Transport of methane in the stratosphere associated with the breakdown of the Antarctic polar vortex



[1] Transport of methane associated with the polar vortex and its breakdown was observed by the data from the Improved Limb Atmospheric Spectrometer (ILAS) during November and December of 1996. The zonal mean mixing ratio in the middle stratosphere at high latitudes in the Southern Hemisphere increased rapidly during the period, and the vertical gradient of methane sometimes showed an unusual reversal. The reversal of the vertical gradient confirms that the erosion of the vortex and the subsequent breakdown occurs in the upper stratosphere first and descends with time. The variation of the tracer mixing ratio was investigated with respect to the boundary of the polar vortex. The mixing ratios inside and outside of the polar vortex evolved with distinctive patterns with time. The small difference in methane between inside and outside of the vortex in the upper stratosphere is presumably a result of the vortex erosion prior to November. Also, the small difference between inside and outside of the vortex in the lower stratosphere confirms the weak barrier effect of the polar vortex on that altitude. High concentrations of methane observed inside the vortex show mixing of lower-latitude air into the vortex. An RDF calculation confirms the behavior of methane transport into the vortex.