Summer Air Temperature Lapse Rates in a Glaciated Alpine Catchment, Northwestern British Columbia, Canada

Air temperature lapse rates are often used in numerical models of alpine glacier mass balance to extrapolate data from a single meteorological station to locations distant from that station. As field measurements of alpine air temperature lapse rates are limited, however, they are often assumed to be constant at -6°C km-1 (moist adiabatic lapse rate; MALR). Three meteorological stations were installed at 585 m, 1180 m and 1887 m asl in the Andrei Glacier catchment, northwestern British Columbia (56° 55' N, 130° 55' W), during the latter half of the summer 2006 melt season. Each station measured hourly average air temperature (°C) at 2 m above the surface. These data were used to calculate the temporal distribution of hourly and daily temperature lapse rates in the region, and determine their proximity to the MALR. Temporal patterns in daily air temperature lapse rates were then compared with gridded daily synoptic maps from the Meteorological Service of Canada (surface, 500 mb, 700 mb, and 850 mb), to determine if specific synoptic configurations correlate with specific lapse rate characteristics. Results suggest that regional synoptic data may be highly useful for deriving local air temperature lapse rates in areas with sparse local field measurements, thus producing more accurate model output than that produced using the constant MALR. These data may also be used to develop methods for downscaling GCM output to derive regional climate change scenarios. However, depending on the extent of the glacier boundary layer, local microclimatic perturbations may decouple local air temperature lapse rates from the regional synoptic configuration.