Sudden stratospheric warming effects during the winter 1998/1999

The Arctic stratospheric polar vortex usually forms in autumn, reaches its peak intensity in mid-winter and decays in spring. The earlier breakdown of the polar vortex (from January to March) occurs due to the upward propagation of planetary waves from the troposphere into the stratosphere, leading to the occurrence of sudden stratospheric warmings (SSWs). SSWs are accompanied by a strong displacement or splitting of the polar vortex. In most cases, SSWs occur from late January to March. In this study, we analyze the effects of one of the earliest SSWs which occurred on 18 December 1998. The Arctic polar vortex recovered in February 1999 after its splitting in December 1998 and decayed in late February after the second splitting of the polar vortex.