Preprints
https://doi.org/10.5194/cp-2020-149
https://doi.org/10.5194/cp-2020-149

  25 Nov 2020

25 Nov 2020

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

Weak Southern Hemispheric monsoons during the Last Interglacial period

Nicholas K. H. Yeung1,2, Laurie Menviel1, Katrin J. Meissner1,2, Andréa S. Taschetto1,2, Tilo Ziehn3, and Matthew Chamberlain4 Nicholas K. H. Yeung et al.
  • 1Climate Change Research Centre, University of New South Wales, Sydney NSW, Australia
  • 2ARC Centre of Excellence for Climate Extremes, University of New South Wales, Sydney NSW, Australia
  • 3CSIRO Oceans and Atmosphere, Aspendale VIC, Australia
  • 4CSIRO Oceans and Atmosphere, Hobart TAS, Australia

Abstract. Due to different orbital configurations, high northern latitude boreal summer insolation was higher during the Last Interglacial period (LIG; 129–116 thousand years before present, ka) than during the preindustrial period (PI), while high southern latitude austral summer insolation was lower. The climatic response to these changes is studied here with focus on the southern hemispheric monsoons, by performing an equilibrium experiment of the LIG at 127 ka with the Australian Earth System Model, ACCESS-ESM1.5, as part of the Paleoclimate Model Intercomparison Project 4 (PMIP4). In our simulation, mean surface air temperature increases by 6.5 °C over land during boreal summer between 40° N and 60° N in the LIG compared to PI, leading to a northward shift of the Inter-Tropical Convergence Zone (ITCZ) and a strengthening of the North African and Indian monsoons. Despite 0.4 °C cooler conditions in austral summer in the Southern Hemisphere (0–90° S), annual mean air temperatures are 1.2 °C higher at southern mid-to-high latitudes (40° S–80° S). These differences in temperature are coincident with a large-scale reorganisation of the atmospheric circulation. The ITCZ shifts southward in the Atlantic and Indian sectors during the LIG austral summer compared to PI, leading to increased precipitation over the southern tropical oceans. However, the decline in Southern Hemisphere insolation during austral summer induces a significant cooling over land, which in turn weakens the land-sea temperature contrast, leading to an overall reduction (−20 %) in monsoonal precipitation over the Southern Hemisphere's continental regions. The intensity and areal extent of the Australian, South American and South African monsoons are consistently reduced. This is associated with greater pressure and subsidence over land due to a strengthening of the southern hemispheric Hadley cell during austral summer.

Nicholas K. H. Yeung et al.

 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Nicholas K. H. Yeung et al.

Data sets

CSIRO ACCESS-ESM1.5 model output prepared for CMIP6 PMIP lig127k Yeung, Nicholas, Menviel, Laurie, Meissner, Katrin, Ziehn, Tilo, Chamberlain, Matthew, Mackallah, Chloe, Druken, Kelsey, and Ridzwan, Syazwan Mohamed https://doi.org/10.22033/ESGF/CMIP6.13703

Nicholas K. H. Yeung et al.

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Short summary
The Last Interglacial period (LIG) is characterised by strong orbital forcing compared to the present day. This study compares the mean climate state of the LIG to the pre-industrial period as simulated by the ACCESS-ESM1.5, with focus on the southern hemispheric monsoons which are shown to be consistently weakened. This is associated with cooler terrestrial conditions in austral summer due to decreased insolation, and greater pressure and subsidence over land from Hadley cell strengthening.