Two Types Of Boreal Wintertime Blocking Highs Around Ural Mountains And Their Associated Dynamic Features

Based on the Japanese 55-year reanalysis dataset,this study identifies 85 blocking high events around the Ural Mountains(UBHs)during the period from 1958 to 2018.According to the influence on the surface air temperature at 2 m(SAT)over the middle and lower reaches of the Yangtze River(YR),the UBHs are classified into the cold type,neutral type and warm type.The cold type is the negative anomaly of SAT in the middle and lower reaches of the Yangtze River,whereas the warm type is the opposite.Although the cold type is the dominant type(51),the number of warm-type UBHs is not negligible(21).The cold UBH event and the warm UBHs occurred in the east and west respectively.The mean duration of warm-type UBHs is 6.5 days,the standard deviation is 1.9,the mean duration of cold-type UBHs is 8.6 days,and the standard deviation is 3.7.This indicates that the duration of cold-type UBHs is longer than that of warmtype UBHs,and the duration of cold-type UBHs deviates greatly from the average duration.The cold type is characterized by a northeast-southwest tilting dipole pattern of the height anomalies over the Eurasian continent,with the anticyclonic anomalies prevailing to the east of the Ural Mountains,which is in contrast to the zonal dipole pattern in the warm type with the anticyclonic anomalies prevailing to the west of the Ural Mountains.Regarding the maintenance of the primary anticyclonic anomalies,the transient eddy feedback forcing plays a more important role for the cold type,while the injection of Rossby wave packets becomes more influential for the warm type.Rossby wave packets tend to propagate along an arc-shape path over the Eurasian continent for the cold-type UBHs,while they generally propagate eastward for the warm-type UBHs.Corresponding to the upper-level height anomalies,the Siberian high is enhanced in the cold type and weakened in the warm type,accounting for the positive SAT anomalies and the negative SAT anomalies over the YR,respectively.