The properties and behaviour of light, and how it interacts with droplets of water, give rise to one of nature's most colourful meteorological events - the rainbow. Most raindrops are spherical rather than the often depicted 'teardrop' shape and it is this spherical shape that provides the conditions for a rainbow to be seen.
The position of the sun and the raindrops in relation to the observer need to be just right for a rainbow to form:. The size of the raindrops does not directly affect the geometry of a rainbow, but mist or fog tends to disperse the effect more see fogbows. Rainbows only appear semi-circular over level ground at sunrise or sunset, when the sun is exactly on the horizon, the majority of the time a smaller segment of an arc is seen.
Because water is denser than air, light passing from air to a raindrop at an angle slows and changes direction, in a process called refraction.
Some scientists call this glow a zero-order glow. Sometimes, a viewer may see a "double rainbow. Double rainbows are caused by light being reflected twice inside the raindrop.
As a result of this second reflection, the spectrum of the secondary rainbow is reversed: red is on the inner section of the arch, while violet is on the outside. Light can be reflected from many angles inside the raindrop. A rainbow's "order" is its reflective number. Primary rainbows are first-order rainbows, while secondary rainbows are second-order rainbows. Higher-order rainbows appear to viewers facing both toward and away from the sun.
A tertiary rainbow, for example, appears to a viewer facing the sun. Tertiary rainbows are third-order rainbows—the third reflection of light. Their spectrum is the same as the primary rainbow. Tertiary rainbows are difficult to see for three main reasons. First, the viewer is looking toward the sun—the center of a tertiary rainbow is not the antisolar point, it's the sun itself.
Second, tertiary rainbows are much, much fainter than primary or secondary rainbows. Finally, tertiary rainbows are much, much broader than primary and secondary rainbows. Quaternary rainbows are fourth-order rainbows, and also appear to viewers facing the sun. They are even fainter and broader than tertiary rainbows.
Beyond quaternary rainbows, higher-order rainbows are named by their reflective number, or order. In the lab, scientists have detected a th-order rainbow. A twinned rainbow is two distinct rainbows produced from a single endpoint.
Twinned rainbows are the result of light hitting an air mass with different sizes and shapes of water droplets—usually a raincloud with different sizes and shapes of raindrops. A supernumerary rainbow is a thin, pastel-colored arc usually appearing below the inner arch of a rainbow.
Supernumeraries are the result of the complex interaction of light rays in an air mass with small, similarly sized water droplets. In supernumerary formation, reflected rays interact in ways called constructive and destructive interference. Light is either reinforce d constructive interference or canceled out destructive interference. Interference is responsible for the lighter hues and narrower bands of supernumeraries. A reflection rainbow appears above a body of water. A primary rainbow is reflected by the water, and the reflected light produces a reflection rainbow.
Reflection rainbows do not mirror the primary rainbow—they often appear to stretch above it. A reflected rainbow appears directly on the surface of a body of water. A reflected rainbow is created by rays of light reflected by the water surface, after the rays have have passed through water droplets.
Reflected rainbows to not appear to form a circle with a primary rainbow, although their endpoints seem to meet in an almond-shaped formation. A red rainbow, also called a monochrome rainbow, usually appears at sunrise or sunset. During this time, sunlight travels further in the atmosphere, and shorter wavelengths blue and violet have been scattered.
Only the long-wavelength red colors are visible in this rainbow. A fogbow is formed in much the same way as a primary rainbow. Light in a fogbow is refracted and reflected by fog water droplets suspended in air. A fogbow seen in the clouds is called a cloud bow.
Because the water droplets in fog are much smaller than raindrops, fogbows have much fainter colors than rainbows. In , theWeather Club documented a record-breaking rainbow reported in Taiwan. Halloween can be a scary time of year when it comes to the weather. From ghost-grey fogs to howling gales, just about anything is possible. Accurate flood forecasting can save lives and livelihoods. Find out how the team at the Environment Agency produces their river flood forecasts, how to stay safe in a flood and what impact climate change will have.
Nowhere on Earth is heating faster than the Arctic. Broadcast meteorologist Laura Tobin visited Svalbard to look at the impacts of climate change, and what it will mean for us.
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