The mid-latitude horizontal and vertical structure of the zonally asymmetric intraseasonal and interannual ozone variability in boreal winters

Abstract

 A singular value decomposition (SVD) is used to calculate SVD-selected fields of ozone and geopotential, which exhibit maximum covariance, from the observed zonally asymmetric total ozone field and that of the three-dimensional geopotential field thus leaving almost purely dynamical induced variations in the remaining ozone field. This procedure was applied to Total Ozone Mapping Spectrometer data (TOMS) and to geopotential values from the National Centers for Environmental Prediction in the boreal mid-latitudes in the winter months of 1979–1992. Intraseasonal variability (December–February) and trend-eliminated interannual winter mean variability of total ozone and geopotential are analyzed. The first four modes of SVD analysis explain more than 70% of the covariance for the intraseasonal variability and more than 80% of that for the interannual variability. The vertical structure of geopotential regression maps reveals a clear wave-1 pattern for modes one and two and a wave-2 pattern for modes three and four. These patterns show differently but generally westward tilted phases and are more complex at heights below 70 hPa. Further a linear transport model of a conservative tracer was applied to each individual geopotential mode found by the SVD analysis in connection with an observed height and latitude dependent zonal mean ozone distribution. The model results of total ozone reproduce the spatial patterns of the SVD-selected total ozone field quite well whereas their magnitudes are variously underestimated. This method allows us to assess the vertical distribution of the contribution of single modes to the total ozone variability. Maximum contributions are found between 150 and 70 hPa. Smaller amplitude maxima are found around 10 hPa, which result from contributions of horizontal advection of ozone alone. These results reflect an expected dynamical link between the variability of the zonally asymmetric parts of geopotential and ozone.