Analysis of the Albedo in transition between snow and no snow in Neustift
Authors: Felix Thiemann, Moritz Trichtl
Peer-review: not peer-reviewed yet!
In our investigation it is hypothesized that the albedo is higher on skiing slopes compared to natural terrain due to a prolonged artifical snow-cover in spring. To get an idea about the differences in albedo of snow and grass, data from the automatic weather station in Neustift (Stubaital) is used. The available data spans over a time-period from 2010 to 2017. In those years especially the transition time from snow to no-snow conditions is interesting.
In the plot above you can see the daily average albedo and the measured snow-height for the whole eight years of available data. Already in this plot it’s easy to see that there is a big difference in the albedo-values between summer and winter. For all years the albedo in summer is quite constant with values a bit above 0.2. In winter the albedo is stronger fluctuating but is mostly in a range between 0.7 and 1.
The positive snow-height measurements in summer are caused by the lawn under the sensor. The sensor is just measuring the distance to the ground and can’t see if the ground is snow or grass. When the snow-height measurements suddenly drop in summer it’s a sign that the grass was cut. It’s interesting to see that with cutting the grass the albedo also drops.
To get an better idea how the albedo is behaving when the snow melts in spring, the time from January until the end of April for each year is investigated more precisely.
In all years it’s clearly visible that there is a time in spring, when the Albedo reaches a value of about 0.2 and stays fairly constant. The attainment of this value is accompanied with a local minima in the snow-height. This indicates the point when the snow is gone and the grass starts growing. So we can conclude that the Albedo of grass is about 0.2. Seperate spikes after the Albedo had already reached it’s value for grass are caused by snowfall and the resulting snowcover.
With snow-cover the Albedo-value is not as constant as it is for grass. It varies between values of above 0.9 for fresh snow and a value of 0.6 for old snow. Compared with the snow-height values we can see, that the Albedo goes up after snow-fall and decreases with snow-age. It’s also decreasing when the snow-cover starts to melt.
The transition between snow-albedo and grass-albedo happens in a matter of days in each year. The decrease in the Albedo before the snow is totally gone is caused by a film of meltwater on top of the snow or by a mix of snow- and grass-albedo caused by patches where the snow is already gone.
- The effect of the decreasing Albedo with age of the snow can nicely be observed in 2011. Between the middle of January and the middle of February the snow-height is fairly constant and the Albedo is slowly decreasing.
- The effect of snowfall after the snow-cover was already melted can be seen in several years, for example in 2014 with snowfall in the end of March and a change in the Albedo from about 0.2 to about 0.9.