Abstract
Elevated stratopauses are typically associated with prolonged disturbed
conditions in the northern hemisphere polar winter. MIPAS and MLS
observed a short-lived and highly zonally asymmetric stratopause at
mesospheric altitudes in November 2009, the earliest in the season
reported so far. The Arctic climatological winter stratopause vanished
and MIPAS and MLS measured temperatures of 260K at 82\,km
and 250K at 75\,km, respectively, in a region smaller
than in typical mid-winter elevated stratopause events. Planetary wave
activity was initially high. Zonal mean zonal winds and the poleward
temperature gradient northward of 70$^\circ$N stayed
reversed during 7 days. The mesosphere did not cool during that phase.
Wave activity dropped until the eastward stratospheric zonal winds
resumed, a strong vortex restored in the mesosphere, and the stratopause
emerged at a high altitude. An enhanced downward transport followed. It
took the stratopause 9 days to move down to its typical winter
altitudes.