The Effects of a 1998 Observing System Change on MERRA‐2‐Based Ozone Profile Simulations. Issue 13 (4th July 2019)

• Record Type: Journal Article
• Authors: Stauffer, Ryan M.; Thompson, Anne M.; Oman, Luke D.; Strahan, Susan E.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 13(2019)
• Page Start: 7429
• Page End: 7441
• Publication Date: 2019-07-04
• Subjects: model evaluation -- MERRA‐2 -- ozonesonde -- CTM -- Replay; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2019JD030257
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Model simulations of ozone (O3 ) driven by meteorological reanalyses are useful for filling observational gaps and interpreting observed O3 variability and trends. However, the transport circulation of reanalysis products is impacted by changes to the observing system (the data assimilated into the reanalyses). We examine the impacts of these changes on simulated O3 from two models, Global Modeling Initiative (GMI) Chemistry Transport Model (GMI CTM) and Modern‐Era Retrospective Analysis for Research Applications version 2 (MERRA‐2) GMI Replay (M2 GMI Replay) simulation, using observations from global ozonesondes (>50, 000 profiles) and satellites from 1980 to 2016. Both models are constrained by meteorology from the NASA MERRA‐2 reanalysis, and both use versions of NASA's GMI chemical mechanism. We focus on an observing system change affecting simulated O3 after 1998, associated with the assimilation of temperature and humidity data from new microwave profiling satellites. A large post‐1998 O3 increase, mainly confined to 15–20‐km altitude, of ~10 Dobson units (DU) in midlatitudes occurs in the GMI CTM, worsening the bias compared to observations. In contrast, an increase in M2 GMI Replay simulation O3 of ~10 DU is observed only near −60° latitude, reducing the bias compared to observations. The GMI CTM O3 high biases display a Quasi‐Biennial Oscillation (QBO)‐like periodicity that result from excessive transport from the tropical stratosphere to the midlatitude lower stratosphere during the QBO westerly phase. We quantify O3 discontinuities caused by MERRA‐2 observing system changes and demonstrate how the MERRA‐2 Global Modeling Initiative Replay simulation dampens the effects of these changes and QBO‐driven artifacts on simulated lower stratospheric and total O3 . We caution against using simulations driven by a reanalysis to derive multidecadal O3 trends, especially prior to 1998. Key Points: Ozonesonde and satellite observations are used to evaluate two 1980–2016 model simulations of O3 driven by MERRA‐2 meteorology An observing system change in 1998 that is known to affect MERRA‐2 meteorology causes major O3 discontinuities in both simulations The 1998 change impacts the stratosphere‐to‐troposphere O3 transport differently in the simulations, improving one and worsening the other