Indian Journal of Radio & Space Physics

(Bimonthly)  

 

 

ISSN : 0367-8393  

                  CODEN : IJRSAK

VOLUME 32

 NUMBER 2

             APRIL 2003

 

 

 

CONTENTS

 

Long-term association of solar activity and cosmic ray intensity for solar cycles 21 and 22

 

65

V K Mishra & D P Tiwari

 

Initial results of VLF emissions observed on the ground station at Maitri, Antarctica

70

Sunil K Singh, Sushil Kumar & A K Gwal

 #a2

Generation of electrostatics ion-cyclotron wave by parallel flow velocity shear in the presence of inhomogeneous electric field in an anisotropic magneto-plasma

 

75

R S Pandey, K D Misra & A K Tripathi 

 

Association between equatorial and tropical spread-F

83

S Alex, H Chandra & R G Rastogi

 

   

Effect of lightning on ionospheric temperature determined by SROSS-C2 satellite

93

D K Sharma, Jagdish Rai, M Israil, P Subrahmanyam, P Chopra & S C Garg

 

Rain structure estimation from X-band radar reflectivity measurements for radio system applications in microwave and millimetre wave frequency bands

 

98

S K Sarkar, Rajesh Kumar, Iqbal Ahmed, M V S N Prasad, J Das & A K De

 

   

A multilayer fuzzy neural network approach for cloud classification

104

R Bhattacharya, S S Dey, T Datta & A B Bhattacharya

 

   

Comparative study of the methods of measurement of dielectric constant at microwave frequencies for dry and wet soil

 

108

O P N Calla, S Agarwal, S K Agarwalla, R Bhattacharjee & A Kalita

 

   

Notes

 

Software development for lidar data analysis

114

Rajesh Kr Baishya, M Devi & A K Barbara

 

 

 

News Scan

 

Grote Reber–Pioneer radio astronomer

118

Tarun Banerjee

 

 

 

 

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 65-69

 

  

Long-term association of solar activity and cosmic ray intensity for solar cycles 21 and 22

 V K Mishra & D P Tiwari

Department of Physics, A P S University, Rewa (M P) 486 003

Received 13 May 2002; revised 26 August 2002; accepted 22 November 2002

Based on the monthly data of solar flare index (SFI), instead of sunspot numbers and cosmic ray intensity (CRI) for the last two solar cycles since 1976, a detailed correlative study has been made by using the “running cross-correlation” method. It has been found that the anti-correlation between SFI and CRI is strong during ascending and descending phases of the solar cycle. The observed cosmic ray modulation during these periods, when compared with other solar activity indices, shows the appropriateness of the SFI as solar activity index, instead of sunspot numbers or even the grouped solar flares (GSF). The effects are found to be distinctly different in the two solar cycles 21 and 22, when the most appropriate solar activity index SFI is used. The observed depth of cosmic ray modulation in cycle 22 is larger than that in cycle 21 in contrast to reverse tendency in SFI, which necessitates further studies on short-term basis.

 

  

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 70-74

 

 

Initial results of VLF emissions observed on the ground station
at Maitri, Antarctica

Sunil K Singh1, Sushil Kumar2 & A K Gwal1

1Space Science Laboratory, Department of Physics & Electronics, Barkatullah University, Bhopal 462 026

2Department of Physics, Faculty of Science, Agra College, Agra 282 002

Received 12 December 2001; revised 17 June 2002; accepted 31 December 2002

The ground based VLF database from Indian Antarctic station Maitri (70°46¢ S, 11° 44¢ E, L ~ 4.6) has been searched for very low frequency (VLF) emissions during January-February of the years 1998 and 1999. The VLF recording system was successfully installed during the XVII Indian Scientific Expedition to Antarctica (ISEA) 1997-98. The spectrograms of analysed data have revealed the common occurrence of various emission events like chorus rising emissions, emission of rising type, falling emission of hook type and multiple emissions. Also the observed emissions (periodic and quasi-periodic) are found to be risers and fallers triggered from the top of hiss band.

 

 

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 75-82

 

 
Generation of electrostatics ion-cyclotron wave by parallel flow velocity shear in the presence of inhomogeneous electric field in an anisotropic magneto-plasma

R S Pandey & K D Misra

Department of Applied Physics, Institute of Technology, Banaras Hindu University, Varanasi 221 005

and

A K Tripathi

Department of Physics, Government Post Graduate College, Satna (M.P.)

Received 23 August 2001; revised 26 June 2002; accepted 20 November 2002

 

Generation of electrostatic ion-cyclotron wave and its harmonics, driven by parallel flow velocity shear in the presence of perpendicular inhomogeneous d.c. electric field and density gradient, is studied by using the characteristic method. The details of particle trajectories, dispersion relation and growth rate have been evaluated in the short wavelength region. The ion-cyclotron waves are excited at various harmonics of ion-cyclotron frequency. The growth rate is evaluated for ion-cyclotron harmonics for plasma parameters suited to magnetosphere. The dominant driving source of this instability is found to be the parallel flow velocity shear rather than the temperature anisotropy and temperature ratios of electron and ion. The electric field inhomogeneity has a destabilizing effect on ion-cyclotron instability.

 

 

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 83-92

 

 

Association between equatorial and tropical spread-F

S Alex

Indian Institute of Geomagnetism, Colaba, Mumbai 400 005

and

H Chandra & R G Rastogi

Physical Research Laboratory, Navarangpura, Ahmedabad 380 009

Received 27 February 2002; revised 6 June 2002; accepted 21 November 2002

Comparative study of spread-F is made from the quarter-hourly ionograms at Huancayo, near the magnetic equator and Bogota, close to the anomaly crest region in the same longitude sector. The occurrence of equatorial spread-F is seen only during nights, preceded by very rapid rise of the F-layer close to the magnetic equator. Based on quarter- hourly ionospheric data at a closely spaced chain of 8 stations in the American sector that operated during IGY, the occurrence of spread-F at low latitudes is shown to be associated with the post-sunset intensification of the ionization anomaly. The ratio of foF2 at Bogota (anomaly crest) to that at Huancayo (dip equator) shows sudden intensification on spread-F days around 1900 hrs LT, peaking between 2000 and 2100 hrs LT and can be used as a precursor to predict spread-F near the magnetic equator. The onset of spread-F at Bogota, however, requires additional condition of strong spread-F at Huancayo covering a wide range of altitudes and stronger uplift of the F-layer. There are indications that the vertical uplift velocity of F-layer between 1800 and 1900 hrs LT could be used to predict the onset of equatorial spread-F even at crest.

 

 

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 93-97

 

  

Effect of lightning on ionospheric temperature determined by
SROSS-C2 satellite

D K Sharma & Jagdish Rai

Department of Physics, Indian Institute of Technology, Roorkee 247 667

and

M Israil

Department of Earth Sciences, Indian Institute of Technology, Roorkee 247 667

and

P Subrahmanyam, P Chopra & S C Garg

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

Received 9 January 2002; revised 10 June 2002; accepted 22 October 2002

The ionospheric temperature in relation with the thunderstorm activity has been studied. The data were obtained by the RPA payload aboard Indian SROSS-C2 satellite, which has yielded valuable information on electron and ion temperatures (Te and Ti) over low latitude locations in the altitude range 425-625 km. The data collected during solar minimum period from 1995 to 1996 have been analyzed for anomalous variations in topside plasma temperature (electron and ion temperature). The data on thunderstorm have been obtained from IMD. The Te is found to increase by 1.2-2.7 times during the thunderstorm activity when compared with the normal days, while Ti increases by about 1.2-2.4 times for the same period. The enhancements in Te and Ti have been attributed to the production of UHF-gamma radiations during a lightning sprite which propagates upward to the height of interest.

 

 

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 98-103

 

 

Rain structure estimation from X-band radar reflectivity measurements for radio system applications in microwave and millimetre wave frequency bands

S K Sarkar, Rajesh Kumar*, Iqbal Ahmed & M V S N Prasad

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

and

J Das & A K De

Electronics and Communication Sciences Unit, Indian Statistical Institute, 203, B T Road, Calcutta 700 035

Received 23 April 2002; revised 20 December 2002; accepted 10 January 2003

The statistical morphology of radar reflectivity as a function of horizontal and vertical extension of rain is of considerable interest to those assessing the possible interference between terrestrial links and earth-space satellite links. In this paper, the horizontal and vertical extension of rain deduced from radar plan position indicator (PPI) and range height indicator (RHI) measurements have been presented. Such results of rain extension have also been deduced as a function of radar reflectivity factor (dBz). The radar reflectivity factor is the measure of the strength of the scattering cross-section of the rain cells. The scattering cross-section is responsible for causing interference to the radio signals. Probability distribution of radar reflectivity (dBz) deduced from both horizontal (PPI) and vertical extension (RHI) of rain cells has also been estimated.

 

 

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 104-107

 

 

A multilayer fuzzy neural network approach for cloud classification

  R Bhattacharya† & S S Dey

Centre for Atmospheric Sciences, University of Calcutta, Kolkata 700 009

and

T Datta* & A B Bhattacharya

Department of Physics, University of Kalyani, Kalyani 741 235

 

Received 27 February 2002; revised 30 May 2002; accepted 29 October 2002

 

Physical processes affecting cloud detection have been analyzed considering both cloud segmentation and cloud labeling in satellite data. Application of neural networks to cloud screening is examined with a special emphasis to cloud segmentation in AVHRR data. Some improved methods for analyzing and comparing satellite and surface observations of cloud patterns have been critically discussed. Finally, multilayer perceptron of neural network has been proposed as a possible better model for cloud label classification.

 

 

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 108-113

 

Comparative study of the methods of measurement of dielectric constant at microwave frequencies for dry and wet soil

O P N Calla

International Center for Radio Science,"OM- NIWAS" A- 23, Shastri Nagar, Jodhpur 342 003

and

S Agarwal, S K Agarwalla, R Bhattacharjee & A Kalita

Department of Electronics and Telecommunication, Assam Engineering College,

Guwahati 781 013

Received 6 December 2001; revised 3 July 2002; accepted 20 September 2002

An attempt has been made to do the comparative study of the three different methods of measurement of dielectric constant of soil collected from Rajasthan at different gravimetric moisture content. The measurements have been made using waveguide cell, resonant cavity and HP network analyzer at X- band.

 

 

 

 

 

Indian Journal of Radio & Space Physics

Vol. 32, April 2003, pp. 114-117

 

 

 Notes

Software development for lidar data analysis

Rajesh Kr Baishya, M Devi & A K Barbara

Department of Physics, Gauhati University, Guwahati 781 014

Received 1 October 2001; revised 20 May 2002, accepted 4 September 2002

A micro pulse lidar (MPL) system was developed and installed at the Department of Physics, Gauhati University, Guwahati, and is in operation from January 2001. The lidar system receives backscattered signal from aerosols and clouds up to a height of 15 km at a resolution of 15 and 30 m. The paper describes the software developed for profiling of aerosols and clouds and also processing technique of the basic data through various tools. The software also takes care of monitoring and recording the system parameters and background conditions. The paper shows some sample outputs of the programme.