University develops rainbow forecasting system for Yangmingshan

12/02/2019 08:47 PM
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Courtesy of Chinese Culture University
Courtesy of Chinese Culture University

Taipei, Dec. 2 (CNA) Chinese Culture University, located in a part of Taipei where the world's longest rainbow ever occurred, has developed a rainbow forecasting system aimed at giving tourists, meteorologists and photographers directions for rainbow watching.

"We hope the service, which is only available for the region, can bring more people to look for rainbows on our campus," said Chou Kun-hsuan (周昆炫), a professor from the university's Department of Atmospheric Science on Monday.

Chou told CNA that the inspiration for the system came after he, his colleagues and students documented a rainbow in Yangmingshan that lasted almost nine hours in 2017, which was recognized by Guinness World Records the next year as the longest rainbow ever recorded.

He received many inquiries wondering when it would be possible to forecast rainbows, prompting him to analyze weather conditions between Nov. 1, 2018 and Jan. 31, 2019, when a rainbow appeared on 23 of those days and established the forecasting system in June.

Chou explained that he compiled data from both the Central Weather Bureau and the university to develop a "Rainbow Weather Index" based on factors such as precipitation, wind speed, wind direction and humidity.

After months of adjustments, Chou launched the forecast in November, and he said it now is 85 percent accurate.

During the 34-day period between Oct. 29 and Dec. 1, forecasts and actual conditions matched 29 days.

The index has been designed to reflect high, medium and low probabilities of a rainbow occurring, with a 74 percent or above chance considered a "high" probability, 63-74 percent considered "medium," and 63 percent or under deemed "low," Chou said.

In "high" probability scenarios, significant northeasterly winds provide sufficient moisture, accompanied with sunlight that is sufficient enough to keep the rainbow bright, he said.

"We have the right formula here in Yangmingshan," Chou said, adding that compared with rainbows that appear after afternoon thunderstorms in summer, rainbows generated by seasonal winds in winter are longer lasting.

Also, one-third of the rainbows that take place in Taiwan each year fall between November and January, described by Chou as a "hot season."

There remains a chance the area in the northern part of Taipei will see an even longer rainbow than the one it saw from 6:57 a.m. to 3:55 p.m. on Nov. 30, 2017, he said.

Chou cautioned, however, that rainbow chasers must be fully prepared to brave the cold and humid weather in the mountains.

But those interested could start Wednesday, when according to his forecast there will be an 87.05 percent chance of seeing a rainbow.

To learn more about the forecasting system, go to

(By Lee Hsin-Yin)


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