Why Hawaii may be the world’s best place to see rainbows

A new study has suggested that Hawaii is the best place on Earth to experience the wonder of rainbows. These multicolored meteorological phenomena are caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky in a circular arc, and the study maintains that Hawaii is the rainbow capital of the world.

In the study, The Secrets of the Best Rainbows on Earth, Dr. Steven Businger explains that rainbows found in the US state are so stunning that visitors and locals alike frequently leave their cars by the side of the road in order to photograph the brilliant bands of light. They are commonly seen in the spray blown up by the wind associated with large, fast-moving wave crests that break near the shore. One reason is that Hawaii is located at ∼20°N latitude in a region of the subtropics that is dominated by the Hadley cell, which results in subsidence and generally clear skies over Hawaii and produces prevailing northeast trade winds.

Rainbow appearing over the highway with Mauna Kea can be seen behind the rainbow — Hawaiian rainbows are known to be stunning © Toshi Sasaki/ Getty Images

Hawaii’s trade wind weather is characterized by convective showers with clear skies between the showers, and according to the study, the spacing between the showers is sufficient to allow sunlight to reach the rain beneath the showers, producing optimal conditions for rainbow sightings. At night, a warm sea surface heats convection from below, while radiation cools cloud tops, resulting in deeper rain showers in the morning that produce rainbows in time for breakfast. A critical factor in producing frequent rainbows is the mountainous character of the Hawaiian Islands. Although each Hawaiian island has unique topography and attendant orographic affects, in every case the mountains produce sharp gradients in clouds and rainfall that are key to abundant rainbow sightings.

Businger, an atmospheric scientist at the University of Hawaii at Mānoa, says that rainbows in Hawaii appear in Hawaiian chants and legends, on license plates and in the names of Hawaiian sports teams and local businesses. The cultural importance of rainbows is reflected in the Hawaiian language, which has many words and phrases to describe the variety of manifestations there, including Earth-clinging rainbows (uakoko), standing rainbow shafts (kāhili), barely-visible rainbows (punakea) and moonbows (ānuenue kau pō).

The full report can be found in the Bulletin of the American Meteorological Society here.