TY  - JOUR
A1  - Schewe, Jacob
A1  - Levermann, Anders
A1  - Cheng, Hai
T1  - A critical humidity threshold for monsoon transitions
JF  - Climate of the past : an interactive open access journal of the European Geosciences Union
N2  - Monsoon systems around the world are governed by the so-called moisture-advection feedback. Here we show that, in a minimal conceptual model, this feedback implies a critical threshold with respect to the atmospheric specific humidity q(o) over the ocean adjacent to the monsoon region. If q(o) falls short of this critical value q(o)(c), monsoon rainfall over land cannot be sustained. Such a case could occur if evaporation from the ocean was reduced, e.g. due to low sea surface temperatures. Within the restrictions of the conceptual model, we estimate q(o)(c) from present-day reanalysis data for four major monsoon systems, and demonstrate how this concept can help understand abrupt variations in monsoon strength on orbital timescales as found in proxy records.
Y1  - 2012
U6  - https://doi.org/10.5194/cp-8-535-2012
SN  - 1814-9324
VL  - 8
IS  - 2
SP  - 535
EP  - 544
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Schewe, Jacob
A1  - Levermann, Anders
T1  - A statistically predictive model for future monsoon failure in India
JF  - Environmental research letters
N2  - Indian monsoon rainfall is vital for a large share of the world's population. Both reliably projecting India's future precipitation and unraveling abrupt cessations of monsoon rainfall found in paleorecords require improved understanding of its stability properties. While details of monsoon circulations and the associated rainfall are complex, full-season failure is dominated by large-scale positive feedbacks within the region. Here we find that in a comprehensive climate model, monsoon failure is possible but very rare under pre-industrial conditions, while under future warming it becomes much more frequent. We identify the fundamental intraseasonal feedbacks that are responsible for monsoon failure in the climate model, relate these to observational data, and build a statistically predictive model for such failure. This model provides a simple dynamical explanation for future changes in the frequency distribution of seasonal mean all-Indian rainfall. Forced only by global mean temperature and the strength of the Pacific Walker circulation in spring, it reproduces the trend as well as the multidecadal variability in the mean and skewness of the distribution, as found in the climate model. The approach offers an alternative perspective on large-scale monsoon variability as the result of internal instabilities modulated by pre-seasonal ambient climate conditions.
KW  - monsoon failure
KW  - climate change
KW  - coupled climate model
KW  - stochastic model
KW  - non-linear dynamics
Y1  - 2012
U6  - https://doi.org/10.1088/1748-9326/7/4/044023
SN  - 1748-9326
VL  - 7
IS  - 4
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -