Strong Local Wind Distributions Estimated by the Wind-Shaped Trees in the Shonai Plain, Yamagata Prefecture

Abstract

In the Shonai Plain, northeastern Honshu, the strong easterlies and the NW winter monsoon prevail. The strong easterlies which blow along the Mogami River are particularly called “Kiyokawa-Dashi”.In order to make clear the detailed distributions of such strong local winds, the author investigated the wind-shaped trees. The wind-shaped trees observed were: Betula platyphylla, Ginkgo biloba, Populus nigra var Italica, Prunus sp., and Cryptomeria japonica.The results are summarized as follows:1. According to some characteristics of deformation of the tree, it is considered that the deciduous trees mentioned above have been deformed by the strong easterlies and cryptomeria japonica deformed by the NW monsoon (Table 1).2. The strong easterlies blow along the valleys coming into the plain. In general, these winds, it begins blowing at the inside of each valley, where is a little upper side near the valley mouth (Fig. 2).3. In southern part of the plain along the Aka River, the strong southerlies are recognized. It may be considered that the southerlies have no relation to the “Kiyokawa-Dashi” winds (Fig. 2).4. The NW monsoon do not blow into the valleys coming into the plain. It may be considered that the Dewa Mountains which is situated on the eastern margin of the plain blocks an intrusion of the NW monsoon. At the inside of the Mogami River valley, however, some wind-shaped trees of Cryptomeria japonica are observable. This fact shows that the NW monsoon exceptionally blow into a large valley as the wind direction agrees with a valley strike (Fig. 3).