Indian Journal of Radio & Space Physics

Total visitors: 857  since 20-06-06

VOLUME 35

CODEN : IJRSAK

NUMBER 3

JUNE 2006

ISSN : 0367-8393

 

CONTENTS

 

Guest Editorial: Lidar probing of the atmosphere

        H Chandra*

 

147

Effects of ionospheric, magnetospheric and induced current on equatorial electrojet over India

        R G Rastogi*

 

 

149

 

Study of cosmic ray intensity variations in relation to solar activity for sunspot cycles
19 to 23

        Meera Gupta, V K Mishra & A P Mishra*

 

 

167

Study of geomagnetic storm induced acoustic gravity waves over equatorial latitude

        M Lal*

 

174

Diurnal and seasonal variation of columnar ozone at Rajkot

        Nandita D Ganguly*, R R Ranjan, H P Joshi & K N Iyer

 

181

Study of amplitude spectrum of VLF sferics and vertical electric field at Kolkata

        S S De*, B K De, S K Adhikari, B K Sarkar & A Guha

 

187

Monitoring and controlling of CO2 concentrations in open top chambers for better understanding of plants response to elevated CO2 levels

        M Vanaja*, M Maheswari, P Ratnakumar & Y S Ramakrishna

 

 

193

Investigation of VHF signals in bands I and II in southern India and model comparisons

        M V S N Prasad*, T Rama Rao, Iqbal Ahmed & K M Paul

 

198

Theoretical and experimental investigations of circular sector microstrip antenna

        Vijay Kumar Tiwari, Aradhana Kimothi, D Bhatnagar*, J S Saini , V K Saxena &        P Kumar

 

206

Frequency agile microstrip antenna using symmetrically loaded tunnel diodes

        Anil K Gautam & B R Vishvakarma*

212

 

 

_____________

*Authors for correspondence

 

 

 


Indian Journal of Radio & Space Physics
Vol. 35, June 2006, pp. 149-166

 

 

Effects of ionospheric, magnetospheric and induced current on equatorial electrojet over India

R G Rastogi

Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India

Received 14 June 2005; revised 22 December 2005; accepted 20 January 2006

The paper describes the diurnal and latitudinal variations of the horizontal (H), eastward (Y) and vertical (Z) components of the geomagnetic field at Central African, East Brazilian and Indian sectors based on the chain of magnetic observatories operated in these areas. The observations in Brazil and African sectors conform fairly well with the expectations of Chapman’s theory of equatorial electrojet. In Indian longitudes the latitudinal variation of DZ shows a large maximum simultaneously with the peak of DH over the dip equator. The daily variation of DZ shows a peak around 0900 hrs LT when the rate of increase of DH with time is largest. The peak of DZ is largest at Kanyakumari and decreases with increasing latitude of the station. The phenomenon is suggested due to sub-surface induction in southern Indian region and not confined to Palk Street. Solar flares cause a temporary increase of the ionospheric current along the pre-flare direction. Faster flares indicate induction effects at each of the equatorial stations. The storm time variation of Z also shows the sub-surface induction effects at electrojet stations in India. Storm time variations in H are shown to be enhanced over the stations close to the dip equator during the local mid-day hours. The equatorial electrojet is shown to be closely affected by ionospheric as well as magnetospheric currents and by the currents induced by these in sub-surface conducting regions.

Keywords: Equatorial electrojet, Electromagnetic induction, Equatorial storm effects.

PACS No.: 92.20 Yx; 94.20 Vv; 96.35 Pb

 

 

Indian Journal of Radio & Space Physics
Vol. 35, June 2006, pp. 167-173

 

 

 

Study of cosmic ray intensity variations in relation to solar activity for sunspot cycles 19 to 23

Meera Gupta,V K Mishra & A P Mishra

Department of Physics, A P S University, Rewa 486 003 (MP), India

Received 23 June 2005; revised 23 December 2005; accepted 14 April 2006

Based on the monthly data of various solar activity (SA) parameters, e.g. sunspot numbers (SSN), solar flux (SF), grouped solar flares (GSF), solar flare index (SFI) and coronal index (CI), a correlative study between solar activity (SA) and cosmic ray intensity (CRI, monthly mean of neutron monitor count rates) has been performed by the “running cross-correlation method”. Overall behaviour of the running cross-correlation function between CRI and different SA parameters is almost similar, except during the maxima of solar cycles. Moreover, the time-lag analysis has been performed by the method of “minimizing correlation coefficient” and it is found that observed time-lag between CRI and various SA parameters is similar, except the coronal index (CI). The time-lag is found to be larger for odd solar cycles (19, 21 and 23) in comparison to even solar cycles (20 and 22), showing odd-even asymmetry of solar cycles. The correlation between CRI and different SA parameters considering time-lag factor during the whole period of investigation has been presented. The differences observed in the time-lag between CRI and different SA parameters, especially for CI, have also been discussed.

Keywords: Cosmic ray; Solar cycles; Sunspot numbers; Solar flux; Grouped solar flares; Solar flare index; Coronal index

PACS No.: 95.85.Ry, 96.60.Qc

 

 

Indian Journal of Radio & Space Physics

Vol. 35, June 2006, pp. 174-180

 

 

Study of geomagnetic storm induced acoustic gravity waves
over equatorial latitude

 

M Lal

Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Krishnapuram,
Maharaganagar, Tirunelveli 627 011, India

E-mail: mlal@iigs.iigm.res.in

Received 23 March 2005; revised 3 January 2006; accepted 17 February 2006

An attempt has been made to study the influence of geomagnetic storm on the tropospheric acoustic gravity waves at equatorial station, Tirunelveli (8.7°N, 77.8°E), India. The daily average of the amplitude and phase of acoustic gravity waves has been studied for the period 2000-2004. Severe geomagnetic storms occurred during April and September 2000, April 2001, October and November 2003 and November 2004. It is found that geomagnetic storm influences the tropospheric acoustic gravity waves. There is a delay between the occurrence of geomagnetic storm and tropospheric acoustic gravity waves. The delay is a function of strength of the geomagnetic storm. Severe geomagnetic storm such as that of November 2004 shows a short-period delay of ~ 5 days, and strong geomagnetic storm like the one of July 2004 shows the long-period delay of about 15 days.

Keywords : Geomagnetic storm, Acoustic gravity waves, Gravity waves, Equatorial latitude

PACS Nos : 94.30.Lr ; 92.60.Dj

IPC Code : G08C23/02; G01W1/02

 

 

 

Indian Journal of Radio & Space Physics

Vol. 35, June 2006, pp. 181-186

 

 

Diurnal and seasonal variation of columnar ozone at Rajkot

 

1Nandita D Ganguly, 2R R Ranjan, 2H P Joshi & 2K N Iyer

1Department of Physics, St. Xavier’s College, Ahmedabad 380 009

nanditad@icenet.net

2Department of Physics, Saurashtra University, Rajkot 360 005

Received 25 July 2005; revised 30 January 2006; accepted 14 April 2006

Ozone data obtained from Earth-Probe Total Ozone Mapping Spectrometer (TOMS) has been used to calibrate a Microtops-II Sun photometer. Results of observed diurnal and seasonal variation of ozone at Rajkot, obtained using Microtops-II Sun photometer is reported. Since the ozone concentrations measured by Dobson spectrometers in India and TOMS are found to correlate well, it is possible to calibrate Microtops-II Sun photometer with the help of TOMS to get accurate ozone values over Indian low latitudes. This will in turn reduce the inconvenience of carrying the Microtops Sun photometer to a Dobson center for calibration. The diurnal variation of ozone measured by Microtops-II Sun photometer indicates a higher vertical column density of ozone during morning compared to evening hours. This may be due to an increase in daytime temperature and the corresponding increase in ozone by photolysis. An examination of the monthly mean ozone values obtained from Microtops-II Sun photometer indicates a marked seasonal variation with a maximum ozone concentration around June and a minimum around December.

Keywords: Columnar ozone, Microtops-II Sun photometer, Diurnal ozone variation, Seasonal ozone variation

PACS No.: 92.70.Cp

 

 

 

Indian Journal of Radio & Space Physics

Vol. 35, June 2006, pp. 187-192

 

 

Study of amplitude spectrum of VLF sferics and vertical electric field at Kolkata

S S De1 , B K De2, S K Adhikari1, B K Sarkar1 & A Guha1

1Centre for 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 6 July 2005; revised 19 October 2005; accepted 7 April 2006

From the measurements of atmospheric electric field and VLF sferics at Kolkata (22o34´ N, 88o30´ E), some correlation studies have been made. It is observed that the diurnal variation of vertical electric field averaged for 20 fair weather days maintains good connectivity with diurnal variation of VLF sferics activity. The variations are in contrast with the accepted unitary diurnal changes of vertical electric field and thunderstorm occurrence frequency curve with a maximum around 1900 hrs UT and a minimum around 0400 hrs UT. Some results in this context are presented in this paper.

Keywords: Vertical electric field, VLF sferics, Thunderstorm activities, Global electric circuit

PACS No:  92.60.Pw

 

 

Indian Journal of Radio & Space Physics

Vol. 35, June 2006, pp. 193-197

 

 

Monitoring and controlling of CO2 concentrations in open top chambers for better understanding of plants response to elevated CO2 levels

M Vanaja, M Maheswari, P Ratnakumar & Y S Ramakrishna

Central Research Institute for Dryland Agriculture, Santhosh Nagar, Hyderdabad 500 059, India

E-mail: mvanaja@crida.ernet.in

Received 25 July 2005; revised 4 January 2006; accepted 7 February 2006

The exponentially rising concentration of CO2 in the atmosphere is one of the important changes, which effectively influences the productivity of agricultural crops. Innovative approaches for conducting long-term experiments on plants have been developed to investigate the growth and yield response of different plants to predicted elevated levels of CO2. The accuracy of the results depends on the system adopted and its maintenance of the desired CO2 levels with near natural conditions for other parameters. In one of such efforts, a system for continuous monitoring and maintaining the desired level of CO2, temperature and relative humidity in open top chambers (OTCs) was developed. Carbon dioxide gas was supplied to the chambers and maintained at set levels using manifold gas regulators, pressure pipelines, solenoid valves, rotameters, sampler, pump, CO2 analyzer, PC linked Program Logic Control (PLC) and Supervisory Control And Data Acquisition (SCADA). These OTCs are cost effective for meeting the requirements of field research on CO2 enrichment.

Keywords: Elevated CO2, Open top chambers, Instrumentation and technology

PACS No.: 89.60-K; 89.60 Ec; 89.60 Fe

IPC Code: G01W1/02

 

 

 

 

 

Indian Journal of Radio & Space Physics

Vol. 35, June 2006, pp. 198-205

 

 

Investigation of VHF signals in bands I and II in southern India and model comparisons

M V S N Prasad1, T Rama Rao2, Iqbal Ahmad1 & K M Paul3

1Radio & Atmospheric Sciences Division, National Physical Laboratory, New Delhi 110 012
2Universidad Carlos III de Madrid, Leganes, Madrid, Spain
3All India Radio, Parliament Street, New Delhi 110 001

Received 29 July 2005; revised 2 January 2006; accepted 10 February 2006

In order to achieve a highly reliable communication with a simple and small receiver, one requires the knowledge of the spatial and temporal variability of field strength. This assumes greater significance in broadcasting applications where the user expects a very high quality signal. The performance of any communication circuit depends on the models employed to calculate the coverage area and interference problems. The development and identification of models is a continuing and ongoing process and there is always scope for refinement. With this objective some field strength measurements were conducted using Chennai TV and FM stations in several radials. The variability of the path loss as a function of distance has been studied and path loss exponents deduced from the observed values were compared with the model available in literature. The agreement and deviations of the model with the observed results are presented and discussed and two approaches have been proposed to compare the observed results.

Keywords: VHF signal, Communication circuit, Pathloss, Field strength.

PACs No: 84.40.Ua,

IPC code: G08C17/02; H04H1/00

 

 

Indian Journal of Radio & Space Physics

Vol. 35, June 2006, pp. 206-211

 

 

Theoretical and experimental investigations of
circular sector microstrip antenna

 

Vijay Kumar Tiwari, Aradhana Kimothi, D Bhatnagar, J S Saini & V K Saxena

Microwave Lab., Department of Physics, University of Rajasthan, Jaipur 302 004, India

and

P Kumar

 Communication System Group, ISRO Satellite Centre, Banglore 560 017, India

Received 20 May 2005; accepted 25 November 2005

An analysis of a general circular sector microstrip antenna (CSMA) with sector angle, a, is presented in this paper. The theoretical analysis is carried out by applying cavity model-based modal expansion technique. The computed results are validated with measured results for CSMA geometry with a = 60o. The computed results show a fairly good agreement with measured results. A reasonably small deviation of 1.06% in the resonant frequency is recorded, while a fairly good agreement between measured and computed return loss and radiation patterns is recorded. This validates the proposed technique of treating CSMA geometry.

Keywords: Microstrip antennas, Cavity model, Radiation patterns, Input impedance

PACS No.: 84.40.Ba, 75.50.Gg

IPC Code: H01Q9/00; H01Q21/00; H01Q23/00

 

 

Indian Journal of Radio & Space Physics

Vol. 35, June 2006, pp. 212-216

 

 

Frequency agile microstrip antenna using symmetrically loaded tunnel diodes

 

Anil K Gautam & B R Vishvakarma

Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005 (UP), India

E-mail: brv@bhu.ac.in

Received 21 March 2005; revised 27 July 2005; accepted 10 January 2006

A frequency agile microstrip antenna using symmetrically loaded tunnel diodes is proposed, in which the operating frequency of the rectangular microstrip antenna is electronically controlled by the bias voltage of the tunnel diode. Theoretical investigations, based on a modal cavity modal are carried out for the GaAs tunnel diode. The tuning range was found to be 55.92 MHz (6.67 %), which is much better than earlier reported result.

Keywords: Microstrip antenna, Tunnel diode loaded patch antenna, Frequency agile patch antenna

PACS No.: 84.40. Ba; 85.30.Mn

IPC Code: H01Q9/00; H01Q21/00; H01Q23/00