The Large-Scale Atmospheric Circulation Pattern over Asia Associated with Formation of Extremely High Surface Ozone Concentrations in the Region of Tomsk (Western Siberia)

The ERA 5 reanalysis data and the daily average surface ozone concentrations (O 3 ) measured at the TOR station from 1993 to 2020 are used to study the circulation pattern favoring the formation of extremely high ozone concentrations (95th percentile, henceforth О 3 95). All months are characterized by an identical circulation mode accompanied by an increase in the surface air temperature in the area encompassing the ozone concentration measuring station. In addition to the increase in the air temperature, О 3 95 events are characterized by strengthening of the southwesterly component of the wind velocity field. It is also found that these circulation features are associated with the development of meridional properties, probably due to the propagation of waves in the upper troposphere in midlatitudes. The identified circulation mode simultaneously favors the transboundary transport of ozone and its precursors from the southern regions, the enhancement of photochemical O 3 formation, and the occurrence of wildfires.