Eocene monsoons

Abstract

a b s t r a c tA prominent example of climate-tectonic coupling is the Asian monsoon and the uplift of the Tibetan Plateau. Here we review some of what is known about the history of the monsoon, within a global context and present results from fully coupled Eocene simulations in which Tibetan Plateau height is varied. Peak elevations were doubled from 2000 m to 4000 m whereas mean elevations increased from 750 to 1500 m. The fully coupled Eocene simulations show that introducing a higher Tibetan Plateau into Asian topography intensifies rainfall over southwest Asia, but induces drying over and behind the Plateau. This atmospheric response is controlled by increases in heating over the Plateau region which drives increases in moisture convergence inducing shifts in lower level atmospheric moisture flux. With Eocene boundary conditions aspects of the canonical response from prior work remain the same: cooling over the uplifted region, a large stationary wave response emanating from the plateau and extending into North America, and a large increase in precipitation in summer in the regions with strongest relief, with a rain shadow behind it. But some important local responses are different from similar studies with modern boundary conditions, such as a warming behind the uplifted mountains, and southward advection of warm, moist air from Paratethys onto the Plateau. These results demonstrate that simulations with fully interactive ocean-atmosphere coupled models with a realistic history of paleogeographic boundary conditions will increase the realism of the resulting climatic simulations and increase the body of available proxy evidence for comparison.More generally we find that a global monsoon distribution of precipitation exists in the Eocene regardless of Tibetan Plateau height. Changing Plateau height has minor global impacts, which include a slight drying of midlatitude and cooling of the North Pacific. The results are robust to changes in climate model resolution and atmospheric pCO 2 changes. In general the impacts of the increase in height of the Plateau are minor and it is unlikely that major patterns in early Cenozoic climate change can be explained by the physical climatic impacts of its uplift.

Pre-Miocene birth of the Yangtze River

“…Prell and Kutzbach (57) are among several studies that predict a correlation between increasing plateau altitude and monsoon intensity. Although it is clear that monsoon intensity is controlled by more than simply Tibetan elevation, recent climate models still show that the presence of a plateau intensifies summer rainfall in the Asian region (58). Thus, the timescale of uplift implied by the start of Yangtze throughflow before 23 Ma is consistent with the more recent climate reconstructions that indicate strengthening around the end of the Oligocene (37,55).…”

Influence of the Tibetan Plateau uplift on the Asian monsoon-arid environment evolution

“…For example, in the climate simulation of the Eocene (45-33 Ma) [58], the maximum height of the TP was set at 2000-4000 m and corresponding average topographic height was set at about only 750-1500 m. This simulation revealed remarkable impacts of the TP topographic change on its neighboring regional climate, but also demonstrated that the plateau topographic reduction during the Eocene had limited impacts on the existing global monsoon and precipitation at that time. Ramstein et al [59] simulated the climate in the early Oligocene (~30 Ma) when the Paratethys Sea occupied many areas of western Asia to central Asia while limited uplift occurred only in the southern TP.…”

The neglected Indo‐Gangetic Plains low‐level jet and its importance for moisture transport and precipitation during the peak summer monsoon

“…We also provide results from CAM5 (S1) [Neale et al, 2010]. We focus on CAM because it has been heavily used in theoretical [Sandeep and Ajayamohan, 2015;Boos and Storelvmo, 2016], idealized [Chen et al, 2014;Zhang et al, 2015], and paleoclimate studies [Huber and Goldner, 2012;Licht et al, 2014]. Additionally, the NCAR CAM physics schemes have been ported to several other climate models such as Global Environmental and Ecological Simulation of Interactive Systems [Thompson and Pollard, 1994] and FOAM [Jacob et al, 2001].…”