edu.ucar.opensky::articles:18368 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-26T02:51:31.714191 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d7t72k0s On the secular trend of COx and CO₂ in the lower thermosphere 2016-04-16T00:00:00Z publication https://n2t.org/ark:/85065/d7t72k0s https://doi.org/10.1002/2015JD024553 García, Rolando R. author López-Puertas, M. author Funke, B. author Kinnison, Douglas E. author Marsh, Daniel author Qian, Liying author UCAR/NCAR - Library publisher An analysis of recent observations (2004-2013) made by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument indicate that total carbon (COx = CO + CO₂) has been increasing rapidly in the lower thermosphere, above 10-3 hPa (90 km). The estimated trend (~9% per decade) is about a factor of 2 larger than the rate of increase that can be ascribed to anthropogenic emissions of CO₂ (~5% per decade). Here we investigate whether the observed trends of CO₂ and COx can be reproduced using the Whole Atmosphere Community Climate Model (WACCM), a comprehensive global model with interactive chemistry, wherein vertical eddy diffusion is estimated from a parameterization of gravity wave breaking that can respond to changes in the model climate. We find that the modeled trends of CO₂ and COx do not differ significantly at any altitude from the value expected from anthropogenic increases of CO₂ and that WACCM does not produce significant changes in eddy diffusivity. We show that the discrepancy between model and observations cannot be attributed to uncertainties associated with geophysical noise and instrumental effects, to difficulties separating a linear trend from the 11 year solar signal, or to sparse sampling by ACE-FTS. Estimates of the impact of vertical diffusion on CO₂ in the model indicate that a large increase in Kzz (~30% per decade) would be necessary to reconcile WACCM results with observations. It might be possible to ascertain whether such a large change in vertical mixing has in fact taken place by examining the trend of water vapor in the upper mesosphere. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Copyright 2016 American Geophysical Union. None eng geoscientificInformation