Seasonal cycles of Stratospheric Aerosol and GasExperiment H near-background aerosol in the lowerstratosphere

摘要

Extinction data from the Stratospheric Aerosol and Gas Experiment (SAGE) II in thelower stratosphere were analyzed for seasonal cycles in the near-background levels ofstratospheric aerosol. The data analyzed were the extinction coefficient at 0.525 tm ((30.525)and the extinction ratio at 0.525 um (E0.525) on the basis of climatological zonal monthlymean for the years 1998-2004. Distinct seasonal cycles were found for 00.525 at 35-15°Sabove 28 km (region A) and at 20°S-30°N from 16 to 20.5 km (region B). In the A region,the seasonal cycle of E0.525 was characterized by a maximum in local fall and can beexplained by the ascent of mean meridional circulation in local summer and descent in localwinter. In the B region, the seasonal cycles of E0.525 were characterized by a maximum inOctober-January, which can be interpreted by meridional transport and mixing. Theamplitude of the seasonal cycles for E0.525 exhibited asymmetry between the NorthernHemisphere (NH) and the Southern Hemisphere (SH); the amplitudes at latitudes of 20-30° were larger in the SH than in the NH above 29 km, whereas they were larger in the NHthan in the SH below 18 km. Comparison of the distribution of E0.525 with that of SAGE IIwater vapor suggested that the E0.525 distribution is controlled by the stratosphericcirculation and troposphere-originated gases. One difference between E0.525 and watervapor was found in the E0.525 maximum that appears over the winter subtropics. The E0.525maximum can be attributed to the dominance of temperature and microphysical effectscompared to transport effects, whereas the water vapor distribution can be attributed totransport effects. Another difference is that an upward propagation of the seasonalcycle of 4.525 at 5°S-30°N disappeared near 23 km. This difference is explained bythe fact that the chemical and microphysical processes of aerosol formation becomesignificant above 23 km.