Analysis of the Characteristics of the Stratospheric Quasi-Zero Wind Layer and the Effects of the Quasi-Biennial Oscillation on it

According to the different forming mechanisms, the stratospheric Quasi-Zero Wind Layers (QZWL) are classified into two categories. The first kind of QZWL is due to the transition between two phases of the Quasi-Biennial Oscillation（QBO）, and the second kind of QZWL is caused by the reversal of meridional temperature gradient in lower stratosphere. Then based on the ERA-40 reanalysis data, the three-dimension structures of the two kinds of QZWL in different seasons are analyzed, further the influence of QBO on them are studied. The results show that the first kind of QZWL can be found at tropical zone in winter, whereas the second kind exists at extratropical areas in summer and over the Pacific Ocean in middle and lower latitude (20°N－40°N) in winter. The height of QZWL in summer is lower and more stable than that in winter. The barometric heights of it in summer are settled from 70 hPa to 50 hPa. Because of the direct effect of QBO, the first kind of QZWL has an obviously interannual variation. The influence of QBO on the second kind of QZWL is that the frequency of QZWL occurring within 20°N－40°N in winter in the westerly phase of QBO is more than in the easterly phase of QBO.