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Abstract. Extraction of wind and temperature information from stratospheric ozoneassimilation is examined within the context of the Navy Global EnvironmentalModel (NAVGEM) hybrid 4-D variational assimilation (4D-Var) data assimilation (DA) system. Ozone can improvethe wind and temperature through two different DA mechanisms: (1) through the“flow-of-the-day” ensemble background error covariance that is blendedtogether with the static background error covariance and (2) via the ozonecontinuity equation in the tangent linear model and adjoint used forminimizing the cost function. All experiments assimilate actual conventionaldata in order to maintain a similar realistic troposphere. In thestratosphere, the experiments assimilate simulated ozone and/or radianceobservations in various combinations. The simulated observations areconstructed for a case study based on a 16-day cycling truth experiment (TE),which is an analysis with no stratospheric observations. The impact of ozoneon the analysis is evaluated by comparing the experiments to the TE for thelast 6 days, allowing for a 10-day spin-up. Ozone assimilation benefits thewind and temperature when data are of sufficient quality and frequency. Forexample, assimilation of perfect (no applied error) global hourly ozone dataconstrains the stratospheric wind and temperature to within ∼  2 m s −1 and ∼  1 K. This demonstrates that there isdynamical information in the ozone distribution that can potentially be usedto improve the stratosphere. This is particularly important for the tropics,where radiance observations have difficulty constraining wind due tobreakdown of geostrophic balance. Global ozone assimilation provides thelargest benefit when the hybrid blending coefficient is an intermediate value(0.5 was used in this study), rather than 0.0 (no ensemble background errorcovariance) or 1.0 (no static background error covariance), which isconsistent with other hybrid DA studies. When perfect global ozone isassimilated in addition to radiance observations, wind and temperature errordecreases of up to ∼  3 m s −1 and ∼  1 K occur in thetropical upper stratosphere. Assimilation of noisy global ozone (2 %errors applied) results in error reductions of ∼  1 m s −1 and ∼  0.5 K in the tropics and slightly increased temperature errors inthe Northern Hemisphere polar region. Reduction of the ozone samplingfrequency also reduces the benefit of ozone throughout the stratosphere, withnoisy polar-orbiting data having only minor impacts on wind and temperaturewhen assimilated with radiances. An examination of ensemblecross-correlations between ozone and other variables shows that a singleozone observation behaves like a potential vorticity (PV) “charge”, or amonopole of PV, with rotation about a vertical axis and vertically orientedtemperature dipole. Further understanding of this relationship may help indesigning observation systems that would optimize the impact of ozone on thedynamics.

Extraction of wind and temperature information from hybrid 4D-Var assimilation of stratospheric ozone using NAVGEM