http://nopr.niscair.res.in/handle/123456789/64 http://nopr.niscair.res.in/retrieve/143 http://nopr.niscair.res.in/handle/123456789/64 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/17463 Title: Vertical profile variations of NO₂<i> </i>and O₃ using slant column density observations during twilight period <br/> <br/>Authors: Londhe, A L; Bhosale, C S; Meena, G S; Jadhav, D B; Gil, M; Puentedura, O; Yela, M <br/> <br/>Abstract: An algorithm developed to derive the vertical profiles of atmospheric species from their slant column density measurements using twilight spectroscopy is discussed. The algorithm has been tested by using the slant column density measurements at polar station, Reykjavik (64°N, 22.6°W) and tropical station, Pune (l8.53°N, 73.85°E). The vertical profiles of NO₂ and O₃ are retrieved by considering slant column densities for ten different solar zenith angles and ten different atmospheric layers of equal thickness. These vertical profiles are used to differentiate the tropospheric and stratospheric contribution of NO₂ and O₃ . The observations of &nbsp;NO₂ at polar station and at tropical station showed frequent higher values of tropospheric concentrations due to pollution episodes and are not correlated with stratospheric NO₂ and O_3. The correlation between total column density variations of NO₂ and O₃ is not observed; however, the stratospheric variations of NO₂ and O₃ showed good correlation. <br/> <br/>Page(s): 291-301 Sun, 28 Nov 1999 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/17462 Title: Determination of photolysis frequency of O¹D in the tropical region <br/> <br/>Authors: Paul, R; Mitra, A P; Mandal, T K; Srivastava, S K <br/> <br/>Abstract: An attempt has been made to estimate the photolysis frequency of O¹D in troposphere and stratosphere of the Indian region. The radiation code Lowtran 7 is used to estimate actinic flux at these altitudes. An accurate and efficient multiple scattering parametrization along with <i>k</i>-distribution method has been used in this model. For ozone, observed averaged profile for the year 1976 as well as 1994 is used for Delhi, Pune and Thiruvananthapuram. Values as recommended by DeMore <i>et al. [JPL Publication, </i>1994, p.94] and Michelsen <i>et al. [Geophys Res Lett (USA). </i>21 (1994) 2227.] have been taken for ozone quantum yield. The values of photolysis frequency of O¹D are found to be significantly higher for the quantum yield given by Michelsen <i>et al. </i>A decrease in these values is also observed in the year 1994 as compared to that in preceding years up to 1976. <br/> <br/>Page(s): 286-290 Sun, 28 Nov 1999 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/17461 Title: Solar beam radiation estimate’s correlation for Bangladesh <br/> <br/>Authors: Rahman, M M; Uddin, M A; Islam, M W <br/> <br/>Abstract: An empirical correlation has been developed which correlates the monthly average daily solar beam radiation with the maximum possible number of bright sunshine hours. Airmass exponential correlation is also established. The applicability of these models in climatic conditions of Bangladesh is also studied. Measured beam radiation and the bright sunshine hour data are analyzed to find out the regression co-efficient of these correlations using computer simulation programme by Gaussian elimination technique. Applying these correlations, solar beam radiation is computed for different locations in Bangladesh. Predicted results are compared statistically with the experimental observations considering different statistical errors. The <i>t</i>-statistics is also applied to test whether or not a model is statistically significant at a particular confidence level. On the basis of the analysis, a model has been recommended which is found to be best suited to the climatic conditions of Bangladesh. <br/> <br/>Page(s): 277-285 Sun, 28 Nov 1999 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/17460 Title: Feasibility study of extended range atmospheric prediction through time average Lorenz attractor <br/> <br/>Authors: Pal, Pradip K; Shah, Shivani <br/> <br/>Abstract: Though the theoretical limit of atmospheric predictability is only up to 1-2 weeks, temporal and spatial averages may be predictable up to certain extent for extended range. It is not known what should be the length of time for averaging to have certain predictability of time average values. The time average behaviour of Lorenz attractor with and without forcing shows that there are upper and lower limits of such length of time for averaging, beyond which the system remains chaotic. <br/> <br/>Page(s): 271-276 Sun, 28 Nov 1999 22:58:59 GMT