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1. Aerosols considered as a dominant factor in influencing the tropical storm variability

A new study (Dunstone et al., 2013) has revealed aerosols as a driving factor in influencing the variability of tropical Atlantic storms. Simulations by CMIP models for the period 1860-2050 have shown that the anthropogenic aerosols lowered the frequency of the North Atlantic tropical storms during the 20th century. Rapid decline in anthropogenic aerosol loading over the North Atlantic at the end of the 20th century has resulted in an increase in the frequency of tropical storms. The decadal variability in the North Atlantic tropical storms has been strongly linked to aerosol-induced north-south shifts of the Hadley circulation. These results indicate the importance of the dynamic impact of anthropogenic aerosols on the atmospheric circulation. This study raises an important issue, which is even more critical in the Indian context because of large anthropogenic aerosol loading in India as documented by numerous studies in the recent past based on in-situ, ship-borne and satellite based observations.

Reference

Dunstone, N. J., D. M. Smith, B. B. B. Booth, L. Hermanson and R. Eade (2013), Anthropogenic aerosol forcing of Atlantic tropical storms, Nat. Geosci., 6, 534-539.

2. Aerosol cooling effect strengthened by biogenic emission in response to warming

A recent study (Paasonen et al., 2013) has confirmed a negative feedback mechanism between the climate, aerosols and biosphere. Measurements at eleven continental stations across the world have revealed an increase in biogenic emission in response to rising air temperature. Enhanced formation of secondary organic aerosols under the warming climate leads to a cooling at the top-of-atmosphere through direct (scattering solar radiation) and indirect (by enhancing cloud albedo) effects, thereby establishing a negative climate feedback. The study has also concluded that the cloud albedo effect dominates over the direct effect in this negative feedback mechanism. Estimated magnitude of this feedback on a global scale is -0.01 W m-2 K-1. In more polluted regions, the biogenic feedback is partly suppressed by anthropogenic aerosol induced radiative forcing.

Reference

Paasonen, P. et al. (2013), Warming-induced in aerosol number concentration likely to moderate climate change, Nat. Geosci., 6, 438-442.

Editorial Board

Dr Sagnik Dey
Asst Professor
CAS, IIT Delhi
sagnik@cas.iitd.ac.in

Dr P. C. S. Devara
Ex-Scientist and
Advisor IITM, Pune
devara@tropmet.res.in

Dr A Jayaraman
Director
NARL
jayaraman@narl.gov.in

Dr B. K. Sapra
Head, E&BDS, RPAD
BARC
bsapra@barc.gov.in

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