Three-dimensional model study of the Arctic ozone loss in 2002/2003 and comparison with 1999/2000 and 2003/2004
[摘要] We have used the SLIMCAT 3-D off-line chemical transport model(CTM) to quantify the Arctic chemical ozone loss in the year2002/2003 and compare it with similar calculations for the winters 1999/2000and 2003/2004. Recent changes to the CTM have improved themodel's ability to reproduce polar chemical and dynamical processes.The updated CTM uses σ-θ as a vertical coordinate whichallows it to extend down to the surface. The CTMhas a detailed stratospheric chemistry scheme and now includes asimple NAT-based denitrification scheme in the stratosphere.
In the model runs presented here the model was forced by ECMWF ERA40and operational analyses. The model used 24 levels extending fromthe surface to ~55km and a horizontal resolution of either7.5° x 7.5° or 2.8° x 2.8°.Two different radiation schemes, MIDRAD and the CCM scheme, were usedto diagnose the vertical motion in the stratosphere. Basedon tracer observations from balloons and aircraft, the more sophisticatedCCM scheme gives a better representation of the vertical transport inthis model which includes the troposphere. The higher resolution modelgenerally produces larger chemical O3 depletion, which agreesbetter with observations.The CTM results show that very early chemical ozone loss occurred inDecember 2002 due to extremely low temperatures and early chlorine activationin the lower stratosphere. Thus, chemical loss in this winter started earlierthan in the other two winters studied here.In 2002/2003 the local polar ozone loss in the lower stratospherewas ~40% before the stratospheric final warming.Larger ozone loss occurred in the cold year 1999/2000 which hada persistently cold and stable vortex during most of the winter.For this winter thecurrent model, at a resolution of 2.8° x 2.8°, canreproduce the observedloss of over 70% locally.In the warm and more disturbed winter 2003/2004 the chemicalO3 loss was generally much smaller, except above620K where large losses occurred due to a period of very low minimumtemperatures at these altitudes.
