Chaos and predictability of the Indian summer monsoon

Predictability of the Indian summer monsoon is investigated by conducting three multiyear integrations with the Geophysical Fluid Dynamics Laboratory’s climate model. The mean monsoon simulated by the model is realistic. It is shown that a significant fraction of the interannual variance of the simulated Indian summer monsoon may be due to internal dynamics. It is discovered that the tropical atmosphere is capable of sustaining a quasi-biennial oscillation (QBO) accounting for most of the internal low frequency variability. It is also shown that neither air-sea interaction nor surface hydrology feedback is essential for the QBO of the model atmosphere. That such a QBO can arise due to modulation of the nonlinear intraseasonal oscillations by the annual cycle is demonstrated using a simple nonlinear dynamical model. The phase and the amplitude of the internal mode is unpredictable and hence may be responsible for limiting the long range predictability of the monsoon.