In order to test the validity of the global wavelet spectrum - a new period analysis method based on wavelet analysis, we carried out some simple experiments. In our experiments we used idealized time series and real Nifio 3 sea surface temperature （SST） for testing purposes. First we combined different signals which have the same power but different periods into some new time series. Then we calculated the global wavelet spectra and Fourier power spectra for the testing time series. The testing results revealed that on some occasions the global wavelet spectrum tends to amplify the relative power of longer periods. By making comparisons with the results obtained by the traditional Fourier power spectrum, we demonstrated that on an occasion when the global wavelet spectrum does not work the Fourier power spectrum can be used to achieve the right results. Hence it is recommended that when making period analysis with the global wavelet spectrum one needs to do further tests to confirm their results.
Zonal wind anomaly over the equatorial west- ern Pacific plays an important role in the occurrence of ENSO. The mechanism to produce zonal wind anomaly over the equatorial western Pacific is studied in this paper. It is shown clearly that zonal wind anomaly over the equatorial western Pacific is closely related to the anomaly of East- Asian winter monsoon. Anomalous strong (weak) East-Asian winter monsoon can excite not only the westerly (easterly) anomaly over the equatorial western Pacific but also a cyc- lonic (an anticyclonic) circulation over the east of the Philip- pines. The above anomalous circulation results from dy- namical impacts of anomalous pressure pattern due to the East-Asian winter monsoon. Because there is westward (eastward) pressure gradient over the equatorial western Pacific, i.e. there is ?? xp <0(> 0), during strong (weak) East-Asian winter monsoon.
The onset of the Asian summer monsoon has been a focus in the monsoon study for many years. In this paper, we study the variability and predictability of the Asian summer monsoon onset and demonstrate that this onset is associated with specific atmospheric circulation characteristics. The outbreak of the Asian summer mol）~soon is found to occur first over the southwestern part of the South China Sea （SCS） and the Malay Peninsula region, and the monsoon onset is closely related to intra-seasonal oscillations in the lower atmosphere. These intra-seasonal oscillations consist of two low-frequency vortex pairs, one located to the east of the Philippines and the other over the tropical eastern Indian Ocean. Prior to the Asian summer monsoon onset, a strong low-frequency westerly emerges over the equatorial Indian Ocean and the low-frequency vortex pair develops symmetrically along the equator. The formation and evolution of these low-frequency vortices are important and serve as a good indicator for the Asian summer monsoon onset. The relationship between the northward jumps of the westerly jet over East Asia and the Asian summer monsoon onset over SCS is investigated. It is shown that the northward jump of the westerly jet occurs twice during the transition from winter to summer and these jumps are closely related to the summer monsoon development. The first northward jump （from 25°-28°N to around 30°N） occurs on 8 May on average, about 7 days ahead of the summer monsoon onset over the SCS. It is found that the reverse of meridional temperature gradient in the upper-middle troposphere （500-200 hPa） and the enhancement and northward movement of the subtropical jet in the Southern Hemispheric subtropics are responsible for the first northward jump of the westerly jet.
Interaction between the Quasi-Biennial Oscillation in far west equatorialPacific (QBOWP) and the El Nino/Southern Oscillation (ENSO) is studied using a new conceptual model.In this conceptual model, the QBOWP effects on ENSO are achieved through two ways: (1) the oceanicKelvin wave along equatorial Pacific, and (2) the Atmospheric Walker Circulation anomaly, while ENSOeffects on QBOWP can be accomplished by the atmospheric Walker Circulation anomaly. Diagnosisanalysis of the model results shows that the Atmospheric bridge (Walker circulation) plays a moreimportant role in interaction between the ENSO and QBOWP than the oceanic bridge (oceanic Kelvinwave along equatorial Pacific); It is found that by the interaction of the ENSO and QBOWP, a freeENSO oscillation with 3-5 years period could be substituted by a oscillation with the quasi-biennialperiod, and the dominant period of SST anomaly and wind anomaly in the far west equatorial Pacifictends to be prolonged with enhanced ENSO forcing. Generally, the multi-period variability in thecoupled Atmosphere-Ocean System in the Tropical Pacific can be achieved through the interactionbetween ENSO and QBOWP.
LIU Qinyu1, LIU Zhengyu2,1 & PAN Aijun 1,3 1. Physical Oceanography Lab. & Atmosphere-Ocean Interaction and Climate Lab., Ocean University of China, Qingdao 266003, China
