Carbon Dioxide in the Polar Stratosphere from AIM/SOFIE Measurements

Carbon dioxide (CO₂) is an important greenhouse gas and it is key to the energetics and dynamics of the stratosphere and mesosphere. Distributions of the CO₂ volume mixing ratios (VMR) in the polar stratosphere (from 30 up to ~ 60 km) have been measured from the CO₂ 4.3 μm band by Solar Occultation for Ice Experiment (SOFIE) onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite since 2007. This is the first time that the CO₂ VMR has been retrieved from space in the 30-60 km altitude range. This data set spans from April 2007 to current date. The retrieval of CO₂ is performed by using a non-local thermodynamic equilibrium (non-LTE) scheme and refraction derived temperature. In this paper we present SOFIE CO₂ VMR time series and its seasonal variation. The agreement between the SOFIE CO₂ trend and Mauna Loa surface CO₂ trend suggests that the retrieval algorithm is reliable. Seasonal variation of CO₂ is compared with simulations from the Specified Dynamics version of the Whole Atmosphere Community Climate (SD-WACCM). The CO₂ distribution is driven by the general circulation, ascending in southern summer (March to May) polar region, and descending in southern winter (July, August and September). In northern hemisphere, Stratospheric sudden warmings (SSWs) cause strong CO₂ variations. At last, we report the variation of CO₂ and temperature during two SSWs in 2009 and 2013, and discuss the potential dynamical mechanisms with the help of SD-WACCM.