One aspect of CHARTER is gaining a better understanding of snow icing events, such as rain-on-snow events and their impacts.
Snow cover layer structures and snow grains in the layers are constantly changing due to temperature differences between the snow surface and ground, and due to new snowfall. Crust layers are typically formed by melting of the snow surface during warm winter events and refreezing when temperature again drops below zero degrees. Ice layers are typically formed either by strong melting events or by rain on snow events followed by refreezing. Icing affects animal movement and digging through the snow, and plant overwintering, and is relevant for local livelihoods like reindeer herding.
Snow profile observations (snow pits, layer structure of the snow cover) are needed for the development of snow monitoring using satellite data in CHARTER Work Package 1. Observations are also used to evaluate climate and snow models in Work Package 5; models are used for future scenarios of snow conditions and impacts. Open data about icing events could also be used by practitioners of land-based livelihoods, like reindeer herders.
Snow profiles are not routinely observed and open data about icing events is poorly available. Because snow cover properties have large temporal and spatial variability, snow profiles are needed from various locations and different times during the snow season. In addition, CHARTER field work was generally cancelled due to the pandemic in 2020-2021. For these reasons CHARTER has created a “Snow Protocol”, which follows the international snow observational standards but is simplified. Snow measurements were collected by reindeer herders and other collaborators already in the Spring of 2021. In the future, the goal is to simplify the protocol further, and utilize citizen science / crowdsourcing possibilities in snow science.
The protocol includes background information such as measurement date and time, location, description of surroundings, reindeer pasture type, and visible trampling or digging in snow. Measurements includes snow depth in 1-5 points and definition of ice and crust layers at 1-2 of the points. A hardness hand test is used for layer detection (pushing snow first with fist, then with 4 fingers, 1 finger, pencil and knife blade, until snow is too hard to be pierced). For each ice and crust layer, distance of the layer top and bottom from the ground is measured. In addition, it is optional to measure properties of all layers in snowpack (hardness, grain type and distances from the ground) and the snow water equivalent by using cylindrical tube to extract and weight sample of snow.