A model intercomparison analysing the link between column ozone and geopotential height anomalies in January

摘要

A statistical framework to evaluate the performance of chemistry-climatemodels with respect to the interaction between meteorology and columnozone during northern hemisphere mid-winter, in particularly January, is used.Different statistical diagnostics from four chemistry-climate models (E39C, ME4C,UMUCAM, ULAQ) are compared with the ERA-40 re-analysis. First, we analysevertical coherence in geopotential height anomalies as described by linearcorrelations between two different pressure levels (30 and 200 hPa) of theatmosphere. In addition, linear correlations between column ozoneand geopotential height anomalies at 200 hPa are discussed to motivate asimple picture of the meteorological impacts on column ozone on interannualtimescales. Secondly, we discuss characteristic spatial structures ingeopotential height and column ozone anomalies as given by theirfirst two empirical orthogonal functions. Finally, we describe the covariancepatterns between reconstructed anomalies of geopotential height andcolumn ozone. In general we find good agreement between the models withhigher horizontal resolution (E39C, ME4C, UMUCAM) and ERA-40.The Pacific-North American (PNA) pattern emerges as a useful qualitativebenchmark for the model performance. Models with higher horizontal resolutionand high upper boundary (ME4C and UMUCAM) show good agreement with the PNA tripolederived from ERA-40 data, including the column ozone modulation over the Pacficsector. The model with lowest horizontal resolution does not show a classic PNApattern (ULAQ), and the model with the lowest upper boundary (E39C) does notcapture the PNA related column ozone variations over the Pacific sector.Those discrepancies have to be taken into account when providing confidenceintervals for climate change integrations.