Equatorial Symmetrical Correlation Structures in the Zonal Wind Field in the Stratosphere

A study of the interlatitude relationships of the Hayashi spectra of the zonal wind propagating to the east (E) and to the west (W) wave disturbances with periods from 8 hours to 150 days is carried out. To do this, hourly ERA5 reanalysis data were used for two five-month periods: November-March and May-September for 1979-2023. As a result, significant positive correlations were obtained, located symmetrically with respect to the equator in the area of quasi-biannual oscillation (QBO) for latitudes 20 N-20 S, and especially for 15 N-15 S and 10 N-10 S.

The closeness of the bonds manifests itself differently for different periodicities of the spectrum under consideration and for waves E and W. The analysis was carried out for wave number 1 due to the large amount of information, although the spectra themselves were calculated in the range of wavenumbers 1-10. It should be noted that the spectral composition for the two five-month periods is generally different, but in general features it has many similarities.

For example, for E waves propagating to the east, the greatest symmetric correlation is observed for surfaces of 20 and 30 hPa for the season from November to March. At the same time, for latitudes 15 N-15 S, the periodicities of 1.1-2.7 days, 4-7 days and 10-16 days are distinguished. Above and below the 20-30 hPa layer, the symmetrical correlation is less pronounced, and at 100 hPa it is virtually absent at all latitudes.

For W waves propagating westward at the level of 10 hPa and above, an increased correlation (more than 0.8) is clearly distinguished for the diurnal tide at all tropical latitudes. For the area of 15 N-15 S, in addition to the diurnal tide, values above 0.8 are observed for correlations with periodicities of 1.2-1.4 days, 2-3 days, and 4-6 days for both five-month periods. For the period from November to March, a high (more than 0.8) correlation is additionally manifested for periods of 8-10 days.

The results obtained indicate that the spectral composition of the correlations is different for E and W waves.

It should be noted that for periodicities of 0.3-1 day, there are significant relationships for individual frequencies both for waves propagating for the eastward and for the westward. However, they are fragmentary in nature and their contribution to overall variability is likely to be better estimated for the frequency range.

For both E and W waves, there are also high correlations for periods exceeding 20 days.

Thus, the study shows the existence of significant correlations symmetrical with respect to the equator in the field of wave disturbances of the zonal wind (E and W) in the region of quasi-biannual oscillation. The established symmetry may be due to the dominance of equatorial-symmetric waves (Kelvin and mixed Rossby-gravitational waves) in the formation of QBO.