NOPR Collection:

Rainrate and rain attenuation statistics for different homogeneous regions of India

Fri, 01 Aug 2014 00:00:00 GMT

Title: Rainrate and rain attenuation statistics for different homogeneous regions of India Authors: Sulochana, Y; Chandrika, P; Rao, S Vijaya Bhaskara Abstract: Rain rate and rain attenuation predictions are one of the most important steps to be considered when analyzing satellite communication links at the Ku and Ka bands. Rain rate distributions are calculated from the global data sets of Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Climatology Project (GPCP) for six rainfall homogeneous regions of India. The rain rate distributions are estimated from the monthly accumulations of TRMM and GPCP for the years 1998-2010. The estimated rain rate distributions are compared with the standard ITU-R P.837-5 (International Telecommunication Union - for Radio wave propagation) and observed relative errors are presented. The specific rain attenuation calculated at 0.01% and 0.001% probabilities of exceedance in an average year for different frequencies are also presented for the six homogeneous regions of India. Observations indicate maximum specific attenuation in the NE region over Cheerapunji at 0.001% of the time, and minimum attenuation of 21.988 dB km^-1 in Bikaner at 0.01% for 50 GHz frequency in the NW region. Rain attenuation and rain rate distribution are found to exhibit similar characteristics over six homogeneous regions of India. Page(s): 303-314

Estimation of daily surface ozone using periodic and stochastic modeling in Chennai region

Fri, 01 Aug 2014 00:00:00 GMT

Title: Estimation of daily surface ozone using periodic and stochastic modeling in Chennai region Authors: Padma, K; Selvaraj, R Samuel; Boaz, B Milton Abstract: The present study deals with the modeling and forecasting of surface ozone time series in an urban area. First, an analysis of the systematic components (periodicity and stochastic components) was performed. Subsequently, prediction model for the daily surface ozone series was developed. In the recent years, there was no permanent measurement of surface ozone at this site, so surface ozone was measured from June 2011 to September 2012 at the urban site Koyembedu, Chennai (the capital of Tamil Nadu), India. Daily cumulative ozone data series was obtained by hourly instantaneous data. It was found, using Mann-Kendall test, that the data series is free of trend. The periodicity of ozone data was analyzed using Fourier Transform method. Stochastic components of ozone data are assumed as residues between observed ozone data and values computed from periodic model. Stochastic model presented in this research is basically a 3rd order autoregressive model. The developed models were validated using correlation coefficient between the predicted values and measured values. The spectrums of series exhibit 100 days period of daily surface ozone and implies that the pattern in the series is repeated every 100 days. The correlation coefficient (R) of this model delivers 0.810 and can provide mean bias error (MBE) = 0.85, and root mean square error (RMSE)=0.83. The result suggests that this approach is good for estimating daily surface ozone with sufficient accuracy. Page(s): 293-302

Chemical characterization of particulate matter at Sinhagad, a high altitude station in Pune, India

Fri, 01 Aug 2014 00:00:00 GMT

Title: Chemical characterization of particulate matter at Sinhagad, a high altitude station in Pune, India Authors: Satsangi, P Gursumeeran; Chavan, Suresh P; Rao, P S P; Safai, P D Abstract: Particulate matter, PM₁₀and PM_2.5, samples were collected at Sinhagad, a high altitude location, near Pune, India during November 2008 - April 2009. The average concentrations of PM₁₀, PM_2.5 and PM_10-2.5 at Sinhagad were 35.8, 14.1 and 21.7 µg m^-3, respectively. The average ratio of PM_2.5/PM₁₀ (0.39) suggested that PM₁₀ at study area is dominated by primary particulate emissions by natural activities. In PM₁₀, anions and cations contributed 33% and 67%, whereas in PM_2.5, these were 43% and 57%. In both PM₁₀ and PM_2.5, contribution of marine components, viz. Na⁺, Cl^- and Mg²⁺ were found to be 58% and 49%, respectively reflecting Arabian Sea is the major source of these components. All the ionic components in PM₁₀ showed higher concentration in summer, whereas in PM_2.5, secondary particles (SO₄^2-, NO₃^- and NH₄⁺) showed higher concentration in winter. The order of neutralization factor was found to be Ca²⁺> Mg²⁺ > NH₄⁺ > K⁺ for PM₁₀; and Ca²⁺ > NH₄⁺ > Mg²⁺ > K⁺ for PM_2.5. Source categorization, i.e. marine, crustal and anthropogenic of chemical components of PM has been done. Sea salt and crustal fractions have been calculated by assuming entire Na and Ca from Sea and crust, respectively. The fraction of the chemical component, which remains after deducting the sea and crust fractions, has been considered as of anthropogenic origin. Major contribution observed was from marine sources [PM_2.5 (43%) and PM₁₀(53%)]; followed by crustal sources [PM_2.5 (25%) and PM₁₀ (30%)]; and then anthropogenic sources [(PM_2.5 (32%) and PM₁₀(17%)]. Page(s): 284-292

Equatorial and mid-latitude ionospheric currents over the Indian region based on 40 years of data at Trivandrum and Alibag

Fri, 01 Aug 2014 00:00:00 GMT

Title: Equatorial and mid-latitude ionospheric currents over the Indian region based on 40 years of data at Trivandrum and Alibag Authors: Rastogi, R G; Chandra, H; Janardhan, P; Shah, Rahul Abstract: Forty years of geomagnetic data obtained from two Indian stations, Trivandrum (TRD) located near the magnetic equator; and Alibag (ABG) located away from the magnetic equator, for the period 1958-1998 are examined to study the daily ranges in H and in the strength of the equatorial electrojet (EEJ) obtained from the differences in the ranges at the two stations. Mean diurnal and seasonal variations in H, averaged over the 40 years are described for the two stations and for EEJ. The annual mean ranges in H show linear increases with sunspot number (Rz) and vary from 65 to 140 nT at TRD, 30 to 70 nT at ABG and from 40 to 72 nT for the EEJ. The rate of increase in H is faster at TRD than at ABG. Seasonal variations show equinoctial maxima for TRD and EEJ during the months of April and October. The range of H at ABG shows a weak secondary maximum during June-July, in addition to maxima during April and October. During the months of June-July, the range of H at ABG is stronger than that of EEJ. The occurrence of the afternoon counter electrojet is highest during low sunspot years and seasonally, during the June solstices. Page(s): 274-283