080- 22932505

Nonlinear dynamics

There has been previous work on bifurcations (”tipping points”) in idealized monsoon models, implying that discontinuous responses (including monsoon shut- down) to changes in forcing could occur. This work had been motivated by the presence of impor- tant nonlinearities as well as observed features such as apparent abruptness of monsoon onset, and rapid changes in the paleoclimate record. None of these are evidence of a bifurcation, but work in- volving idealized box-models of mean monsoon conditions (Levermann, 2009) has postulated that a destabilizing feedback associated with moisture advection, being nonlinear, inevitably leads to a bifurcation being present in such models. Recent work by us (Seshadri2017a) suggests that this is not the case; despite nonlinearity of advection, a bifurcation is not generic in models. Moreover, our work shows that it is more likely that a bifurcation is not present in monsoon models, since instabilities are too weak. The difference with prior models is due to inclusion of effects of vertical temperature structure on energy balance, suggesting its important role in nonlinear dynamics of monsoons.