Abstract
Proxy and model-based studies suggest multi-scale temporal variability in the Indian summer monsoon (ISM). In this study, using the CESM1 atmospheric general circulation model, we carried out multiple ensemble AGCM simulations for the Mid-Holocene (MH; ≈ 6 kyr BP), Medieval Warm Period (MWP; ≈ 1 kyr BP), Little Ice Age (LIA; ≈ 0.35 kyr BP), and Historical (HS; ≈ CE 2000) periods. We used the PMIP3/CMIP5 boundary conditions for this purpose. Our simulations indicate that the ISM during the MH was stronger compared to HS and the rainfall higher, in agreement with several proxy studies. The experiments also suggest that the ISM rainfall (ISMR) was higher during MWP relative to the LIA in agreement with our earlier results from the PMIP3 models. A relatively northward migration of the ITCZ over the Indian region and strengthening of the neighboring subtropical high over the northwestern Pacific, both associated with stronger insolation associated with the obliquity and precision during the MH, seem to be important reason Indian summer monsoon during the MH.
Highlights
The Indian monsoon system is a complex phenomenon
The Paleo Model Intercomparison Project 3 (PMIP3) is a collective initiative endorsed by the World Climate Research Programme (WCRP) and JSC/CLIVAR working group on coupled models and the International Geosphere and Biosphere Programme (IGBP; PAGES) (Braconnot et al, 2012)
Possible Mechanisms for the Stronger Mid-Holocene Summer Monsoon In Figure 7, we show the differences in the simulated insolation between the MH and the HS climate periods, associated with
Summary
The Indian monsoon system is a complex phenomenon. Its seasonal evolution and variability on multiple time scales involve individual and coupled land, ocean, and atmospheric processes, in addition to the annual progression of the Earth’s revolution around the Sun. The seasonally phase-locked rainfall and associated circulation are referred to as the southwest monsoon or Indian summer monsoon (ISM). The Indian summer monsoon rainfall (ISMR) is weakening over several regions (e.g., Krishnan et al, 2020), with a simultaneous increase in the extreme events in the recent ∼150 years (Boyaj et al, 2020, and the references therein). Observation-based studies in the last 50–100 years suggest that, on interannual time scales, tropical oceanic phenomena such as the ENSO dominantly influence the ISM variability (see Webster et al, 1998, and the recent reviews by Ashok et al, 2019; Mohanty et al, 2020, and the references therein). Proxy studies indicate that ISMR varied on the decadal, centennial, and millennial to multi-millennial time scales, in addition to intra-annual, and interannual scales (e.g., Ramesh et al, 2010; Chakraborty et al, 2012)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
