Indian Journal of Radio & Space Physics


Total visitors: 1,383  since 23-09-05

 

 

 

ISSN : 0367-8393

VOLUME 34

 

NUMBER 5

CODEN:IJRSAK 

OCTOBER 2005

 

 

CONTENTS

 

Guest Editorial: Some of the recent aspects of microwave communication in India

297

        S K Sarkar*

 

 

Patterns of long-term variations of cosmic ray intensities

299

        R P Kane*

 

 

Study of wave-particle interaction in the disturbed magnetosphere

305

        Devendraa Siingh*, Shubha Singh & R P Singh

 

 

Possible detection of ionospheric disturbances during the Sumatra-Andaman islands earthquakes of December, 2004

 

314

        Sandip K Chakrabarti*, M Saha, R Khan, S Mandal, K Acharyya & R Saha

 

 

Estimation of vertical profiles of raindrop size distribution from the VHF wind profiler radar Doppler spectra

 

319

        K Krishna Reddy*, Toshiaki Kozu, Yuichi Ohno, A R Jain & D Narayana Rao

 

 

Effect of western disturbances on LF 164 kHz propagation

328

        Darshan Singh* & Manjit Singh

 

 

Aerosols behaviour in sensitive areas of the northwestern Himalaya—A case of Kullu-Manali tourist complex, India

 

332

        Jagdish C Kuniyal*, G A Momin, P S P Rao, P D Safai, S Tiwari, K Ali & Khwairakpam Gajananda

 

 

Low frequency dielectric dispersion and microwave permittivities of Indian granites

341

        R J Sengwa* & A Soni

 

 

A new whistler recorder and analyzer developed at Agra

349

        Vikram Singh, Manoj Kumar & Birbal Singh*

 

 

Investigation of radiation properties of a right isosceles triangular microstrip antenna

353

        V K Tiwari, D Bhatnagar*, J S Saini & P Kumar

 

 

Electronic scanning in linear active antenna array

357

        Vijay K Pandey & Babau R Vishvakarma*

 

 

 

Commentary

 

 

Role of wireless technologies in connecting rural India

363

        Ashok Jhunjhunwala* & Sangamitra Ramachander

 

 

__________

 

*Corresponding authors

 

 


Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 299-304

 

 

 

Patterns of long-term variations of cosmic ray intensities

 

R P Kane

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

Received 12 January 2005; revised 5 August 2005; accepted 8 August 2005

The recovery of cosmic ray intensity has been earlier reported to have followed two distinct patterns, slow recovery during odd solar activity cycles 17, 19, 21, and fast recovery during even cycles 18, 20. Further analysis shows that the recovery in cycle 22 was fast and fitted this pattern. However, it was noticed that the sunspot number pattern also was different in even cycles as compared to the odd cycles in cycles 17-22, with step functions almost similar for sunspots and cosmic rays in even cycles. Thus, the differential effects on cosmic rays in alternate cycles could be related to sunspot activity itself. In addition, it was noticed that the correlations improved still further if solar indices in the corona, like coronal green line intensity index, were considered instead of the sunspot numbers. Hence, the hypothesis that the cosmic ray patterns might have been caused by solar polar magnetic field reversals may not be necessary.

Keywords: Cosmic ray intensity; Solar cycle; Sunspot number; Solar polar magnetic field

PACS No.: 96.60.Vg; 96.40.-z

 

 

Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 305-313

 

 

 

Study of wave-particle interaction in the disturbed magnetosphere

 

Devendraa Siingh

Indian Institute of Tropical Meteorology, Pune 411 008, India

and

Shubha Singh & R P Singh

Department of Physics, Banaras Hindu University, Varanasi 221 005, India

Received 11 October 2004; revised 23 February 2005; accepted 14 July 2005

Doppler-shifted cyclotron resonance interaction between whistler mode wave and counter streaming energetic electrons has been invoked to explain whistler triggered emissions recorded at low latitude station Varanasi (Geomagnetic latitude 14°55˘, L = 1.07) during moderate magnetic storm activity (ĺKP = 28-, KP index varies from 4- to 4+ during the observation period) on 28 Feb. 1993. The mechanism of generation of triggered emissions is briefly discussed. Parallel resonance energy of participating electrons under normal and disturbed magnetospheric conditions have been evaluated, which is found to decrease with increase in L-value and wave frequency. Applying a simplified approach we have estimated the interaction length, wave magnetic field and transverse resonant current, which are found to increase during the disturbed magnetospheric conditions. However, the number of energetic electrons participating in resonance process under normal and disturbed magnetosphere remains approximately the same.

Keywords: ELF/VLF wave, Wave-particle interaction, Magnetosphere, Whistler mode, Whistler triggered emission, Resonance energy

PACS No: 94.20Rz; 94.20 Yx; 94.30Tz;

 


Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 314-318

 

Possible detection of ionospheric disturbances during the Sumatra-Andaman islands earthquakes of December, 2004

Sandip K Chakrabarti*, M Saha, R Khan, S Mandal, K Acharyya & R Saha

Centre for Space Physics, 43 Chalantika, Garia Station Road, Kolkata 700 084

Received 17 March 2005; revised 23 June 2005; accepted 27 July 2005

The results of the continuous monitoring of ionospheric disturbances using very low frequency (VLF) radio waves during the recent Sumatran earthquake are presented. Strong and anomalous shifts in the sunset-terminator are found during 22-31 Dec. 2004. Anomalous behaviours in daytime observation are also detected. On 26 Dec. 2004, there were altogether 23 major earthquakes and aftershocks (magnitudes 5.0-9.0 on Richter scale). There were 10 such earthquakes on 27 Dec., 2 on 28 Dec., 7 on 29 Dec. and 4 on the 30 Dec. 2004. Given that there was no major earthquake on 22 December, though anomaly began on that day, it is believed that VLF monitoring could be a useful tool for earthquake predictions as well.

Keywords: Earthquake, Ionospheres, Ionospheric disturbances, Radio waves, VLF

PACS Nos.: 91.30.Px; 94.30.Va; 95.85.bh; 96.35.Kx

IPC Code: G01V1/36

 

Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 319-327

 

Estimation of vertical profiles of raindrop size distribution from the
VHF wind profiler radar Doppler spectra

 

K Krishna Reddy

Institute of Observational Research for Global Change (IORGC)/Japan Agency for
Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan

and

Toshiaki Kozu

Department of Electronic and Control Systems Engineering, Shimane University, Matsue, Japan

and

Yuichi Ohno

National Institute of Information & Communications Technology (NICT), Tokyo, Japan

and

A R Jain

Radio & Atmospheric Science Division, National Physical Laboratory, New Delhi 110 012, India

and

D Narayana Rao

National MST Radar Facility, Gadanki, Tirupati 517 502, India

Received 23 August 2004; revised 2 March 2005; accepted 5 May 2005

This paper describes research on a new form of gamma drop size distribution (DSD) model that employs two arbitrary moments as free DSD parameters to enhance the flexibility in studying the characteristics of gamma DSD model to fit the spectrum. The validity of a DSD model is evaluated in terms of the stability in solving non-linear least-squares (NLLS) problem and the accuracy in DSD moment estimates. The microphysical [i.e., raindrop size distributions (DSD)] parameters are retrieved during stratiform precipitating cloud system passed (on 23 Oct.1997) overhead of 53-MHz VHF wind profiler radar at Gadanki. The retrieved rain integral parameters were compared to the corresponding disdrometer data and a reasonably good agreement between the measurements has been found, lending credence to the VHF wind profiler radar retrievals of DSD parameters. Wind profiler radar estimated DSD during stratiform precipitation has been compared with the lognormal Indian climate model. It is observed that the pattern of DSD agrees closely with both models.

Keyword: Raindrop size distribution, Radar reflectivity, Rainfall

PACS No.: 92.60.Jq; 92.60.Ry

IPC Code: G01S13/53,G01W1/14


Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 328-331

 

Effect of western disturbances on LF 164 kHz propagation

Darshan Singh & Manjit Singh

Physics Department, Punjabi University, Patiala 147 002

E-Mail:- dsjphy@yahoo.com

Received 8 September 2004; accepted 11 May 2005

The western disturbances affect the mesosphere/lower thermosphere such that low frequency propagation field strength exhibits fadings/scintillations. The degree of effect depends upon the severity of disturbance. Periodic variations are due to internal atmospheric gravity waves and scintillations are due to irregularities produced by thundercloud activity. The study represents magnitude of electrostatic coupling between the troposphere and ionosphere.

Keywords: Western disturbances, Thunderclouds, Fadings, Scintillations

PACS No.: 92.60. Nv; 92.60. Ta; 94.20. Yx

 

Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp.332-340

 

Aerosols behaviour in sensitive areas of the northwestern Himalayaľ
A case of Kullu-Manali tourist complex, India

 

Jagdish C Kuniyal

G. B. Pant Institute of Himalayan Environment and Development, Himachal Unit, Mohal-Kullu (HP) 175 126, India
E
-mails: kuniyaljc@yahoo.com/jckuniyal@rediffmail.com

and

G A Momin, P S P Rao, P D Safai, S Tiwari & K Ali

Indian Institute of Tropical Meteorology, Dr Homi Bhabha Road, Pashan, Pune 411 008, India

and

Khwairakpam Gajananda

Shriram Institute for Industrial Research, Environment Protection Division, 19, University Road, Delhi 110 007, India

Received 4 June 2004; revised 20 April 2005; accepted 14 June 2005

Total suspended particulate (TSP) matter on fortnightly basis throughout the year and mass size distribution of aerosols as well as ultrafine aerosols on weekly basis in the months of May and June were monitored during 1996-2003 at different altitudinal locations of the Kullu-Manali tourist complex in the northwestern Himalaya. Concentration of TSP ranged from 35.8 (August 1996) to 207.3 µg m-3 (June 2003) at Mohal [1150 m from average sea level (ASL)] and from 31.7 (July 2003) to 239 µg m-3 (April 2001) at Manali (2050 m ASL). The mass size distribution of aerosols showed a bimodal distribution having one peak in the coarse size range (3.3-9 µm dia) and the other in the fine size range (0.08-2.1 µm dia) at both the locations. Ultrafine aerosol (UA) (0.001-0.1 µm radius) concentrations were found to be highest at the lowest experimental altitude site (Mohal) and vice versa. The diurnal variation of UA concentration for three years showed that the concentration ranges from 2640 (at 0500 hrs LT) to 5160 Number (N) cm-3 (at 1300 hrs LT) at Mohal and from 400 (at 0400 hrs LT) to 2190 N cm-3 (at 1300 hrs LT) at Kothi. On an average, TSP crossed its permissible limit set by National Ambient Air Quality Standard (NAAQS) level in the sensitive areas such as Kullu-Manali hill spots. Bimodal nature of mass size distribution indicates two important sources contributing in total aerosols—the fine mode, primarily due to anthropogenic activities and the coarse mode aerosols, mainly due to natural sources. Large number of concentration of ultrafine particles indicates the presence of air pollutants more at low altitudes as compared to high altitudes.

Keywords: Aerosols’ behaviour, Total suspended particulates, Mass size distribution, Ultrafine aerosols, Kullu-Manali tourist complex, Northwestern Himalaya

PACS No.: 92.60. Mt; 92.60 Sz; 92.70 Cp

IPC Code: GO1J15/06; G01W1/17

Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 341-348

 

 

Low frequency dielectric dispersion and microwave permittivities of

Indian granites

 

R J Sengwa* & A Soni

Microwave Research Laboratory, Department of Physics, J N V University, Jodhpur 342 005, Rajasthan, India

*E-mail: rjsengwa@rediffmail.com

Received 29 April 2004; revised 6 June 2005; accepted 4 July 2005

The complex dielectric permittivity e*(w) = e˘-je˘˘ of 20 Indian granite samples from various localities in India were studied in the low frequency range 0.10-100 kHz and also at microwave frequency, i.e. 10.1 GHz at room temperature. All the studied dry samples showed the dielectric dispersion in the low frequency range. These are characterized by principal relaxation time with Cole-Cole dielectric dispersion model. The values of static dielectric constant eo, high frequency limiting dielectric constant eĄ, distribution parameter a, and relaxation time t of these samples were determined from their Cole-Cole plots. The frequency dependent ac conductivity of these granite samples were also determined and discussed. The real part of dielectric constant e˘of dry granite samples at 10.1 GHz was found to be in the range 4.5-8.3. Clear convincing correlation was observed between the microwave frequency e˘ values with the samples bulk density. The plots of e˘ values versus bulk density of the studied granite samples were represented by two straight lines of different slopes. The density reduced microwave permittivity values e˘dr of granite samples were found to be in the range 1.81-1.99. For all the studied granite samples dielectric loss e˘˘ was found to be less than 0.5 at microwave frequency. Microwave permittivities of porous samples with water saturation were also measured and these values were compared with the permittivity values computed from the dielectric mixing equation, complex refractive index model and the self-similar model using the microwave permittivities of dry samples and water.

Keywords: Dielectric dispersion, Indian granite, Granite, Microwave permittivity, Permittivity

PACS No.: 91.60.Pn

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 349-352

 

 

 

A new whistler recorder and analyzer developed at Agra*

 

Vikram Singh & Manoj Kumar

Department of Physics, R B S College, Bichpuri, Agra 283 105, India

and

Birbal Singh

Department of Electronics and Communication Engineering, Faculty of Engineering and Technology,
RBS College, Bichpuri, Agra 283 105, India

Received 14 January 2005; accepted 3 May 2005

A new experimental set-up for recording and analysis of whistlers and VLF emissions has been developed at Agra, which is less expensive, automatic and time saving in comparison to earlier experimental set-up being used in different whistler stations in India. The new experimental set-up employs a crossed loop antenna, amplifiers, low pass filter, a sound card and PC with a software specially designed for recording and analysis of VLF data. Some examples of whistlers and VLF emissions recorded by the new set-up are presented and their frequency-time characteristics are discussed thoroughly.

Keywords: Whistlers, VLF emissions, DSP, New technique

PACS No.: 94.30.Tz; 94.20 B6; 84.40.-x

IPC Code: H01P5/00; H01Q1/00


Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 353-356

 

 

 

Investigation of radiation properties of a right isosceles
triangular microstrip antenna

 

V K Tiwari, D Bhatnagar, J S Saini & P Kumar*

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

*Communication System Group, ISRO Satellite Center, Bangalore 560 017

Email: dbhatnagar_2000@rediffmail.com

Received 15 January 2004; revised 29 June 2004; accepted 25 July 2005

Radiation properties of a probe fed linearly polarized right isosceles triangular microstrip antenna (RITMA) with single feed point are experimentally investigated in this paper. Radiation patterns, return loss, bandwidth and gain results obtained are compared with theoretical results. The theoretical analysis is carried out by applying cavity model based modal expansion technique. A fairly nice agreement between computed and measured results is recorded that validates the accuracy and utility of proposed technique for the analysis of RITMA geometry.

Keywords: Microstrip antenna, Cavity model, Radiation patterns, Return loss

PACS No.: 84.40 Ba; 75.50 Gg

IPC Code : H01Q-9/00; H01Q-21/00; H01Q-23/00

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, October 2005, pp. 357-362

 

 

Electronic scanning in linear active antenna array

Vijay K Pandey & Babau R Vishvakarma

Department of Electronics Engineering,

Institute of Technology, Banaras Hindu University, Varanasi 221 005, India

E-mail: brv@bhu.ac.in

Received 8 November 2004; revised 25 February 2005; accepted 21 June 2005

The beam scanning characteristics of 1×4 linear Gunn-integrated active antenna array are investigated by varying the bias voltages of the different elements in the array keeping the side lobe level at least 10 dB down the main beam level. The optimization of beam scanning by varying the bias voltage of all the four elements simultaneously exhibited a beam scanning of 40° with power deviation of 1.85 dB in main beam, which is better than the earlier reported data.

Keywords: Gunn-diode, Active antenna array, Beam-scanning

PACS No.: 84.40.Ba; 84.40.Lj

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