Current Science

S. Manu ¹, R. Rawat ², A. K. Sinha ², S. Gurubaran ², K. Jeeva ¹

Affiliations
1 Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli 627 011, IN
2 Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai 410 218, IN

Abstract

Schumann resonances (SRs) are the AC components of the global electric circuit and are excited by the lightning activity within the Earth-ionosphere waveguide. An induction magnetometer, which was operated from the Indian Antarctic station, Maitri (70.8°S, 11.7°E), served to examine the SR parameters, namely the amplitude and frequency, in the north-south (H_NS) and east-west (H_EW) magnetic components. The analysis for the first resonant mode presented in this work reveals a strong UT variation in its amplitude in seasonal as well as yearly timescales. The NS amplitude reveals a semi-diurnal variation with peaks at ~1000 and ~2100 UT, whereas the EW amplitude exhibits a strong diurnal variation with a pronounced peak at 1600 UT. The diurnal curves for the frequency for both components are similar in nature to those for the amplitude, but for a time shift. The diurnal trend in the amplitude is retained irrespective of seasons, whereas significant difference are noticed in the frequency behaviour between the summer and winter seasons, especially in the EW component. The observed diurnal variation in the SR intensity is explained in terms of the dominant thunderstorm activity centred over the three convectively active regions: Asia/Maritime Continent (Indonesia), South America and Africa. The diurnal variation in frequency depends not only on the location of the thunderstorm region with respect to the observer, but also on the ionospheric day/night conditions and the Earth-ionosphere cavity thickness.

Keywords

Diurnal Variations, Global Electric Circuit, Lightning, Schumann Resonances.

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N. Garg ¹, A. K. Sinha ², M. K. Sharma ³, V. Gandhi ², R. M. Bhardwaj ², A. B. Akolkar ², R. K. Singh ³

Affiliations
1 CSIR-National Physical Laboratory, New Delhi 110 012, IN
2 Central Pollution Control Board, Parivesh Bhawan, East Arjun Nagar, Delhi 110 032, IN
3 Delhi Technological University, Delhi 110 042, IN

Abstract

We describe the diversified National Ambient Noise Monitoring Network (NANMN) set up across 7 major cities of India and covering 70 stations for continuous noise monitoring throughout the year. The annual average L_day (06–22 h) and L_night (22–06 h) values observed in 2015 for these 70 locations are described. Of these, 25 locations are in commercial zones, 12 in industrial, 16 in residential and 17 in silence zones. Each city has 10 noise monitoring stations installed for analysing environmental noise pollution levels round the clock (24 x 365 h). The long-term noise monitoring shows that ambient noise levels are very high compared to the recommended standards for some sites and thus noise abatement measures are essentially required for controlling these levels. The present study is focused on evaluation, analysis and reporting of environmental noise pollution in seven major cities of India and is instrumental in planning for the noise abatement measures for controlling noise pollution in these cities. Such a noise monitoring network established in India is unique and one of the largest noise monitoring networks of its kind across the globe.

Keywords

Day Equivalent Level, Day–Night Average Sound Level, National Ambient Noise Monitoring Network, Night Equivalent Level.

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