Quasi-periodic imprints in the equatorial troposphere and stratosphere in three decades of reanalysis data

Abstract

Wavelet analysis is applied to zonal mean zonal wind and temperature fields to represent characteristics of temporal periodic features different from the annual and semi-annual recurrence in the troposphere and stratosphere. A daily database of reanalyses is used for the period 1979-2008, which comprises the era of satellitebased data, as some discontinuities have been observed around 1978 in previous studies. Levels for this study have been chosen at 400 and 10 hPa, respectively in the middle troposphere and middle stratosphere. As representative for diverse latitudinal regions we have respectively selected 0, ±20, ±40, ±60, ±80 deg. Significant features were only found at the equator. The period of the quasi-biennial oscillation (QBO) is found to exhibit a decreasing trend in time over the 30 years studied. Potential harmonics of the QBO are found in the tropical stratosphere but also troposphere. However, they do not exhibit the same tendency. This fact supports in particular the idea that the QBO and the tropospheric biennial oscillation may be unrelated phenomena. Some of the observed features lie within the known range of variability of the El Niño Southern Oscillation. Faint effects of the 11-year solar cycle variability may have been observed in the troposphere and stratosphere, but no firm assertion may be made due to the low number of observed cycles for this kind of phenomenon in the used data-set time span. Short-term solar variabilities leave no relevant imprint.