Yearly variations of the stratospheric tides seen in the CFSR reanalysis data

The three main tidal components, i.e., the migrating components DW1, SW2 and the non-migrating component DE3, at the two stratospheric altitudes (20 and 43 km) and in the latitude range between ±60°, are obtained from the temperature data of National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) during the interval from 1979 to 2010. We analyze in detail these components and obtain the main properties of their yearly variations. It is found that the migrating tidal components (i.e., DW1, SW2) occur mainly in two regions of latitudes: roughly the mid-latitudes and equatorial latitudes. The mid-latitudinal tidal component appears mainly in the upper stratosphere (43 km), extending to the lower stratosphere (20 km) and to the higher low-latitudes (20-30°). This kind of components manifests chiefly the seasonal variation: DW1 is stronger in summer than in winter months, while SW2 is stronger in winter than in summer months. At the same time, the equatorial maximum of the tidal component appears mainly in the lower stratosphere, extending to the upper stratosphere. The equatorial DW1 component displays mainly the semi-annual variation that the amplitudes are larger in months around solstices than in those around equinoxes at the two altitudes. It should be noticed that the equatorial SW2 component displays the semi-annual variation: in the lower stratosphere, the peak and valley amplitudes occur respectively at equinoctial and solstitial months, while in the upper stratosphere they appear in the opposite months. In addition, the seasonal and semi-annual variations can also be seen in the non-migrating component DE3, although the yearly variations are not as remarkable as those of the migrating components. Comparing with GSWM model, the yearly variations of the diurnal tidal component DW1 in the CFSR reanalysis are good at reproducing realistic tides. At the same time, the SW2 and DE3 components are different from the results of GSWM model. In summary, the above yearly variations of the main tidal components may demonstrate that the CFSR reanalysis data can be used as a supplementary observation in the investigation of the stratospheric tidal components.