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PICTURE: RAINBANDS (WHITE) OF A TROPICAL CYCLONE AND RELATED OCEAN COLD WATCH (COLORED SHADOWS) SIMULATED BY THE CLIMATE MODULE SIMULATION WITH ULTRA-HIGH RESOLUTION FOR PRESENT CONDITIONS (LEFT). THE SIMULATION WAS PERFORMED WITH… show more
CREDIT: IBS
A study based on new high-resolution supercomputer simulations, published in this week’s issue of Science Advances, shows that global warming will amplify the landing of Category 3 or higher tropical cyclones in the Indian and Pacific Oceans while suppressing the formation of weaker events .
Tropical cyclones (including typhoons and hurricanes) are the deadliest and costliest weather disasters on our planet. Millions of people are affected by the destructive power of these extreme weather systems each year, but how the properties of tropical cyclones – especially in coastal areas – will change in response to global warming has long been a mystery. To answer this question, scientists have been using the world’s largest supercomputers for over two decades to run climate model simulations that show important aspects of these devastating storms. Until recently, however, the computing power was insufficient to capture both atmospheric details and resolve the full interaction with the ocean on a global scale.
A team of researchers from the South Korean IBS Center for Climate Physics (ICCP) at Pusan National University recently performed one of the most computationally intensive and detailed simulations of global warming. The global climate model records small-scale atmospheric and oceanic processes on a horizontal scale of 25 km and 10 km, respectively. This unprecedented resolution is sufficient to simulate tropical cyclones and oceanic cold wakes (Fig. 1) that arise when a strong, slow moving tropical cyclone brings cold, deep water to the ocean surface and further affects the trail and intensity of tropical cyclones.
In order to determine the sensitivity of tropical cyclones to global warming, the research team carried out computer model simulations for today’s atmospheric greenhouse gas composition and for double and quadruple CO2 concentrations. The simulations ran for 13 months on one of the fastest academic supercomputers in South Korea called Aleph (Fig. 1) and resulted in the equivalent of about two thousand 1TB hard drives with data.
This climate computer model is also unique in other respects. For example, it has much weaker sea temperature errors than the previous generation of climate models. “This improvement was important for a realistic simulation of typhoons in the Indian and Pacific Oceans,” says Dr. Jung-Eun Chu, lead author of the study and project leader at the ICCP.
Air rises above the warm tropical oceans, flows upwards at great heights and sinks in the subtropical regions. The surface return flow of this so-called Hadley circulation feeds the global trade wind system. According to the new study, the Hadley circulation is expected to weaken in the future in the summer due to the accelerated warming of the atmosphere at an altitude of 5 to 15 km relative to the ground. “A future reduction in ascending movement in the tropical atmosphere will make tropical cyclones more difficult to develop, which explains the projected future suppression of tropical cyclone seeds and the total number in the Pacific and Indian Oceans (Fig. 2)”, explains Dr. Sun-Seon Lee from ICCP, who ran the simulations on Aleph. “Interestingly, the simulated pattern of future tropical cyclone changes is quite similar to recently observed trends, which supports the assumption that global warming is already changing global extreme weather,” adds Dr. Lee added.
However, the story of how global warming will transform tropical cyclones is more complex. Although the total number of tropical cyclones is expected to decrease in the future for a CO2 doubling, development events have a much higher chance of intensifying beyond Category 3 due to the higher humidity and higher energy levels in the atmosphere. “This finding confirms earlier studies that used less detailed global climate models. By depicting coastal processes more accurately than ever in a global model, we now have much greater confidence in these robust model projections, especially for tropical cyclone landings. “, Says Prof. Axel Timmermann, co-author of the study and director of the ICCP.
For even higher greenhouse gas concentrations (CO2 quadrupling), the research team discovered an important, previously unknown saturation effect: over ~ 5? Due to global warming, the suppression of tropical cyclone seeds is so strong that the number of strong landing events (category 3 or higher) is also gradually decreasing. “Even so, the precipitation associated with each event will continue to increase, increasing the risk of extreme coastal flooding. Our study provides important policy-relevant information for countries affected by the effects of tropical cyclones, ”says Dr. Chu.
The ICCP research team will continue to analyze the large amount of data generated by these computer simulations in order to better understand the interaction between ocean heat content and tropical cyclones under current and future conditions.
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From EurekAlert!
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