Gradients between land-surface and sea-surface heating could affect strength and location of Azores, North Pacific highs
By Summit Voice
SUMMIT COUNTY — The big subtropical high pressure systems that already shape mid-latitude weather patterns to a large degree could become even bigger players on the global climate scene as they intensify under the influence of global warming, according to a new study led by Duke University researchers.
The study suggests that, as summertime near-surface high-pressure systems over the northern Pacific and Atlantic oceans strengthen, they could influence the occurrence of drought and extreme summer rainfall, in coming years.
The high pressure systems include the Bermuda, or Azores High, which dominates the south-central Atlantic Ocean in the summer. When it shifts westward, it can bring hot and dry conditions to the Southeast and central plains. It also affects the northward flow of summer monsoon moisture, as well as the path of hurricanes that often track along the Bermuda high’s southern edge, then move clockwise around its western periphery.
Its counterpart in the Pacific is the North Pacific High, often situated east of Hawaii. It is also strongest in the summer, influencing weather in the western U.S. Both systems play a major role in shaping Mediterranean weather patterns in their respective regions, with distinct dry and rainy seasons.
Wenhong Li, assistant professor of earth and ocean sciences at Duke’s Nicholas School of the Environment, and colleagues used climate model simulations to predict future changes in the strength of the annually occurring North Atlantic Subtropical High, also known as the Bermuda High, and the North Pacific Subtropical High.
According to the simulations, these high-pressure systems will intensify over the 21st century as a result of increasing greenhouse-gas concentrations. The simulations suggest that an increase in the land-sea thermal contrast – the difference between ocean and land heating, as Earth’s climate warms – will fuel the systems’ intensification.
Li’s co-authors on the new study are Laifang Li, a PhD student at Duke’s Nicholas School; Mingfang Ting of the Lamont-Doherty Earth Observatory at Columbia University’s Earth Institute; and Yimin Liu of the Chinese Academy of Sciences’ Institute of Atmospheric Physics.
They used climate model simulations from the Intergovernmental Panel on Climate Change Fourth Assessment Report and 40 years of atmospheric circulation data from the European Centre for Medium-Range Weather Forecasts for the months of June, July and August to conduct their research.