Elevated Humidity in the Stratosphere as a Gain Factor of Ozone Depletion in the Arctic According to Aura MLS Observations

The analysis of Aura MLS data showed that the temperature in the Arctic stratosphere was much lower than normal throughout the period from January to March 2011 in the altitude range 20–35 km. That led to a considerable spread of polar stratospheric clouds (PSCs), which were formed most intensely in periods and at altitudes of minimal temperatures (maximal temperature drop below PSC formation threshold). The main ozone losses were observed in March. They were due to a photochemical release of chlorine that avoided deactivation in view of the nitrogen deficit caused by denitrification in the course of frequent dehydration events indicated by oscillations of the altitude of maximal humidity distortion. Elevated humidity in the stratosphere had raised the threshold temperature of formation of PSCs that persisted until late March; this promoted the chlorine activation and, thereby, delayed the chlorine deactivation, resulting in an even higher level of overall ozone losses during March 2011.