Reply on RC2

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> South Asian monsoon rainfall varies rapidly in the paleoclimate record, and this has been interpreted using simple models as arising from tipping points. This study explores a class of simple monsoon models, based on convective quasi-equilibrium, and the bifurcations permitted by their mathematical forms. Specifically, low-order models are derived starting from the Quasi-equilibrium tropical circulation model (QTCM) to examine the bifurcations present. Previous studies that have pointed to an abrupt transition in low-order monsoon models typically identify a saddle node bifurcation occurring as a result of changes in the radiation budget. The present study shows how such saddle node structures arise across a wide range of modeling assumptions and parameter values, and yet permit a continuous transition into and out of precipitating regimes without any bifurcation being physically manifest. This is because the bifurcation points lie in a regime that is not physically relevant when the dry thermal stratification is sufficiently large. As a result, these low-order models can be interpreted as possessing abrupt transitions that are latent in the equations but do not express themselves physically. However, when the dry thermal stratification is reduced, bifurcations can occur. This paper also shows that these latent saddle-node structures are themselves part of the unfolding of a pitchfork bifurcation. These findings help understand the role of stabilizing phenomena on the general absence of abrupt monsoon transitions despite the presence of nonlinear terms in these models.