centimeters or even millimeters thick .
Conversely, wind displacement can also build up enormous snow cover thicknesses that go far beyond the depth of new snow. Even where avalanches have started (mass transport), there are abnormal snow depths, so that avalanche remnants remain far beyond the surrounding areas.
Measurements
Snow levels and snow probes are used to precisely measure the amount of snow or the depth of snow . They can provide precise information based on the difference between the ground level and the snow depth. Thanks to newer technology, so-called snow depth sensors , this is also possible using ultrasound . Due to the temperature dependence of the speed of sound, this type of measurement can guarantee a maximum measurement accuracy of ± 2 cm.
forecast
Predicting or forecasting snow depths is particularly difficult due to several factors. She is dependent on
In mountains, where it is necessary to query the snow depth for winter sports, accurate forecasts are complicated because of the meteorological and altitude conditions.
Avalanche knowledge
The thickness of the snow cover, as well as the amount of fresh snow, are decisive parameters in avalanche science. In principle, if the ceiling becomes too thick, avalanches are triggered solely by their own weight, but the precise layering and snow quality, as they develop from the boundary conditions during and between snowfalls, are much more decisive. While layers of snow that are many meters thick sometimes lie in one place, in other years layers that are not very thick are triggered. In addition, in the vast majority of avalanches - apart from the base avalanche and the lower course section of a dust avalanche - it is not the cover over the entire depth of snow, but only a certain layer. Therefore, in addition to the pure snow depth measurement, a snow profile analysis is necessary, through sampling and on-site testing, increasingly through exact and continuous logging of the course of the snowpack. These data are now also networked and compared online (snow cover modeling) so that areas that have not been examined can also be interpolated if, for example, sampling in the terrain is already too dangerous due to changes in weather, or if too many places would have to be examined at the same time in the event of heavy snow events .
Tourism and winter sports
Mountain regions that are only covered with snow in winter often live from tourism . The snow depths are crucial for winter sports enthusiasts and other tourists. Mountain tourism and winter sports are heavily dependent on the depth of snow, as these can influence income for an entire season. Winter sports enthusiasts call up the current snow depths in the holiday areas around the world on a daily basis via the Internet and thus decide where to spend their ski holiday.
Global warming
Since the current global warming is accompanied by an increase in temperature also in the higher mountain and thus snow regions, the snow depth can be seen as an example and statistical value for global warming (another example is the increase in the snow line). Due to the higher temperature, the snow melts faster and the general, average snow depth also decreases.
However, this statement is extremely global; in fact, a significant increase in snow depths can be determined in entire regions due to the changed large-regional air humidity transport, such as the snowfall in Central Europe in January 2019 . Since snowfall typically only occurs in the temperature range between about −7 ° C to +2 ° C, areas of winter drought due to heavy frost can also slowly turn into winter precipitation zones, or the precipitation maxima shift from early and late winter to midwinter, so that the snow cover in the meantime less melts, and more precipitation falls as snow than as rain.
In the winter tourism industry, one speaks of “winners” and “losers” of climate change.
Web links
- The problem of determining snow depth
- Federal Office for Meteorology and Climatology : Records and Extremes
Individual evidence
- ↑ Heavy snow: How heavy is snow actually? Lower Austrian Civil Defense Association, noezsv.at, accessed January 11, 2019.