Equivalent Elevation: A New Method to Incorporate Variable Surface Lapse Rates into Mountain Permafrost Modelling

Abstract

Permafrost is present at multiple elevations with no defined lower limit in the southern Yukon Territory, Canada. Empirical statistical modelling of permafrost probability in the region required the development of equivalent elevation, a new variable that reflects measured differences between surface air temperature lapse rates below and above treeline. In areas where surface lapse rates are negative (normal) but gentle up to the altitudinal treeline, equivalent elevation results in a compressed elevational range. Where surface lapse rates are positive (inverted) in the forest due to the strength of winter inversions, equivalent elevations calculated for valley floors are higher than those at treeline. There is a strong relationship between the magnitude and sign of surface lapse rates below treeline and the annual amplitude of monthly air temperatures at nearby climate stations, which permits prediction of equivalent elevation for the entire region. Permafrost probability modelling using equivalent elevation produced statistically significant results in several study areas whereas actual elevation values did not. The concept is of particular use where forested areas are underlain by permafrost and may be transferable to areas with similar terrain and climate such as those in the Canadian Northwest Territories, Alaska and Mongolia. Copyright © 2011 John Wiley & Sons, Ltd.

Quantifying Surface Temperature Inversions and Their Impact on the Ground Thermal Regime at a High Arctic Site

“…Although the levels of absolute relief are less in the High Arctic compared to areas of complex topography in western Canada, the inversion strength when compared directly is substantially greater. During the winter months the surface lapse rate around Dawson City in the continental Yukon has been shown to be greater than +5 °C km -1 for an annual surface lapse rate of about +1 °C km -1 (Lewkowicz and Bonnaventure, 2011), which is similar to that found by Taylor et al (1998) at Norman Wells, Northwest Territories (NWT), and O'Neill et al (2015) across an alpine treeline on Peel Plateau, NWT. At the Alert site this value appears to be about an order of magnitude greater, averaging +50 °C km -1 (+5 °C/100 m) between BH4 and BH5 and +24 °C km -1 (+2.4 °C/100 m) between BH4 and BH3 (Table 3), which agrees with earlier observations in the High Arctic by Bradley et al (1992).…”

“…Recent examples in the literature include the work done by Pagès and Miró (2009) in the Pyrenees, as well as work in western Canada by Taylor et al (1998), Lewkowicz and Bonnaventure (2011), Chaput and Gajewski (2014), and O'Neill et al (2015. The conclusions thus far indicate that inversions are more persistent in winter under stable air conditions.…”

“…Another major conclusion is that although inversions appear to occur commonly in areas where relief is present, their intensity and the impact on the ground thermal regime can be substantially different in areas of differing climate. Lewkowicz and Bonnaventure (2011) showed that both latitude and continentality affect the inversion itself, ultimately aiding to control permafrost distribution. These conclusions have been significant, as often climate models and projections utilize standard surface lapse rates (e.g.…”

“…Atmospheric temperature inversions are characterized by an increase in air temperature with altitude and represent an atypical situation in the lower atmosphere (Oke, 1987). Inversions are also present at the surface, as the elevation increases and boundary level conditions change or have less effect in steeper terrains (Lewkowicz and Bonnaventure, 2011). Temperature inversions are frequent in the High Arctic and in highelevation mountain locations due to a variety of causes and are often influenced by the characteristics of the terrain and vegetation distribution (Bonnaventure et al, 2012).…”

Variability and change in the Canadian cryosphere

“…Prior to the IPY, the thermal characteristics of permafrost in the Yukon mountains were virtually unknown except for the main valley floors. Analysis of a network of 100 air temperature monitoring sites throughout the southern Yukon is providing insights into the role that atmospheric temperature inversions may play in determining the distribution of mountain permafrost (Lewkowicz and Bonnaventure 2011), and indicates that permafrost extent may be much less than predictions made based on air temperature measured at standard weather stations located in the main valley floors (Smith et al 2010b).…”