Changes in General Atmospheric Circulation in the Northern Hemisphere in 1998–2018

Abstract

The analysis of systematic changes in the Northern Hemisphere 500 hPa geopotential height field is performed. The dataset of the 5-day mean values of 500 hPa geopotential height during 1998–2018 is used for this purpose and is represented by the coefficients of its expansions in spherical functions. It is found that the hemispheric mean value of 500 hPa geopotential height increased by 1.0–2.0 dam during the analyzed 20-year period depending on a season. The west-to-east propagation of air particles in the mid-latitudes systematically weakened in the cold season (January, October) but increased in the warm season (April, July). A small negative trend in the amplitudes of some ultralong waves is detected. This can facilitate a weakening of the planetary blocking of zonal circulation. Besides, a weak positive trend in the amplitudes of some synoptic waves is found, which can favor an increase in the cyclone activity.