Dynamical changes in the Arctic and Antarctic stratosphere during spring

Short- and long-term changes in the intensity and persistence of the Arctic and Antarctic stratospheric polar vortices during spring have been analyzed, using NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalyses. For the Arctic the results confirm the existence of low frequency variability in the winter stratosphere. During the 1980s and early to mid-1990s the northern hemisphere (NH) polar vortex was intensified in spring and broke up late. Since the late 1990s however, major stratospheric warmings occurred more frequently, so that the polar vortex in spring still intensified in March but with a smaller magnitude. As some of the major warmings occurred early in winter, the polar vortex was able to recover leading to late breakup dates in spite of the dynamical disturbances. In the long-term, there is no statistically significant change in Arctic vortex intensity or lifetime. In the Antarctic, the significant intensification of the polar vortex found in the 1980s and 1990s has been considerably reduced due to an unexpected enhancement of dynamical activity in southern hemisphere (SH) winter since 2000, masking the significant increase in polar vortex persistence found for the period 1979-1999. Still on the long-term, the Antarctic vortex shows a significant deepening and shift towards later spring transitions.