**Author details**

Sanat Kumar Das *Department of Atmospheric Sciences, National Taiwan University, Taiwan*

## **9. References**

[1] Ackerman, A. S., Toon, O. B., Stevens, D. E., Heymsfield, A. J., Ramanathan, V. & Welton, E. J. [2000]. Reduction of tropical cloudiness by soot, *Science* 288: 1042–1047.

106 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics Natural vs Anthropogenic Background Aerosol Contribution to the Radiation Budget over Indian Thar Desert <sup>27</sup> Natural vs Anthropogenic Background Aerosol Contribution to the Radiation Budget over Indian Thar Desert 107

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26 Will-be-set-by-IN-TECH

from a variety of ground-based and satellite-borne instruments. Mt. Abu is situated in the semi-arid region of Thar Desert and is less influenced by the local anthropogenic aerosols. It is therefore, a unique site for the observation of background aerosols over semi-arid region. Also, the Aravalli mountains are located in between Thar Desert and IGP which has large abundance of anthropogenic aerosols. Therefore, there is a significant variation of aerosol properties over Mt. Abu during different seasons, namely, winter (DJF), premonsoon (MAM), monsoon (JJA) and postmonsoon (SON). Ground-based observations show that AOD is maximum during premonsoon due to the large dust loading in the atmosphere by frequently occurring dust storms over Thar desert and minimum during winter due to low boundary layer height. Space-borne observations suggest that natural dust aerosols are dominating during premonsoon while anthropogenic aerosols are dominating during winter over western India. An interesting observation of CALIPSO is a layer of transported seasalt aerosols during monsoon over western India coming from Arabian Sea. These aerosols increase the contribution of natural forcing to the total atmospheric radiative forcing. Atmospheric radiative forcing is found to be maximum of about 23.6±5.5 Wm−<sup>2</sup> during premonsoon and minimum of about 6.1±1.8 Wm−<sup>2</sup> during winter. Another interesting result is TOA forcing is positive due to the bright land surface over western India during premonsoon, while it is negative during other seasons. The contribution of natural aerosols is found to be higher during premonsoon and monsoon and that of anthropogenic aerosols is higher during postmonsoon. During winter, they contribute equally. The annual average of natural and anthropogenic contribution is about 55% and 45%, respectively, indicating that the anthropogenic effects are also very significant. Thus the background aerosols over western India are not only influenced by desert dust aerosols but also by seasalt coming from Arabian

Author would like to thank his Ph. D. thesis supervisor, Prof. A. Jayaraman, for his guidance, constant help, inspiration and support during this research work initiated at PRL. Author would also like to acknowledge NOAA National Center for Environmental Prediction and Air Resources Laboratory for providing reanalysis data and online HYSPLIT model output for back-trajectories analysis. Author acknowledges Terra, Aqua, Aura and CALIPSO mission scientists and associated NASA personnel for the production of the data used in this research effort. Special thanks to Prof. J. P. Chen and Dr. U. Das for the valuable scientific discussions.

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E. J. [2000]. Reduction of tropical cloudiness by soot, *Science* 288: 1042–1047.

This work is partially supported by NSC grant 100-2119-M-002 -023 -MY5, Taiwan.

*Department of Atmospheric Sciences, National Taiwan University, Taiwan*

Sea and anthropogenic aerosols transported from IGP.

**Acknowledgment**

**Author details** Sanat Kumar Das

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© 2012 Sunilkumar et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Sunilkumar et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Distribution of Particulates in the Tropical UTLS** 

Particulates in the Upper Troposphere and Lower Stratosphere (UTLS) gained considerable interest due to their role in the dehydration of tropospheric air entering the stratosphere [1,2] as well as their potential to influence the radiation budget of the Earth-atmosphere system [3]. The upper troposphere region, which is also conducive for the formation of cirrus, plays a major role in the transport of water vapour and other chemical constituents into the stratosphere. The physical processes responsible for maintaining the observed aerosol distribution in the tropical UTLS, the process with which it interacts with cirrus clouds and the effect of these particulates on the radiation budget are not fully understood [4]. Studies have shown that the microphysical (such as particle shape, size, and size distribution) as well as the chemical properties of particles in the UTLS region [5-7] are mainly governed by the strength of tropospheric convection and the prevailing dynamics of the underlying troposphere. The formation and persistence of cirrus clouds in the upper troposphere is mainly governed by the concentration of available condensation nuclei in this region and their physical and chemical properties. These clouds are believed to be a significant contributor to atmospheric greenhouse effect [8,9] as well as hypothesized to play a major role in the dehydration of the lower stratosphere [1,2] and thus becomes an

important factor governing global climate, through their positive feedback.

The last four decades of the 20th century have been marked by relatively intense volcanic activity [10] and hence long-term measurements of aerosols during this period mostly characterize the volcanically perturbed aerosols system rather than 'background' conditions [11-13]. During this period the increase in aerosol loading in the stratosphere could accelerate the heterogeneous chemistry of sulfate aerosols leading to a decrease in ozone amount [14-17], altering the NO2 concentration [18-20] and hence modifying the earth's

**over the Asian Summer Monsoon Region and** 

**Its Association with Atmospheric Dynamics** 

S.V. Sunilkumar, K. Parameswaran and Bijoy V. Thampi

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/50552

**1. Introduction** 
