Persistence of upper stratospheric winter time tracer variability into the Arctic spring and summer

Abstract. Using data from the Aeronomy of Ice in the Mesosphere (AIM) and the Aura satellites, we have categorized the interannual variability of winter and spring time upper stratospheric CH4. We further show the effects of this variability on the chemistry of the upper stratosphere throughout the following summer. Years with strong mesospheric descent followed by dynamically quiet springs, such as 2009, lead to the lowest summertime CH4. Years with relatively weak descent, but strong springtime planetary wave activity, such as 2011, have the highest summertime CH4. By sampling the Aura Microwave Limb Sounder according to the occultation pattern of the AIM Solar Occultation for Ice Experiment, we show that summertime upper stratospheric ClO almost perfectly anticorrelates with the CH4. This is consistent with the reaction of atomic chlorine with CH4 to form the reservoir species, HCl. The summertime ClO for years with strong, uninterrupted mesospheric descent is about 50 % greater than in years with strong horizontal transport and mixing of high CH4 air from lower latitudes. Small, but persistent effects on ozone are also seen such that between 1–2 hPa, ozone is about 4–5 % higher in summer for the years with the highest CH4 relative to the lowest. This is consistent with the role of the chlorine catalytic cycle on ozone. These dependencies may offer a means to monitor dynamical effects on the high latitude upper stratosphere using summertime ClO measurements as a proxy. Also, these chlorine controlled ozone decreases, which are seen to maximize after years with strong uninterrupted wintertime descent, represent a new mechanism by which mesosospheric descent can affect polar ozone. Finally, given that the effects on ozone appear to persist much of the rest of the year, the consideration of winter/spring dynamical variability may also be relevant in studies of ozone trends.