Impact of the 2018 major sudden stratospheric warming on weather over the midlatitude regions of Eastern Europe and East Asia

Abstract

The impact of the Arctic major sudden stratospheric warming (SSW) in 2018 on regional cold weather in the northern midlatitudes is analyzed. Data from temperature observations in East Asia (Changchun, Northern China) and Eastern Europe (Kharkiv, Northern Ukraine) and NCEP–NCAR and ERA5 reanalyses are used. The variability of the vertical meridional profiles of temperature, temperature anomalies, vertical velocities and geopotential height during two strong surface cooling events is compared. Weather anomalies in Changchun and Kharkiv appeared under strong vortex conditions with wave 1 dominance (the pre-SSW period in January) and during vortex perturbation and split due to intensification of wave 2 (major SSW in February), respectively. The results show that the positive stratospheric temperature anomaly migrated both downward to the lowermost stratosphere at 200–300 hPa, and equatorward, reaching midlatitudes. In both events, the change in the lowermost stratosphere heating was associated with a lowering of the tropopause by 2–3 km in 5–8 days. The descent of the tropopause over Changchun (Kharkiv) was accompanied by a downward air motion so that the midtropospheric layer at altitudes 4–5 km (3–4 km) and temperature − 20 °C to −30 °C (−10 °C to −20 °C) was pushed down to the surface. Observations showed that the surface temperatures during these events dropped by 18 °C in Changchun and by 14 °C in Kharkiv. Besides the altitudinal (3–5 km), the results indicate latitudinal (near the climatological mean edge of the stratospheric polar vortex at ∼60°N) location of the cold air source for the occurrence of extreme low temperatures in East Asia and Eastern Europe. Preliminary analysis of cooling events suggests a relatively smaller contribution of meridional surface transport of cold air to the midlatitudes compared to its downwelling from the midtropospheric level. Possible mechanisms of strong surface cooling in midlatitudes are discussed.