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  - 
TY  - JOUR
A1  - Lehmann, Jascha
A1  - Coumou, Dim
A1  - Frieler, Katja
A1  - Eliseev, Alexey V.
A1  - Levermann, Anders
T1  - Future changes in extratropical storm tracks and baroclinicity under climate change
JF  - Environmental research letters
N2  - The weather in Eurasia, Australia, and North and South America is largely controlled by the strength and position of extratropical storm tracks. Future climate change will likely affect these storm tracks and the associated transport of energy, momentum, and water vapour. Many recent studies have analyzed how storm tracks will change under climate change, and how these changes are related to atmospheric dynamics. However, there are still discrepancies between different studies on how storm tracks will change under future climate scenarios. Here, we show that under global warming the CMIP5 ensemble of coupled climate models projects only little relative changes in vertically averaged mid-latitude mean storm track activity during the northern winter, but agree in projecting a substantial decrease during summer. Seasonal changes in the Southern Hemisphere show the opposite behaviour, with an intensification in winter and no change during summer. These distinct seasonal changes in northern summer and southern winter storm tracks lead to an amplified seasonal cycle in a future climate. Similar changes are seen in the mid-latitude mean Eady growth rate maximum, a measure that combines changes in vertical shear and static stability based on baroclinic instability theory. Regression analysis between changes in the storm tracks and changes in the maximum Eady growth rate reveal that most models agree in a positive association between the two quantities over mid-latitude regions.
KW  - storm tracks
KW  - baroclinicity
KW  - climate change
Y1  - 2014
U6  - https://doi.org/10.1088/1748-9326/9/8/084002
SN  - 1748-9326
VL  - 9
IS  - 8
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -