资源环境科技发展态势分析平台

A marked seasonality in the occurrence of Madden-Julian Oscillation (MJO) events is well known. The core region of oscillation is located at low latitudes (between the equator and 15 degrees) in the summer hemisphere. The eastward progression of MJO signal interacts with the monsoon circulation and modulates the advance period of Indian summer monsoon (ISM). The analyses suggest that the mean advance period of ISM (41 days) is comparable with the life cycle of the MJO (30-60 days). The advance period of ISM has been categorised into normal, fast and slow-advance years to decide the pace of the monsoon during progression of monsoon. During the period 1983-2015, the fastest progress of the monsoon was seen in the year 2013 (fastest advancement in the last 33 years) and slowest progress of monsoon was seen in the year 2002 (most lethargic advancement in the last 33 years). The results of the analyses show that variation in daily MJO-amplitude during fast-advancement years is more as compared with the normal and slow-advancement years. The normal-advancement years mostly occur during MJO phase 1 and phase 2 and fast-advancement years frequently occur during MJO phase 2; however, slow-advancement years are found to occur during MJO phase 5 and phase 6. The MJO phase 2 is the most frequent phase and MJO phase 8 is the least frequent phase during advance of monsoon. However, the highest amplitude is recorded during MJO phase 8. The strong (weak) monsoon current is modulated by strong (weak) MJO phases.