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

Abstract

Abstract. Using data from the Aeronomy of Ice in the Mesosphere (AIM) and Aura satellites, we have categorized the interannual variability of winter-and springtime upper stratospheric methane (CH 4 ). We further show the effects of this variability on the chemistry of the upper stratosphere throughout the following summer. Years with strong wintertime mesospheric descent followed by dynamically quiet springs, such as 2009, lead to the lowest summertime CH 4 . Years with relatively weak wintertime descent, but strong springtime planetary wave activity, such as 2011, have the highest summertime CH 4 . By sampling the Aura Microwave Limb Sounder (MLS) according to the occultation pattern of the AIM Solar Occultation for Ice Experiment (SOFIE), we show that summertime upper stratospheric chlorine monoxide (ClO) almost perfectly anticorrelates with the CH 4 . This is consistent with the reaction of atomic chlorine with CH 4 to form the reservoir species, hydrochloric acid (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 CH 4 air from lower latitudes. Small, but persistent effects on ozone are also seen such that between 1 and 2 hPa, ozone is about 4-5 % higher in summer for the years with the highest CH 4 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. Additionally, these chlorine-controlled ozone decreases, which are seen to maximize after years with strong uninterrupted wintertime descent, represent a new mechanism by which mesospheric 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.

Response to Reviewer #3

“…2 are consistent with similar calculations in Smith et al (2011) and Straub et al (2012), for the general shape of the trajectory and in that the parcels do not originate above approximately 100 km. The parcels at 80 • N arrive from higher altitudes due to a stronger vertical component of the circulation compared to 67 • N. Conversely, the horizontal component of the circulation is stronger at 67 • N and the parcels arriving there originate from lower latitudes compared to those arriving at 80 • N. The magnitude of the TEM wind is larger for the higher altitudes, as is also shown in Smith et al (2011), and the air parcels that arrive above 66 km altitude originate in the summer hemisphere. The parcels that arrive below this altitude, which could be considered as part of the Brewer-Dobson circulation (Brewer, 1949), originate at latitudes closer to the equator.…”

“…The TEM zonal-mean tracer continuity equation has been described in various works (e.g. Garcia and Solomon, 1983;Andrews et al, 1987;Brasseur and Solomon, 2005;Monier and Weare, 2005;Smith et al, 2011):…”

“…The rate of the descent of air above the poles during winter has been an area of interest for some time because it influences the transport of trace gases from the thermosphere to the middle atmosphere (mesosphere and stratosphere; e.g. Plumb et al, 2002;Engel et al, 2006;Smith et al, 2011;Manney et al, 2009). This vertical branch of the meridional circulation can transport gases with high thermospheric volume mixing ratios (VMRs), and change the composition of the middle atmosphere (e.g.…”

“…This vertical branch of the meridional circulation can transport gases with high thermospheric volume mixing ratios (VMRs), and change the composition of the middle atmosphere (e.g. Solomon et al, 1985;Allen et al, 2000;Hauchecorne et al, 2007;Smith et al, 2011;Garcia et al, 2014;Manney et al, 2009;2015;Funke et al, 2014aFunke et al, , b, 2017. The downward transport of nitrogen oxide (NO), produced at around 110 km through energetic particle precipitation (EPP) events (e.g.…”

Assessing the ability to derive rates of polar middle-atmospheric descent using trace gas measurements from remote sensors

“…Randall et al (2009) suggest that, in these cases, VMRs of EPPproduced NO x are controlled more by mesosphere and lower thermosphere (MLT) descent rates than by the structure of the vortex. Siskind et al (2016) found that due to downward transport of methane (CH 4 ) in years with strong, uninterrupted mesospheric descent, summertime upper stratospheric chlorine monoxide (ClO) is about 50 % greater than in years with strong horizontal transport.…”