Carbon dioxide trends in the mesosphere and lower thermosphere

Abstract

We investigated trends of carbon dioxide (CO2) in the upper atmosphere, using data from the Atmosphere Chemistry Experiment Fourier Transform Spectrometer and from the Sounding of the Atmosphere using Broadband Emission Radiometry. Recent analyses of these measurements had indicated that CO2 above approximately 90 km appeared to be increasing about twice as fast as it was in the lower atmosphere. Models could not reproduce this differential CO2 trend, calculating instead that the proportional CO2 increase is approximately constant with altitude. We found three issues with the methodologies used to derive trends from CO2 profiles: the way that seasonal changes and sampling are accounted for in the analysis, referred to as deseasonalizing; the registration of profiles in pressure versus altitude coordinates; and data quality indicators. Each of these can have significant effects on the derivation of trends. We applied several deseasonalizing procedures, using both pressure and altitude coordinates, also used a time series fit without deseasonalizing, and applied data quality filters. The derived trends were approximately constant with pressure or altitude, about 5.5% per decade, consistent with lower atmosphere CO2 trends, and consistent with model calculations. We conclude that the difference between the trend of CO2 above the CO2 homopause and the trend in the lower, well‐mixed atmosphere is not statistically significant.

On Long‐Term SABER CO2 Trends and Effects Due to Nonuniform Space and Time Sampling

“…In addition, there is close resemblance between the vertical profile shapes for the SABER data (blue) and WACCM‐sub (red), although the absolute values do not agree. Furthermore, we should also note that the SABER bimonthly relative trend is about 8% per decade around 1 × 10 −4 mb (110 km), which is consistent (within error bars) with those derived in Qian et al (). We would like to stress that the agreement between our results, when accounting for the 60‐day binning, and Qian et al () rules out the deseasonalization as the cause of the discrepancy, as claimed in Qian et al (; (see Appendix ).…”

“…The SABER instrument description and characteristics, including satellite orbit and the viewing direction, are originally described in Russell et al (), and also briefly reviewed in works already mentioned (e.g., Qian et al, ; Rezac, Kutepov, et al, ; Yue et al, ). The SABER CO 2 VMR data are post‐operationally retrieved simultaneously with temperatures, however, only for daytime conditions (solar zenith angle <80°) as detailed in Rezac, Kutepov, et al ().…”

Long‐Term Trends in the Low‐Latitude Middle Atmosphere Temperature and Winds: Observations and WACCM‐X Model Simulations

“…Trends in the temperature are being reported using the long-term measurements from network of radiosondes (Philipona et al, 2018, and references therein), Rayleigh lidars (Kishore et al, 2014), and satellite observations (Akhil Raj et al, 2018;Huang et al, 2014;Randel et al, 2017, and references therein). Few modeling studies are also made to understand the mechanisms behind the observed changes (Fomichev et al, 2007;Garcia et al, 2007;Lübken et al, 2013;Qian et al, 2017Qian et al, , 2019. From these studies, significant decreasing trend in the zonal wind in the middle mesosphere and no significant trend in the upper mesosphere using network of MF/Meteor radars in the equatorial latitudes is observed.…”

Long‐Term Trends in Tropical (10°N–15°N) Middle Atmosphere (40–110 km) CO2 Cooling

“…Recent results from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) observations showed that the CO 2 vmr trend is ~5%/decade up to ~80 km and ~12% at ~110 km in the latitude range of ±54° during 2002–2014 (Yue et al, ). However Qian et al () found the CO 2 trends of ~5.5%/decade above ~90 km, which are consistent with that of lower atmosphere using the corrected SABER observations for 2002–2016.…”

“…The CO 2 is well mixed in troposphere (~0–15 km) and stratosphere, and the eddy diffusion leads to its constant vmr even up to ~80–90 km. The CO 2 vmr decreases exponentially above this height due to photolysis (CO 2 + hν → CO + O( 1 D) at λ ~ 120–210 nm) and increasing molecular diffusion (e.g., Garcia et al, ; Qian et al, ; Rezac et al, ; Yue et al, ). Recent results from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) observations showed that the CO 2 vmr trend is ~5%/decade up to ~80 km and ~12% at ~110 km in the latitude range of ±54° during 2002–2014 (Yue et al, ).…”