To make a vibrant iridescent rainbow, two ingredients are needed: water and light. In Hawaiʻi, those two components are not in short supply. The islands' abundance of sunlight and water, combined with their geographical location, make rainbows a common occurrence on the islands. Because of their ubiquity, the bands of light are deeply intertwined in Hawaiian culture, reports the Deccan Herald.
Rainbows form their signature colors through atmospheric optical effects when raindrops refract and reflect light, just like a prism does. The raindrop bends the waves of light as they enter the droplet, where they reflect once inside, and then refract again upon exit. Various colors are seen in a rainbow because each color wavelength refracts at different angles, and when they do, they are seen as separate bands of color in the rainbow, reports Lauren J. Young for Science Friday. When we view a rainbow on the Earth's surface, we are only seeing half of it at a time. When soaring high above a rainbow in an aircraft, sometimes you can see a rainbow in its entirety as a 360-degree ring of color, Science Friday reports.
There are various factors as to why rainbows frequently form over the archipelago that can last for several hours. Hawaiʻi's location in the subtropical Pacific makes it susceptible to northeast trade winds. The winds bring infrequent rain showers with clear skies between the rainfall, which create optimal rainbow watching conditions, reports George Dvorsky for Gizmodo. Heat off the ocean's surface from the day's sunlight eventually radiates into the night's atmosphere. This occurrence leads to showers and rainbows adorning the morning skies, reports Bryan Lawver for Inverse. Mountains also redirect winds up towards the sky, creating more rainclouds on one side while the other is clear for rainbow viewing, Inverse reports.
Heat throughout the day also circulates winds around the islands. Lighter winds in the afternoon form light rain showers around the mountains, creating the perfect conditions for sunset rainbows, reports Inverse. Hawaiʻi's remote location also keeps the islands' crisp, clean air free of pollutants where rainbows can shine in all their vibrancy without any contaminants to dim their glow.
"In Mānoa Valley there are these misty rains that come into the valley and the winter sun comes down and creates a rainbow. I've seen the rainbow start in the morning to the west and it gradually shifts throughout the entire day," says Businger to Science Friday. "Can you imagine a rainbow that lasts seven hours? It's really fun."
Businger and his team developed an app called RainbowChase that you can use to find the best rainbows in Hawaiʻi. The app uses radars, satellite images of rain clouds and tracks weather conditions to direct users to the multicolored arches, reports Gizmodo.
Rainbows are a common occurrence on Earth, but if you want to see moonbows, double rainbows, or a whole 360-degree rainbow, Hawaiʻi—also known as the Rainbow State—is the best place to look.
The colorful arches adorn the state's license plates, and they're featured as the University of Hawaiʻi's mascot, the Rainbow Warriors. Rainbows appear in Hawaiian mythology and hold cultural importance in the Hawaiian language, explains Steven Businger, an atmospheric scientist and professor at the University of Hawaiʻi Mānoa, in his study published last month in the Bulletin of the American Meteorological Society.
"There are words for Earth-clinging rainbows (uakoko), standing rainbow shafts (kāhili), barely visible rainbows (punakea), and moonbows (ānuenue kau pō), 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," Businger says in a statement.
In Hawaiian folklore, rainbows symbolize "the veil between the realms of the gods and the realms of the humans," M. Puakea Nogelmeier, professor emeritus of Hawaiian language at the University of Hawaiʻi, tells Science Friday.