Impact of Greenland blocking on midlatitude extreme cold weather:Modulation of Arctic sea ice in western Greenland

In this study,we analyzed 1979–2019 daily ERA-Interim reanalysis data in winter and performed atmospheric circulation experiments to examine the modulation of Arctic sea ice in western Greenland(Baffin Bay,Davis Strait,and the Labrador Sea,BDL)on winter Greenland blockings.It is found that low BDL sea ice and high BDL surface temperature favor frequent,long-lived,westward-moving Greenland blockings in winter,which cause frequent and strengthening cold surges over the mid-eastern United States.In contrast,high BDL sea ice and low BDL surface temperature favor short-lived,less frequent and quasi-stationary Greenland blockings,mainly leading to cold anomalies in North Europe.Low wintertime BDL sea ice reduces the background potential vorticity meridional gradient(PVy)and zonal wind over the mid-high latitudes of the North Atlantic,which enhances the nonlinearity of Greenland blocking,accelerates the phase speed of its westward movement,and weakens its energy dispersion,thus favoring the occurrence and persistence of Greenland blocking.High BDL sea ice strengthens the background PVyand zonal wind in the mid-high latitudes of the North Atlantic,which weakens the nonlinearity and movement of Greenland blocking,enhances its energy dispersion,and thus suppresses the occurrence and persistence of Greenland blocking and its retrogression.A set of atmospheric circulation experiments supports the above results based on the reanalysis dataset.

The influence of extreme cold ambient temperature on out of hospital cardiac arrest: A systemic review and meta-analysis

Objective:Many researches have demonstrated the effects of the extreme cold ambient temperature on the risk of out-of-hospital cardiac arrest(OHCA);yet,the results have been inconsistent.We performed a meta-analysis to evaluate whether extreme cold ambient temperature is related to OHCA.Methods:We searched for time-series studies reporting associations between extreme cold ambient temperature and OHCA in PubMed,web of science and Cochrane database.Results:Six studies involving 2337403 cases of OHCA were qualified for our meta-analysis.The odds ratio(OR)of OHCA was significantly increased in extreme cold weather(defined as the 1st or 5th centile temperature year-round)compared to reference temperature(as the 25th centile temperatures or daily mean temperature with minimum risk of OHCA)(OR=1.49,95%CI 1.18-1.88).The subgroup analysis for the elderly and the female failed to detect the influence of extreme cold weather on OHCA,the ORs are 1.25(95%CI 0.89-1.75)and 1.19(95%CI 0.87-1.64),respectively.Conclusion:The risk of OHCA is significantly higher in extreme cold ambient temperatures than in reference temperature,according to a relative temperature scale with percentiles of the region-specific temperature distribution.