Rainbows are some of the most spectacular optical phenomena in the natural world and Hawaii has an abundance of them. In fact, the island state of the US is best place to experience its natural wonder in the entire planet, suggested an atmospheric scientist from the University of Hawaii at Manoa.
And to ensure people saw the full spectrum of this light play, the scientist has co created an app. The app uses Doppler radar data and high-resolution satellite data that alerts users when nearby conditions become conducive for rainbow sightings. "After a few years of false starts, Paul Cynn and I finally connected with Ikayso, a Hawaiian smartphone app developer in April of 2020. I am very excited to say that our app, called RainbowChase, is now available to the public for free," said Steven Businger, a professor in the University's School of Ocean and Earth Science and Technology.
In the recent publication, Businger highlighted the Hawaiian cultural significance of rainbows and reviewed the science of rainbows and the special combination of circumstances that makes Hawaii a haven for rainbows.
"The cultural importance of rainbows is reflected in the Hawaiian language, which has many words and phrases to describe the variety of manifestations in Hawai," said author Steven Businger, a professor in the University's School of Ocean and Earth Science and Technology. "There are words for Earth-clinging rainbows (uakoko), standing rainbow shafts (kahili), barely visible rainbows (punakea), and moonbows (anuenue kau po), among others. 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," he added
Hawaii's subtropical climate and overall weather pattern, dominated by trade winds, results in frequent rain showers and clear skies between the showers, Businger explained. In addition to this, there are four other factors affecting the prevalence of rainbows throughout the islands, he added.
"At night, a warm sea surface heats the atmosphere from below, while radiation to space cools cloud tops, resulting in deeper rain showers in the morning that produce rainbows in time for breakfast," said Businger.
Another critical factor in producing frequent rainbows is Hawaii's mountains, which cause trade wind flow to be pushed up, forming clouds and producing rainfall. Without mountains, Hawaii would be a desert with a scant 17 inches annual rainfall.
A third factor, Businger pointed out, conducive to rainbow sightings is daytime heating, which drives island-scale circulations. During periods of lighter winds, showers form over the ridge crests over Oahu and Kauai in the afternoon, resulting in prolific rainbows as the sunsets.
Due to the remoteness of the Hawaiian Islands, the air is exceptionally clean and free of pollution, continental dust, and pollen, contributing to the numerous bright rainbows with the full spectrum of colours.
The essential ingredients for rainbows are, of course, rain and sunlight. To see a rainbow on flat ground the sun must be within about 40 degrees of the horizon. As the sun rises to higher angles in the sky during the morning, the height of the rainbow diminishes until no rainbow is visible above the horizon. The pattern is reversed as the sun lowers in the afternoon, with rainbows rising in the east and the tallest rainbows just prior to sunset.