The spatial and temporal distribution characteristics of the main convectively-coupled equatorial waves were analyzed with the OLR data provided by NOAA and the method of wavelet analysis.The results indicate that the wavelet analysis can effectively distinguish MJO,Kelvin,ER,TD,and EMRG wave and the characteristics of their activities in 1992.The propagation speeds of MJO and ER wave are the slowest,following by Kelvin and TD wave and with MRG the fastest.The MJO from the Indian Ocean to the West Pacific Ocean,the Kelvin wave near the International Date Line,the ER and the TD wave around the West Pacific Ocean and the MRG in the eastern of the International Date Line have the biggest wave amplitude.The MJO in boreal winter and spring,the Kelvin wave in boreal spring and summer,the ER wave in boreal autumn,and the TD wave in boreal summer are active.The WMRG wave activates in boreal autumn,whereas EMRG wave appears year-round.These spatial and temporal characteristics agree well with the results of relevant theoretical studies,indicating that the wavelet analysis in the time-frequency domain is another effective method to reveal the evolution of convectively-coupled equatorial waves.
Interannual variation in summer rainfall over South China(SC)was investigated on the monthly timescale.It was found that monthly rainfall from May to August exhibits different features of variation,and the amounts are basically independent of each other.There is a significant negative correlation,however,between May and July SC rainfall,which is partially related to the developing phases of ENSO events.It was also found that stronger(weaker)lower-tropospheric winds over SC and the upstream parts are responsible for more(less)SC rainfall in every month from May to August.Despite this monthly consistent enhancement of horizontal winds,the wind anomalies exhibit distinct differences between May–June and July–August,due to the remarkable change in climatological winds between these two periods.More SC rainfall is associated with a lower-tropospheric anticyclonic anomaly over the SCS and the Philippine Sea in May and June,but with a cyclonic anomaly centered over SC in July and August.
Using the observational data of total solar irradiance(TSI)from 1976 to 2006,the evolution of total solar irradiance and the rela-tionship between TSI and sunspot number(SSN)have been analyzed with the wavelet technique.The results of the continuous wavelet transform(CWT)indicate that the TSI has multi-scale evolutionary characteristics.In the low frequency band,the TSI and SSN show similar variation with a significant and steady oscillation period from 8 to 11.4 a.While in the high frequency band,only around the maximum time of solar cycles,both the TSI and SSN present a significant intermittent oscillation period from 2 to 6 months.The results of the cross wavelet transform indicate that there is significant in-phase resonance oscillation between the TSI and SSN in 8-11.4 a band,where the variation of the SSN is 2 months ahead of that of TSI.Those results confirm the SSN as the primary cause for TSI's periodic variation in the time scale of 8-11.4 a.However for the 2-6 month band,significant resonance periodicity is observed only within the maximum time of solar cycle,but the phase relationship between the TSI and SSN is unsteady.Finally,a reliable TSI monthly series from 1878 to 1975 is reconstructed and tested.
After studying the relationship between SST in the tropical Indian Ocean(TIO),tropical western Pacific(TWP),and tropical eastern Pacific(TEP)and East Asian summer rainfall(EASR),using data provided by NOAA/OAR/ESRL PSD and the National Climate Center of China for the period 1979–2008,an index,SSTDI,was defined to describe the SST diference between the TIO and TWP.In comparison with the winter ENSO,the spring SST contrast between the TIO and TWP was found to be more significantly associated with summer rainfall in East Asia,especially along the EASR band and in Northeast China.This spring SST contrast can persist into summer,resulting in a more significant meridional teleconnection pattern of lower-tropospheric circulation anomalies over the western North Pacific and East Asia.These circulation anomalies are dynamically consistent with the summer rainfall anomaly along the EASR band.When the SSTDI is higher(lower)than normal,the EASR over the Yangtze River valley,Korea,and central and southern Japan is heavier(less)than normal.The present results suggest that this spring SST contrast can be used as a new and better predictor of EASR anomalies.
