Forest line altitude and periglacial environment on the Jounen-nokkoshi Pass, the northern Japanese Alps, estimated from air temperature observation data

Abstract

On the Jounen-nokkoshi Pass, in the southern part of the northern Japanese Alps, the formation of forest is checked by the influence of the westerly prevailing wind, and it leads to wind-blown ground. The annual mean air temperature was found to be 3.9°C as a result of air temperature observations from November 1997 to October 1998 at the site of the wind-blown ground. Based on these data and the air temperature data of Hotaka, the nearest meteorological observation site from AMeDAS, the normal annual mean air temperature is estimated to be 2.7°C. Based on the monthly normal mean air temperature, the warmth index (WI) on the Jounen-nokkoshi Pass is 27.2°C - months, which suggests that the Jounen-nokkoshi Pass is positioned in a subalpine zone in terms of thermal conditions. In this case, the altitude of the forest line defined by WI 15°C - months is estimated to be 2833 m a. s. l. Actually, however, the westerly prevailing wind produces wind-blown ground and a periglacial environment on the Jounen-nokkoshi Pass. Consequently, the landscape is similar to that of the periglacial area in the alpine zone of the northern Japanese Alps or the Daisetsuzan Mountains. There were 72 freeze-thaw days during the observation period on the Jounen-nokkoshi Pass, which were mainly recorded during the period from October to April. The number of freeze-thaw days exceeds that of the periglacial area in the alpine zone of the northern Japanese Alps or the Daisetsuzan Mountains. Moreover, the time of occurrence of freeze-thaw days on the Jounen-nokkoshi Pass is clearly different from that in the periglacial area in the alpine zone, where the occurrence is bisected between March to June and September to November.