Scientists reveal non-linear response of blockage of Urals to warming arctic in early winter
Chinese Academy of Sciences
The blockade of the Urals (UB), a persistent and large-scale high pressure system around the Ural Mountains, is intimately linked to cold waves in Eurasian mid-latitudes. Long-lived, quasi-stationary BU generally leads to extremely cold temperatures over mid-latitude Eurasia.
Short-lived westward moving BUs are found in recent winters with extremely low sea ice conditions over the Barents-Kara Seas (BKS), contrary to previous notions.
CHEN Xiaodan, a Ph.D. The student and her advisor, Professor LUO Dehai of the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences, studied UB’s responses to early BKS warming of winter with different warming forces.
Their results were published in Climate Journal.
“We are impressed with a striking nonmonotonic response from UB and attempt to reveal the underlying role of the stratospheric pathway in zonal movement of UB in this study,” CHEN said.
Using a set of atmospheric circulation simulations, they found that the persistence of BU over the Ural Mountains was first prolonged and then shortened as the warming of the BKS gradually strengthened.
In the case of a weak warming of the BKS, the southern gradients of bottom temperature and potential vorticity were reduced around the Ural Mountains but increased in the upstream area, resulting in low energy dispersion and less of retrogression of the UB, and consequently stationary UB. In this case, the stratospheric pathway is inactive; thus, background circulation changes and UB responses are primarily attributed to the tropospheric pathway.
As the BKS continues to warm, the amplified tropospheric planetary waves propagate upward in the stratosphere and weaken the stratospheric polar vortex at the onset of winter, which is distinct from the case of weak warming of the BKS. The downward influence of the weakened stratospheric polar vortex leads to eastern anomalies in mid-latitudes from the North Atlantic to Europe in winter, which favors the westward movement of the BU.
After the artificial stopping of the stratospheric path in the simulations, the westward movement of the BU disappears in the event of strong heating of the BKS. In other words, the bottom circulation response resulting from the tropospheric pathway favors the long-lived and quasi-stationary BUs, while the downward influence of the stratospheric pathway favors the westward displacement of the BUs.
These results may have important implications for winter weather forecasting in the future.