Sun, Dec 08, 2019 - Page 2 News List

CCU launches its weather index to predict rainbows

Staff writer, with CNA

A rainbow recognized as the world’s longest-lasting stretches across Taipei’s Yangmingshan on Nov. 30 2017.

Photo provided by Chinese Culture University via CNA

A Chinese Culture University (CCU) professor last month launched a rainbow forecasting system aimed at helping tourists, meteorologists and photographers know when and where to find rainbows.

Atmospheric science professor Chou Kun-hsuan (周昆炫) said earlier this week that the “Rainbow Weather Index” is based on data from the Central Weather Bureau and the university, such as precipitation, wind speed, wind direction and humidity.

After months of adjustments, Chou launched the system and said it is now 85 percent accurate in predicting a rainbow.

“We hope the service, which is only available for this region, can attract more people to look for rainbows on our campus,” Chou said.

He created the index after he, his colleagues and students documented a rainbow in Taipei’s Yangmingshan (陽明山) that lasted almost nine hours in 2017, and was last year recognized by Guinness World Records as the longest rainbow recorded, he said.

Chou analyzed the weather conditions between Nov. 1 last year and Jan. 31, and found that a rainbow appeared on 23 of those days, which he used to establish the forecasting system in June, he said.

The index was designed to reflect high, medium and low probabilities of a rainbow occurring, with a 74 percent or higher chance considered high, 63-74 percent considered medium and 63 percent or lower deemed low, Chou said.

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

Between Oct. 29 and Sunday last week, forecasts and actual conditions matched 29 days for a rainbow to occur.

“We have the right formula here in Yangmingshan,” Chou said, adding that compared with rainbows that appear following summer afternoon thunderstorms, rainbows generated by seasonal winds in winter last longer.

One-third of Taiwan’s rainbows each year occur between November and January, which Chou calls the “hot season.”

Rainbow chasers could start on Wednesday, when according to the index, there is an 87.05 percent chance of seeing a rainbow.

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