Abstract
The quasi-biennial oscillation is the primary mode of variability of the equatorial mean zonal wind in the lower stratosphere, which is characterized by downward propagating easterly and westerly wind regimes from 10 hPa level with a period approximately 28 months. The effects of the stratospheric quasi-biennial oscillation in zonal winds (SQBO) are not only confined to atmospheric dynamics but also seen in the chemical constituent (trace gases) anomalies such as ozone, water vapor, carbon monoxide and methane in the lower stratosphere. In this study, we examined the SQBO and associated ozone quasi-biennial oscillation (OQBO) using the chemistry-climate model CHASER (MIROC-ESM) simulations and ECMWF ERA-Interim ozone reanalysis for the period 2000-2015. We used lower stratospheric zonal wind from the radiosonde observations and total column ozone (TCO) from Aura Satellite (OMI Instruments) over Singapore to compare the SQBO and OQBO phases with model and reanalysis. The SQBO shows large variations in magnitude and periodicity during the period of study and the amplitude of OQBO also changes in accordance with the westerly (+ve ozone anomaly) and easterly (-ve ozone anomaly) phases of SQBO. During the Westerly phase of Ozone QBO (WQBO) corresponds to average positive total ozone anomaly of ~10 DU and in the Easterly phase of Ozone QBO (EQBO) corresponds to an average negative total ozone anomaly ~−10 DU in the tropical lower stratosphere. Since the SQBO phases were explained by the vertical propagations of Mixed-Ross by Gravity (MRG) waves and Kelvin waves, the correlation of ozone volume mixing ratio with zonal and vertical velocities gives quasi-biennial signals, which indicate the OQBO mechanism more related to dynamical transport than the stratospheric photochemical variations. Since the average amplitude of OQBO phases gives ~+/− 10 DU from the observations during easterly and westerly phases SQBO, we need more research focused on the dynamical transport than the photochemical changes to understand the tropical ozone variability due to the ozone quasi-biennial oscillations.
Highlights
The quasi-biennial oscillation is a regular variation of the zonal winds that blow high above the equatorial lower stratosphere
We examined the Quasi-Biennial Oscillation (QBO) signals in ozone (OQBO) using the chemistry-climate model CHASER (MIROC-ESM) and European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim ozone Reanalysis for the period 2000-2015
Reed explained ozone quasi-biennial oscillation (OQBO) mechanism, which emphasized on the ozone concentration changes during stratospheric quasi-biennial oscillation in zonal winds (SQBO) phases [18]
Summary
The quasi-biennial oscillation is a regular variation of the zonal winds that blow high above the equatorial lower stratosphere. The stratospheric quasi-biennial oscillations in zonal wind (hereafter, SQBO) are driven by vertically propagating atmospheric planetary waves (equatorially trapped Kelvin and Mixed Ross by Gravity Waves) that originate from the troposphere and are produced by intense weather systems due to convection and topography These waves break in the tenuous stratosphere and provide a force to “push” wind and make it descend with time (at a rate of about 1 km per month). In the tropical latitudes the quasi-biennial oscillation in total ozone, which is dynamically coupled with the equatorial zonal wind and temperature QBO in the lower stratosphere, has been reported by several authors using the ground-based observations [12] [39] and the zonal mean ozone from the satellite observations [27]. The manuscript is organised in such a way that, the introductory part gives a brief idea about SQBO and its impact on tracer distributions and link with regional weather changes, Section 2 describes model details and ECMWF ERA-Interim Ozone reanalysis, Section 3, describes the results and discussion on SQBO and OQBO characteristics from the model simulations, reanalysis and observations and Section 4, summary and conclusions
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