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Mass Conservation in a Chemical Transport Model and its Effect on CO2 and SF6 SimulationsChemical transport models (CTMs) must conserve mass to be useful for applications involving assessment of the effect of various pollutants on the troposphere and stratosphere. Furthermore, calculations of the evolution of constituents such as SF6 are used to evaluate overall model transport, and interpretation of such simulations is clouded if mass conservation is not assured. For realistic simulations or predictions, it is crucial that constituents are not produced or lost by transport or other processes in the CTMs. Analysis of CO2 and SF6 experiments using a CTM shows that problems with mass conservation can seriously degrade the simulations. Failure to conserve mass results from inconsistency of the surface pressure tendency and the divergence of horizontal mass flux when the model is forced by assimilated meteorological data. We have developed an effective method to eliminate the inconsistency by modifying the divergent part of the wind field. The changes in the wind fields are quite small but the impact on mass conservation is large. Parameterizations of physical processes such as convection or turbulent transport can also affect mass conservation. The lack of conservation is small but accumulates when integrations are lengthy such as required for SF6. This lack of conservation is found using winds from either a GCM or from an assimilation system. A simple adjustment removes much of the inaccuracy in the convective parameterization. A CO2 simulation using assimilated winds from the most recent version of the Goddard Earth Observing System Data Assimilation System will be used to illustrate the impact of these transport improvements.
Document ID
20020070380
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Zhu, Z.
(Science Systems and Applications, Inc. United States)
Weaver, C.
(Maryland Univ. Baltimore County Catonsville, MD United States)
Kawa, S. R.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Douglass, A. R.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Bhartia, P. K.
Date Acquired
August 20, 2013
Publication Date
January 1, 2002
Subject Category
Environment Pollution
Meeting Information
Meeting: American Geophysical Union Spring Meeting
Location: Washington, DC
Country: United States
Start Date: May 28, 2002
End Date: May 31, 2002
Sponsors: American Geophysical Union
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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