Why Rainbows Look Totally different in Hawaii

Rainbow over east Oʻahu.

Rainbow over east Oʻahu.
Picture: Steven Businger

Rain and daylight are the important thing elements of rainbows, however many different environmental elements are required to constantly pull off this visible trick, as new analysis reveals.

“Rainbows are some of the most spectacular optical phenomena in the natural world, and Hawaii is blessed with an amazing abundance of them,” opens a brand new science paper revealed within the Bulletin of the American Meteorological Society. The paper explains why that is the case, itemizing such elements as sea floor temperature, prevailing commerce winds, and topography, amongst different variables.

In an related press launch, Steven Businger, the only real writer of the paper and a meteorologist from the College of Hawaii at Mānoa, mentioned the cultural significance of rainbows in Hawaii is clear within the indigenous language.

“There are words for Earth-clinging rainbows (uakoko), standing rainbow shafts (kāhili), barely visible rainbows (punakea), and moonbows (ānuenue kau pō), among others,” he mentioned “In Hawaiian mythology the rainbow is a symbol of transformation and a pathway between Earth and Heaven, as it is in many cultures around the world.”

Image conveying the cultural importance of rainbows in Hawaii.

Picture conveying the cultural significance of rainbows in Hawaii.
Picture: Steve Businger/Bulletin of the American Meteorological Society

At their most elementary degree, rainbows are simple to clarify: These iconic multicolored arcs are brought on by the reflection, refraction, and dispersion of sunshine touring via water droplets. We see rainbows when the Solar is located at round a 40-degree angle to the horizon.

“Billions of raindrops distributed along a cone at the correct viewing angles contribute to the phenomenon we perceive as a primary rainbow,” in keeping with the paper.

Through the morning because the Solar rises within the sky, the peak of potential rainbows shrink, whereas the reverse occurs through the afternoon, with the tallest rainbows showing earlier than sundown.

Diagram showing the effect of sunlight angle on the appearance of rainbows.

Diagram displaying the impact of daylight angle on the looks of rainbows.
Picture: Steven Businger/Bulletin of the American Meteorological Society

However there’s extra to rainbows than water droplets and the right angle of daylight. As the brand new paper factors out, Hawaii’s location within the subtropical Pacific is good; the archipelago’s climate is closely influenced by northeast commerce winds, which seem 9 days out of 10 through the summer season, and 6 of 10 days through the winter months. Rain showers are frequent on this local weather, with clear skies showing through the intervals.

Heat sea floor temperatures warmth the air near the floor, whereas “radiation to space cools cloud tops, resulting in deeper rain showers in the morning that produce rainbows in time for breakfast,” mentioned Businger within the College of Hawai’i press launch.

On the similar time, mountains redirect commerce winds up into the sky, aiding with cloud manufacturing on the lee facet. Certainly, mountains are vastly essential in Hawaii, because the islands could be deserts with out them owing to scant rainfall, in comparison with the a whole bunch of inches of rain the archipelago receives yearly, in keeping with the analysis.

Daytime, or diurnal, heating helps wind to flow into across the islands. When winds are gentle within the afternoon, rain showers will kind over the ridge crests and mountain slopes—a set of circumstances that results in a plethora of rainbows previous to sundown.

One other issue has to do with how clear the air is in Hawaii, a results of its isolation.

“Hawaii is known as one of the most remote island chains on Earth,” writes Businger within the paper. “Hawaii’s remoteness means that the air is exceptionally clean and free of air pollution, continental dust, and pollen. As a consequence, there is less scattering of sunlight by aerosol, and the sunlight contains the full spectrum of colors even at low angles when the sun is close to setting.”

So not solely are rainbows plentiful in Hawaii—they’re additionally visually spectacular.

For these of you who stay in Hawaii or are hoping to go to, there’s a brand new app known as RainbowChase that will help you discover the colourful arcs and a pot of gold. The app, developed by Businger and his colleagues, permits customers to view radar and satellite tv for pc pictures of rain clouds, along with monitoring the native climate circumstances.

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