An 11-year solar cycle in tropospheric ozone from TOMS measurements

Tropospheric column ozone derived from Nimbus 7 total ozone mapping spectro meter (TOMS) footprint measurements from 1979 to 1992 provide the first obs ervational evidence of changes in tropospheric ozone in the marine atmosphe re of the tropics which are out of phase with the stratospheric ozone chang es on a time scale of a solar cycle. The estimated changes in tropospheric and stratospheric column ozone over a solar cycle are respectively -2.98 +/ - 1.31 and +8.63 +/- 1.99 Dobson units (DU) or -12.6 +/- 5.6 and +3.69 +/- 0.86 % from solar minimum to solar maximum. These values are statistically significant at the 2 sigma level. In comparison, linear trends in tropical tropospheric ozone are not statistically significant. These observations ar e qualitatively consistent with a modulation effect on tropospheric ozone p hotochemistry by W-induced changes ih stratospheric ozone. However, in the low NOx regime of the marine atmosphere, the observed changes are significa ntly larger than estimated from a photochemical model. Explanation for the solar signal may include subtle solar-induced changes in transport in the t roposphere involving law boundary-layer ozone and ozone precursors.