n-factor
Link: http://w3id.org/permafrost/v/ipaglossary/t0212
Within: IPA Permafrost Glossary
Definition: The ratio of the surface freezing or thawing index to the air freezing or thawing index.
| Term |
n-factor
en
facteur n fr |
|---|---|
| Comment |
At any site, (standard) air temperatures are seldom the same as surface (air/substrate boundary) temperatures. Because air temperatures (measured at weather stations) are usually available and surface temperatures are not, the n- factor (an empirically determined coefficient) is used to relate air temperatures to surface temperatures in order to establish the thermal boundary condition at the surface, particularly for engineering purposes. The difference between air and surface temperatures at any specific time and location is greatly influenced by climatic, surface and subsurface conditions (e.g., latitude, cloud cover, time of day or year, relative humidity, wind speed, type of surface--wet, dry, moss, snow, natural vegetated terrain, mineral soil, pavements-- and thermal properties of the ground). The average surface temperature and n- factor may vary significantly from year to year, even for a given surface and location, as well as for different sites, surfaces and soil systems. Values of the freezing and thawing n-factors have been determined for a large number of sites and surfaces and are widely used for predicting surface temperatures and the thermal regime of the ground. The data vary widely, however, and indicate that a rigorous value of n for a given site cannot simply be chosen from these data. Direct determination of the n-factor for a specific location is much better and requires concurrent observations of air and surface temperatures throughout at least one and preferably several complete freezing and thawing seasons.
en
|
| dcterms:source |
https://doi.org/10.4224/20386561
xsd:anyURI
|