edu.ucar.opensky::articles:19605 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-26T02:34:56.580565 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d71r6s9v Quantifying the causes of differences in tropospheric OH within global models 2017-02-16T00:00:00Z publication https://n2t.org/ark:/85065/d71r6s9v https://doi.org/10.1002/2016JD026239 Nicely, J. M. author Salawitch, R. J. author Canty, T. author Anderson, D. C. author Arnold, S. R. author Chipperfield, M. P. author Emmons, Louisa K. author Flemming, J. author Huijnen, V. author Kinnison, Douglas E. author Lamarque, Jean-François author Mao, J. author Monks, S. A. author Steenrod, S. D. author Tilmes, Simone author Turquety, S. author UCAR/NCAR - Library publisher The hydroxyl radical (OH) is the primary daytime oxidant in the troposphere and provides the main loss mechanism for many pollutants and greenhouse gases, including methane (CH4). Global mean tropospheric OH differs by as much as 80% among various global models, for reasons that are not well understood. We use neural networks (NNs), trained using archived output from eight chemical transport models (CTMs) that participated in the Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols and Transport Model Intercomparison Project (POLMIP), to quantify the factors responsible for differences in tropospheric OH and resulting CH4 lifetime (tau(CH4)) between these models. Annual average tau(CH4), for loss by OH only, ranges from 8.0 to 11.6 years for the eight POLMIP CTMs. The factors driving these differences were quantified by inputting 3-D chemical fields from one CTM into the trained NN of another CTM. Across all CTMs, the largest mean differences in tCH4 (Delta tau(CH4)) result from variations in chemical mechanisms (Delta tau(CH4) = 0.46 years), the photolysis frequency (J) of O-3 -> O(D-1) (0.31 years), local O-3 (0.30 years), and CO (0.23 years). The Delta tau(CH4) due to CTM differences in NOx (NO + NO2) is relatively low (0.17 years), although large regional variation in OH between the CTMs is attributed to NOx. Differences in isoprene and J(NO2) have negligible overall effect on globally averaged tropospheric OH, although the extent of OH variations due to each factor depends on the model being examined. This study demonstrates that NNs can serve as a useful tool for quantifying why tropospheric OH varies between global models, provided that essential chemical fields are archived. 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 2017 American Geophysical Union. None eng geoscientificInformation