Mid-Holocene East Asian summer monsoon strengthening: Insights from Paleoclimate Modeling Intercomparison Project (PMIP) simulations

The East Asian summer (June-July-August) monsoon (EASM) is typically thought to have been stronger during interglacial periods based on spatially sparse proxy data. On a large scale, however, whether this view is true and if so, its underlying dynamic mechanisms remain unclear. Using all pertinent experiments within the Paleoclimate Modeling Intercomparison Project (PMIP), here we present an analysis of the EASM during the mid-Holocene, 6000 years ago. Supporting the paleodata, the mid-Holocene EASM, as measured by regionally averaged meridional wind at 850 hPa, became stronger than the baseline period in 27 out of 28 PMIP models with a demonstrable ability to simulate the modern EASM climatology. On average, the EASM strengthened by 32% across all the models and by a larger magnitude in 23 coupled models (35%) than in five atmospheric models (20%). It is proposed that an enhanced land-sea thermal contrast, and hence sea level pressure gradient, between the East Asian continent and adjacent oceans as a result of orbital forcing was responsible for the EASM strengthening during the mid-Holocene. (C) 2012 Elsevier B.V. All rights reserved.