The Connections between the Establishment and Maintenance of Ural Blockings in Winter and Intra-seasonal Oscillation of Geopotential Height

Abstract

The Ural blocking high （UB） in winter is an important influence system leading to widespread cold snap in China.Exploring exploring the connections between its establishment and maintenance processes and intra-seasonal oscillations of geopotential height can provide reference factors for extended range forecasting and short-term climate prediction.By using the ERA5 daily reanalysis data provided by European Centre for Medium-Range Weather Forecasts （ECMWF） from 1979/1980 to 2019/2020， 114 winter UB events were selected by using a combined subjective and objective method， in which the cumulative number of blocking high days reached 591.The connections between the Ural blockings and the intra-seasonal oscillations of the 500 hPa geopotential height were analyzed by using power spectrum analysis， correlation analysis， synthesis analysis and other statistical methods.The results show that： （1） Geopotential height over the Ural Mountains has significant periods of 10~20 days， 30 days and 45 days during the last 41a winter.Through multi-scale analysis， we find that different time scale components of the geopotential height contribute differently during the establishment and maintenance processes of the Ural blockings， where the largest contribution to the establishment of Ural blocking highs is the quasi-biweekly geopotential height anomaly （10~20 days）， and the maintenance of blocking high events is determined by intra-seasonal oscillations with a scale of 20~80 days.During the establishment and maintenance processes of blockings， the quasi-biweekly geopotential height anomaly propagates from west to east， while the intra-seasonal oscillations of the geopotential height anomaly have no significant propagation.（2） According to the time intervals between the occurrences of two events， blockings are classified into continuous blocking high events and other blocking high events.Through multiple case synthesis analysis and typical individual case analysis， we find that for continuous blocking high events， the intra-seasonal oscillations of the geopotential height anomaly contribute most to their establishment and maintenance processes， but have no significant propagation.The geopotential height anomaly shows a westward propagating signal on the quasi-biweekly scale.The connections between other non-continuous blockings and atmospheric circulation at different time scales are similar to the results of all blocking high events.

Keywords

• ural blockings
• geopotential height
• atmospheric intra-seasonal oscillation