Northern Hemisphere stratospheric winds in higher midlatitudes: longitudinal distribution and long-term trends
Abstract. The Brewer–Dobson circulation (mainly meridional circulation) is very important for stratospheric ozone dynamics and thus for the overall state of the stratosphere. There are some indications that the meridional circulation in the stratosphere could be longitudinally dependent, which would have an impact on the ozone distribution. Therefore, we analyse here the meridional component of the stratospheric wind at northern middle latitudes to study its longitudinal dependence. The analysis is based on the NCEP/NCAR-1 (National Centers for Environmental Prediction and the National Center for Atmospheric Research), MERRA (Modern Era-Retrospective Analysis) and ERA-Interim (European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis Interim) reanalysis data. The well-developed two-core structure of strong but opposite meridional winds, one in each hemisphere at 10 hPa at higher northern middle latitudes, and a less pronounced five-core structure at 100 hPa are identified. In the central areas of the two-core structure the meridional and zonal wind magnitudes are comparable. The two-core structure at 10 hPa is almost identical for all three different reanalysis data sets in spite of the different time periods covered. The two-core structure is not associated with tides. However, the two-core structure at the 10 hPa level is related to the Aleutian pressure high at 10 hPa. Zonal wind, temperature and the ozone mixing ratio at 10 hPa also exhibit the effect of the Aleutian high, which thus affects all parameters of the Northern Hemisphere middle stratosphere. Long-term trends in the meridional wind in the "core" areas are significant at the 99% level. Trends of meridional winds are negative during the period of ozone depletion development (1970–1995), while they are positive after the ozone trend turnaround (1996–2012). Meridional wind trends are independent of the sudden stratospheric warming (SSW) occurrence and the quasi-biennial oscillation (QBO) phase. The influence of the 11-year solar cycle on stratospheric winds has been identified only during the west phase of QBO. The well-developed two-core structure in the meridional wind illustrates the limitations of application of the zonal mean concept in studying stratospheric circulation.