The impact of model grid zooming on tracer transport in the 1999/2000 Arctic polar vortex

[摘要] We have used a 3D chemistry transport model to evaluate the transport of HF andCH₄ in the stratosphere during the Arctic winter of 1999/2000. Several model experiments were carriedout with the use of a zoom algorithm to investigate the effect of different horizontalresolutions. Balloon-borne and satellite-borne observations of HF and CH₄ were used to testthe model. In addition, air mass descent rates within the polar vortex were calculated andcompared to observations.

Outside the vortex the model results agree well with the observations, but inside the vortexthe model underestimates the observed vertical gradient in HF and CH₄, even when thehighest available resolution (1º x 1º) is applied. The calculated diabatic descent rates agreewith observations above potential temperature levels of 450 K. These model results suggestthat too strong mixing through the vortex edge could be a plausible cause for the modeldiscrepancies, associated with the calculated mass fluxes, although other reasons are alsodiscussed.

Based on our model experiments we conclude that a global 6º x 9º resolution is too coarse torepresent the polar vortex, whereas the higher resolutions, 3º x 2º and1º x 1º, yield similar results, even with a 6º x 9º resolution in the tropical region.

[学科分类] 大气科学