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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-802
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
04 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Extraction of wind and temperature information from hybrid 4D-Var assimilation of stratospheric ozone using NAVGEM
Douglas R. Allen, Karl W. Hoppel, and David D. Kuhl Remote Sensing Division, Naval Research Laboratory, Washington, DC, USA
Abstract. Extraction of wind and temperature information from stratospheric ozone assimilation is examined within the context of the Navy Global Environmental Model (NAVGEM) hybrid 4D-Var data assimilation (DA) system. Ozone can improve the winds and temperatures through the two different DA mechanisms. First, through the flow-of-the-day ensemble background error covariances that are blended together with the static background error covariance. Second, via the ozone continuity equation in the tangent linear model and adjoint used for minimizing the cost function. All experiments assimilate actual conventional data and satellite-derived wind vectors in order to maintain nearly the same realistic troposphere. In the stratosphere, the experiments assimilate simulated ozone and/or radiance observations in various combinations. The simulated observations are taken from a 16-day truth experiment (TE), which is an analysis with no stratospheric observations. The impact of ozone on the analysis is evaluated by comparing the experiments to the TE. Ozone assimilation is found to benefit the winds and temperatures when data are of sufficient quality and frequency. For example, global hourly ozone data with no error constrains the stratospheric winds and temperature to within ~2 m s−1 and ~1 K, respectively. This demonstrates that there is dynamical information in the ozone distribution that can potentially be used to improve the stratosphere. This is particularly important for the tropics, where radiance observations have difficulty constraining winds due to their broad weighting functions and breakdown of geostrophic balance. Global ozone assimilation provides the largest benefit when the hybrid blending coefficient is an intermediate value (0.5 was used in this study), rather than 0.0 (no ensemble background error covariances) or 1.0 (no static background error covariances), which is consistent with other hybrid DA studies. Reduction of the ozone sampling frequency, addition of observational noise, or inclusion of radiance observations all reduce the benefit of ozone. For example, a single polar-orbiting ozone measurement set with realistic errors has no significant impact on the wind analysis when a full suite of radiance observations is also assimilated. An examination of cross-correlations between ozone and other variables shows that a single ozone observation behaves like a potential vorticity (PV) charge, or a monopole of PV, with rotation about a vertical axis and vertically oriented temperature dipole. Further understanding of this relationship may help in designing observation systems that would optimize the impact of ozone on the dynamics.

Citation: Allen, D. R., Hoppel, K. W., and Kuhl, D. D.: Extraction of wind and temperature information from hybrid 4D-Var assimilation of stratospheric ozone using NAVGEM, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-802, in review, 2017.
Douglas R. Allen et al.
Douglas R. Allen et al.
Douglas R. Allen et al.

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Short summary
This study examines whether ozone data in the stratosphere (10–50 km altitude) can be used to benefit weather forecasts. The approach involves creating simulated ozone data and assimilating these into the U.S. Navy’s global weather model. Key findings are that assimilation of dense and accurate ozone data markedly benefits winds and temperature. However, the benefit is small when realistic ozone data are assimilated along with currently available microwave and infrared sounding measurements.
This study examines whether ozone data in the stratosphere (10–50 km altitude) can be used to...
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