Articles | Volume 11, issue 3
Research article
06 Jun 2017
Research article |  | 06 Jun 2017

Numerical modelling of convective heat transport by air flow in permafrost talus slopes

Jonas Wicky and Christian Hauck

Abstract. Talus slopes are a widespread geomorphic feature in the Alps. Due to their high porosity a gravity-driven internal air circulation can be established which is forced by the gradient between external (air) and internal (talus) temperature. The thermal regime is different from the surrounding environment, leading to the occurrence of permafrost below the typical permafrost zone. This phenomenon has mainly been analysed by field studies and only few explicit numerical modelling studies exist. Numerical simulations of permafrost sometimes use parameterisations for the effects of convection but mostly neglect the influence of convective heat transfer in air on the thermal regime. In contrast, in civil engineering many studies have been carried out to investigate the thermal behaviour of blocky layers and to improve their passive cooling effect. The present study further develops and applies these concepts to model heat transfer in air flows in a natural-scale talus slope. Modelling results show that convective heat transfer has the potential to develop a significant temperature difference between the lower and the upper parts of the talus slope. A seasonally alternating chimney-effect type of circulation develops. Modelling results also show that this convective heat transfer leads to the formation of a cold reservoir in the lower part of the talus slope, which can be crucial for maintaining the frozen ground conditions despite increasing air temperatures caused by climate change.

Short summary
Talus slopes are a widespread geomorphic feature, which may show permafrost conditions even at low elevation due to cold microclimates induced by a gravity-driven internal air circulation. We show for the first time a numerical simulation of this internal air circulation of a field-scale talus slope. Results indicate that convective heat transfer leads to a pronounced ground cooling in the lower part of the talus slope favoring the persistence of permafrost.