The Seasonality And Locality Of MJO And Its Relationship With SST And Diabatic Heating

The low frequency oscillation (LFO) is one of the dominant signals of the atmosphere variability in tropics. The LFO activety and its anomaly activity and its anomaly may have impact on the weather and climate in tropics as well as the whole world. Based on the daily data of the NCEP/NCAR reanalyses for the period from1980to2009, the OLR data and Optimal Interpolation SST version2provided by NOAA, this study investigates the seasonal and regional variations in the LFO period and its relationship with SST by means of statistical methods, such as power spectraum analysis, wavelet analysis, wavenumber-frequency analysis, Wheeler-Kiladis wavenumber-frequency cross spectrum analysis, time lead-lag correlation analysis as well as probability distribution function (PDF) analysis. Relationships between the period variations and the diabatic heating are also examined in this paper by both case study and numerical study. Some preliminary results can be obtained.The LFO has strong seasonal and regional variations in its period. The power spectra of the observed winter LFO reveals a wider band of its significant period when it is compared with the summer seasons. The central period which corresponds to the spectra peak is longer in winter than in summer. The period of the LFO in tropical Indian Ocean also covers a wider band when compared with the period in the tropical western Pacific. And the central period of the LFO tends to be shorter in the tropical Indian Ocean while it tends to be longer in the tropical western Pacific.In tropics, the period of the LFO exhibits obvious seasonal variations which can be divided into four major types. The four patterns are prescribed as Pattern Ⅰ--the wavelet significant period varies from the long period to the short, Pattern Ⅱ--from the short to the long, Pattern Ⅲ-no significant variations, Pattern Ⅳ-the branching wavelet energy (WE).The LFO has a strong negative correlation with SST. The LFO period becomes shorter when the SST increases, and vice versa. It can be found that the variations of the LFO period are mainly affected by the changes of the diabatic heating rate in the middle and low troposphere. The LFO period turns to shorter while the rate becomes higher, and vice versa.When considering both the results from the numerical experiment and the mobile wave CISK theory, the reason of the changes in the LFO period can be concluded as follows:the variations in SST change its thermal effect on the atmosphere. Then, the energy balance will be re-adjusted, which could also affect the intensity of the convection. This would weaken or strengthen the latent heat release. And the changes in both sensible and latent heat could modify the diabatic heating rate in the middle and low troposphere which lead to the variations of the LFO period.