Study on the quasi-biennial oscillation using a general circulation model.

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We investigate the quasi-biennial oscillation (QBO) in the equatorial lower stratosphere using a general circulation model (GCM). The CCSR/NIES GCM is used.From the new result about the forcing to the QBO, it seems that gravity waves are more important to the QBO than Kelvin wave and Rossby-gravity wave. So we tested the possible role of the gravity wave to the QBO using a two-dimensional model which derived from the GCM.A QBO-like oscillation is easily obtained in the two-dimensional model. However, the period of the oscillation is too short, about 100 days. It is due to strong gravity wave in the two-dimensional model. It is because the model is two-dimensional and no-rotation.In the second year, we performed the QBO simulation using the GCM which is 1/5 sector model. The horizontal resolution is T106 and vertical resolution is 1km in the stratosphere in order to resolve the wave in the model. We have obtained a QBO like oscillation in the GCM.It is the first result in the world. However, there are some discrepancies to the real QBO.The height of the oscillation is higher than that of the QBO.The period is short, about 400 day ( about 800 days in the real QBO ).As mentioned above, this result is first trial in the world. It is a great step to the QBO work using a full GCM.