立春過ぎの余寒が雪を呼んでいるのでしょうか、全国各地に降った想像を超える大雪に驚嘆しているこの頃です。さて、先日の『広報あおもり』に八甲田の樹氷ツアーの案内が掲載されていました。樹氷は冬の雪山ではどこでも見られるものと思っていましたが、実は一定の条件を満たした場所にしか樹氷はできないようです。では、その条件とは何でしょう。まずひとつめは、樹氷のできる木は“青森市の木”に制定されているアオモリトドマツだということです。アオモリトドマツは葉の密度が高く、樹皮がギザギザしているため、ほかの樹木より氷や雪がつきやすいのです。そして冬の日本海の水分を含んだ湿った季節風が吹きつけること。この二つの条件がそろうと樹氷が生まれます。
ではその条件がそろうと、どのようにしてできるのでしょう。大気中で気温が0度以上の時にできた水滴は、気温が徐々に低下して、氷点下に下がっても水滴のまま存在することができます。これを過冷却水滴というそうですが、これは非常に不安定で、ほかの物体に触れると瞬時に凝結して固体になります。樹氷は日本海から運ばれてきた過冷却水滴がアオモリトドマツの樹皮に付着し、氷りついたものです。小さな過冷却水滴が氷結して次々に風上に成長してゆくため、ささくれ立った表面となり、その形からエビの尻尾と言われています。また3メートルにもなる純白のオブジェはスノーモンスター、アイスモンスターなどと呼ばれています。そして、樹氷はアオモリトドマツにとって、寒さから身を守ってくれる分厚いコートの役割も果たしているようです。
また、樹氷ができやすい気象条件は、『新青森市史』別編4自然 によると気温がマイナス5度からマイナス13度、風速毎秒8メートル以下であるため、暖地の山岳は気温が高すぎ、寒地の山岳は気温が低すぎて、樹氷が成長しにくいそうです。八甲田をはじめ東北地方の山々は寒さに強いアオモリトドマツが自生していることと、気温の変動範囲が適当であるため、樹氷には最適な環境であるといえるようです。
青森市街からいつも眺められる八甲田にあって、いくつもの条件をクリアして存在している樹氷は青森市民の貴重な財産といえます。樹氷ツアーにもぜひ、参加したいものですね
It is these days which have admired the heavy snow beyond the imagination which the lingering cold of past the first day of spring is calling snow, or came down all over the country.
Now, guidance of the silver frost tour of 8 Koda was published at "public-relations あおもり". [ the other day ]
It seems that silver frost is made in fact only at the place which fulfilled certain conditions although he thought that silver frost was seen anywhere in the snow-covered mountain of winter.
What is the condition?
I hear that the tree to which eye one is made as for silver frost is aomori todomatu enacted by "the tree of Aomori" first.
The density of アオモリトドマツ of a leaf is high, and since the bark is carrying out the notch, it tends to attach ice and snow than other trees.
And the damp monsoon containing moisture of the Sea of Japan during winter should blow.
Silver frost will be produced if these two conditions are met.
Then, if the condition is met, what does it do?
The waterdrop made when temperature was 0 times or more in the atmosphere can exist with waterdrop, even if temperature falls gradually and falls below the freezing point.
Although it is said that this is called supercooled water droplet, this is very unstable, if other objects are touched, will be solidified in an instant and will become a solid.
The supercooled water droplet carried from the Sea of Japan adheres to the bark of aomori todomatu, and freezes and attaches silver frost to it.
In order for a small supercooled water droplet to freeze over and to grow up on the wind one after another, it becomes the surface which split finely and is called the tail of the shrimp from the form.
Moreover, the snow-white object which can also be 3 meters is called a snow monster, an ice monster, etc.
It seems that and silver frost has also played for aomori todomatu the role of the thick coat which protects itself from cold.
Moreover, the climate condition which can tend to do silver frost is 4 edited by a "history of Shin-Aomori" exception nature. The mountains of a warm district are too high-temperature, the mountains of a cold region are too low-temperature, and, seemingly, silver frost cannot grow easily, since temperature is 13 minus and 8 meters/s or less of wind velocity from five minus when it depends.
It seems that it can be told to silver frost that it is the optimal environment since aomori todomatu with mountains of the Tohoku district strong against cold including 8 Koda growing wild and the variation range of temperature are suitable.
It is in 8 Koda at which it can always look from the Aomori street, and the silver frost which clears many conditions and exists can be called Aomori residents' precious property.
I would like to participate also in silver frost tour very much.