No abstract

Distributed glacier surface melt models are often forced using air temperature fields that are either downscaled from climate models or reanalysis, or extrapolated from station measurements. Typically, the downscaling and/or extrapolation are performed using a constant temperature lapse rate, which is often taken to be the free-air moist adiabatic lapse rate (MALR: 68-78C km 21 ). To explore the validity of this approach, the authors examined altitudinal gradients in daily mean air temperature along six transects across four glaciers in the Canadian high Arctic. The dataset includes over 58 000 daily averaged temperature measurements from 69 sensors covering the period 1988-2007. Temperature lapse rates near glacier surfaces vary on both daily and seasonal time scales, are consistently lower than the MALR (ablation season mean: 4.98C km 21 ), and exhibit strong regional covariance. A significant fraction of the daily variability in lapse rates is associated with changes in free-atmospheric temperatures (higher temperatures 5 lower lapse rates). The temperature fields generated by downscaling point location summit elevation temperatures to the glacier surface using temporally variable lapse rates are a substantial improvement over those generated using the static MALR. These findings suggest that lower near-surface temperature lapse rates can be expected under a warming climate and that the air temperature near the glacier surface is less sensitive to changes in the temperature of the free atmosphere than is generally assumed.

Canada's Queen Elizabeth Islands contain ∼14% of Earth's glacier and ice cap area. Snow accumulation on these glaciers is low and varies little from year to year. Changes in their surface mass balance are driven largely by changes in summer air temperatures, surface melting and runoff. Relative to 2000–2004, strong summer warming since 2005 (1.1 to 1.6°C at 700 hPa) has increased summer mean ice surface temperatures and melt season length on the major ice caps in this region by 0.8 to 2.2°C and 4.7 to 11.9 d respectively. 30–48% of the total mass lost from 4 monitored glaciers since 1963 has occurred since 2005. The mean rate of mass loss from these 4 glaciers between 2005 and 2009 (−493 kg m−2 a−1) was nearly 5 times greater than the 1963–2004 average. In 2007 and 2008, it was 7 times greater (−698 kg m−2 a−1). These changes are associated with a summer atmospheric circulation configuration that favors strong heat advection into the Queen Elizabeth Islands from the northwest Atlantic, where sea surface temperatures have been anomalously high.

Polar Bear Pass (PBP) (75°40'N, 98°30'W) is considered a critical wetiand area for migratory birds, caribou and muskox. Little is known of its climatology and hydroiogy. Here we evaiuate both the short-term and long-term summer climatic record for this wetland. A 10 m high automatic weather station (AWS) was established here 27 years ago, and in 2007 this centraiiy located AWS was suppiemented by three more weather stations placed across the wetiand pass.The iong-term climate record here indicates little significant departure when compared to the long-term climate means at Resolute Bay, a government weather station lying 90 km to the southwest (74°43'N, 94°59'W). Exceptions exist for July minimum air temperature (PBP > Resoiute) and number of days in June, July and August < 0°C (PBP < Resolute).Climate variabiiity from year to year remains the norm. Radiation receipt, air temperature, humidity and wind speed vary little across the wetiand pass, whiie terrain-modified fluxes do.The precipitation regime is similar to Resolute Bay but local site conditions modify the amounts. In 2007, July evaporation levels were twice as high as that of 2008; more akin to Low Arctic sites. As yet, no clear trend in iong-term climatic signals can be established.