Preprints
https://doi.org/10.5194/cp-2021-17
https://doi.org/10.5194/cp-2021-17

  17 Feb 2021

17 Feb 2021

Review status: a revised version of this preprint was accepted for the journal CP and is expected to appear here in due course.

Mid-Holocene monsoons in South and Southeast Asia: dynamically downscaled simulations and the influence of the Green Sahara

Yiling Huo, William Richard Peltier, and Deepak Chandan Yiling Huo et al.
  • Department of Physics, University of Toronto, Toronto, M5S 1A7, Canada

Abstract. Proxy records suggest that the Northern Hemisphere during the mid-Holocene (MH), to be assumed herein to correspond to 6,000 years ago, was generally warmer than today during summer and colder in the winter due to the enhanced seasonal contrast in the amount of solar radiation reaching the top of the atmosphere. The complex orography of both India and Southeast Asia (SEA), which includes the Himalayas and the Tibetan Plateau (TP) in the north and the Western Ghats mountains along the west coast of India in the south, renders the regional climate complex and the simulation of the intensity and spatial variability of the MH summer monsoon technically challenging. In order to more accurately capture important regional features of the monsoon system in these regions, we have completed a series of regional climate simulations using a coupled modeling system consisting of the University of Toronto version of the Coupled Climate System Model version 4 (UofT-CCSM4), the Weather Research and Forecasting (WRF) regional climate model and the 3D Coastal and Regional Ocean Community model (CROCO) to dynamically downscale MH global simulations constructed using UofT-CCSM4. In the global model, we have taken care to incorporate Green Sahara (GS) boundary conditions in order to compare with standard MH simulations and to capture interactions between the GS and the monsoon circulations in India and SEA. In both the global and the regional models, the response of the South Asia (SA) and SEA monsoons to MH orbital forcing is intensified and accompanies lower surface temperature which is likely related to the increased reflectance of shortwave flux at high levels from the greater cloud cover. Comparison of simulated and reconstructed climates suggest that the dynamically downscaled simulations produce significantly more realistic anomalies in the Asian monsoon than the global climate model, although they both continue to underestimate the inferred changes in precipitation based upon reconstructions using climate proxy information. Monsoon precipitation over SA and SEA is also greatly influenced by the inclusion of a GS, with a large increase in particular being predicted over northern SA and SEA, and a lengthening of the monsoon season. Data-model comparison with downscaled simulations outperform those with the coarser global model, highlighting the crucial role of downscaling in paleo data-model comparison.

Yiling Huo et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2021-17', Anonymous Referee #1, 15 Mar 2021
    • AC1: 'Reply on RC1', Yiling Huo, 24 May 2021
  • RC2: 'Comment on cp-2021-17', Chris Brierley, 29 Apr 2021
    • AC2: 'Reply on RC2', Yiling Huo, 24 May 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2021-17', Anonymous Referee #1, 15 Mar 2021
    • AC1: 'Reply on RC1', Yiling Huo, 24 May 2021
  • RC2: 'Comment on cp-2021-17', Chris Brierley, 29 Apr 2021
    • AC2: 'Reply on RC2', Yiling Huo, 24 May 2021

Yiling Huo et al.

Yiling Huo et al.

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Short summary
Regional climate simulations were constructed to more accurately capture regional features of South and Southeast Asian monsoon during the mid-Holocene. Comparison with proxies shows that our high-resolution simulations outperform those with the coarser global model in reproducing the monsoon rainfall anomalies. Incorporating the Green Sahara climate conditions over Northern Africa into our simulations further strengthens the monsoon precipitation, and leads to a better agreement with proxies.