Inter-annual variations of 6.5-day planetary waves and their relations with QBO

Abstract

This paper studies inter-annual variations of 6.5-Day Waves (6.5DWs) in 20−110 km between 52°S−52°N during March 2002−January 2021 and their relations with equatorial stratospheric Quasi-Biennial Oscillation (QBO). 6.5DWs' amplitudes in temperature are calculated based on SABER/TIMED observations. QBO zonal winds are obtained from ERA5 reanalysis dataset. QBO phases are derived from Empirical Orthogonal Functions (EOF) method. Wavelet analysis of 6.5DW variations demonstrates obvious spectral maximums around 28−38 months in 32°−52°N and 26−30 months in 32°−52°S. In the Northern Hemisphere, peak periods get longer poleward, while they remain unchanged with latitude in the Southern Hemisphere.Residual 6.5DWs' amplitudes are calculated by removing composite amplitudes from 6.5DWs' amplitudes.Comparisons between QBO and the monthly maximum residual 6.5DWs' amplitudes (𝐴𝐴 Mmax ) show clear relations between QBO and 6.5DWs in both hemispheres, especially in the NH. When 𝐴𝐴 Mmax is large in the NH, mean QBO profile is easterly at all levels from 70 to 5 hPa. When it's weak, mean QBO wind is weak westerly below 30 hPa. Linear Pearson correlation coefficients between QBO phases and 𝐴𝐴 Mmax show large positive values in 60−110 km between 20°−52°N in April and around 64 km at 24°S in February, and large negative values from 80 to 110 km between 20°N−50°N in August and at 96−106 km between 20°S−44°S in February. These results indicate quantitative relations between QBO and 6.5DWs and provide credible evidences for further studies of QBO modulations on long-term variations of 6.5DWs.

The Key Role of the Vertical Structure of the Stratospheric Quasi‐Biennial Oscillation in the Variations of Asian Precipitation in Summer

“…Given that our study period spans from 1959 to 2020, the radiosonde data is composed of data from three different stations during this period (Kawatani et al., 2016). To avoid any inconsistencies that may arise from the use of different stations, we use the tropical (5°S–5°N) zonal‐mean zonal wind from ERA5 averaged over summer (June, July and August; JJA) to represent the QBO (Huang et al., 2022; Yamazaki et al., 2020). Our findings with this definition are consistent with those obtained by using the radiosonde data.…”