Indian Journal of Radio & Space Physics
VOLUME 31
NUMBER 3
JUNE 2002
CONTENTS
Approximate derivation of self-exciting whistler-mode sideband frequencies
M Ikeda
Characteristics of tropical easterly jet over Gadanki : Comparison with
radiosonde and rawinsonde
B Vasantha, M Venkat Ratnam, K Mohan, S Kamala, D Narayana Rao &
G Venkata Rama
121
130
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
140
Water soluble components of dry deposition at Delhi
Monika J Kulshrestha, Umesh C Kulshrestha, A K Sarkar, D C Parashar &
M Vairamani
151
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
155
Wideband linear array antenna in C-band for beam-pointing for SAR
applications
S B Chakrabarty & S B Sharma
159
Analysis of rectangular waveguide with quadruple groove using finite element
method
Ajay S Chaudhari
162
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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 Dopplershifted 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 BruntVaisala frequency and Ri, the Richardson’s number, respectively).
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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 () showed that it is highest at site 5 and is least at site 1. Wavelength exponent () 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  and  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
Physical Laboratory, New Delhi 110 012
2National
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
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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.
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