**Acknowledgement**

We thank the NASA Langley Research Center (NASA-LaRC) and the NASA Langley Aerosol Research Branch for providing the SAGE-II data through the web site ftp://ftprab.larc.nasa.gov/pub/sage2/v6.20. The authors are thankful to the technical and scientific staff of National Atmospheric Research Laboratory (NARL), Gadanki for their dedicated efforts in conducting the Lidar observations. One of the authors, Dr. K. Parameswaran would like to acknowledge CSIR for providing grant through the Emeritus Scientist scheme.

## **19. References**

154 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

circulation).

**Author details** 

Bijoy V. Thampi

scheme.

**Acknowledgement** 

S.V. Sunilkumar and K. Parameswaran

side of the equator with a well pronounced summer-winter contrast. However, organized convection during the ASM period enhances the particulate loading in the UT in the northern latitudes even beyond 25°N. While the particulate optical depth in the 18–21 km region (lowest part of the stratosphere) is relatively low in the equatorial region, it shows an increase in the off-equatorial region mainly due to this enhancement in particulate concentration above the cold point, particularly over the Indo-Gangetic Plain, during this period. At a higher altitude (21–30 km) it shows a different pattern, with high values near the equator and low values in the off-equatorial region. This confirms the existence of a stratospheric aerosol reservoir. This spatial distribution could be attributed to horizontal advection in the lower regime (rapid transport from near equatorial region to higher latitudes) as well as lofting to higher altitudes over the equatorial region (B-D

Spectral analysis of zonal mean particulate optical depth in the stratosphere (18-32km) revealed the existence of a strong QBO both in the equatorial and off-equatorial regions. The phase of the QBO signal in particulate extinction (QBOa) around 25 km is found to be in opposite phase with that in the upper (28-32 km) and lower regime (18-22 km), illustrating the existence of a secondary meridional circulation (SMC) produced due to vertical shear of QBO phase in zonal wind (QBOU). While the particulate optical depth in the lower stratosphere is relatively large during the westerly phase of QBOU in the equatorial region, relatively high values are observed during the easterly phase of QBOU in the off-equatorial region. During the westerly phase of stratospheric QBOU, the mean particulate optical depth rapidly decreases with increase in latitude on either side of equator in both the hemispheres. During the easterly phase, this remains fairly steady between ±15° latitude, with a small

bite-out around the equator, and decreases steadily for latitudes beyond 15°.

*Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram, India* 

We thank the NASA Langley Research Center (NASA-LaRC) and the NASA Langley Aerosol Research Branch for providing the SAGE-II data through the web site ftp://ftprab.larc.nasa.gov/pub/sage2/v6.20. The authors are thankful to the technical and scientific staff of National Atmospheric Research Laboratory (NARL), Gadanki for their dedicated efforts in conducting the Lidar observations. One of the authors, Dr. K. Parameswaran would like to acknowledge CSIR for providing grant through the Emeritus Scientist

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**Chapter 6** 

© 2012 Rashki 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 Rashki 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.

**Changes of Permanent Lake Surfaces, and Their** 

**Consequences for Dust Aerosols and Air Quality:** 

Alireza Rashki, Dimitris Kaskaoutis, C.J.deW. Rautenbach and Patrick Eriksson

Changes in the frequency and extent of natural inundation occurring on large permanent and ephemeral lake systems may lead to significant fluctuations in regional dust loading on both a seasonal and an inter-annual basis [1]. As surface water diversion increases, arid-land surfaces that were previously wet or stabilized by vegetation are increasingly susceptible to deflation by wind, resulting in desertification and increase in dust outbreaks [2-4]. Desiccation of lake beds, whether due to drought or to water diversion schemes, as in the Aral Sea in Turkmenistan [5,6], Owens lake in California [7,8], lake Eyre in Australia, Hamoun lakes in Iran [9-12], can lead to increased dust storm activity. Thus, some dust may be derived from dried lake beds and can be highly saline, while the finest aerosols can be injurious to health. Anthropogenic sources were previously considered as important dust contributors [13], but more recent estimates of only 5-7% of total mineral dust from such sources gives major importance to natural sources [14]. Each year, several billion tons of soil-dust are entrained into the atmosphere playing a vital role in solar irradiance attenuation, and affects marine environments, atmospheric dynamics and weather [15-20].

Atmospheric aerosols affect the global climatic system in many ways, i.e. by attenuating the solar radiation reaching the ground, modifying the solar spectrum, re-distributing the earthatmosphere energy budget and influencing cloud microphysics and the hydrological cycle. Mineral dust plays an important role in the optical, physical and chemical processes in the atmosphere, while dust deposition adds exogenous mineral and organic material to terrestrial surfaces, having a significant impact on the Earth's ecosystems and biogeochemical cycles. The impact of dust aerosols in the Earth's system depends mainly on particle characteristics such as size, shape and mineralogy [21], which are initially determined by the terrestrial sources from which the soil sediments are entrained and from

**The Hamoun Lakes of the Sistan Area, Iran** 

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48776

**1. Introduction** 
