Seasonally steady planetary disturbances in the troposphere and stratosphere as seen in 30 years of NCEP reanalysis data

Abstract

Zonal velocity and temperature daily global reanalysis data of 30 years are used to search seasonally steady planetary disturbances in the middle troposphere (400 hPa) and middle stratosphere (10 hPa). Significant wavenumber 1, 2 and 3 modes are found. Constant phase lines of zonal velocity 1 modes exhibit significant inclination angles with respect to the meridians. The winter hemisphere generally shows a more significant presence of structures. The Northern Hemisphere (NH) exhibits all over the year a larger amount of structures and more intense amplitudes than the Southern Hemisphere (SH). Middle latitudes exhibit the most significant cases and low latitudes the least significant ones. Longitudinally oriented land-sea transitions at +- 65 deg and -35 deg latitudes appear to play a significant role for the presence of steady planetary modes. The stratosphere exhibits a much simpler picture than the troposphere. Large scale structures with respectively NE-SW (NH) and NW-SE (SH) tilts in the observed temperature and zonal velocity constant phase lines recall the quasi-stationary Rossby wave trains that favor the poleward transport of angular momentum.