Abstract
We examine the response of the Indian and East Asian summer monsoons to separate precession and obliquity forcing, using a set of fully coupled high-resolution models for the first time: EC-Earth, GFDL CM2.1, CESM and HadCM3. We focus on the effect of insolation changes on monsoon precipitation and underlying circulation changes, and find strong model agreement despite a range of model physics, parameterization, and resolution. Our results show increased summer monsoon precipitation at times of increased summer insolation, i.e. minimum precession and maximum obliquity, accompanied by a redistribution of precipitation and convection from ocean to land. Southerly monsoon winds over East Asia are strengthened as a consequence of an intensified land-sea pressure gradient. The response of the Indian summer monsoon is less straightforward. Over south-east Asia low surface pressure is less pronounced and winds over the northern Indian Ocean are directed more westward. An Indian Ocean Dipole pattern emerges, with increased precipitation and convection over the western Indian Ocean. Increased temperatures occur during minimum precession over the Indian Ocean, but not during maximum obliquity when insolation is reduced over the tropics and southern hemisphere during northern hemisphere summer. Evaporation is reduced over the northern Indian Ocean, which together with increased precipitation over the western Indian Ocean dampens the increase of monsoonal precipitation over the continent. The southern tropical Indian Ocean as well as the western tropical Pacific (for precession) act as a moisture source for enhanced monsoonal precipitation. The models are in closest agreement for precession-induced changes, with more model spread for obliquity-induced changes, possibly related to a smaller insolation forcing. Our results indicate that a direct response of the Indian and East Asian summer monsoons to insolation forcing is possible, in line with speleothem records but in contrast to what most marine proxy climate records suggest.
| Original language | English |
|---|---|
| Pages (from-to) | 121-135 |
| Number of pages | 15 |
| Journal | Quaternary Science Reviews |
| Volume | 188 |
| DOIs | |
| Publication status | Published - 15 May 2018 |
Funding
The EC-Earth experiments were performed by Joyce Bosmans, who was funded by a “Focus en Massa” grant of Utrecht University, the Netherlands . Computing time for EC-Earth was provided by the Royal Netherlands Meteorological Institute (KNMI) and the European Center for Medium-range Weather Forecast (ECMWF). Michael Erb performed the GFDL CM2.1 and CESM experiments, and was supported by a postdoctoral fellowship from the University of Texas Institute for Geophysics and a Paleo Perspectives on Climate Change grant from the National Science Foundation (Grant ATM0902735 ). Computing resources for GFDL CM2.1 were provided by the Geophysical Fluid Dynamics Laboratory at Princeton and resources for CESM were provided by the Climate Simulation Laboratory at NCAR's Computational and Informational Systems Laboratory (ark:/85065/d7wd3xhc), which is sponsored by the National Science Foundation and other agencies. We would like to thank Tony Broccoli for help running the GFDL CM2.1 experiments and Charles Jackson for guidance in running CESM. The Had-CM3 experiments were performed by Aisling Dolan, James Pope and Dominic Edge. Aisling Dolan acknowledges receipt of funding from the European Research Council under the European Union's Seventh Framework Programme ( FP7/2007–2013 )/ ERC grant agreement no. 278636 and also the EPSRC-funded Past Earth Network. Appendix
Keywords
- Climate dynamics
- Monsoon
- Multi-model
- Orbital forcing
- Paleoclimate modelling
- South-east asia
