Basic mechanism for abrupt monsoon transitions
- 8 December 2009
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 106 (49), 20572-20577
- https://doi.org/10.1073/pnas.0901414106
Abstract
Monsoon systems influence the livelihood of hundreds of millions of people. During the Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. Though details of monsoon circulations are complicated, observations reveal a defining moisture-advection feedback that dominates the seasonal heat balance and might act as an internal amplifier, leading to abrupt changes in response to relatively weak external perturbations. Here we present a minimal conceptual model capturing this positive feedback. The basic equations, motivated by observed relations, yield a threshold behavior, robust with respect to addition of other physical processes. Below this threshold in net radiative influx, R(c), no conventional monsoon can develop; above R(c), two stable regimes exist. We identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition. This dynamic similitude may be helpful in understanding past and future variations in monsoon circulation. Within the restrictions of the model, we compute R(c) for current monsoon systems in India, China, the Bay of Bengal, West Africa, North America, and Australia, where moisture advection is the main driver of the circulation.This publication has 42 references indexed in Scilit:
- Tipping elements in the Earth's climate systemProceedings of the National Academy of Sciences of the United States of America, 2008
- Impact of the Indian Ocean SST basin mode on the Asian summer monsoonGeophysical Research Letters, 2007
- Integrated model shows that atmospheric brown clouds and greenhouse gases have reduced rice harvests in IndiaProceedings of the National Academy of Sciences of the United States of America, 2006
- A comparison of interpolated NCEP (I‐NCEP) rainfall with high‐resolution satellite observationsGeophysical Research Letters, 2006
- SST forcing of decadal Indian Monsoon rainfall variabilityGeophysical Research Letters, 2006
- ENSO control on the south Asian monsoon through the length of the rainy seasonGeophysical Research Letters, 2005
- Is the Indian summer monsoon stable against global change?Geophysical Research Letters, 2005
- Simulated changes of the Indian summer monsoon under enhanced greenhouse gas conditions in a global time‐slice experimentGeophysical Research Letters, 2002
- On the stability of the atmosphere‐vegetation system in the Sahara/Sahel regionJournal of Geophysical Research: Atmospheres, 1998
- A Soil Moisture–Rainfall Feedback Mechanism: 1. Theory and observationsWater Resources Research, 1998