Indian Journal of Radio & Space Physics

VOLUME 31

NUMBER 3

JUNE 2002

 

CONTENTS

 

Approximate derivation of self-exciting whistler-mode sideband frequencies

121

M Ikeda

 

 

 

Characteristics of tropical easterly jet over Gadanki : Comparison with radiosonde and rawinsonde

 

130

B Vasantha, M Venkat Ratnam, K Mohan, S Kamala, D Narayana Rao &

G Venkata Rama

 

 

 

Aerosol size distributions and their temporal variations in relation to urban activity

140

P Ernest Raj, R S Maheskumar, P C S Devara, S M Sonbawne, S K Saha &

K K Dani

 

 

 

Water soluble components of dry deposition at Delhi

151

Monika J Kulshrestha, Umesh C Kulshrestha, A K Sarkar, D C Parashar &

M Vairamani

 

 

 

Comparison of evaporation duct models to compute duct height over Arabian sea and Bay of Bengal

 

155

P K Pasricha, M V S N Prasad & S K Sarkar

 

 

 

Wideband linear array antenna in C-band for beam-pointing for SAR applications

159

S B Chakrabarty & S B Sharma

 

 

 

Analysis of rectangular waveguide with quadruple groove using finite element method

162

Ajay S Chaudhari

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Indian Journal of Radio & Space Physics

Vol. 31, June 2002, pp. 121-129

 

 

Approximate derivation of self-exciting whistler-mode sideband wave frequencies

 

M Ikeda

Musashi University, Toyotamakami 1-26-1, Nerima-ku, Tokyo 176-8534, Japan

Received 14 September 2001; revised 4 February 2002; accepted 19 March 2002

Using a new equation system, a possibility of the sideband wave generation in whistler-mode via a non-linear Doppler-shifted cyclotron resonant interaction between untrapped electrons and the whistler mode carrier signal is examined. The untrapped electrons resonant with the quasi-monochromatic whistler mode signal are phase-bunched with the trajectory gap, just outside the separatrix, on the phase space in the frame of electron of the Doppler-shifted cyclotron resonance with the carrier. Then, they may be able to radiate the whistler mode sideband waves with frequencies of fundamental, second and third harmonics, whose currents may never be zero because of strong non-linear interaction. It is imagined that, at the same time, two kinds of plasma may interact with the carrier signal to form the broadening, and with the sideband waves showing frequencies of fundamental, second and third harmonics. The fundamental, second and third harmonics sideband wave frequencies may be related to the saturated amplitude of the carrier signal.

 

 

Indian Journal of Radio & Space Physics

Vol. 31, June 2002, pp. 130-139

 

 

Characteristics of tropical easterly jet over Gadanki: Comparison with

radiosonde and rawinsonde

 

B Vasantha, M Venkat Ratnam, K Mohan, S Kamala, D Narayana Rao

Department of Physics, Sri Venkateswara University, Tirupati 517 502

and

G Venkata Rama

SHAR Centre, Shriharikota 524 124

 

Received 11 June 2001; revised 1 October 2001; accepted 4 December 2001

 

Wind velocities obtained from the Indian mesosphere, stratosphere and troposphere (MST) radar (for about three years) are used to study the characteristics of tropical easterly jet (TEJ) over a tropical station, Gadanki (13.47° N, 79.18°E). The TEJ is active over the site during the south-west monsoon (June, July and August). The average zonal winds observed over the observing sites are westerlies up to 8 km and become easterlies above 8 km with maximum winds (~ 40 m/s­) occurring at around 16 km height. The characteristics of TEJ, i.e., maximum zonal wind, height of maximum zonal wind, height of maximum shear and refractivity structure constant, are determined. The characteristics of TEJ over the observing site are compared with those estimated from the nearest radiosonde and rawinsonde observations. Special emphasis has been given to the simultaneous MST radar and radiosonde observations, which are carried out to understand the effect of temperature, humidity gradient and wind shear in the formation of the turbulent layers near TEJ zones. These regions of intense turbulence are identified during the observation period with N2 and Ri values close to or less than 0.25 (N being the Brunt-Vaisala frequency and Ri, the Richardson’s number, respectively).

 

 

 

 

Indian Journal of Radio & Space Physics

Vol. 31, June 2002, pp. 140-150

 

 

Aerosol size distributions and their temporal variations

in relation to urban activity

 

P Ernest Raj, R S Maheskumar, P C S Devara,

S M Sonbawne, S K Saha & K K Dani

Indian Institute of Tropical Meteorology, Pune 411 008

Received 16 March 2001; revised 6 July 2001; accepted 29 October 2001

Multiwavelength columnar aerosol optical depth measurements have been made at a few traffic junctions in the city of Pune, India, to examine the nature of aerosol size distributions close to urban activity. Aerosol loading inferred from Angstrom turbidity coefficient (b) showed that it is highest at site 5 and is least at site 1. Wavelength exponent (a) showed that the above two sites have larger sized particles in the atmosphere than those at sites 2, 3 and 4 which are in the core of the urban area. Daytime temporal variations in both a and b broadly followed those in traffic activity. Aerosol size distributions retrieved by inversion technique were predominantly (60%) single mode or two-slope type. Bimodal type size distributions were also observed at the traffic junctions on about 25% of the time. Time evolution of aerosol size distribution at the traffic junctions varied from day to day and also showed the influence of urban activity.

 

 

Indian Journal of Radio & Space Physics

Vol. 31, June 2002, pp. 151-154

 

 

Water soluble components of dry deposition at Delhi

Monika J Kulshrestha1, Umesh C Kulshrestha1, A K Sarkar2, D C Parashar2 & M Vairamani1

1Indian Institute of Chemical Technology, Hyderabad 500 007
2National Physical Laboratory, New Delhi 110 012

Received 26 March 2001; revised 6 November 2001; accepted 3 January 2002

Dry deposition rates of major water soluble components, namely Cl, NO3, SO4, NH4, Na, K, Ca and Mg, are estimated at National Physical Laboratory, New Delhi. The pH of water soluble fraction of dry deposition samples has been observed to lie between 5.8 and 8.0 at this site which is in agreement with soil pH of this region. It suggested that dry deposition is mainly dominated by soil-derived particles which add higher alkalinity due to presence of components like Na, K, Ca, etc. Dry deposition rates are found to be maximum for Ca. In general, the dry deposition rates are highest in summer, moderate in winter and lowest in monsoon.

 

 

Indian Journal of Radio & Space Physics

Vol. 31, June 2002, pp. 155-158

 

Comparison of evaporation duct models to compute duct height over
Arabian sea and Bay of Bengal

P K Pasricha, M V S N Prasad & S K Sarkar

Radio and Atmospheric Sciences Division, National Physical Laboratory, New Delhi 110 012

Received 18 December 2001; revised 12 February 2002; accepted 15 March 2002

Various models exist that calculate evaporation duct height in terms of directly measureable meteorological parameters in the surface layer over the sea-surface. One of these models (Paulus-Jeske model) is a straightforward model employing certain empirical formulae, and the other (Babin-Young-Carton model) an exhaustive model employing Monin-Obukhov similarity theory. In this paper, a comparison is made between these two models for ‘a test data set’ off the coast of California and sample marine data over the Arabian sea and Bay of Bengal. The applications of these two models to compute evaporation duct heights over the warm tropical oceans are highlighted.

 

 

 

Indian Journal of Radio & Space Physics

Vol. 31, June 2002, pp. 159-161

 

 

Wideband linear array antenna in C-band for beam-pointing for SAR applications

 

S B Chakrabarty & S B Sharma

Antenna and Feed Group, Space Applications Centre (ISRO), Ahmedabad 380 015

Received 14 September 2001; revised 26 November 2001; accepted 11 December 2001

The design and development of a wideband dual polarized linear array antenna of 3 elements in C-band is presented. The centre frequency is 5.3 GHz. The single radiating element used in the array configuration is of stacked strip slot foam inverted patch (SSFIP). The antenna has been developed for beam-pointing of 10° and side-lobe level better than –15 dB by properly choosing the complex excitation co-efficients. The array antenna offers bandwidth of 22% for a VSWR of 2:1. The measured S-parameters and radiation patterns are presented.

 

 

 

Indian Journal of Radio & Space Physics

Vol. 31, June 2002, pp. 162-165

 

 

Analysis of rectangular waveguide with quadruple groove

using finite element method

 

Ajay S Chaudhari*

19, Gayatri Colony, Shirpur, Dist-Dhule (M.S.), India 425 405

Received 10 September 2001; revised 20 November 2001; accepted 7 December 2001

The x-band rectangular waveguide with groove on each side wall is analyzed using finite element method (FEM). By keeping the width and height of the groove fixed, the outer length of the groove is varied. The width of the groove is kept fixed at 0.6 cm, whereas three different groove heights are considered to be 0.2 cm, 0.4 cm and 0.6 cm. The effect of different dimensions of the groove on the cut-off frequencies for the dominant mode TE10 and TE20 as well as on bandwidth is studied. The cut-off frequencies for TE10 and TE20 mode get lowered, whereas the passband is found to be raised.