The long-term trends in blocking events frequencies in the Euro-Atlantic sector of NH midlatitudes

Blocking anticyclones are planetary-scale phenomenon. They typically develop close to the Pacific and Atlantic jet-streams. Blocking anticyclones  usually have a strong impact on weather, not only in the regions they occur, but also in their surroundings, sometimes leading to heat waves in summer and cold spells in winter (Trigo et al., 2004). The strong decrease in ice cover extent and thickness together with accompanying warming in the Arctic caused changes in frequency, persistence and mean localization of blocking anticyclones in the middle and high latitudes of Northern Hemisphere. This paper is aimed on the analysis of spatial and temporal variability of blocking events in the middle and latitudes in the sector 60W to 120E, i.e. in the region where blocking anticyclones have a strong impact on weather in Europe.

The daily values of geopotential at 500 hPa level (G500) from ERA5 dataset acquired from the ECMWF's Meteorological Archival and Retrieval System (MARS) were used. A blocking index based on the modificated Tibaldi and Molteni method was used. In the area extending from 60ºW to 120ºW and from 35ºN to 65ºN, the daily values of blocking index were calculated for each grid point and and the extend of blocking events was extablished. On this basis the frequencies of blocking episodes were assessed as the number of days per month where a blocking event can be identified in the surrounding of selected grids. Then the trends in these frequencies were identified and discussed.

This research was funded by National Science Center (NCN), grant number 2019/33/B/ST10/01136