1.4 Concluding remarks
It is well known that the two main contrasting seasons over northern India (late post-monsoon/winter and pre-monsoon/monsoon), dictate variations in aerosol type and their spatial, temporal and vertical distribution. Recently, ground-based and satellite observations agree to a significant differentiation in aerosol-loading trends between these two seasons. The trends (increasing for the first and declining for the second season) have been established and consolidated by several recent works and the critical is to examine if they will be in force during the next years also. However, some critical issues have to be better clarified and answered in order the current knowledge about aerosol trends in India to be enhanced further. Some of these issues are summarized in the followings:
Why the neutral-to-declining trend is observed only during the hot and dry period of the year, when the natural aerosols dominate over northern India ? Why this phenomenon is not so obvious over the central Deccan plateau and along the coastal regions ? Does it depend only on the anomalous high aerosol loading during pre-monsoon of 2003 and monsoon of 2002 or do other factors play a role as well? Is this trend a fingerprint of variations in specific aerosol types? Is the change in meteorological conditions, monsoon system and/or El-Nino Southern Oscillation in specific periods and years able to control the aerosol trends and over which regions ? Why the aerosol built-up over whole Indian sub-continent is nearly vanished during late pre-monsoon and monsoon seasons? Is this phenomenon based mostly on the unchanged anthropogenic emissions or on the intra-annual fluctuations of the natural aerosols ? In order to have a clear view of all the above-mentioned queries, systematic monitoring of the aerosol
properties from ground and space is needed, along with improvement in the current inventories that the chemical transport models use for the aerosol simulations. Furthermore, the specific role of the synoptic and dynamic meteorology in the aerosol trends over India as well as the changes in the monsoon circulation and annual variations of ENSO have to be better consolidated.
References
- Badarinath, K. V. S., A. R. Sharma, D. G. Kaskaoutis, S. K. Kharol and H. D. Kambezidis (2010), Solar dimming over the tropical urban region of Hyderabad, india: Effect of increased cloudiness and increased anthropogenic aerosols, J. Geophys. Res., 115, D21208.
- Dey, S. and L. Di Girolamo (2011), A decade of change in aerosol properties over the Indian subcotinent, Geophys. Res. Lett., 38, L14811.
- Kambezidis, H. D, D. G. Kaskaoutis, S. K. Kharol, K. Krishna Moorthy, S. K. Satheesh, M. C. R. Kalapureddy, K. V. S. Badarinath, A. R. Sharma and M. Wild (2012), Multi-decadal variation of the net downward shortwave radiation over south Asia: The solar dimming effect, Atmos. Environ., 50, 360-372.
- Kaskaoutis, D. G., S. K. Kharol, P. R. Sinha, R. P. Singh, H. D. Kambezidis, A. R. Sharma and K. V. S. Badarinath (2011), Extremely large anthropogenic-aerosol contribution to total aerosol laod over the Bay of Bengal during winter season, Atmos. CHem. Phys., 11, 7097-7117.
- Kaskaoutis, D.G., Gautam, R., Singh, R.P., Houssos, E.E., Goto, D., Singh, S., Bartzokas, A., Kosmopoulos, P.G., Sharma, M., Hsu, N.C., Holben, B.N. and Takmura, T. (2012a). Influence of Anomalous Dry Conditions on Aerosols over India: Transport, Distribution and Properties, J. Geophys. Res. 117, D09106, doi: 10.1029/2011JD017314.
- Kaskaoutis, D. G., R. P. Singh, R. Gautam, M. Sharma, P. G. Kosmopoulos and S. N. Tripathi (2012b), Variability and trends of aerosol properties over Kanpur, northern India using AERONET data (2001-10), Environ. Res. Lett., 7, doi:10.1088/1748-9326/7/2/024003.
- Kharol, S. K., K. V. S. Badarinath, A. R. Sharma, D. G. Kaskaoutis and H. D. Kambezidis (2011), Multiyear analysis of Terra/Aqua MODIS aerosol optical depth and ground observations over tropical urban region of Hyderabad, India, Atmos. Environ., 45, 1532-1542.
- Lau, K. M., M. K. Kim and K. M. Kim (2006), Asian summer monsoon anomalies induced by aerosol direct forcing: the role of Tibetan Plateau, Clim. Dyn., 26, 855-864.
- Lodhi, N. K., S. N. Beegum, S. Singh and K. Kumar (2013), Aerosol climatology at Delhi in the western Indo-Gangetic Plain: Microphysics, long-term trends and source strengths, J. Geophys. Res., 118, 1361-1375.
- Moorthy, K. K. et al. (2013). Buildup of aerosols over the Indian region, Geophys. Res. Lett., 40, 1011-1014.
- Ramachandran, S., and R. Cherian (2008), Regional and seasonal variations in aerosol optical characteristics and their frequency distributions over India during 2001-2005, J. Geophys. Res., 113, D08207.
- Ramanathan, V. et al. (2007), Atmospheric brown clouds: Hemispherical and regional variations in long-range transport, absorption, and radiative forcing, J. Geophys. Res., 112, doi:10.1029/2006JD008124.
Dr. Dimitris G. Kaskaoutis
Shiv Nadar University, Noida;
E-Mail: dimitriskask@hotmail.com
