Dipole pattern of Indian Summer Monsoon precipitation modulated by the Circumglobal Teleconnection during the Last Deglaciation

Abstract

Modern observations have demonstrated that the Indian Summer Monsoon (ISM) rainfall shows a west-east dipole pattern influenced by the Circumglobal Teleconnection (CGT). In this study, we investigated the temporal evolution of the ISM rainfall and the dynamic mechanisms using a set of transient simulations (TraCE-21 ka, simulation of Transient Climate Evolution over the past 21,000 years) during the Last Deglaciation. The results show that, the responses of ISM rainfall always present west-east dipole patterns under different forcing factors and such responses are closely related to the CGT-like wave trains in the Northern Hemisphere summer. During the Last Deglaciation, the ISM is strengthened and summer precipitation is increased over northwestern India but decreased over northeastern India. With increased solar insolation and atmospheric CO2, as well as reduced global ice volume, the positive-phase CGT-like wave trains, characterized by an anticyclonic anomaly over west-central Asia (WCA) and a cyclonic anomaly over the Tibetan Plateau (TP), tends to shift the South Asian High (SAH) westward and strengthens (weakens) the divergence in the upper-troposphere over northwestern (northeastern) India. Simultaneously, the intensification of the monsoon trough (MT) due to the local baroclinic atmospheric circulations over Arabian Peninsula-Iranian Plateau leads to the moisture convergence (divergence) over northwestern (northeastern) India in the lower troposphere. For the Younger Dryas (YD) cooling event, the pattern of CGT-like wave trains and Indian summer rainfall do the reverse. Theses rainfall responses highlight the spatial complexity of multi-scale Indian monsoon evolution and it should be cautious when explaining geological proxies.