First results and interpretation of energy-flux measurements over Alpine permafrost

Abstract

The interaction of energy-exchange processes between the atmosphere and the Earth surface determines the surface temperature regime. It is of fundamental importance to the question whether frozen ground exists at a given site and how rapidly it may decay in response to a climatic perturbation. To further our understanding of these processes, measurements concerning near-surface energy-exchange processes were initiated in January 1997 on creeping permafrost at a high mountain site, Murtèl-Corvatsch, upper Engadin, Swiss Alps. Data on all important energy-balance fluxes were collected. In this paper, we present ground-temperature and energy-balance measurements from Murtèl-Corvatsch for a 2 year period, 1997–99. We will examine the relative importance of the energy-balance components and discuss special problems relating to the coarse surface layer. The results indicate a non-zero energy budget, with a positive deviation of up to 78 W m 4 in winter and a negative deviation of up to –130 W nT2 in summer. We propose that this overall imbalance of the energy-exchange fluxes, as well as the significant difference between mean annual surface and ground temperatures/can be explained by unmeasured advective energy fluxes that occur within the layer of large boulder blocks at the top of the permafrost.

A two-sided approach to estimate heat transfer processes within the active layer of the Murtèl–Corvatsch rock glacier

“…cannot be simulated directly in a one-dimensional model, but are supposed to have a significant impact on the thermal regime of the active layer in coarse debris-covered permafrost (Delaloye and Lambiel, 2005;Mittaz et al, 2000;Hanson and Hoelzle, 2004), a layer that serves as a heat source/sink is introduced in the model. It adds energy to the soil system in the summer season (June-mid September) and extracts energy in winter (mid September-mid January).…”

“…The thickness is chosen large enough to approximate the natural situation (i.e., 40 % porosity in the active layer) and thin enough not to cause numerical problems. This energy source/sink layer is parametrized based partly on knowledge taken from an observational study done by Mittaz et al (2000), who found significant deviations to a zero energy balance in summer and winter in measurements at the Murtèl rock glacier site. The values for the parametrization were then adjusted experimentally during the calibration phase of the model.…”

“…A micrometeorological station established in 1997 at 2700 m a.s.l. next to the borehole measures short-wave and long-wave incoming and outgoing radiation, air temperature, surface temperature, relative humidity, wind speed and direction (Mittaz et al, 2000;Hoelzle and Gruber, 2008). The site is characterized by a coarse blocky surface layer of approximately 3-3.5 m in thickness above a massive ice core down to 28 m and a frozen blocky layer underneath, reaching from 28 to 50 m probably adjacent to the bedrock (Arenson et al, 2002).…”

“…In surface energy balance measurements even under less complicated circumstances, e.g., arctic plains with sparse vegetation, there are usually deviation terms of up to 20 Wm −2 to a zero energy balance reported due to method-related errors and parametrizations (Westermann et al, 2009). A study by Mittaz et al (2000) at the Murtèl rock glacier found deviations from a zero energy balance of up to 78 Wm −2 in winter and −130 Wm −2 in summer, which were explained by advective heat transfer processes through voids within the debris.…”

Influence of surface and subsurface heterogeneity on observed borehole temperatures at a mountain permafrost site in the Upper Engadine, Swiss Alps

“…A micrometeorological station located at the Murtèl rock glacier measures air temperature, wind speed and direction, humidity, in-and outgoing longwave radiation, in-and outgoing shortwave radiation and the height of the snow cover since January 1997 (Mittaz et al, 2000). …”