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Indian Journal of Radio & Space Physics

 

ISSN : 0367-8393 CODEN : IJRSAK

VOLUME 33

NUMBER 2

APRIL 2004

 

 

CONTENTS

 

 

First observations of geomagnetic field variations within equatorial electrojet belt in Sri Lanka

 

83

R G Rastogi*, Talichi Kitamura & Kentarou Kitamura

 

Magnetic disturbance effect on geomagnetic field at low latitudes

88

M E James, R G Rastogi* & D E Winch

 

 

Relationship of first two harmonics of cosmic ray daily variation with solar activity

95

C M Tiwari, D P Tiwari*, Sant P Agrawal & Pankaj K Shrivastava

 

 

Relation between shear-zone thickness, boundary layer instability and plasmoids in geomagnetosphere

 

99

G Renuka*, R Raji, M Sindhu & C Venugopal

 

 

Variations of O3 , NO2 and O4 densities in association with NAO indices during winter/spring of 1993/94 and 1994/95 at sub-Arctic station

 

104

C S Bhosale*, G S Meena, A L Londhe, D B Jadhav, Olga Puentedura & Manual Gil

 

 

Integrated satellite microwave and infrared measurements of precipitation during a Bay of Bengal cyclone

 

115

R M Gairola*, A K Varma, Samir Pokhrel & Vijay K Agarwal

 

 

Variability of dielectric constant of dry soil with its physical constituents at microwave frequencies and validation of the CVCG model

 

125

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

 

Potential and field distribution inside an axially split cylinder

130

B N Das* & Arun Gayen

 

 

A compact broadband gap-coupled microstrip antenna

139

S N Mulgi, R M Vani, P V Hunagund* & P M Hadalgi

 

 

*Corresponding authors

 

 

Indian Journal of Radio & Space Physics

Vol. 33, April 2004, pp. 83-87

 

 

First observations of geomagnetic field variations within equatorial electrojet belt in Sri Lanka

 

R G Rastogi*and Talichi Kitamura & Kentarou Kitamura

 

The daily variations of the geomagnetic horizontal (H), eastward (Y) and vertical (Z) fields at any equatorial electrojet station south of India have been described, for the first time, using the data from Peredinia, Sri Lanka (geogr. lat. 7.3°N, long. 80.6°E, dip lat. 1.3°S). An abnormal positive peak in the daily variation of the Z field at Peredinia (PRD) in the forenoon hours, stronger in magnitude to corresponding abnormality in Z at Trivandrum (TRD), India has been detected. There is a remarkable correspondence between DZ at Trivandrum and Peredinia on day-to day-basis, the variations being stronger at Peredinia than at Trivandrum. During a magnetic storm a sharp decrease of DZ is observed few hours before the maximum decrease of H at both PRD and TRD. These observations show, for the first time, that the induction anomalies in the equatorial electrojet region in Indo-Sri Lanka longitudes extend well beyond the southern tip of Indian Peninsula. The phenomenon of subsurface induction in Indian longitudes needs to be seriously reconsidered.

 

Keywords: Equatorial electrojet, Geomagnetic storm, Sri Lanka, Electromagnetic induction

PACS No.: 94.30.Lr; 94.30.Kq

 

 

 

Indian Journal of Radio & Space Physics

Vol. 33, April 2004, pp. 88-94

 

Magnetic disturbance effect on geomagnetic field
at low latitudes

M E James & R G Rastogi and D E Winch

 

Relationship between daily means of H and Y fields with Dst index for stations with in a low latitude belt around the world has been investigated. The H field decreases linearly with decreasing Dst, the slope being less than unity at all stations. But Y field variation with Dst exhibited a longitudinal dependence. The ring current follows the dipole coordinates and not the dip coordinates and hence changes in Y field are related to both dipole declination (y) and dip declination (D) such that DY/DH = sin(y-D), both in sign and magnitude. Good correspondence is seen between DY/DH and sin(y-D) for all stations in the equatorial belt.

 

Keywords: Geomagnetic storms, Dst index, Dipole and dip declination

PACS No: 91.25-r ; 94.30.Lr

 

 

 

Indian Journal of Radio & Space Physics

Vol. 33, April 2004, pp. 95-98

 

Relationship of first two harmonics of cosmic ray daily
variation with solar activity

C M Tiwari, D P Tiwari & Sant P Agrawal and Pankaj K Shrivastava

 

Systematic correlative studies have been performed since long to establish the relationship of cosmic ray anisotropy with solar activity parameters, and the studies are extended for the recent periods. In this analysis, yearly averages of sunspot numbers Rz have been used to correlate with the yearly average amplitudes and phases of the first two harmonics of the daily variation of cosmic rays derived from the data of stations Kiel and Tokyo, representative of low and high cut-off rigidity, respectively. Significant positive correlations, both for the diurnal amplitude and phase, have been observed. Similarly, positive correlations with sunspot numbers are also noticed in case of semi-diurnal phase for both the stations. However, the semi-diurnal amplitudes of the daily variation of cosmic rays show small negative correlation with Rz.

 

Keywords: Cosmic rays, Sunspot number, Solar activity

PACS No.: 96.40cd; 96.40Kk

 

 

 

Indian Journal of Radio & Space Physics

Vol. 33, April 2004, pp. 99-103

 

Relation between shear-zone thickness, boundary layer instability and plasmoids in geomagnetosphere

 

G Renuka & R Raji, M S Sindhu and C Venugopal

 

A study of the dependence of shear-zone thickness on the growth rate and frequency of Kelvin-Helmholtz instability (KHI) in the shear-zone between low latitude boundary layer (LLBL) and central plasma sheet (CPS) is carried out. It is found that the growth rate and frequency are maximum for a shear-zone of minimum thickness. The amplitude of plasma sheet (PS) oscillation is found to be positive as the PS thickness increases and is maximum when PS thickness is 2RE (1RE = 6378 km) for a shear-zone of minimum thickness. This perturbation generates tearing mode instability (TMI) which leads to the formation of plasmoids.

 

Keywords : Plasmoid, Kelvin-Helmholtz instability, Tearing mode instability, Shear-zone thickness, Geomagnetotail

PACS No. 52.35. Py

 

 

 

Indian Journal of Radio & Space Physics

Vol. 33, April 2004, pp. 104-114

 

Variations of O3, NO2 and O4 densities in association
with NAO indices during winter/spring of 1993/94 and 1994/95 at sub-Arctic station

C S Bhosale, G S Meena, A L Londhe & D B Jadhav  and  Olga Puentedura & Manual Gil

 

A study of the atmospheric trace constituents like O3, NO2 and O4 has been made in the visible spectral region 550-595 nm. The data for the above study have been obtained from the daily observations of the light intensity taken at twilight hours in the early morning and evening by using an automatic spectrometer at the sub-Arctic station Reykjavik (64°N, 22.6°W) for the months December-April (winter/spring) of 1993/94 and 1994/95. The Differential Optical Absorption Spectroscopy (DOAS) technique has been used to obtain slant column density (SCD) of O3, NO2 and O4 from the above light intensity. Further, vertical column densities (VCDs) of O3 and NO2 have also been calculated at solar zenith angle (SZA) 90° by dividing above SCD with a proper value of air mass factor. The results of the above analyses have shown that there exists a predominant daily variation in the VCDs of O3 and VCDs of NO2 at both morning and evening twilight hours. There exists one oscillation within the daily variations of O3 and NO2; this oscillation is confined to the same period of 3-10 days (visual appearance). These periodic oscillations are found to have coincided with the oscillation of the stratospheric warm and cold episodes during the above period of observations. It is interesting to note that the evening twilight hour magnitudes of O3 and NO2 are slightly higher than those of the morning twilight hour magnitudes, but they are in phase with each other. The variations of the VCD O3 and VCD NO2 have been correlated with the North Atlantic oscillation (NAO) index. The correlation coefficients are +0.21 and +0.25 between VCD O3 and NAO index in 1993/94 and 1994/95, respectively. But VCDs of NO2 seldom show any relationship with NAO index. Also, the daily variations in SCDs of O4 are studied in connection with the different types of clouds prevailing at the Arctic station during winter/spring of 1993/94 and 1994/95. There exists strong variability of O4 with variations of the type of clouds.

 

Keywords: Trace constituents, Stratospheric warmings, Potential vorticity, Vertical Column Density, Polar Vortex, North Atlantic oscillation index

PACS No: 92.60.Hp

IPC Code: G01W 1/10

 

 

  

Indian Journal of Radio & Space Physics

Vol. 33, April 2004, pp. 115-124

 

Integrated satellite microwave and infrared measurements of precipitation during a Bay of Bengal cyclone

R M Gairola, A K Varma, Samir Pokhrel & Vijay K Agarwal

 

In the present paper, an approach for integrated IR and microwave measurements using various satellite sensors have been used for the study of a severe cyclone over Bay of Bengal and adjoining Eastern India and Bangladesh during 24-29 April 1991. The rain estimates from measurements of brightness temperatures from Special Sensor Microwave/Imager (SSM/I) and Outgoing Longwave Radiation (OLR) from IR radiances of polar orbiting and geostationary satellites have been used. Since the OLR derived rainfall exhibit a larger spatial spread with lower intensities in rainfall fields, we have followed the above procedure for optimally combining both the observations for more realistic rainfall on regional scale to study precipitation fields. Since the OLR rains are well represented spatially and temporally by more frequent observations from both geostationary and polar orbiting satellites, the algorithm sharpens the IR derived rains and augments it to the microwave derived rain. The combined IR and microwave rain algorithm brings out the finer details of the cyclone structure and precipitation fields, and thus seems to be highly promising for operational applications. Some aspects of the associated wind fields are also examined for their relationship with tropical rain intensity in the present case. A comparison of rainfall is performed with rare in-situ observations over the coastal regions during the severe cyclone.

 

Keywords: Infrared; Microwave; Precipitation; Cyclone; SSM/I; Outgoing Longwave Radiation

PACS No.: 92.40.Ea; 92.60.Qx

IPC Code: G01W1/00; G01W1/02

 

 

 

Indian Journal of Radio & Space Physics

Vol. 33, April 2004, pp. 125-129

 

Variability of dielectric constant of dry soil with its physical constituents at microwave frequencies and validation of the CVCG model

 

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

 

In the designing of active and passive sensors for microwave remote sensing of soil, its electrical parameters like scattering coefficient and emissivity play a vital role. One of the important parameters on which these two depend is the value of the dielectric constant that again varies with the physical constituents of the soil. In this paper, an attempt has been made to study the variability of the dielectric constant of dry soil with its physical constituents. The soil samples are taken from different parts of northern India and variations of dielectric constant as observed in the X-band are presented here. The CVCG model, generated to compute the dielectric constant for dry soil from its physical constituents has also been validated.

 

Keywords: Dielectric constant, Soil, CVCG model, Sensors, Remote sensing, Microwave remote sensing

PACS No. 95.75 Rs; 84.40 Xb

IPC Code: G01N33/24

 

 

 

Indian Journal of Radio & Space Physics

Vol. 33, April 2004, pp. 130-138

 

Potential and field distribution inside
an axially split cylinder

 B N Das & Arun Gayen

 

The paper presents a method of evaluation of potential and field distribution inside an axially split cylinder, one part of which is insulated and other maintained at ground potential. The Laplace’s equation expressed in cylindrical polar co-ordinates is solved assuming no axial variation, and using boundary condition for the potential. The radial and angular components of the field intensity are found using the appropriate derivative operator in the cylindrical co-ordinate system. The condition under which the radial field is maximum, is derived in terms of angular widths of the conductors. If the radial field intensity exceeds the breakdown limit, the resulting breakdown of the gas leads to plasma generation inside the structure.

 

Keywords: Split cylinder, Laplace’s equation, Potential distribution, Field intensity distribution.

PACS No: 77.22 Jp, 84.40 Ua

IPC Code: H01S-3/00

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, April 2004, pp. 139-141

 

A compact broadband gap-coupled microstrip antenna

S N Mulgi1, R M Vani2, P V Hunagund1 & P M Hadalgi1

 

A method for improving the bandwidth of microstrip antenna by incorporating a common parasitic element, which is gap-coupled to the radiating edges of rectangular patches, is described. This technique makes the proposed antenna structure compact in size with a bandwidth of around 22%. The theoretical bandwidth and input impedance for the proposed configuration are also evaluated. Experimental and theoretical results are found to be in good agreement.

 

Keywords: Microstrip antenna, Gap-coupled antenna, Broadband antenna

PACS No.: 84.40Ba

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