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Arabian Sea tropical cyclones intensified by emissions of black carbon and other aerosols


Throughout the year, average sea surface temperatures in the Arabian Sea are warm enough to support the development of tropical cyclones1, but the atmospheric monsoon circulation and associated strong vertical wind shear limits cyclone development and intensification, only permitting a pre-monsoon and post-monsoon period for cyclogenesis1,2,3,4. Thus a recent increase in the intensity of tropical cyclones over the northern Indian Ocean5 is thought to be related to the weakening of the climatological vertical wind shear3,4. At the same time, anthropogenic emissions of aerosols have increased sixfold since the 1930s, leading to a weakening of the southwesterly lower-level and easterly upper-level winds that define the monsoonal circulation over the Arabian Sea6,7,8,9. In principle, this aerosol-driven circulation modification could affect tropical cyclone intensity over the Arabian Sea, but so far no such linkage has been shown. Here we report an increase in the intensity of pre-monsoon Arabian Sea tropical cyclones during the period 1979–2010, and show that this change in storm strength is a consequence of a simultaneous upward trend in anthropogenic black carbon and sulphate emissions. We use a combination of observational, reanalysis and model data to demonstrate that the anomalous circulation, which is radiatively forced by these anthropogenic aerosols, reduces the basin-wide vertical wind shear, creating an environment more favourable for tropical cyclone intensification. Because most Arabian Sea tropical cyclones make landfall1, our results suggest an additional impact on human health from regional air pollution.

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Figure 1: Tropical cyclone tracks, aerosol optical depth and meridional SST trends in the Arabian Sea.
Figure 2: Distributions of pre-monsoon and post-monsoon LMI and storm-ambient vertical wind shear.
Figure 3: Thirty-year trends in pre-monsoon SST and vertical wind shear.


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Partial funding for this work was provided by National Oceanic & Atmospheric Administration (NOAA)/Climate Program Office (NA10OAR4310136), Korea’s Research Agency for Climate Science (RACS 2010-2603) and the National Science Foundation (ATM-0721142). Data from National Centers for Environmental Prediction reanalyses 1 and 2 were provided by the NOAA/Office of Oceanic and Atmospheric Research/Earth System Research Laboratory Physical Sciences Division, Boulder, Colorado, USA, from their website (

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Authors and Affiliations



A.E. and V.R. conceived the project. A.E. and J.K. designed the study. A.E., J.K. and E.C. provided model and observational data. All authors participated in data interpretation and co-wrote the manuscript.

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Correspondence to Amato T. Evan.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

The file contains Supplementary References, Supplementary Figures 1-6 with legends, and Supplementary Tables 1-2. (PDF 2636 kb)

Supplementary Data

This file contains raw data used to make all Figure and Tables in this study. These include: climatological fine mode AOD from MODIS, Arabian Sea TC tracks, maximum intensities, and storm-ambient shear, and SST and vertical shear trends from models and observations/reanalysis. (XLS 1942 kb)

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Evan, A., Kossin, J., ‘Eddy’ Chung, C. et al. Arabian Sea tropical cyclones intensified by emissions of black carbon and other aerosols. Nature 479, 94–97 (2011).

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