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Department Solar System (D.S.S.)

Instituto de Astrofisica de Andalucia (I.A.A.)
Apdo. 3004, 18080 Granada, Spain
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Retrieval of CO abundance in the stratosphere and mesosphere from the 
non-LTE radiances measured by the Improved Stratospheric and Mesospheric 
Sounder (ISAMS) on  UARS . This is the first time that retrievals from 
IR emissions presenting variability from LTE to non-LTE regions are 
performed operationally to obtain full profile abundances. The results 
represent the first global measurements of this important dynamics tracer 
in the mesosphere and in polar regions.

Results of the validation and some scientific studies carried out with these data 
can be found in the publications:

Global and seasonal variations in middle atmosphere CO from UARS/ISAMS
Lopez-Valverde et al., Geophys. Res. Lett., 20, 1247-1250, 1993

    Abstract [ ASCII text file ]

Validation of measurements of carbon monoxide from the Improved 
Stratospheric and Mesospheric Sounder
Lopez-Valverde et al., J. Geophys. Res. 101, 9929-9955, 1996 

   Postscript File [ GNUzipped Tar files , 297 Kb ]

Observations of Midel Atmosphere CO from the UARS ISAMS During the Early 
Northern Winter 1991/1992
Allen et al., J. Atmos. Sci., 56, pp.563-583, 1999

   Postscript File [ GNUzipped Tar files , 5.9 Mb!! ]

A selection of results from these works follow. 

CO ISAMS Figure 1 of Allen et al., JAS, 56, pp.563-583, 1999, adapted from the pioneering work by Solomon et al., JAS, 42, pp.1072-1083, 1985, on photochemistry and transport of Co in the middle atmosphere. This is a schematic of the chemical and transport processes that dominate the latitudinal distribution of CO in the middle atmosphere. Notice the downwelling transport of air in the polar night region. Air rich in CO from mid-latitudes will descent and CO is accumulated at high latitudes.

CO ISAMS Figure 10 of Lopez-Valverde et al., JGR, 101, pp.9929-9955, 1996. It is a sequence of zonal mean cross sections of CO volume mixing ratio (in parts per million by volume, with 3 contours per decade) throughout the mission. The data are averages of ISAMS daytime data. See the paper for more details. The figure shows nicely, for the first time with a single instrument, the seasonal and latitudinal distribution of CO. Particularly interesting is to see how this atmospheric gas traces very clearly the reversal of the meridional circulation during equinoxes.

CO ISAMS This is a coloured version of Figure 11 in Lopez-Valverde et al., J. Geophys. Res. 101, 9929-9955, 1996. Now these are longitude-height cross sections of CO and N2O volume mixing ratios at 64 degree North measured by ISAMS on Jan 9th, 1992. The figure shows beautifully how a mass of mesospheric air rich in CO descends into the stratosphere at polar regions. Actually the area of rich CO air extends to lower latitudes, as low as 44 N. Parallel analysis of the temperature field by Reburn et al., GRL, 20, pp.1231-1234, 1993 indicates that this area corresponds to the polar vortex, which was highly displaced from the North Pole that day. Similar tongues of descending air have been simulated by GCMs (see the N2O simulations by Nielsen et al, JGR, 99, pp.5399-5420, 1994). This suggest that CO can be an excellent tracer of polar dynamics even at stratospheric altitudes where, in the abscence of OH during the polar night, its chemical lifetime is quite long.

CO ISAMS Figure 8 from Allen et al., JAS, 56, pp.563-583, 1999 These are projections of CO ISAMS data at 1 mb (around the stratopause) in the polar winter during the first days of January 1992, together with PV contours. See the paper for more datails. This is another beautiful view of how the CO data traces the evolution of the polar vortex. The polar vortex, initially centered over the pole, quickly developes a tail that elongates until joining the main cell 4 days later. The shape of the vortex can be very comma-like and displaced from the pole. Allen et al. show other interesting results and numerical simulations.

Last update: 15-July-1999