Modelling of air circulation and energy fluxes in the coarse debris layer of high Alpine permafrost sites (MODAIRCAP)

Summary

Mountain permafrost is currently undergoing substantial changes due to climate change as a whole and especially due to the observed and projected air temperature increase. Among the typical mountain permafrost substrates, i.e. rock, fine sediments and coarse blocky surfaces, the latter play an important role because of their high insulating characteristics for the subsurface underneath due to the low thermal conductivity of the air voids between the blocks. In addition, air convection with upward transport of warmer air from the permafrost body and downward transport of cold air from the surface can take place within the coarse blocky layer, both, vertically (in flat terrain) as well as in form of a 2-dimensional slope circulation. These two effects lead to (i) low altitude permafrost occurrences in form of undercooled scree/talus slopes (e.g. Kneisel et al. 2000, Delaloye and Lambiel 2005), (ii) persisting permafrost occurrences at the lower limit of permafrost (in form of rock glaciers, ice-cored moraines and talus slopes) and (iii) much colder surface and subsurface temperatures for surfaces with coarse blocky surface layers (e.g., Schneider et al. 2012, Gubler et al. 2011, Gruber & Hoelzle 2008).

In this project we will use and adapt the modelling concepts from civil engineering (eg., Arenson et al. 2006, Goering & Kumar 1996) to model heat transfer in air flow in talus slopes and rock glaciers, and quantify the cooling effect in comparison with the other terms of the energy balance determined by existing energy balance approaches (e.g., Scherler et al. 2014).

Webpage: http://p3.snf.ch/project-169499

Duration: 2017-2020

Funded by: Swiss National Science Foundation (SNF)

Project lead/principal investigator (PI): Christian Hauck (Prof.)

Collaborators: Jonas Wicky (PhD student)

External collaboration with

  • PERMOS network

Contact at University of Fribourg: jonas.wicky[at]unifr.ch, christian.hauck[at]unifr.ch

Publications

Wicky, J. and Hauck, C. (2017). Numerical modelling of convective heat transport by air flow in permafrost talus slopes, The Cryosphere, 11, 1311-1325, https://doi.org/10.5194/tc-11-1311-2017.

Research aims/sciences questions

This project aims at:

1) Adapt existing engineering software that has already been tested for permafrost applications for real field cases in the Swiss Alps to enhance the process understanding

2) Quantify the amount of cooling due to convective air circulation within the coarse blocky layer to assess (i) the influence on the ground thermal regime, (ii) the importance on the energy balance and (iii) the development under climate warming.  

3) Validate the simulation results by ground surface temperature and borehole temperature data from the PERMOS network

Exemplary

 

Figure 1: Simulated temperature distribution (colours) and air current vectors in a talus slope for an open-to-atmosphere boundary for day 300 (winter circulation). The intensity of the circulation is marked by the grey/black colour of the vector arrows and is given in m day-1.

 

 

Figure 2:  Mean monthly air flow in a talus slope for an open-to-atmosphere boundary over 13 modelled years. The dashed line marks the domain of the talus slope. The seasonal differences in intensity and direction of the air circulation are clearly shown by the direction and colour of the arrows.

 

References

Arenson LU, Sego DC and Newman G (2006) The use of a convective heat flow model in road designs for Northern regions. 2006 IEEE EIC Climate Change Technology. 1–8 (doi:10.1109/EICCCC.2006.277276)

Delaloye R and Lambiel C (2005) Evidence of winter ascending air circulation throughout talus slopes and rock glaciers situated in the lower belt of alpine discontinuous permafrost (Swiss Alps). Norsk Geografisk Tidsskrift - Norwegian Journal of Geography 59(2), 194–203 (doi:10.1080/00291950510020673)

Goering DJ and Kumar P (1996) Winter-time convection in open-graded embankments. Cold Regions Science and Technology 24(1), 57–74 (doi:10.1016/0165-232X(95)00011-Y)

Gruber S and Hoelzle M (2008) The cooling effect of coarse blocks revisited: a modeling study of a purely conductive mechanism. 9th International Conference on Permafrost.

Gubler S, Fiddes J, Keller M and Gruber S (2011) Scale-dependent measurement and analysis of ground surface temperature variability in alpine terrain. The Cryosphere 5(2), 431–443 (doi:10.5194/tc-5-431-2011)

Kneisel C, Hauck C and Vonder Mühll D (2000) Permafrost below the Timberline Confirmed and Characterized by Geoelectrical Resistivity Measurements, Bever Valley, Eastern Swiss Alps. Permafrost Periglac. Process. 11(4), 295–304 (doi:10.1002/1099-1530(200012)11:4<295::AID-PPP353>3.0.CO;2-L)

Scherler M, Schneider S, Hoelzle M and Hauck C (2014) A two-sided approach to estimate heat transfer processes within the active layer of the Murtèl–Corvatsch rock glacier. Earth Surface Dynamics 2(1), 141–154 (doi:10.5194/esurf-2-141-2014)

Schneider S, Hoelzle M and Hauck C (2012) Influence of surface and subsurface heterogeneity on observed borehole temperatures at a mountain permafrost site in the Upper Engadine, Swiss Alps. The Cryosphere 6(2), 517–531 (doi:10.5194/tc-6-517-2012)

Unit of Geography - Chemin du Musée 4 - 1700 Fribourg - Tel +41 26 / 300 90 10 - Fax +41 26 / 300 9746
nicole.equey [at] unifr.ch - Swiss University