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Indian Journal of Radio & Space Physics

 

 

 

ISSN : 0367-8393

 

       CODEN : IJRSAK

VOLUME 34

NUMBER 1

FEBRUARY 2005

 

 

CONTENTS

 

 

Editorial: Radio Science and South Asia

9

A P Mitra*

 

 

Comparative study of different solar parameters with sunspot numbers

13

V K Mishra*, D P Tiwari, C M Tiwari & S P Agrawal

 

 

Alfven wave in the presence of parallel electric field in the magnetospheric plasma

17

J Shrivastava & M S Tiwari*

 

 

Spatial correlation function of intensity variations in the ground scintillation pattern produced by equatorial spread-F irregularities

 

23

B Engavale & A Bhattacharyya*

 

 

Modified Angstrom coefficients for the sunshine-irradiation correlation

33

M M Rahman* & M Zakaria

 

 

Chemistry of sulphur and nitrogen species and other major cations/anions in fog water

42

Anita Lakhani*, G S Satsangi, R S Parmar & Satya Prakash

 

 

Interannual variability of precipitable water vapour – ENSO/LNSO signal

50

A A L N Sarma* & V Vizaya Bhaskar

 

 

Effect of aerosols on erythemal ultraviolet radiation

56

K Madhavi Latha* & K V S Badarinath

 

 

Study of infrasonic waves at low latitude northern hemisphere, India

62

M Lal*

 

 

Estimation of emissivity and scattering coefficient of the constituents of vegetation at microwave frequencies

 

67

O P N Calla*, Avdhesh Roop Rai, Prannoy Mathur, Deepak Mathur & Dinesh Bohra

 

 

Characterization of ferrite and silicon carbide based microwave absorber using FSS structures at X-band

 

71

M R Meshram*, Nawal K Agrawal, Bharoti Sinha & P S Misra

 

 

Dual-frequency slot-loaded rectangular microstrip antenna

75

Usha Kiran K, R M Vani & P V Hunagund*

 

 

 

____________________

 

*Corresponding authors

 

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 13-16 

 

Comparative study of different solar parameters with sunspot numbers

V K Mishra*, D P Tiwari, C M Tiwari & S P Agrawal

 

Based on the monthly data of various solar parameters e.g. sunspot numbers (SSN), sunspot area, grouped solar flares (GSF) and solar flare index (SFI) for the last four solar cycles (19 to 22) as well as for the present cycle 23 (up to year 2003), a detailed correlative study has been performed. It has been found that, on monthly average basis, the SSN are highly correlated with other solar parameters and hence, SSN can be safely used as a solar parameter for any correlative study, until and unless there are some specific reasons to use other easily available solar parameters (or indices). Moreover, it was found that with the progression of solar cycle, from cycle 20 to 23 the slope of the regression line between SSN and GSF or SFI decreases continuously. However, no such unidirectional change is observed in the correlation coefficient.

 

Keywords: Sunspot number; Sunspot area; Grouped solar flares; Solar flare index; Solar cycles

PACS No: 96.60 Rd; 96.60 Qe

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 17-22

 

Alfven wave in the presence of parallel electric field in the magnetospheric plasma

J Shrivastava & M S Tiwari

 

The effect of upward parallel electric field observed along the auroral field lines on the Alfven wave model of magnetosphere-ionosphere coupling is examined through the modification of the particle thermal velocity parallel to ambient magnetic field. Effects of electron beam generated in the plasma-sheet region and impinging the ionosphere, and temperature anisotropy of the acceleration region have been also considered. The enhancement of the auroral upward field-aligned current in the region of parallel electric field is predicted as observed by S3-3 satellite and polar satellite data.

 

Keywords: Alfven wave, Magnetosphere, Electron-beam, Field-aligned currents

PACS No.: 52.35 Hr, 94.10 Rk

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 34, February 2005, pp. 23-32

 

Spatial correlation function of intensity variations in the ground scintillation pattern produced by equatorial spread-F irregularities

B Engavale & A Bhattacharyya

 

A theoretical model is used to relate the spatial variations found in intensity scintillation patterns formed on the ground due to scattering of VHF radio waves by equatorial ionospheric irregularities, with the spatial structure of these irregularities. As equatorial ionospheric irregularities are closely aligned with the geomagnetic field, they may be considered to constitute a two-dimensional dispersive random medium. Electron density variations, which produce refractive index irregularities in the medium, are assumed to be characterized by a power law spectrum. A numerical solution of the equation satisfied by the fourth moment of intensity variations, in the plane of the receiver, is obtained using the split step method. The S4-index, which is the standard deviation of normalized intensity variations as well as spatial correlation function of intensity, is obtained by considering special cases of the fourth moment of intensity variations. Variation of S4-index with the standard deviation of phase fluctuations imposed by the ionospheric irregularities is studied for irregularities with different power spectral indices. Effect of varying phase fluctuations on the 50% de-correlation scale length is also studied for weak as well as strong scintillations. The S4-index and spatial scale lengths in the ground scintillation pattern depend on parameters like thickness and height of the irregularity layer, background plasma density, standard deviation of electron density fluctuation and irregularity power spectrum. The theoretical model is used to understand the roles of these parameters in determining the S4-index and spatial correlation function of intensity in the ground scintillation pattern.

 

Keywords: Equatorial ionosphere, Ionospheric irregularities, Scintillations, Correlation function

PACS No.: 92.20 Bb; 94.20 Rr

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 33-41

 

Modified Angstrom coefficients for the sunshine-irradiation correlation

M M Rahman & M Zakaria

 

Model parameters are achieved very often by the least square method (LSM) and regression technique between irradiation and bright sunshine data. A new variance method (VRM) is used for finding the modified Angstrom coefficients (a, b) using the same set of data. Some other methods (such as latitude method (LM), Reitveld method (RVM) etc.), which are dependent on geographical as well as meteorological parameters, are also employed in this work. The study of levels of performance of these methods shows that the VRM and LSM predict the global solar radiation H with better accuracy than other methods. The index of agreement d indicates a little better performance of VRM over LSM. Latitude method (LM) does not give satisfactory results at lower latitude f of the site. Analysis shows that the LM might be applicable for the latitudes ³10°N safely with a maximum deviation of 6 % where only the sunshine data are available. Polynomial behaviour of the sunshine-irradiation relationship along with the linear form is also studied to know actually which form belongs to them.

 

Keywords: Angstrom coefficients, Modified Angstrom coefficients, Solar radiation, Global solar radiation

PACS No.: 96.60.Tf

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 34, February 2005, pp. 42-49

 

Chemistry of sulphur and nitrogen species and
other major cations/anionsin fog water

Anita Lakhani, G S Satsangi*, R S Parmar & Satya Prakash

 

Fog water, aerosols and gas phase samples were collected during the months of December 2000 and January 2001 at Dayalbagh, Agra. Major cations (Ca2+, Mg2+, Na+ and K+) and anions (F-, Cl-, NO3- and SO42-) were analysed by ICP-AES and ion chromatography in the fog and aerosol samples, while gaseous species like SO2, HNO3, NH3 (as NH4+) and O3 were measured by colorimetric method. The species NH4+, NO3- and SO42- were the dominant ions in fog water, which was  inferred as the influence of agricultural and fuel combustion activities on fog composition. In all the samples, Ca2+/Mg2+ ratio was almost constant indicating their origin from soil, while the Ca2+/K+ ratios was highly variable indicating release of K+ from combustion sources. High concentration of SO42- in fog water samples are attributed to its formation by the aqueous phase oxidation of SO2. Calculated values show that oxidation of SO2 is facilitated by O3 concentration rather than Mn2+ catalyzed reactions. High concentrations of NO3- and NH4+ in fog water samples may be due to dissolution of NO3- and NH4+ aerosols.

 

Keywords: Aerosols, Cations, Anions, Fog water, Chromatography

PACS Nos: 92.60.Jq;  92.60. Mt

IPC Code: G01W1/02

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 50-55

 

Interannual variability of precipitable water vapour—ENSO/LNSO signal

 A A L N Sarma and V Vizaya Bhaskar

 

Knowledge of the quantity of precipitable water vapour content (PWVC) in space and time over a region is of fundamental importance in hydro-meteorological studies. In the present investigation using the radiosonde data for a 17-year period from 1984 to 2000, the mean monthly precipitable water for Visakhapatnam (lat.17°43¢N, long.83°14¢E) is evaluated for the layers surface to be 500 mbar. The inter-annual and intra-seasonal variation of precipitable water vapour and its relation to the mean monthly rainfall have been discussed. Seasonal cycles of precipitable water during ENSO (El Nino Southern Oscillation) and LNSO (La Nina Southern Oscillation) periods along with normal are reported. The paper also deals with cycling rates of moisture flux and percentage occurrence of rainfall from the corresponding amount of precipitable water vapour content.

 

Keywords: Precipitable water vapour, ENSO event, LNSO event, El Nino, La Nina

PACS No: 92.40.Ea; 92.60.Jq


 

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 56-61

  

Effect of aerosols on erythemal ultraviolet radiation

K Madhavi Latha & K V S Badarinath

 

The present study reports, for the first time, on seasonal variation of UV erythema (UVery) and its relation with aerosols over a typical urban environment of Hyderabad, India during 2001-2003. Drastic reduction in UV intensities has been observed during periods of high aerosol loading. Comparison of UVery intensities with aerosol optical depth on normal summer day and a day after heavy rainfall suggests ~ 45% increase in UVery intensities because of scavenging of particles in the atmosphere. Total columnar ozone showed negative correlation with UVery. The results are discussed in the paper.

 

Keywords: Aerosols, UV radiation, Aerosol optical depth

PACS No: 42.68Jg; 92.60Mt

 

  

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 62-66

 

Study of infrasonic waves at low latitude northern hemisphere, India

M Lal

 

The infrasonic waves have been studied at the low latitude station Tirunelveli (8.7oN,77.8oE), India, in northern hemisphere. Almost 50 events of the severe earthquake (Ms > 6.0) have been studied. The changes in surface pressure as well as acoustic waves produced have been recorded immediately after the earthquake. The Rayleigh waves-induced changes in surface pressure which cause significant changes in pressure have been recorded by all the systems. The arrival of acoustic waves followed by large decrease in pressure has also been recorded in almost all the cases. Only a few cases have been reported. The infrasonic waves between 10 and 100 s have been observed. The infrasonic waves produced from the unknown sources have also been observed. But their variation feature is different from the earthquake-induced infrasonic waves. The corresponding microbaroms obtained at this station show variation similar to the infrasonic waves.

 

Keywords: Infrasonic waves, Earthquake, Surface pressure, Pressure fluctuation

PACS No.: 91.30.Fn

IPC code: G01V1/16

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 67-70

  

Estimation of emissivity and scattering coefficient of the constituents of vegetation at microwave frequencies

O P N Calla, Avdhesh Roop Rai, Prannoy Mathur, Deepak Mathur & Dinesh Bohra

 

A vegetation canopy is a dielectric mixture consisting of discrete dielectric inclusions (leaves, stalks and fruits) distributed in a host material (air). The scattering and emission behaviour of vegetation canopy made up of neem-like trees has been studied. The estimation of emissivity, brightness temperature and scattering coefficient has been made using the measured values of dielectric constant. The measurement of dielectric constant of neem leaves has been carried out using waveguide cell method in the frequency range of X-band (8.2 GHz - 12.4 GHz) at 9.035 GHz. The estimations of emissivity, brightness temperature and scattering coefficient are made for incidence angles varying from 0° to 80° for both horizontal and vertical polarization. The results of emissivity and scattering coefficient so obtained have been presented.

 

Keywords: Emissivity, Scattering coefficient, Canopy, Microwave frequency, Dielectric constant

PACS No. : 78.20 Ci; 84.40 Xb

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 71-74

 

Characterization of ferrite and silicon carbide based microwave absorber using FSS structures at X-band

M R Meshram and Nawal K Agrawal & Bharoti Sinha and P S Misra

 

In this paper the experimental result of microwave absorber with a single layer coating of ferrite and silicon carbide (SiC) based paint for X-band is presented. Samples of M-type hexagonal ferrite powder [Ba(MnTi)18Fe8.4O19] has been developed by dry attrition and sintering process. These developed ferrite powder and SiC powder have been mixed in epoxy resins to form a microwave absorbing paint. This paint was coated on aluminum sheet for absorption studies. The frequency selective surface (FSS) patterns are embedded on the surface of absorber sheet and tested experimentally at X-Band. It was found that SiC based microwave absorbing paint provide wide band absorption characteristics with minimum absorption of 10 dB from 9.5 to 12 GHz for a coating thickness of 1.84 mm.

 

Keywords: Hexagonal ferrite, Silicon Carbide, Microwave absorber , Frequency selective surface. Radar cross-section

PACS No.: 94.106b; 42.68 Ay

IPC Code: 601N22/00

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, February 2005, pp. 75-78

 

Dual-frequency slot-loaded rectangular microstrip antenna

Usha Kiran K1, R M Vani 2 & P V Hunagund1

 

In this study, dual-frequency slot-loaded rectangular microstrip antennas were designed, fabricated and evaluated. The design consists of rectangular patch microstrip antenna loaded with a pair of narrow slots parallel and close to the radiating edges on the patch, which is fed by centre-fed microstripline feed. Spacing of the slots was taken equally from both edges of the corners. The characteristics like VSWR, return loss, input impedance, bandwidth, radiation pattern, HPBW, frequency ratio and gain were measured and analyzed for different spacings. Dual frequency operation has been achieved having low frequency ratio.

 

Keywords: Dual-frequency, Slot-loaded, Low frequency ratio.

PACS No.: 84.40 Ba

IPC Code: H01 Q 9/00; H01Q 21/00; H01 Q 23/00