Icing - Chakuhyo (English spelling)

Japanese: 着氷 - ちゃくひょう（英語表記）icing

A phenomenon in which moisture in the air freezes on the surface of an object. When it forms on tree branches, it is classified into two types. One is frost, which is water vapor in the air that sublimes and condenses on cooled branches. It usually develops when radiation cooling occurs on clear nights with little wind, and frost itself is a collection of fine frost crystals. It has poor mechanical strength and adhesive power, so it disappears when the sun shines. The other is when supercooled water droplets in the air collide with the branches and freeze, which is called frost, and is classified into three types: frost, rough ice, and glaze. Ice is formed when supercooled water droplets that collide freeze one after another. Ice is white and weak because it contains many air bubbles. The "Monster" and "Shrimp Tail" on Mount Zao, which straddles Yamagata and Miyagi prefectures, are typical examples of frost. When supercooled water droplets collide before the first one has completely frozen, the ice that forms becomes transparent and is called glaze ice. Glaze ice is ice that is firmly attached to branches, making it difficult to remove and very strong. Crude ice is somewhere between glaze ice and frost on trees. Icing on power lines, antennas, aircraft, ships, and other objects can cause serious damage. Various methods are used to prevent icing, such as applying paints or chemicals that make it difficult for ice to adhere to objects, making ice that has formed mechanically easier to remove, or warming the surface of the object. Snow accretion is the phenomenon in which snow adheres to objects during snowfall or a blizzard. Similar measures are being considered for snow accretion as for icing.

[Kiichi Maeno]

Hull Icing

Icing on a ship occurs when seawater splashes onto the ship's hull, handrails, bulwarks, rigging, antennas, and other parts exposed to the outside air, and if the ice is not removed, the center of gravity rises and the ship's stability decreases. If strong winds or large waves come along, the ship may suddenly capsize, and this is feared to be one of the causes of accidents at sea. In winter, meteorological offices in northern Japan, such as Hokkaido, issue "icing warnings" when there is a risk of icing, calling attention to the risk.

[Masao Hanzawa]

Icing on spacecraft

Problems related to icing include ice that has adhered to the fuel tank during the launch of the space shuttle and breaks off, damaging the heat-resistant tiles of the spacecraft's hull, and the freezing of waste liquid from the space shuttle. These problems are caused by different factors than the above-mentioned supercooled water droplets and seawater splashes, but they are both caused by ice.

[Masao Hanzawa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

物体の表面に大気中の水分が凍りつく現象。樹木の枝につく場合は2種類に分類されている。一つは樹霜で、これは大気中の水蒸気が冷えた枝に昇華凝結したものである。多くは風の弱い晴天夜に放射冷却したとき発達し、樹霜そのものは細かな霜の結晶の集合である。機械的強度も付着力も弱いため、日が照ると消滅してしまう。もう一つは、大気中の過冷却した水滴が枝に衝突して凍結する場合、すなわち霧氷で、樹氷、粗氷、雨氷の3種に小分類される。衝突した過冷却水滴が次々と凍結してできるのが樹氷である。樹氷は多くの気泡を含むため白く強度も弱い。山形・宮城両県にまたがる蔵王山(ざおうさん)の「モンスター」や「エビのしっぽ」が樹氷の代表的な例である。衝突した過冷却水滴が凍りきらないうちに次の過冷却水滴が衝突するような場合、着氷体は透明な氷となり雨氷とよばれる。雨氷は枝にしっかりと凍りついた氷であるから、とれにくく強度も強い。雨氷と樹氷の中間が粗氷である。送電線、アンテナ、航空機、船体、などにつく着氷は大きな被害を及ぼすことがある。着氷防御法としては、物体に氷がつきにくい塗料や薬剤を塗ったり、ついた着氷を機械的に除去しやすくしたり、あるいは物体の表面を暖めたりなど種々の方法が実施されている。着雪は、降雪や吹雪(ふぶき)のとき雪が物体につく現象である。着雪に関しても、着氷と同じような対策が考えられている。

［前野紀一］

船体着氷

船体への着氷は、外気に露出している船体、ハンドレール、ブルワーク、索具、アンテナ類などに海水の飛沫が凍り付くもので、着氷を除去しないと重心位置が上昇し、船体の復原力が低下する。そこへ強風や大波がくると突然転覆することもあり、海難原因の一つとして恐れられている。冬季、北海道など北国の気象官署では、着氷のおそれのある場合に「着氷注意報」を出して注意を喚起している。

［半澤正男］