The quasi-biennial oscillation in the equatorial stratosphere: Seasonal regularity in zonal wind changes, discrete QBO-cycle period and prediction of QBO-cycle duration

Abstract

The changes of vertical wind structure in equatorial stratosphere in course of Quasi-Biennial Oscillation (QBO) demonstrates the evident seasonal dependence. The easterly wind regime descending from the middle to lower stratosphere always includes the stationary period—the stagnation stage. At stagnation stage the bottom boundary of the easterly wind is located in different QBO-cycles at different altitude in the range from ∼22 to ∼26 km, but in each QBO-cycle this altitude is actually constant during the whole stagnation period. Stagnation always begins in solstice (in June–July or December–January). Descent of the easterly wind after stagnation is always resumed near equinox—in March–April or September–October. Consequently, the duration of stagnation stage varies discretely and can be equal to one, three, or five seasons (three, nine, or fifteen months, respectively) in different QBO-cycles. The QBO-cycle period determined as an interval between the beginnings of two successive stagnation stages turns out to be of discrete duration also, and can be equal to 24, 30, or 36 months. The dependence of many atmosphere phenomena determining the Earth’s climate on QBO-phase suggests the need to forecast the QBO-cycle evolution. The established seasonal regularity and discrete QBO-cycle period make it possible the forecasting the QBO-cycle evolution, its duration, and the dates of the QBO-phase changing.