The Energy Balance of Permafrost Soils and Ecosystems

Abstract

Thawing of permafrost ice requires energy transfer from the atmosphere and solar radiation to the permafrost soil. Snow and vegetation dominate the energy exchange at the surface of permafrost soils. The radiation balance (shortwave and longwave radiation) is the primary source of energy. Only a small part of this energy is available for warming the ground. Which part, depends strongly on the surface cover. A snow cover reflects solar radiation. A vegetation cover shades the soil surface and returns energy to the atmosphere as latent heat (vaporisation of water) and sensible heat (warming of the air). In this chapter, the basic principles of the exchange of energy at the surface are discussed: the radiation balance, the exchange of energy by turbulence- driven latent and sensible heat fluxes. The partitioning of these fluxes throughout the season is shown based on examples. This chapter shows why snow cover has a warming effect on permafrost and vegetation has a cooling effect. Next, the heat transfer into the soil is discussed. Here, the role of latent heat of freezing and thawing and the thermal properties of the soil are important, which vary strongly with soil material and soil water content. Together with the snow and vegetation characteristics, these thermal properties determine soil temperature and the active layer thickness.