Indian Journal of Radio & Space Physics

CODEN: IJRSAK        ISSN: 0367-8393 (print); 0975-105X (online)

http://www.niscair.res.in; http://nopr.niscair.res.in

VOLUME 38

NUMBER 4

AUGUST 2009

 

                                                                           CONTENTS

 

High amplitude anisotropic events (HAE) in cosmic ray diurnal variation during Solar cycle 23

189

        R P Kane

 

 

Diurnal and seasonal variation in Pc4 occurrence at low latitudes in India

197

        I A Ansari*, K A Nafees, M T Khan, A K Sinha & B M Pathan

 

 

Analyses of Schumann resonance spectra from Kolkata and their possible interpretations

208

        S S De*, B K De, B K Sarkar, B Bandyopadhyay, D K Haldar, Suman Paul & S Barui

 

 

Subsurface thermal mapping during contrast seasons over Central Kerala

215

        Michael G Pious, S Abraham Thambi Raja* & Oscar Dhas T Xavier

 

 

Subsurface VLF electric field emissions associated with regional earthquakes

220

        Raj Pal Singh*, Manoj Kumar, O P Singh & Birbal Singh

 

 

Thermal analysis of coaxial coupler for a space helix TWT

227

Mukesh Kumar Alaria, A K Sinha & V Srivastava

 

 

PSO driven RBFNN for design of equilateral triangular microstrip patch antenna

233

Vidya Sagar Chintakindi, Shyam Sundar Pattnaik*, O.P.Bajpai & S.Devi

 

 

*Authors for correspondence

 

 

 

 

 

 

 

Indian Journal of Radio & Space Physics

Vol. 38, August 2009, pp.189-196

 

 

High amplitude anisotropic events (HAE) in cosmic ray diurnal variation during Solar cycle 23

R P Kane

Instituto Nacional de Pesquisas Espaciais – INPE, C. P. 515, 12245-970 – São José dos Campos, SP, Brazil

kane@dge.inpe.br

Received 8 November 2008; revised received 16 April 2009; accepted 20 April 2009

Cosmic ray (CR) intensity shows significant diurnal variations of day-to-day most probable amplitudes of ~0.5% (annual vector averages <0.35%), often with wave trains of high amplitude anisotropic events (HAEs) and low amplitude anisotropic events (LAEs). Using the pressure-corrected data for the neutron monitor at Calgary (51oN, 114oW, cut-off rigidity 1.09 GV) during Solar cycle 23 (1996-2005), trends were removed by subtracting 24-hour running means from the hourly values. In the residues, days were searched when the maximum value of the diurnal amplitudes exceeded 1.0%. It was noticed that there were several HAE single events (amplitude exceeding 1.0% only on one day, not on the previous or succeeding day), double events (amplitudes exceeding 1.0% on two successive days), triple events (three successive days), and so on, with some having 10 or more days in succession. These events occurred at all levels and phases of CR variations, namely when CR daily values were almost constant for several days, or when daily values decreased slowly or increased slowly (few percent in several days, including 27-day variations) or just before the start of a Forbush decrease (FD) or during the recovery of a FD (During the main phase of sharp, strong FDs, the diurnal variation is highly distorted and difficult to access, hence omitted from the study). The occurrence of HAEs was found to be unrelated to geomagnetic indices or any interplanetary near-Earth parameters and is probably related to features in remote regions of the heliosphere.

Keywords: Cosmic ray diurnal variation, High amplitude anisotropic event (HAE), Low amplitude anisotropic event (LAE), Solar cycle 23

            PACS Nos: 96.50.Wx; 96.60.qd

 

 

Indian Journal of Radio & Space Physics

Vol. 38, August 2009, pp. 197-207

 

 

Diurnal and seasonal variation in Pc4 occurrence at low latitudes in India

I A Ansari1,$,*, K A Nafees1, M T Khan1, A K Sinha2 & B M Pathan2

1Department of Physics, Aligarh Muslim University, Aligarh 202 002 (UP), India

2Indian Institute of Geomagnetism, Navi Mumbai 410 218, India

$E-mail: iaaamuphysics@gmail.com

Received 12 August 2008; revised received and accepted 19 March 2009

A study has been carried out for Pc4 geomagnetic pulsations (in 6.7 - 22.2 mHz frequency range) recorded on ground at three very low latitude stations, viz. Hanle, Nagpur and Pondicherry, in India employing three axis fluxgate magnetometers, established and operated by Indian Institute of Geomagnetism (IIG), Navi Mumbai. Digital dynamic spectra for north-south (X), east-west (Y) and vertical (Z) components of the recorded data were constructed for each day for one year (1 January 2005 to 31 December 2005). The X- and Y-component of these dynamic spectra were investigated for carrying out statistical study of diurnal and seasonal variation of occurrence of Pc4 events. The main peaks of Pc4 occurrence were detected between 1500 hrs UT (2030 hrs IST) and 2000 hrs UT (0130 hrs IST). The monthly diurnal variation provided Pc4 peak occurrence between 1700 and 1900 hrs UT (2230 - 0030 hrs IST). The seasonal variation of hourly Pc4 occurrence in both local winter and autumn was detected at 1800 - 1900 hrs UT (2330 - 0030 hrs IST) that occurred one hour later than the main peak of occurrence for the total year determined at 1700 - 1800 hrs UT (2230 - 2330 hrs IST). However, the peak in the seasonal variation of hourly Pc4 occurrence for both local autumn and summer was detected at 1700 - 1800 hrs UT (2230 - 2330 hrs IST). The observed diurnal characteristics suggest that Pc4 pulsations detected on the nightside actually originated on the dayside by an extended origin of ULF waves in the bow shock.

Keywords: MHD waves and instabilities, Solar wind - Magnetospheric interactions, Geomagnetic pulsations

            PACS Nos: 91.25.lf; 94.30.cq

 

 

Indian Journal of Radio & Space Physics

Vol. 38, August 2009, pp. 208-214

 

 

Analyses of Schumann resonance spectra from Kolkata and their possible interpretations

S S De1,$,*, B K De2, B K Sarkar1, B Bandyopadhyay1, D K Haldar1, Suman Paul1 & S Barui1

1Centre of Advanced Study in Radio Physics and Electronics, University of Calcutta, Kolkata 700 009, India

2Department of Physics, Tripura University, Tripura 799 130, India

$E-mail: de_syam_sundar@yahoo.co.in

Received 21 May 2008; revised 26 November 2008; accepted 2 March 2009

The paper deals with the study of Schumann resonance data set recorded at Kolkata (Latitude 22.56ºN). The results of analyses are confined to a period of one year (January to December 2000). The amplitude and frequency fluctuations along with some aspects of Schumann resonances (SR) during the period are investigated. The variation of global thunderstorm activity as inferred from monthly intensity fluctuations of global SR signals over Kolkata and Modra (Latitude 48.61ºN) is presented and the observed difference has been interpreted.

Keywords: ELF emission, Schumann resonance, Upper atmosphere, Lightning

            PACS No: 92.60.Pw; 92.60.Qx; 94.20.Vv

 

 

Indian Journal of Radio & Space Physics

Vol. 38, August 2009, pp. 215-219

 

 

Subsurface thermal mapping during contrast seasons over Central Kerala

Michael G Pious1, S Abraham Thambi Raja2,$,* & Oscar Dhas T Xavier2

1Manonmaniam Sundaranar University, Tirunelveli, Tamil Nadu

2Department of Physics, Lekshmipuram College of Arts and Science, Neyyoor 629 802, Tamil Nadu

$E-mail: abrahamthambiraja@yahoo.co.in

Received 19 June 2007; revised 20 June 2008; accepted 2 April 2009

Thermal mapping of seasonal variation of soil temperature at four locations of increasing altitudes in Central Kerala, India during cold and hot weather is presented based on special observations carried out during 1998. Subsurface characteristics like soil temperature, such as time lag, range of temperature; soil heat flux; and speed of the seasonal variation of annual soil temperature are determined and it is seen that lower annual rainfall at Chinnar WLS has influenced temperature range and time lag at different soil depths. The loss or gain of heat either in cold or hot weather periods are totally location based. The velocity of annual wave during cold weather is lower than hot weather as the presence of soil moisture dampens the penetration of the wave into downward layers of the soil except at Silent Valley. Non-linear behaviour of seasonal soil temperature characteristics gives the impression that localized effect due to non-homogeneous soil pattern would have played a part, apart from soil moisture.

Keywords: Thermal mapping, Seasonal variation, Soil temperature, Soil heat flux

           PACS No.: 92.40.Lg

 

 

Indian Journal of Radio & Space Physics

Vol. 38, August 2009, pp. 220-226

 

 

Subsurface VLF electric field emissions associated with regional earthquakes

Raj Pal Singh1,$,*, Manoj Kumar2, O P Singh3 & Birbal Singh3

1GLA Institute of Technology and Management, Mathura 281 406, India

2Chrysler Crop, Auburn Hills, MI, USA

3Faculty of Engineering and Technology, R B S College, Bichpuri, Agra, India

E-mail: rpsingh_ashu@yahoo.co.in

Received 18 August 2008; revised 12 March 2009; accepted 19 March 2009

A borehole antenna has been installed at Agra (latitude 27.20N, longitude 780E), India since 01 June 2006. The subsurface very low frequency (VLF) electric field emissions (f = 3.042 kHz) data has been recorded round the clock for a period of nineteen months from 01 June 2006 to 31 December 2007. This statistical analysis of data is presented in the paper. The occasional amplitude enhancement is observed in the data and  examined in the light of magnetic storms, earthquakes, and lightning activities. It is found that in majority of the cases, amplitude anomalies are correlated with moderate seismic activities occurred during the period in the region. The propagation mechanism of VLF signals from the hypocenters of earthquakes to the observing station is discussed in the paper.

Keywords: Earthquake, VLF electric field emissions, Borehole antenna

         PACS No.: 91.30.pa

 

 

Indian Journal of Radio & Space Physics

Vol. 38, August 2009, pp. 227-232

 

 

Thermal analysis of coaxial coupler for a space helix TWT

Mukesh Kumar Alaria$,*, A K Sinha & V Srivastava

Microwave Tubes Area, Central Electronics Engineering Research Institute (CSIR), Pilani 333 031, Rajasthan, India

$Email: mukesh_pilani@yahoo.co.in; mka@ceeri.ernet.in

Received 9 September 2008; revised 17 March 2009; accepted 20 April 2009

Thermal and structural analysis of the coaxial coupler for Ku-band 140 W helix space TWT have been carried out using ANSYS software v.10.1 and discussed in the present paper. To evaluate thermal and structural aspects of the coaxial coupler and helix assembly with three APBN support rods, related studies of the coupler assembly with ten turn of helix and output wave guide coupler for the Ku-band 140 W space TWT during extreme case of operation, i.e. at saturation and with perfectly rigid base-plate at 80°C have also been carried out.

           Key words: Thermal analysis, Space helix travelling wave tube, Stress analysis, Ceramic window, RF transformer, Anisotropic Pyrolytically Boron Nitrate (APBN)

           PACS Nos: 81.70.Pg; 84.40.Fe; 84.40.Ua

 

 

Indian Journal of Radio & Space Physics

Vol. 38, August 2009, pp 233-237

 

 

PSO driven RBFNN for design of equilateral triangular microstrip patch antenna

Vidya Sagar Chintakindi1,$, Shyam Sundar Pattnaik1,#,*, O P Bajpai2 & S Devi1

1Dept of ETV&ECE, NITTTR, Chandigarh 160 019, India

2Director, UIET, Kurukshetra University, Kurukshetra

E-mail: #headetv@yahoo.co.in, $chvidya66@gmail.com

Received 26 November 2008; revised received and accepted 11 May 2009

Recent advances in computer aided design packages for electromagnetic applications have helped antenna engineers to design, simulate and synthesize antennas efficiently. The PSO driven RBFNN has been developed to calculate the resonant frequency of equilateral triangular microstrip patch antenna (ETMPA). The present paper highlights the simplicity, computational efficiency and accuracy of the proposed method. The achieved results have been compared with published experimental and theoretical findings to validate the presented approach, which seems to be in very good agreements.

Keywords: Particle swarm optimization (PSO), Radial basis neural network (RBFNN), Artificial neural network (ANN), PSO drven RBFNN, Equilateral triangular microstrip patch antenna (ETMPA)

           PACS No.: 84.40.Ba