ERL." href="http://images.iop.org/objects/erw/news/12/4/27/pic1.jpg">Geopotential heights
Interference between the pattern’s centres and atmospheric waves can enhance wave amplitude and upward wave activity fluxes into the stratosphere, which is favourable for triggering sudden stratospheric warmings. Understanding major sudden stratospheric warmings in more detail offers insight into a range of climate behaviours.
"When a major sudden stratospheric warming occurs, it causes not only abrupt changes in the polar stratospheric circulations, but also rapid changes in the distribution of ozone concentration in the stratosphere – more ozone will be transported from the source region in the tropics into the high polar latitudes," Benkui Tan of Peking University told environmentalresearchweb.
There are also further changes in weather to consider, as the anomalous circulation of a major sudden stratospheric warming can propagate downwards into the troposphere over a period of a few weeks. "A negative phase of the Arctic Oscillation forms near the surface, which leads to a strong anomalous warm Arctic and a strong anomalous cold Eurasia," Tan added.
The study – published in Environmental Research Letters (ERL) – allowed Tan and his colleague Ying Dai to look more closely into the ENSO modulation. This included examining the dynamics behind an apparent inconsistency observed between seasonal-mean and extreme stratospheric responses.
"Major sudden stratospheric warmings are found to occur as often during El Niño as during La Niña winters, which is nearly twice as often as during ENSO-neutral winters," said Tan. "This is contrary to the usual thought that major sudden stratospheric warmings should occur much more often during El Niño than during La Niña, as the numerical modelling also suggests."
The researchers point to a number of influencing factors such as the partial contribution of eastern Pacific blockings during La Niña winters to the increase in frequency of sudden stratospheric warmings. Taking these, and other observations recorded by the team, into account could help predict the onset of sudden stratospheric warmings and the follow-on effects highlighted above.
The scientists believe their work has the potential to improve extended-range and seasonal forecasts of surface weather and climate in northern Hemisphere extratropical regions.
Related links
- The western Pacific pattern precursor of major stratospheric sudden warmings and the ENSO modulation Ying Dai and Benkui Tan 2016 Environ. Res. Lett. 11 124032
- ERL