Near-surface-temperature lapse rates on the Prince of Wales Icefield, Ellesmere Island, Canada: implications for regional downscaling of temperature

摘要

Screen temperatures were monitored from May 2001 to April 2003 in an array of 25 sites on the Prince of Wales Icefield, Ellesmere Island, Canada. The observational network covered an area of ca 15 650 km(2) and spanned an altitude ranging from 130 to 2010 m above sea level. The spatial array provides a record of near-surface-temperature lapse rates and mesoscale temperature variability on the icefield. The mean daily lapse rate in the 2-year record is -4.1 degrees C km(-1), with an average summer lapse rate of -4.3 degrees C km(-1). Surface-temperature lapse rates in the region are therefore systematically less than the free-air lapse rates that are typically adopted for extrapolations of sea-level temperature to higher altitudes. Steep lapse rates, resembling moist adiabatic rates in the free air (-6 to -7 degrees C km(-1)), are more common in summer at our site and are associated with enhanced cyclonic activity (low-pressure and high relative vorticity) and southerly flow aloft. In contrast, northerly, anticyclonic flow prevails when summer lapse rates are weak (above -2 degrees C km(-1)). The low surface-temperature lapse rates and their systematic synoptic variability have important implications for applications that require downscaling or extrapolation of surface- or boundary-layer temperatures, such as modelling of glacier mass balance. We illustrate this in an analysis of observed versus modelled snowmelt on the icefield. Copyright (C) 2006 Royal Meteorological Society.