Temporal and spatial variations of upper tropospheric and lower stratospheric carbon dioxide

Abstract

Systematic collection of air samples was made using commercial jet airliners between Tokyo, Japan and Anchorage, Alaska and between Tokyo and Sydney, Australia in 1984 and 1985. The amplitude of the seasonal CO2 cycle in the upper troposphere was found to be largest in high latitudes of the northern hemisphere but decreased and lagged in phase as the equator was approached. The cycle was still clearly observable in the southern hemisphere, due to southward transport of the northern hemispheric air through the upper troposphere by a monsoon circulation. The yearly mean value of the upper tropospheric CO2 was high in the equatorial region and decreased poleward. The seasonal cycle of the lower stratospheric CO2 in northern high latitudes showed a minimum concentration early in May and a maximum concentration early in September, with a peak‐to‐peak amplitude of 2.2 ppmv. Yearly mean CO2 concentrations were lower by 1.4‐2.2 ppmv than those in the upper troposphere. The difference in yearly mean CO2 concentrations between 1984 and 1985 was about 1.1 ppmv at all locations covered by this measurement.

Methane Emissions Deduced from a Two-Dimensional Atmospheric Transport Model and Surface Measurements

“…Plumb and Mahlman (1987) and Plumb and McConalogue (1988) pointed out that the tropical tropopause calculated by their transport parameters was too high. In fact, such a situation was also found to be the case in our own numerical experiments with CO2; when compared with the annual mean CO2 concentration obtained in the upper troposphere (Nakazawa et al, 1991), the model results showed higher values. To reduce the vertical transport, we decreased the vertical diffusion coefficients at 50 and 150hPa between 18N and 18S (P. P. Tans, private communication).…”

“…The concentration difference between the surface and 8 km is about 10 ppbv. The fact that the destruction of CH4 with OH is enhanced in the lower troposphere (Langenfelds et al, 1993) and that the northern hemispheric air with high CH4 concentrations is transported to the southern hemisphere through the upper troposphere (Pearman and Beardsmore, 1984;Nakazawa et al, 1991) is responsible for such a ver- April 1998 T. Saeki, T. Nakazawa, M. Tanaka and K. Higuchi 311 tical CH4 profile. On the other hand, the calculated values of the tropospheric CH4 concentration for latitudes 37-44 S decrease slightly from the surface to the middle troposphere and then increase with height.…”

Measurement of 14C Concentrations of Stratospheric CO2 by Accelerator Mass Spectrometry

“…Concerning the exchange of CO2 between troposphere and stratosphere, Nakazawa et al (1991) clearly observed a seasonal cycle of the CO2 mixing ratio, as well as the definite annual increase of the ratio, in lower-stratospheric air, both of which were caused most probably by air transport from the troposphere, as there are no major CO2 sources in the stratosphere. They considered two possibilities for this transport process, i.e., vertical diffusion of tropospheric air through the tropopause, and upwelling of tropospheric air through cumulus convection near the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ).…”

“…The mixed air in the lower stratosphere moves through the mid-latitudes towards the North and South Poles, with velocities dependent on altitude (i.e., faster at lower altitudes), and returns to the troposphere at both poles (Nakazawa et al 1991).…”

“…Gamo et al (1989) and studied the effects of storing the sampling tubes on the isotopic fractionation of CO2 and CO2 concentrations, and found them to be negligible. We analyzed the air samples for 14C, and also made routine measurements of halocarbons, CH4 and CO2 concentrations (Makide et al 1987;Nakazawa et al 1991), and the b13C and 8180 values of their CO2 ), which will be reported elsewhere.…”