Ground temperature response to winter warm events in Svalbard

Abstract

The Svalbard archipelago is subject to winter warm events, where daily mean air temperature exceeds 0°C. These warm events occur when low pressure systems direct air northwards across the Nordic Seas towards the west coast of Spitsbergen (Svalbard’s largest island). If the advected air is moist, rain-on-snow (ROS) events result. In this thesis, ground temperatures and meteorological data are coupled to assess the impact of ROS and warm events on periglacial landform ground temperatures. The four landforms chosen for analysis – a loess terrace, solifluction sheet, blockfield, and strandflat – are representative of the varied terrain and ground materials on Svalbard. Analysis of winter meteorological data from the Longyearbyen area between 1958 and 2015 shows that mean winter (November through April) air temperatures are increasing. While there is no clear trend in winter rainfall (ROS amount), the five rainiest winters of the 1958-2015 record have occurred since 1994. Winter rainfall and the number of days of rain during winter bear some correlation to winter thawing degree days (TDD). Three winters during the investigated ground temperature series had major ROS events (>10 mm). A comparison of 2014-2015 winter air temperatures at the landform locations indicates that winter air temperatures rarely exceed 0°C at higher elevations, which precludes precipitation falling as rain in the winter at these sites. Warm events result in increased ground temperatures. The thermal disturbance is observed down to 2 m depth in the loess terrace and solifluction sheet, 1 m depth in the blockfield, and 5 m depth in the strandflat. The depth of warm event propagation is dependent on the thermal properties of the substrate, in addition to snow cover. This study shows that the largest ROS events impact shallow ground temperatures more than dry warm events, as liquid water can collect at the ground surface and freeze, releasing latent heat. Neither ROS nor warm events individually impact seasonal or annual ground temperatures; winter ground temperatures are primarily controlled by air temperature and the duration and depth of snow cover. However, the combined effect of multiple warm events can impact mean winter ground temperatures, and may contribute to the observed permafrost warming trend in these landforms.