Umbrella effect - Umbrella effect

A phenomenon in which atmospheric aerosols (floating particles, aerosols) scatter solar radiation and bounce some of it back into space, blocking it like a parasol. It is also called the umbrella effect. It is seen when a large amount of aerosols are introduced into the stratosphere due to a volcanic eruption. The umbrella effect leads to a drop in the earth's surface temperature, but this is only one aspect of the aerosol's function. Aerosols also have the property of absorbing solar radiation, so the temperature of the entire system including the earth's surface and atmosphere does not necessarily decrease. For example, snow and ice areas are close to a completely reflective surface, so even if aerosols have little solar radiation absorption, the system including the earth's surface and atmosphere will heat up. Conversely, the sea surface is close to a completely absorbing surface, so even if aerosols have a large solar radiation absorption, the system will cool. However, when considering the impact of aerosols increasing due to human activities, it is appropriate to first consider the umbrella effect.

[Hiroo Misaki]

"The Basics of Aerosol Science" by Kanji Takahashi, edited by the Japanese Society of Aerosol Science (2003, Morikita Publishing) " "Fine particles change the climate - Another perspective on the atmospheric environment" by Katsuro Misaki (Chuko Shinsho)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

大気中のエーロゾル（浮遊微粒子、煙霧質。エアロゾルともいう）が日射を散乱し、その一部を宇宙空間に跳ね返して、あたかも日傘のように日射を遮る現象。雨傘効果(あまがさこうか)ともいう。火山噴火により、成層圏にエーロゾルが大量に導入されたときにみられる。日傘効果は地表面温度の低下をもたらすことになるが、それはエーロゾルの働きの一面にすぎない。エーロゾルには日射を吸収する性質もあるので、地表面と大気を含めた系全体はかならずしも温度が低下するとは限らない。たとえば雪氷域は完全反射面に近いので、エーロゾルの日射吸収性が小さくても、地表面と大気を含めた系は加熱される。反対に海面は完全吸収面に近いので、エーロゾルの日射吸収性が大きくても、系は冷却される。しかしながら、人間活動で増加するエーロゾルの影響としては、まず日傘効果を考えるのが妥当であろう。

［三崎方郎］

『日本エアロゾル学会編、高橋幹二著『エアロゾル学の基礎』（2003・森北出版）』▽『三崎方郎著『微粒子が気候を変える――大気環境へのもう一つの視点』（中公新書）』

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