The stratospheric major warming of early December 1987

The NMC observations of temperature and geopotential carried out during the stratospheric major warming event of early December 1987 are analyzed. The December 1987 warming event displayed features typical of other major warmings, including vortex displacement, erosion, and splitting and, as such, was the earliest major warming yet observed in the Northern Hemisphere winter. The December 1987 major warming was unusual in that it took place during the (deep) westerly phase of the equatorial quasi-biennial oscillation and was not preceded by any significant preconditioning of the extratropical vortex. It is suggested that this unusually early major warming was mainly attributable to an anomalously large tropospheric forcing.