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The main thrust of this effort is to develop a more complete understanding of the processes that control the Earth's protective ozone layer. There are two main contributors that influence ozone in the stratosphere, transport and photochemistry. These components are being studied using a 3-dimensional (longitude, latitude, and height) full chemistry and transport model (FCTM). The transport is calculated in an off-line manner, with the constituents having no influence on the dynamical fields. The results from this model have help interpret results from NASA sponsored field campaigns (ASHOE/MAESA and POLARIS) and remote sensors (most notably Upper Atmosphere Research Satellite-UARS).
The FCTM is a combination of off-line transport combined with a chemical constituent model. The FCTM is currently configured with 2.5 degree longitudinal by 2 degree latitudinal horizontal resolution and 28 vertical levels (about 2 km resolution below 60 hPa and 3.5 km above). The vertical grid is a sigma-p hybrid scheme with sigma coordinates used below the interface (currently 247 hPa) and pressure coordinates above, to a top at 0.43 hPa. We have heterogeneous chemistry, as well as gas-phase chemistry. This model is designed for stratospheric studies, and as such ignores some important tropospheric chemical constituents and reactions. We currently carry 36 transported species and 32 inferred species, for a total of 68 constituents. The vertical coordinate is a hybrid sigma-p grid. There have been two interface levels used, 130 hPa (11 tropospheric sigma and 14 stratospheric pressure levels - generally used prior to mid-1999) and 247 hPa (7 tropospheric sigma and 21 stratospheric pressure levels - generally used since mid-1999, we had an interface of 100 hPa and 11 tropospheric levels). The lower interface was adopted to reduce the mass conservation error in the sigma regions of the transport method.
The off-line transport in the FCTM is done using the 3-D flux form semi-Lagrangian transport scheme of Lin and Rood (Mon. Wea. Rev. 1996). The horizonal transport is calculated using an upstream, monotonic, piece-wise parabolic method (PPM) developed by Colella and Woodward (iord=jord=3) (J. Comput. Phys. 1984). The vertical transport algorithm, generally used since mid-1999, follows the Huynh/Van Leer/Lin method with a full monotonicity constraint (kord=7). Previously, the vertical transport was a semi-monotonic PPM (allowing overshoots, but not undershoots - kord=4, which is less diffusive than the horizontal transport).
The input wind data for the transport has been exclusively DAO products. Most of the experiments have been done using assimilated meteorological fields, with one three-year simulation that used fvCCM model output. The meteorological data is brought over from the DAO in the original form and pre-processed by us for use in the FCTM. All of the data is "mapped" in the vertical using routines supplied by S. J. Lin (DAO). This method of interpolation is used to integrate in the vertical the divergence field to conserve the layer mean vertical motion field as we take the assimilated products to a coarser vertical resolution. If necessary, we also adjust the horizonal resolution to our 2.5x2 degree resolution. The mapping also takes a layer integral of scalar quantities, such as temperature.
The sporadic appearance and disappearance of high ClO observed by the Microwave Limb Sounder (MLS) on UARS in December 1991 is simulated using the Full Chemistry Transport Model (FCTM). The high values of ClO are observed when air which has experienced temperatures cold enough for polar stratospheric cloud formation is transported from the polar night to lower latitudes where the chlorine released from the HCl and ClONO2 reservoirs is converted to ClO and seen by MLS. The subsequent decrease in the ClO signal is attributed largely to transport and mixing processes, emphasizing the importance of accounting for transport processes when deriving chemical time scales from observations.
The FCTM was used to examine the influence of a strong cut-off low system on the polar vortex during late January 1992. Tracer studies are used to show that horizontal mixing processes associated with this unusually strong event mix some air from the polar vortex to middle latitudes, and at the same time pull middle latitude air into the polar vortex. The vertical transport associated with this event is found to be minimal.
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Look at a list of the publications related to this modelling effort. Links to popular summaries are included where appropriate
Last Updated: Dec 2004
Page Author: Stephen D. Steenrod (SSAI) steenrod@code916.gsfc.nasa.gov)
Responsible NASA organization/official: Dr. A. R. Douglass, Atmospheric Chemistry and Dynamics Branch
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