Total visitors:1,080 since 24-09-04

Indian Journal of Radio & Space Physics

 

 

 

ISSN : 0367-8393

 

CODEN:IJRSAK

VOLUME 33

NUMBER 5

OCTOBER  2004

 

CONTENTS

Unusual behaviour caused by interplanetary turbulences in cosmic ray intensity

285

Rajesh K Mishra* & Rekha Agarwal Mishra

 

 

Thermodynamics of near earth plasma sheet and specific entropy parameter during substorm A case study

 

294

P R Prince* & G Renuka

 

 

Analytic solution of scattering field and its characteristics for an ellipsoid

301

Li Ying-le* & Huang Ji-ying

 

 

Antarctica sea-ice and monsoon variability

306

S S Dugam* & S B Kakade

 

 

Electric field measurements of overhead thunderstorm at a tropical station using network of plate antennas

 

310

M Mohanty & P Pradeep Kumar*

 

 

Neural network implementation of transmission line model for loss evaluation in sand and dust storms

 

316

R P S Gangwar, S Mathur & Avinash Kumar*

 

 

Emission and scattering behaviour of dry soils from northeast India

321

O P N Calla*, A Baruah, B Das, K P Mishra, M Kalita & S S Haque

 

 

Dielectric behaviour of shale and calcareous sandstone of Jodhpur region

329

R J Sengwa*, A Soni & B Ram

 

 

Investigations of radiation properties of a circular disk microstrip antenna with a slot

336

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

 

 

Compact rectangular microstrip antenna with group of slots on ground plane

341

R M Vani*, S F Farida & P V Hunagund

 

 

*Corresponding authors

 

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, October 2004, pp. 285-293

 

Unusual behaviour caused by interplanetary turbulences in cosmic ray intensity

Rajesh K Mishra1 & Rekha Agarwal Mishra2

 

The unusually high/low amplitude anisotropic wave train events (HAEs/LAEs) in cosmic ray intensity using the ground based Deep River neutron monitor data have been studied during the period 1991-94. It has been observed that the phase of diurnal anisotropy for majority of HAE/LAE cases remains in the same co-rotational direction. The phase of diurnal anisotropy has shifted to later hours for some of the HAE cases, whereas it shifts towards earlier hours for some of the LAE cases. Further, for majority of HAE/LAE cases the amplitude of semi-diurnal anisotropy remains statistically the same; whereas, the phase of semi-diurnal anisotropy for all HAE/LAE cases has shifted to later hours. Furthermore, for tri-diurnal anisotropy the phase shifts towards later hours for both type of events; while, amplitude remains statistically the same. The interplanetary magnetic field (IMF) and solar wind plasma (SWP) parameters during these events are also investigated. The possible sources causing these types of unusual events have been proposed.

 

Keywords: Cosmic rays, Diurnal anisotropy, Semi-diurnal anisotropy

PACS Nos.: 96.40.Kk, 96.40. -z, 96.40.cd

 

  

 

Indian Journal of Radio & Space Physics

 Vol. 33, October 2004, pp. 294-300

 

Thermodynamics of near earth plasma sheet and specific entropy parameter during substorm A case study

P R Prince and G Renuka

 

Heat transactions in the near earth plasma sheet at ISEE-2 site during the full course of a single substorm is analysed. The selected substorm was shown to exhibit an adiabatic growth phase with non-adiabatic expansion and recovery phases. During growth phase, the sheet acts as a mere passage for the flow of energy from solar wind into the earths atmosphere, supporting the driven model of substorms. The substorm analysed, in general, was a non-adiabatic event. The polytropic index η has proved to be unsuccessful in predicting the thermodynamic state of plasma sheet during substorm. Specific entropy parameter is suggested as a better tool for such predictions.

 

Keywords: Near earth plasma sheet, Substorm, Specific entropy

PACS No.: 52.35.Py

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, October 2004, pp. 301-305

 

Analytic solution of scattering field and its characteristics for an ellipsoid

Li1,2 Ying-le & Huang Ji-ying1

 

The analytic solution of scattered field by an ellipsoid of any shape is presented utilizing transformation of coordinates. The cross polarization discrimination (XPD) of electromagnetic waves induced by the ellipsoid is derived and simulated. Results show that XPD changes depend on ellipsoidal size, shape and observing location. The XPD varies smoothly with the shape at the forward points in comparison with that at the backward points. For a given shape, measuring in opposition to the incident direction provides the maximum in XPD.

 

Keywords: Coordinate transformation, Ellipsoid, Scattering field.

PACS No: 92.60.Jq; 92.60.Mq

 

 

 

Indian Journal of Radio & Space Physics

Vol. 33, October 2004, pp. 306-309

 

Antarctica sea-ice and monsoon variability

S S Dugam & S B Kakade

 

This study statistically evaluates the relationship between satellite derived Antarctic sea ice extent and Indian summer monsoon variability over the various homogeneous regions of India. Analysis is carried out for 22 years (1979-2000). From the analysis it is observed that preceding winter (December-January-February) sea-ice anomaly has an inverse association with the performance of the following monsoon. It is observed that deficient monsoon years are preceded by more than normal sea-ice extent, and in excess or normal monsoon years the sea ice extent is less than the normal. The relationship is statistically significant at 1% level. From the study it is found that southern peninsular India does not show a significant relationship.

 

Keywords: Antarctic sea-ice, Monsoon variability, Indian summer monsoon

PACS No: 92.60.Wc; 92.60.Ry

IPC Code: G01 W 1/00; G01 W 1/10; G01 W 1/11

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, October 2004, pp. 310-315

 

Electric field measurements of overhead thunderstorm at a tropical station
using network of plate antennas

M Mohanty & P Pradeep Kumar

 

Electric field measurements due to lightning discharge from overhead thunderstorms were carried out by using a network of five plate antennas which covered an area of 6 km2 over Pune, a tropical station and a plateau region about 560 m above mean sea level. Three ground lightning discharges from two thunderstorms were analyzed. From the field measurements the height and magnitude of the charge centre has been determined. Two of the ground discharges analyzed originated from the lower positive charge pocket and were located below the freezing level. The negative charge centre is located above the freezing level. The recovery time of electric field due to positive discharge (positive charge getting destroyed in the cloud) is about three times more than that of the field recovery after a negative discharge.

 

Keywords: Lightning discharge, Thunderstorm, Plate antenna

PACS No.: 92.60.Pw

IPC Code: G 01 W 1/16; H 01 Q 21/00

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, October 2004, pp. 316-320

 

Neural network implementation of transmission line model for
loss evaluation in sand and dust storms

R P S Gangwar, S Mathur & Avinash Kumar

 

Neural network implementation of transmission line model (TLM) for loss evaluation in sand and dust storm is carried out for different path lengths and visibilities as the function of frequency. A neural network model (NNM) is developed for the transmission line model. The data obtained from the developed model are in good agreement with transmission concept for the various transmission parameters.

 

Keywords: Neural network, Sand storm, Dust storm, mm-wave propagation

PACS No: 84.35.+I, 41.20 Jb

IPC Code: G 08 C 17/02

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, October 2004, pp. 321-328

 

Emission and scattering behaviour of dry soils from northeast India

O P N Calla and A Baruah, B Das, K P Mishra, M Kalita & S S Haque

 

With the database of the dielectric constants of four dry soils from Assam and one dry soil from Meghalaya, the computations of emissivity and scattering coefficient have been carried out using emissivity model and perturbation model, respectively. The database of estimated emissivity and scattering coefficient have been generated at different frequencies of X-band from 8 GHz to 10 GHz. The estimations are made at 12 different angles of incidence and for both vertical and horizontal polarization. The values of emissivity and scattering coefficient can be used for designing passive and active remote sensing sensors.

 

Keywords: Dielectric constant, Emissivity, Scattering coefficient, Soil, Sensors, Remote sensing

PACS No: 45.75 Rs; 84.40 Xb

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, October 2004, pp. 329-335

 

 

Dielectric behaviour of shale and calcareous sandstone of Jodhpur region

R J Sengwa1, A Soni1 & B Ram2

 

Dielectric permittivity e and loss e of dry and water saturated shale, sandy sandstone (sandy shale) and calcareous sandstone of Jodhpur region were studied at room temperature in the frequency range from 100 Hz to 100 kHz and also at 10.1 GHz. It is observed that the e values of these samples decrease with increase in frequency. The complex plane plots (e versus e) of these geological materials are Cole-Cole arcs. The low frequency limiting dielectric constant eo, high frequency limiting dielectric constant e, dielectric relaxation time t and distribution parameter a of these samples have been determined from these Cole-Cole plots. The ac conductivity of dry and water-saturated samples has also been reported. The large enhancement in the permittivity value of water-saturated samples was found due to electrochemical polarization. Further it is observed that the increase in e value of water saturated shale and sandy sandstone is proportional to the volume fraction of water absorbed in the samples. The effect of the density, porosity, grain sizes and chemical composition on the frequency dependent dielectric permittivity of these samples has been explored.

 

Keywords: Dielectric permittivity, Dielectric relaxation time, Cole-Cole plots, Sandstone, Conductivity

PACS No: 77.22 Gm; 84.40 Xb

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, October 2004, pp. 336-340

 

Investigations of radiation properties of a circular disk microstrip antenna with a slot

V K Tiwari1, V Bhardwaj2, J S Saini1, P Kumar3, K B Sharma2 & D Bhatnagar1

 

The radiation characteristics of a circular disc microstrip antenna (CDMAS) carrying a narrow slot on its surface are investigated experimentally and measured results are compared with computed results. The theoretical analysis of this antenna is carried out by applying cavity model-based modal expansion technique. A reasonably good agreement between computed and measured results is recorded which verifies the theoretical formulation applied in this work.

 

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. 33, October 2004, pp. 341-343

 

Compact rectangular microstrip antenna with group of slots on ground plane

R M Vani, S F Farida and P V Hunagund

 

A compact rectangular microstrip antenna is realized by embedding slots on the ground plane with increased impedance bandwidth and gain. In this paper the typical configurations of slots are studied by putting group of narrow vertical slots on ground plane parallel to the patch radiating edge. The experimental results show a good agreement with the simulated results.

 

Keywords: Compact microstrip antenna, Microstrip antenna, Ground plane slots, Bandwidth enhancement

PACS No: 84.40 Ba

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