Forecast of development of quasi-biennial oscillation in the equatorial stratospheric wind until April 2014

Abstract

As is well known, the quasi-biennial oscillation (QBO) of wind in the equatorial stratosphere has a significant influence on the processes not only at tropical but also at middle and high latitudes in both stratosphere and troposphere. Consequently, a forecasting the dates of QBO-phase (W or E) transitions is required for the solution of many problems (for instance, for investigation of possible climate changes, for studying of solar activity effects in atmospheric phenomena, for predicting the trends of various atmospheric parameters, etc.). The type of QBO-phase is commonly determined by the zonal wind direction at fixed altitude. The quasi-biennial alternations of wind direction are related with a successive descent of easterly and westerly wind regimes. The paper describes the peculiarities of the wind evolution during QBO-cycle and reveals that the easterly regime propagates downward always with stop at some altitude in the range 20-40. hPa. This time period (no less than three months) of the easterly descent interruption is termed as the stagnation stage. Seasonal regularities of stagnation stage cause the discreteness of QBO-cycle period. If the interval between beginnings of successive stagnation stages is identified as a QBO-cycle length, it appears that no QBO-period other than 24, 30, or 36 months can be realized. The QBO-cycle period is unambiguously related with the stagnation duration that allows making an early forecast of the QBO-phase transition dates. The paper discusses the stagnation stage features occurring during QBO-cycles of different period, and describes the technique of forecasting the QBO-cycle evolution by analyzing the vertical profiles of wind speed. The study is based on experimental observation of zonal wind in the equatorial stratosphere during 1953-2011. It is shown that the previous quasi-biennial cycle has begun in January 2009, lasted for 30 months and completed in June 2011. The current cycle has begun in July 2011, will last for 30 months and will end in December 2013. Subsequent cycle will begin in January 2014. The QBO-phase transition dates for different height levels are determined for all months up to April 2014. © 2012 Elsevier Ltd.