Trace gas transport in the 1999/2000 Arctic winter: comparison of nudged GCM runs with observations

[摘要] We have compared satellite and balloon observations of methane(CH₄) and hydrogen fluoride (HF) during the Arctic winter 1999/2000 with results from the MA-ECHAM4 middleatmospheric general circulation model (GCM). For this purpose, themeteorology in the model was nudged towards ECMWF analyses. This nudging technique is shown to workwell for this middle atmospheric model, and offers good opportunities for the simulation ofchemistry and transport processes. However, caution must be used inside the polar vortex,particularly late in the winter. The current study focuses on transport of HF andCH₄, initialized with satellite measurements from the HALOE instrument aboard the UARS satellite.We have compared the model results with HALOE data and balloon measurements throughout the winter,and analyzed the uncertainties associated with tracer initialization, boundary conditions and thepassive tracer assumption. This comparison shows that the model represents some aspects of the Arctic vortex well, including relatively small-scale features.However, while profiles outside the vortex match observations well, the model underestimatesHF and overestimates CH₄ concentrations inside the vortex, particularly in the middlestratosphere. This problem is also evident in a comparison of vortex descent rates based uponvortex average tracer profiles from MA-ECHAM4, and various observations. This could be dueto an underestimate of diabatic subsidence in the model, or due to too much mixing betweenvortex and non-vortex air.

[学科分类] 大气科学