Tropics face bigger more organised thunderstorms as climate warms


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Image above from Mike Hollingshead on his website Extreme Instability.

Climate scientists have long predicted that certain parts of the tropics will get wetter the more the Earth warms. Now an Australian team has worked out the mechanism which will involve an a change in type of large thunderstorms rather than an increase in the number of them.

At the same time, other types of rainfall will diminish.

"What we are seeing is more big and organised storms and fewer small and disorganised storms," says Jackson Tan, lead author of a report by the Monash branch of the Australian Research Council Centre of Excellence for Climate System Science (ARCCSS) and NASA.

What is more, the increased rainfall is a result of changes to the underlying circulation in the tropics, rather than just warmer weather.

"If this rainfall change was caused simply by a warmer atmosphere holding more moisture, we would have expected an increase in the average rainfall when each system, organised or disorganised, occurs," said Dr Tan.

The research was published in Nature.

But scientists are struggling to include the process of the creation of thunderstorms in climate models given current computing power. The small-scale processes giving rise to thunderstorms make their direct simulation impossible.

"This limitation, which is a well-known issue in global climate models, might well be a contributing factor to the precipitation errors and the bias towards light rain," said another author from Monash University, Christian Jakob.

"Given how important these large storms are to rainfall in the tropics, it is vital that there is a renewed effort to represent convective organisation in global climate models if we are to fully understand precipitation changes in the future."

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