Storm Eowyn has unleashed strong and damaging winds over the British Isles, especially Ireland and Scotland.
The air pressure at the center of the storm plummeted by 50 millibars in the 24 hours leading up to midnight on January 24. That is more than double what is required in the definition of “explosive cyclogenesis”, in other words, the development of a cyclone (counterclockwise). rotating) storm that is both fast and violent – like a bomb going off. As a result, Eowyn can be called a “bomb cyclone”.
It is not unusual for winter storms to reach bomb cyclone status in this part of the world. However, few have shown a level of deepening pressure in recent years comparable to that of Storm Eowyn.
The exceptional intensity of Storm Eowyn was forecast and has prompted the Met Office and Met Eireann to issue red warnings for the entire island of Ireland and central and southern Scotland. This tells the public that widespread wind gusts of 130 to 140 km/h and up to 160 km/h can be expected in the most exposed locations. A record-breaking wind gust of 180km/h has been tentatively reported this morning at Mace Head on the west coast of Ireland.
Similar violent storms have caused extensive damage and tragically claimed lives. Some of these, such as the infamous Great Storm of 1987, have entered popular culture.
Eowyn's place in history
The maximum gust during the Big Storm was measured at 115mph at Shoreham, on the west coast of Sussex. However, the anemometer stopped registering immediately afterwards, so the real peak may have been higher.
A scientific paper has cast doubt on the UK's national record for low-level wind gusts of 140mph (230km/h). This was recorded on February 13, 1989 at the Kinnaird Head Lighthouse in Fraserburgh in Aberdeenshire, Scotland. The researchers documented brief power outages of the recording anemograph, which could have produced an erroneous reading.
The record highest wind gust measured in England is 200 km/h. This was recorded at the Needles, a highly exposed location on the edge of the Isle of Wight, during Storm Eunice in February 2022. Less than two years later (November 2023), two gusts of similar strength were recorded in Brittany during Storm Ciarán.
In Ireland, the strongest gust of wind recorded by a low-altitude inland weather station was during former Hurricane Debbie in 1961, at 180 km/h measured at Malin Head, the northernmost point of mainland Ireland. In October 2017, a wind gust of 157 km/h was measured at Roche's Point, at the entrance to Cork Harbour, during former Hurricane Ophelia.
The measurements we are now seeing during the passage of Storm Éowyn are comparable to those of the most infamous storms of recent years and decades.
What causes a storm to 'explode'
Just like making a cake, there are several key ingredients to preparing an explosively developing bomb cyclone like Storm Éowyn.
A strong jet stream – the ribbon of winds about six miles high in the atmosphere above the North Atlantic Ocean – is one of them. Winds here are currently exceeding 200 miles per hour – their strength is related to the stark temperature contrast between the cold airflow in the eastern US and the much warmer air over the western North Atlantic.
This powerful jet provided the energy for the storm's development and is also the cause of its race towards Britain across the North Atlantic. Storm Éowyn came to life off the east coast of the US on Wednesday, January 22 and will have traveled more than 2,000 miles before arriving off the coast of western Scotland on Friday afternoon.
Storm Éowyn's low-pressure center crossed the jet stream from south to north on its way, an ideal track for explosive development.
The heavy rainfall in Eowyn as it flows towards Britain is due to another key ingredient for the development of explosive storms: deep clouds within the storm that generate energy when their water condenses. These clouds are fueled by strong heat and moisture fluxes from the warm ocean surface, and scientists have observed record warm surface temperatures in the North Atlantic Ocean in recent years.
The role of climate change
When a storm like Eowyn occurs, people think about the role of climate change in fueling its strength. Our experiences with future storms will depend on the tracks these storms typically follow and how that affects their intensity. Stormy weather is of course not unusual in autumn and winter over the British Isles and it would take detailed research to attribute the strength of a specific storm to climate change.
To date, observed trends in storminess have not provided a conclusive link to climate change. The latest assessment report from the Intergovernmental Panel on Climate Change, experts on all aspects of climate change, convened by the United Nations, states that there is “low confidence” toward trends in the number and intensity of extratropical storms ( that have formed over the past century outside the warm band around Earth's equator.
One reason it's difficult to make this connection is that the storm's position and variability are highly dependent on the jet stream, and its position varies widely from day to day, week to week, and even beyond. Large-scale climate patterns such as the El-Niño Southern Oscillation and North Atlantic Oscillation, and sea surface temperature and sea ice extent are also likely to be important factors.
Despite this uncertainty, there are indications that winter storms may become more frequent and more clustered in the future (such that multiple storms occur within a few days of each other), which could increase their overall impact. The frequency of storms with extreme winds may also increase. It is very likely that precipitation will increase because a warmer atmosphere can hold more moisture.
Another thing that could change about intense storms in the future is their tendency to develop “sting jets.” Sting jets are descending air currents that can produce particularly destructive surface winds, such as the Great October Storm, Storm Eunice and Storm Ciarán. Stingjets have a short lifespan and occur in very small areas, making them difficult to predict and identify.
There is speculation as to whether a stab jet landed during Storm Éowyn. Post-event verification is required. Although the overall impact on wind speed is uncertain, the small number of studies that have considered stab jets in future cyclones have predicted an increase in their likelihood.
Cyclones that can produce stab jets also tend to exhibit stronger cloud cover, consistent with the hypothesis that the intense storms of the future will be influenced by our hotter and wetter atmosphere.
(Author: Suzanne Gray, Professor of Meteorology, University of Reading and Ambrogio Volonté, Senior Research Fellow in Meteorology, University of Reading)
(This article is republished from The Conversation under a Creative Commons license. Read the original article.)
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