Evolution of the Asian–African Monsoonal Precipitation over the last 21 kyr and the Associated Dynamic Mechanisms

Abstract

The Asian–African monsoonal precipitation (AAMP) has a significant impact on the water availability, biodiversity, and livelihoods of billions of people. A comprehensive understanding of the AAMP behavior over Earth’s history will help to make better future projections. Using a set of transient climate simulations over the last 21 000 years (21 ka), the variation of the AAMP and its responses to various external forcings, including orbital insolation, greenhouse gases (GHGs), and ice sheets, are explored. The precipitation evolutions in the individual monsoon domains have the characteristic of hemispheric synchrony over the last 21 ka. Specifically, the AAMP increased from the Last Glacial Maximum to the early Holocene with several abrupt events and then decreased subsequently. The raised orbital insolation and GHGs lead to an overall AAMP increase, but the enhanced insolation tends to induce a systematic northward shift of the Asian–African monsoon domain. Decreased meltwater discharge could promote the African and Indian monsoonal precipitation through strengthening the Atlantic Ocean meridional overturning circulation. However, the lowering of ice sheets (i.e., orographic effect) results in an anomalous dipole precipitation pattern between North China and India. An analysis of the moisture budget suggests that, although different external forcings may lead to the same sign of precipitation change (e.g., both increased insolation and GHGs can cause the enhanced AAMP), the thermodynamic and dynamic contributions to precipitation could vary greatly by region and forcing. This study provides a reference for the long-term behavior of the AAMP with rising GHGs, higher insolation, and potential melting of the Greenland Ice Sheet.

Different precipitation response over land and ocean to orbital and greenhouse gas forcing

“…This simulation captures the key climatic features over the last 22,000 years 13 , 38 . The long term trends in the African and Asian monsoons are reproduced quite well 24 , 26 , 39 , 40 . There is, however, a dry bias 26 , 41 .…”

The Roles of Wind and Sea Ice in Driving the Deglacial Change in the Southern Ocean Upwelling: A Modeling Study

“…The model output is publicly available for download from the National Center for Atmospheric Research Climate Data Gateway. TraCE-21ka model simulations have been shown to replicate many vital features of the global climate evolution during the last deglaciation [46,49], including El Niño [50], Asian-African monsoon [51], and high-latitude temperature [52]. It also demonstrated good agreement regarding the simulated atmospheric regional surface air temperature over Antarctica, the Atlantic Meridional Ocean Circulation transport, and local sea surface temperature in the south Pacific and the SO with paleo data [53].…”

Peatland area and carbon over the past 21 000 years – a global process based model investigation

“…The termination is divided into the HS1 (17.43 -14.63 kyr BP) northern hemisphere (NH) cold period, the Bølling-Allerød (BA, 14.63 -12.85 kyr BP) NH warm period, and the Younger Dryas (YD, kyr BP) NH cold period (Rasmussen et al, 2014), These NH cold-warm swings are associated with a large-scale reorganization of ocean circulation, thought to have been provoked by freshwater release from ice sheet melting leading to changes in the ocean heat transport (Stocker and Johnsen, 2003). With changing low-to high-latitude temperature gradients the ITCZ shifted and with it the high precipitation zones in the tropics (McGee et al, 2014;Shi and Yan, 2019;Cao et al, 2019). These climate dynamics are well captured by the transient TraCE21k simulation (Liu et al, 2009).…”