Annual cycle of ozone at and above the tropical tropopause: observations versus simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS)

摘要

Multi-annual simulations with the Chemical Lagrangian Model of the Stratosphere(CLaMS) were conducted to study the seasonality of O within thestratospheric part of the tropical tropopause layer (TTL),i.e. above θ=360 K potential temperature level.In agreement with satellite (HALOE) and in-situ observations (SHADOZ),CLaMS simulations show a pronounced annual cycle in O,at and above θ=380 K, with the highest mixing ratios in the lateboreal summer. Within the model, this cycle is driven by the seasonality ofboth upwelling and in-mixing. The latter process occurs through enhancedhorizontal transport from the extratropics into the TTL that is mainlydriven by the meridional, isentropic winds.The strongest in-mixing occurs during the late boreal summer from theNorthern Hemisphere in the potential temperature range between 370 and420 K. Complementary, the strongest upwelling occurs in winterreducing O to the lowest values in early spring.Both CLaMS simulations and Aura MLS O observations consistentlyshow that enhanced in-mixing in summer is mainly driven by theAsian monsoon anticyclone.