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| Titel |
Wind extraction potential from ensemble Kalman filter assimilation of stratospheric ozone using a global shallow water model |
| VerfasserIn |
D. R. Allen, K. W. Hoppel, D. D. Kuhl |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 10 ; Nr. 15, no. 10 (2015-05-27), S.5835-5850 |
| Datensatznummer |
250119759
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| Publikation (Nr.) |
 copernicus.org/acp-15-5835-2015.pdf |
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| Zusammenfassung |
| The feasibility of extracting wind information from stratospheric ozone
observations is tested using ensemble Kalman filter (EnKF) data assimilation
(DA) and a global shallow water model that includes advection of an
ozone-like tracer. Simulated observations are created from a truth run (TR)
that resembles the Northern Hemisphere winter stratosphere with a polar
vortex disturbed by planetary-scale wave forcing. Ozone observations mimic
sampling of a polar-orbiting satellite, while geopotential height
observations are randomly placed in space and time. EnKF experiments are
performed assimilating ozone, height, or both, over a 10-day period. The DA
is also implemented using two different pairs of flow variables: zonal and
meridional wind (EnKF-uv) and stream function and velocity potential
(EnKF-ψχ). Each experiment is tuned for optimal localization
length, while the ensemble spread is adaptively inflated using the TR. The
experiments are evaluated using the maximum wind extraction potential (WEP).
Ozone only assimilation improves winds (WEP = 46% for EnKF-uv, and 58%
for EnKF-ψχ), but suffers from spurious gravity wave generation.
Application of nonlinear normal mode initialization (NMI) greatly reduces
the unwanted imbalance and increases the WEP for EnKF-uv (84%) and
EnKF-ψχ (81%). Assimilation of only height observations also
improved the winds (WEP = 60% for EnKF-uv, and 69% for EnKF-ψχ), with much less imbalance compared to the ozone experiment. The
assimilation of both height and ozone performed the best, with WEP
increasing to ~87% (~90% with NMI) for
both EnKF-uv and EnKF-ψχ, demonstrating that wind extraction from
ozone assimilation can be beneficial even in a data-rich environment. Ozone
assimilation particularly improves the tropical winds, which are not well
constrained by height observations due to lack of geostrophy. |
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