Odd nitrogen species play an important role in the stratospheric ozone balance through catalytic ozone destruction. A layer of strongly enhanced NO2 was detected in the north polar mesosphere by the GOMOS/ENVISAT stellar spectrometer in mid-January 2004. Large NO2 enhancements in the polar winter mesosphere have been previously reported by several authors and have been attributed to NO production by solar proton or by energetic electron precipitations. The simultaneous occurrence of an intense mesospheric warming observed by the SABER/TIMED instrument indicates that a strong air descent occurred in the polar region, transporting a large quantity of NO from the upper mesosphere-lower thermosphere to the lower mesosphere. The proposed mechanism may have a significant contribution to the budget of polar stratospheric ozone.