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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D23103, doi:10.1029/2006JD007673, 2007

Stratospheric transport using 6-h-averaged winds from a data assimilation system

Steven Pawson

Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA


Ivanka Stajner

Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Science Applications International Corporation, Beltsville, Maryland, USA


S. Randolph Kawa

Atmospheric Chemistry and Dynamics Branch, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA


Hiroo Hayashi

Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore, Maryland, USA


Wei-Wu Tan

Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Science Applications International Corporation, Beltsville, Maryland, USA


J. Eric Nielsen

Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Science Systems and Applications Inc., Lanham, Maryland, USA


Zhengxin Zhu

Atmospheric Chemistry and Dynamics Branch, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Science Systems and Applications Inc., Lanham, Maryland, USA


Lang-Ping Chang

Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Science Applications International Corporation, Beltsville, Maryland, USA


Nathaniel J. Livesey

Jet Propulsion Laboratory, Pasadena, California, USA


Abstract

Stratospheric transport calculated using assimilated winds has been shown to be too fast in many cases, because of excessive mixing and an overstrong residual circulation. It is shown that the use of 6-h-averaged wind fields instead of instantaneous analyses can substantially reduce this problem for NASA's Goddard Earth Observing System version 4 (GEOS-4) sequential data assimilation system. Two examples are used to illustrate impacts in an off-line chemistry transport model. An age-of-air computation shows that the stratosphere becomes substantially older when time-averaged winds are used, yet still not as old as that determined from observations. An ozone assimilation experiment reveals improvements in the spatial structure of assimilated ozone, better agreement with independent observations, and a 40–60% reduction in observation-minus-forecast residuals. The averaged meteorological fields have also been incorporated in the on-line transport computations: This is equivalent to using a 6-h square-wave filter at the analysis times. Sub-6-h noise in the system is substantially reduced with this approach. Two additional examples of transport are shown. A simulation of 2004–2005 shows that the descent of N2O in the Arctic polar vortex is represented more accurately than in previous studies. A tape recorder signal is evident in the tropical moisture; it ascends about 30% faster than that in the real atmosphere. In summary, the use of 6-h-averaged winds substantially improves the transport characteristics of the assimilated data, although the circulation remains too fast.

Received 19 June 2006; accepted 10 August 2007; published 8 December 2007.

Keywords: transport; data assimilation; stratosphere.

Index Terms: 3334 Atmospheric Processes: Middle atmosphere dynamics (0341, 0342); 0341 Atmospheric Composition and Structure: Middle atmosphere: constituent transport and chemistry (3334); 3315 Atmospheric Processes: Data assimilation.

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Citation: Pawson, S., I. Stajner, S. R. Kawa, H. Hayashi, W.-W. Tan, J. E. Nielsen, Z. Zhu, L.-P. Chang, and N. J. Livesey (2007), Stratospheric transport using 6-h-averaged winds from a data assimilation system, J. Geophys. Res., 112, D23103, doi:10.1029/2006JD007673.