The secrets of the best rainbows on Earth

Date:
March 11, 2021
Source:
University of Hawaii at Manoa
Summary:
An atmospheric scientist makes an impassioned case for Hawaii being
the best place on Earth to experience the wonder of rainbows. He
begins by highlighting the Hawaiian cultural significance of
rainbows, he reviews the science of rainbows and the special
combination of circumstances that makes Hawai'i a haven for
rainbows.



FULL STORY ========================================================================== [Double rainbow, Kauai, | Credit: (c) fnendzig / stock.adobe.com] Double rainbow, Kauai, Hawaii (stock image).

Credit: (c) fnendzig / stock.adobe.com [Double rainbow, Kauai, | Credit:
(c) fnendzig / stock.adobe.com] Double rainbow, Kauai, Hawaii (stock
image).

Credit: (c) fnendzig / stock.adobe.com Close Rainbows are some of the
most spectacular optical phenomena in the natural world and Hawai'i
has an amazing abundance of them. In a new publication, an atmospheric scientist at the University of Hawai'i at Mānoa makes an impassioned
case for Hawaii being the best place on Earth to experience the wonder of rainbows. He begins by highlighting the Hawaiian cultural significance of rainbows, he reviews the science of rainbows and the special combination
of circumstances that makes Hawai'i 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'i," said author Steven Businger, professor in the
UH Mānoa School of Ocean and Earth Science and Technology. "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." Why is Hawai'i the rainbow capital of the world? 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.

Hawai'i's location in the subtropical Pacific means the overall weather
pattern is dominated by trade winds, with frequent rain showers and
clear skies between the showers.

Businger outlines four additional factors affecting the prevalence of
rainbows throughout the islands.



==========================================================================
"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 Hawai'i's
mountains, which cause trade wind flow to be pushed up, forming clouds
and producing rainfall. Without mountains, Hawai'i would be a desert
with a scant 17 inches annual rainfall.

A third factor 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 sun sets.

Due to the remoteness of the Hawaiian Islands, the air is exceptionally
clean and free of pollution, continental dust, and pollen. This is the
fourth factor that contributes to the numerous bright rainbows with the
full spectrum of colors.

Chasing rainbows As Businger pursued his passion for finding and
photographing these beautiful light displays, he began to imagine a
smartphone app with access to Doppler radar data and high-resolution
satellite data that could alert 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 Businger.

RainbowChase is available at:https://rainbowchase.com/. Users can view
radar and satellite images of rain and clouds, along with current and
future weather, and collect rainbow photos.

========================================================================== Story Source: Materials provided
by University_of_Hawaii_at_Manoa. Original written by Marcie
Grabowski. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Steven Businger. The Secrets of the Best Rainbows on Earth. Bulletin
of
the American Meteorological Society, 2021; 102 (2): E338 DOI:
10.1175/ BAMS-D-20-0101.1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/03/210311123516.htm

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