Tracking cyclones

6 April 2016

Professor Johnny Chan (Croucher Senior Research Fellowship 1998) is Chair Professor of Atmospheric Science and the founding Dean of the School of Energy and Environment at the City University of Hong Kong. He is an internationally acknowledged authority on tropical cyclones and chairs the United Nations World Meteorological Organisation's Tropical Cyclone Panel and first became interested in meteorology during boyhood scouting expeditions in Hong Kong.

“I remember on summer scout camps, it was often brilliant sunshine in the morning but our campsite might be evacuated in the evening due to a heavy rainstorm. It just fascinated me,” he says.

After graduating in physics from the University of Hong Kong, he was uninspired by most of the post-graduate options until he met Gordon Bell, the then Director of the Royal Hong Kong Observatory, who wanted a more reliable means of measuring the size of raindrops.

Chan helped develop a system utilising a laser beam across a horizontal plane so that a falling raindrop blocked the signal and its size could be accurately measured by calibrating the laser signal with fixed-size droplets from hypodermic needles.

After a period studying cloud physics at the University of Hawaii, one of his classmates suggested to him that switching to typhoon research might be far more relevant to Hong Kong, so Chan approached William M Gray, Professor of atmospheric science at Colorado State University, who offered him a place to complete his PhD.

“That’s how I ended up studying typhoons for the last 30 plus years,” he says.

Dr Johnny Chan

He continued with his studies at the US Naval Postgraduate School in Monterey, California but after nine years of work and study in the USA, he started to think about returning home. A colleague suggested that his expertise in tropical cyclones might make a much more significant impact in Hong Kong where typhoons were a regular and life-threatening weather event but in 1986, it proved very difficult to find suitable employment in the Hong Kong academia.

“There were no academic positions in my field, but I managed to get a job at the Royal Observatory,” he says.

He remained at the Observatory for three and a half years but as a research scientist at heart, he was frustrated because the Observatory had very little resources to support research, even to just find out why a particular forecast was wrong.

In 1989 he accepted a senior lecturer position in atmospheric physics in the new Applied Science Department at City Polytechnic of Hong Kong (now City University) and helped develop courses teaching students in atmospheric science while continuing his research into track forecasting of tropical cyclones.

After a chance meeting with their Director in Beijing in 1992, he was invited to the UK Meteorological Office to help them improve their tropical cyclone prediction model and achieved an improvement of over 30%. It was informally referred to as ‘Chan’s method’.

His Croucher senior research fellowship in 1998 allowed him the freedom to “do what [he] wanted” in terms of research, which was to further explore tropical cyclone climate- the frequency of these storms and where and when they might strike.

Thanks partly to his research, the accuracy of typhoon forecasting has improved dramatically, so that errors over a three day forecast are now about the same as those for a one day forecast, two decades ago. Despite these improvements, there are still occasions when an intense tropical cyclone will make a sudden turn for no apparent reason.

“Sometimes we see the direction change by up to 90 degrees in 6-12 hours,” says Chan and believes there are currently several hypotheses that require further investigation.

Chan explains that a powerful computer must solve a lot of equations to predict the track of a low pressure area but to solve these equations it needs adequate data. Sometimes there is insufficient data or the assumptions made about the precise structure and scale of a typhoon are inaccurate. Each typhoon has unique wind characteristics and his team have discovered that big tropical cyclones move differently to small ones, so if the exact description of the typhoon structure is erroneous, the computer model will fail.

He has been also researching the effect of climate change and global warming on the frequency and intensity of tropical cyclones. This research started after what he calls the “hype” generated after the 2005 Hurricane Katrina in the U.S., which prompted a series of academic papers that claimed Katrina was evidence of an increase in frequency of extreme weather events, due to global warming creating more energy in the atmosphere.

When Chan examined the frequency and intensity of tropical cyclones during rising global temperatures over a sixty year period, he discovered that they followed a cycle with peaks every thirty years or so. The year of the Katrina event in 2005 happened to be near the peak of an upward cycle and his research showed that there was no correlation between increased temperatures and the frequency and intensity of tropical cyclones. However he did discover something else that was of vital significance for policy to mitigate the devastating impact of these storms.

“Even if there is no increase in amplitude and frequency of typhoons there will be an increase in rainfall and tidal surge, so flooding is an increased risk,” he explains.

Professor Johnny Chan obtained his bachelor and master degrees in physics from the University of Hong Kong and his PhD in atmospheric science from Colorado State University in the USA. After two years as a Research Associate at the US Naval Postgraduate School, he stayed there as an Adjunct Research Professor for one year. He then returned to Hong Kong and joined the then Royal Observatory as a Scientific Officer. In 1989, he began his academic career as a Senior Lecturer at the then City Polytechnic of Hong Kong, where he is now Chair Professor of Atmospheric Science and founding Dean of the School of Energy and Environment, as well as the Director of the Guy Carpenter Asia-Pacific Climate Impact Centre. 

To view Professor Chan’s personal Croucher profile, please click here.