Increased humidity in the stratosphere as a possible factor of ozone destruction in the Arctic during the spring 2011 using Aura MLS observations

Analysis of data from Microwave Limb Sounder (MLS) on Aura satellite showed that the temperature in the stratosphere of the Arctic was much lower than normal during the entire period of January-March 2011 in the altitude range of 20-35 km. This had led to a considerable spread of polar stratospheric clouds (PSCs) that presumably formed most intensely in periods and at heights of minimal temperatures (maximal temperature drops below the PSC formation threshold). Water vapour and ozone deviations from multiyear averages are found to correlate strongly both between themselves and with deviations in the temperature. The largest ozone losses were observed in March, probably due to a photochemical release of chlorine that avoided deactivation in view of nitrogen deficit caused by denitrification. Presumably, elevated humidity in the stratosphere had raised the threshold 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.