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Peraiah A.,Dollar Scheme and 57 | Srinivasa Rao M.,Indian Institute of Astro Physics
Astrophysics and Space Science | Year: 2013

We have investigated the effects of Compton broadening due to electron scattering in an expanding stellar atmospheres. The line transfer equation is solved by including the second approximation of Edmonds (Astrophys. J. 119:58, 1954) which is due to Compton broadening and obtained the line profiles in (1) plane parallel (PP) (2) spherical (SS) atmospheres. The effect on spectral line formation is studied for different parameters like (a) optical depths (b) densities (c) frequencies (d) temperatures (e) thickness of the atmosphere and (f) expanding velocities. Various combination of the above parameters are used in computing the line profiles observed at infinity. Line profiles are compared for the above said parameters. It is noticed that the expansion of the gases in the atmosphere produces P-Cygni type profiles and at higher optical depths the line profiles change from emission to absorption with their line centers shifting to blue side in the expanding atmospheres. © 2012 Springer Science+Business Media B.V.

Babu S.S.,Vikram Sarabhai Space Center | Chaubey J.P.,Vikram Sarabhai Space Center | Krishna Moorthy K.,Vikram Sarabhai Space Center | Gogoi M.M.,Vikram Sarabhai Space Center | And 7 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2011

The first ever, year-round measurements of aerosol black carbon (BC) over the western part of trans-Himalayas are reported from Hanle (∼4520 m above mean sea level). The daily mean BC concentrations varied from as low as 7 ng m-3 to as high as 296 ng m-3 with an annual average of 77 ± 64 ng m-3, indicating significant BC burden even at free-tropospheric altitudes. Variation with in the day as well as from day to day were highly subdued during winter season (December to February) while they used to be the highest in Spring (March to May). In general, the less frequently occurring high BC values contributed more to the annual and seasonal means, while 64% of the values were below the annual mean. Seasonally, highest BC concentration (109 78 ng m-3) occurred during Spring and lowest (66 ± 42/66 ± 62 ng m3) during Summer/Winter season(June to August/December to February). Diurnal variations in general were very weak, except during Spring and Summer when the effects of convective boundary layer dynamics is discernible. Back trajectory clustering and concentration weighted trajectory (CWT) analyses indicated that, most time of the year the sampling location is influenced by the advection from West and Southwest Asia, while the contribution from the Indo-Gangetic Plains (IGP) remained very low during Spring and Summer. The seasonal and annual mean BC at Hanle are significantly lower than the corresponding values reported for other Himalayan stations, while they were quite higher than those reported from the South Pole and pristine Antarctic environments. Copyright 2011 by the American Geophysical Union.

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