QBO of the Equatorial-Stratospheric Winds Revisited: New Methods to Verify the Dominance of 28-Month Cycle

Abstract

The equatorial-stratospheric wind that shows a Quasi Biennial Oscillation (22–32 months) has been revisited using a dual statistical detail regarding the search of the dominance harmonics. Data were used from the Freie Universitat of Berlin since 1953 for different heights combining the observations of the three radiosonde stations. The dominant period of 28 months has been reaffirmed but with a discernible amplitude and a phase, respectively, inversely varying with height. Such a cycle suggests an estimate for the coming easterly equatorial wind occurrence at 15 hPa level at the end of 2009. The 28-month harmonic is found to take about a year to descend from 15 to 70 hPa with a progressive lag of about 1 month/km. At the top of the stratosphere, easterlies dominate, while at the bottom, westerlies are more likely to be found. Correlation with sunspot numbers and seasonal rainfall is discussed.