Estimates of Tropospheric Ozone from Nimbus 7 LIMS and TOMS Datasets

Abstract. This work is a diagnostic study of distributions of tropical tropospheric column ozone (TRCO) based on subtracting Limb Infrared Monitor of the Stratosphere (LIMS) Version 6 (V6) Level 3 stratospheric column ozone (SCO) values from Total Ozone Mapping Spectrometer (TOMS) total ozone for several selected days of 1978–1979. The focus of this study is the low latitudes, where the tropopause is near 100 hPa and zonal wave activity is weak. TRCO exhibits a zonal wave-1 feature in the southern tropics with maximum values near 0° longitude during November 1978. Its zonal variation is 70 to 30 Dobson units (DU) and agrees with that of other similar analysis studies. V6 estimates of SCO and calculated TRCO are less reliable in March and May 1979 because those data are affected by temperature biases of order -1.0 to -2.0 K at 30 and 50 hPa; retrieved ozone at those levels may be too large by ~20 % as a result. The LIMS Level 3 sequential estimation algorithm provides smoothed zonal wave ozone amplitudes and reduced zonal variations of SCO. The corresponding calculated TRCO amplitudes are enhanced and not quantitative in those instances. The findings herein should be helpful to others, as they analyze infrared limb measurements of ozone and subtract their stratospheric column amounts from coincident total ozone to obtain accurate zonal variations of tropospheric ozone.