Spatial distribution of surface hoar crystals in sparse forests
Other literature type
(issn: 1684-9981, eissn: 1684-9981)
Surface hoar size and location relate directly to avalanche initiation
trigger points, and they do so in small-scale spatial distributions.
Physically, surface hoar will grow where the snow surface is cold relative to
the air and water vapour is plentiful. Vapour aside, snow cools at night
primarily by longwave radiation emittance. Emittance can be restricted by
clouds, trees, and terrain features. With 96 independent spatial point
samples of surface hoar size, we show the extreme small-scale size variation
that trees can create, ranging from 0 to 14 mm in an area of 40<sup>2</sup> m<sup>2</sup>.
We relate this size variation to the effects of trees by using satellite
photography to estimate the amount that trees impinge on sky view for each
point. Though physically related to longwave escape, radiation balance can be
as difficult to estimate as surface hoar size itself. Thus, we estimate point
surface hoar size by expected maximum areal crystal size and dry terrain
greyscale value only. We confirm this relation by using it at a different
area and in a different formation cycle. There, its overall average error was
1.5 mm for an area with surface hoar sizes ranging from 0 to 7 mm.