Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
The climate of the St. Elias Mountains, which straddle the border betweensoutheast Alaska and the Yukon, is known mostly from indirect observations bysatellites (e.g., cloud cover), or from surface and/or upper-air soundings madefrom weather stations in the Yukon continental interior, or in coastal Alaska. Noyear-round meteorological observations were performed in this region until2000, when automated weather stations (AWS) were established there by theGeological Survey of Canada in support of a programme of glaciologicalstudies. This thesis presents a summary of surface climatological observationsobtained from these AWS between the years 2000 and 2013. These includeannual and seasonal mean variations of air temperature, wind, pressure,insolation, and snow accumulation.The AWS data reveal large altitudinal and longitudinal variations intemperature, winds and snow accumulation across the central St. EliasMountains, which are largely controlled by orographic effects and by therelative distance from the Gulf of Alaska. Despite the high elevation range inthe St. Elias Mountains, positive summer temperatures were recorded at all butthe highest AWS site (Mount Logan plateau, 5400 m asl), indicating that somesummer melt occurs regularly over most of the glaciated part of the range. Areconstructed profile of snow accumulation changes from the Alaskan coast tothe Yukon interior confirms and refines earlier (1960s) observations showing avery strong decreasing west-east precipitation gradient across the mountainrange. Calculated mean monthly atmospheric temperature lapse rates in thestudy area average -0.7 °C per 100 m altitude gain up to 5340 m asl. The lapserates are steeper in the lowermost ~2 km on the Alaskan side of the mountains,owing to the influence of relatively mild Pacific air along the coast. On thecontinental (Yukon) side, steep temperature inversions occur in winter monthsdue to surface radiative cooling and/or Arctic air intrusions. The surface windfield shows variable directions close to the Pacific coast, and nearly uniformkatabatic flow on the Kaskawulsh glacier system on the Yukon interior side ofthe mountains. At the Divide site on the icefields of the central St. EliasMountains, surface winds are closer to the regional geostrophic flow pattern,which is probably strongly influenced by the semi-permanent low-pressurecenter in the Gulf of Alaska.Finally, monthly mean summer air temperatures recorded by one AWS (Dividesite) over the period 2000-2013 were compared with those recorded at the samelocation during the mid-1960’s. Results indicate that summer temperatures haveincreased in all months, and most significantly in July, possibly by as much as +1.8 °C, which translates to a mean warming rate of +0.45 °C per decade sincethe mid-1960s. Such a warming rate is consistent with various observations ofaccelerating glacier thinning and wastage across the region in the last halfcentury.