Characterization of Wind Channeling Around Longyearbyen, Svalbard

Sammanfattning: Due to climate change and arctic amplification, the avalanche activity is expected to increase at higher latitudes (Hall et al., 1994). The arctic settlement of Longyearbyen, Svalbard, situated inside the valley Longyeardalen, is yearly threatened by avalanche activity (Eckerstorfer & Christiansen, 2011a). The surrounding slopes are known to produce avalanche, and during the last century they have proven to be able to cause substantial damages and even fatalities (Hallerstig, 2010). Previous studies investigated magnitude and forcing of the avalanches, including a meteorological perspective (Eckerstorfer & Christiansen, 2011b). This allowed for the usage of forecasts from the weather model AROME-Arctic in order to have an avalanche bulletin.The forecast for the area of Longyearbyen suffers from the location and the insufficient resolution of its source data. The data are obtained from an AWS located at the local airport, at the mouth of a relatively wide NW/SE oriented valley. Conversely, Longyeardalen is oriented NE/SW and is narrower. Because of the topography, channeling of winds is expected to produce difference weather conditions at the two sites, generating two distinct local weather conditions (Whiteman, 2000). If these different weather conditions are not taken into account, the weather model may provide forecasts that are not reliable for the area of Longyeardalen, hence resulting in biased avalanche bulletins.In this work I compare the data from the airport, from Longyeardalen and from the plateau above in order to assess if relevant differences exist in some important meteorological parameters (temperature, wind speed and direction, precipitation) between these sites. The weather station at the airport is an official AWS while the data from the other two sites were obtained using portable weather stations deployed during a field campaign between March 1st and April 11th 2018. During this time, snow data from the slopes surrounding Longyeardalen were also obtained. These data have been used to look for correlations among the wind conditions in the valley and the depth of the snow, as it is known that snow transport is a major factor determining snow accumulation in the area (Jaedicke and Sandvik, 2002; Hestnes, 2000).Temperature and precipitation have been found to be consistent among the two investigated valleys, while wind parameters differed significantly. Wind speed in Longyeardalen is on average overestimated by 3 m/s if only the data from the airport are used while the direction data are uncorrelated. This is due to the different circulations that occur at the two sites. Adventdalen is mostly influenced by southeasterly winds that are forcedly channeled or induced by the synoptic circulation, while in the smaller Longyeardalen southerly winds prevail due a thermal circulation induced by the presence of two glaciers on the top part of the valley. Snow depth is altered by the wind transport but it was not possible to find any correlation due to the low resolution of the snow depth data.