Distribution of alpine permafrost in the northern hemisphere and its relationship to the environmental condition

Present paper describes the distribution of alpine permafrost in the northern hemisphere and its relation to environmental condition, defining the permafrost occures in the mountain areas south of the southern limit of discontinuous permafrost zone as alpine permafrost. The summaries are shown as follows. 1) The area of alpine permafrost in the northern hemisphere is estimated as 2.3 × 106km and the 80% occures in the Tibetan Plateau and the surrounding high mountain area. 2) The altitude of the lower limit of alpine permafrost decreases with latitude, the latitudinal gradient being 115m/degree in the Rockies, 100m/degree in Japan and 220m/degree in the Asian highlands. The gradient shows good correlation with that of the isothermal surface of mean annual air temperature. 3) The lower limit of alpine permafrost approximates the -2-4°C mean annual air isotherm. This value is lower than -1-2°C isotherm for the southern limit of discontinuous permafrost zone in high latitudes. 4) The condition for occurrences of discontinuous and continuous permafrost in high latitudes and alpine permafrost can be classified clearly by air temperature condition at each distribution limits. Alpine permafrost occures under the combined air temperature condition which is less than 11°C of the mean monthly air temperature in the warmest month and less than 30°C of the annual range of air temperature calculated as the difference between the temperatures in the warmest and the coldest months. 5) Alpine permafrost occures above tree line and the lower limit is 600900m lower than snow line.