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. 




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.




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. 



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.




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.