Near-Surface Temperature Lapse Rates over Arctic Glaciers and Their Implications for Temperature Downscaling

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.

Recent air and ground temperature increases at Tarfala Research Station, Sweden

“…Snow and ice melt models often use temperature lapse rates, that is, linear temperature decreases with increasing elevation to extrapolate point temperature measurements to the domain of interest (e.g., Hock & Holmgren 2005;Gardner et al 2009). Here, we use the mean daily temperature measurements at Tarfala and at the PACE borehole site, located 410 m higher than Tarfala (Fig.…”

High-resolution interactive modelling of the mountain glacier–atmosphere interface: an application over the Karakoram

“…To overcome these issues, forcing data can be obtained by extrapolation from point measurements by automated weather stations, where available, or interpolation from climate reanalyses and atmospheric model output, using surface-and free-air lapse rates. Surface lapse rates exhibit significant spatial and temporal variability, however, leading to uncertainty in temperature downscaling from altitude changes (Marshall et al, 2007;Gardner et al, 2009;Petersen and Pellicciotti, 2011). In addition, the assumption of linear lapse rates over glacier surfaces may be inappropriate (Petersen and Pellicciotti, 2011) and may under-predict nearsurface temperature over debris-covered regions (Reid et al, 2012).…”

Online dynamical downscaling of temperature and precipitation within the <i>i</i>LOVECLIM model (version 1.1)

“…Since the along-slope lapse rate is generally smaller than the free-atmosphere lapse rate (e.g. Marshall et al, 2007;Gardner et al, 2009;Minder et al, 2010), its use leads to an overestimation of the temperature changes with elevation. In order to artificially reduce the value of the vertical lapse rate in the model, we apply a global tunable correcting factor (f s in Eq.…”