Informatics Publishing Limited

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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A. K. Sharma ¹, D. P. Nade ¹, S. S. Nikte ¹, R. N. Ghodpage ², P. T. Patil ², M. V. Rokade ¹, R. S. Vhatkar ¹, S. Gurubaran ³

Affiliations
1 Earth and Space Science Laboratory, Department of Physics, Shivaji University, Kolhapur 416 004, IN
2 Medium Frequency Radar, Indian Institute of Geomagnetism, Shivaji University Campus, Kolhapur 416 004, IN
3 Indian Institute of Geomagnetism, New Panvel, Navi Mumbai 410 218, IN

Abstract

This article describes the possibility of using the fast image analysis technique for qualitative and quantitative analysis of equatorial plasma bubble obtained using All-Sky imager (ASI) data. Automated image processing (generally) is useful for identification of equatorial plasma bubbles (EPBs) and its parameters. We have developed a fast (and efficient) analysis technique essential to study the data of images. The present work reports the results of a statistical study of the zonal plasma bubble velocities using nightglow OI 630.0 nm emission data, acquired by ASI (FOV 140°) at the low-latitude station Kolhapur (16.42°N, 74.2°E and 10.6°N dip lat.). Based on the observations of 15 nights made in January 2012, we have determined the velocity of EPB using our new method. The daily mean values of the EPB velocity match well with those of the earlier studies made at Kolhapur. We have found that, generally, the mean zonal drift velocities of the plasma bubbles tend to decrease with local time (after midnight). The most significant finding from this work is that the calculated velocities of plasma bubble using fast and scanning methods are nearly equal.

Keywords

All-Sky Imager, Equatorial Plasma Bubble, Nightglow Emissions, Zonal Drift Velocity.

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R. N. Ghodpage ¹, A. Taori ², P. T. Patil ¹, Devendraa Siingh ³, S. Gurubaran ⁴, A. K. Sharma ⁵

Affiliations
1 Medium Frequency Radar, Indian Institute of Geomagnetism, Shivaji University Campus, Kolhapur 416 004, IN
2 Atmospheric Research Laboratory, Gadanki 517 112, IN
3 Indian Institute of Tropical Meteorology, Pune 411 008, IN
4 Indian Institute of Geomagnetism, Navi Mumbai 410 218, IN
5 Department of Physics, Shivaji University, Kolhapur 416 004, IN

Abstract

The photometric measurements of mesospheric OH and O(¹S) emission, carried out from Kolhapur (16.8°N, 74.2°E), Maharashtra during January-April 2005 are used to study the wave characteristics. The nocturnal variability reveals the dominant long-period wave signatures with significant amplitudes of embedded short-period waves. We carry out a sensitivity study on the vertical wavelength (VW) derived with the help of Krassovsky parameters (η = |η|e^iΦ) of the OH data, which reveals VW to vary from 38.9 to 110.2 km. This was compared with the VW estimates using the phase difference of the simultaneously observed waves in both OH and O(¹S) emission intensities. Results reveal that in the absence of attitudinally resolved measurements, the VW estimated using Krassovsky method can be used.

Keywords

Airglow, Atmospheric Gravity Waves, Lower Thermosphere, Mesosphere, Vertical Wavelength.

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K. Jawahar ¹, S. Manu ¹, S. Gurubaran ²

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

Vector measurements of middle atmospheric electric fields are mostly carried out using a double-Langmuir probe technique on platforms like balloons and rockets. High impedances (up to 10¹³ ohms) and low signal levels (~few millivolts) are the factors that are to be considered in the design of an electrometer for one such experiment. Here, we offer a simple circuit concept that invokes an instrumentation amplifier capable of meeting our several needs, namely generating the guard voltage, ultra-high impedance (10¹⁵ ohms) input terminals, femtoampere bias current, differencing, gain setting, etc. all in one package. A three-channel differential electrometer was developed based on this concept and flown on a high-altitude balloon platform. Results reveal that the instrument is capable of detecting weak electric field variations at stratospheric altitudes.

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K. Jeeva ¹, C. Panneerselvam ¹, K. U. Nair ¹, C. Selvaraj ¹, Ajay Dhar ², B. M. Pathan ², S. Gurubaran ¹

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

Abstract

The global component of fairweather electricity is subject to special attention to watch the solar-terrestrial effects and secular changes in climate. It is generally considered that the diurnal variation of atmospheric electricity parameters, if they are not following the Carnegie pattern, are not representative of the global thunderstorm activity. Some of the results obtained from Maitri (70°45'54"S, 11°44'03"), are discussed here in context with global thunderstorm activity and space weather influences. The diurnal pattern of the Potential Gradient and current density strongly deviate from the Carnegie curve. We have showed that this deviation is not due to the local electrical influence but due to the global thunderstorm activity. During fairweather condition the parameters are representing the global thunderstorm activity and to some extent they respond to the upper atmospheric electro dynamic phenomenon. The mean value of the potential gradient (77.7 V/m) and current density (2.13 pA/m²) well below the expected global mean but close to the value reported from the same location and season in the past years. The mean conductivity, 3.34 × 10^-14 mhom^-1, is slightly at higher side and they exhibit a different diurnal trend comparing to the past measurements at this location.

Keywords

Conductivity, Conduction Current, Potential Gradient, Global Lightning Flash Numbers, Geomagnetic Substorm.

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