Changes of atmospheric gravity waves, equatorial quasi-biennial oscillation and semiannual oscillation associated with global warming climate

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The effects of sea surface temperature (SST) and carbon dioxide (CO2) on future changes in the quasi-biennial oscillation (QBO) are investigated using a climate model. Idealized model experiment using the future SST with the present CO2 and the present SST with the future CO2 are conducted. We found that increasing SST mainly plays roles in decreasing the amplitude of the QBO in the lower stratosphere.Next, we analyzed near-equatorial radiosonde observations for 1953-2012 and reveal a long-term trend of weakening amplitude in the zonal wind QBO in the tropical lower stratosphere. The trend is particularly notable at 70 hPa, where the QBO amplitudes dropped by roughly 30% over the period. This trend is also apparent in the global warming simulations of the four models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) that realistically simulate the QBO.