Indian Journal of Radio & Space Physics

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(CODEN : IJRSAK        ISSN : 0367-8393)

VOLUME 36

NUMBER 2

APRIL 2007

 

CONTENTS

 

Guest Editorial: The transient nature of thunderstorm charging theories – A personal view

        Clive Saunders*

 

 

83

Role of coronal index of solar activity in long-term cosmic ray modulation

        R K Tiwari*, Manoj K Pandey & Pankaj K Shrivastava

 

87

 

 

Some features of plasma bubble induced scintillations during the AICPITS campaigns of 1991

        P N Vijayakumar*, T R Tyagi, Lakha Singh, H Chandra, G D Vyas, D R K Rao, B M Pathan, A Iype, B Ramsekaran, A Naidu, S M Sadique, K N Iyer, P N Pathak, A K Gwal, Sushil Kumar, R P Singh, U P Singh, Birbal Singh, Pawan Kumar, G N Navneeth, P V S Koparkar, P V S Ramarao, P T Jaychandran, P Sriram, R Sethuraman, A Dasgupta, K Basu & R G Rastogi

 

 

91

Observations of ULF/ELF anomalies detected by DEMETER satellite prior to earthquakes

        S Bhattacharya*, S Sarkar, A K Gwal & M Parrot

 

 

103

Rainfall retrieval from TRMM radiometric channels using artificial neural networks

      Rajesh Kumar, I M L Das*, R M Gairola, A Sarkar, Vijay K Agarwal

 

 

114

 

Annual cycle of surface meteorological and solar energy parameters over Orissa

        G N Mohapatra, U S Panda & P K Mohanty*

 

128

Implementation of multilayer ferrite radar absorbing coating with genetic algorithm for radar cross-section reduction at X-band

        Ramesh C Parida*, D Singh & N K Agarwal

 

 

145

 

 

___________________

*Authors for correspondence

 

 

 

 

 

 

Indian Journal of Radio & Space Physics

Vol. 36, April 2007, pp. 87-90

 

Role of coronal index of solar activity in long-term cosmic ray modulation

R K Tiwari & Manoj K Pandey

Department of Physics, Government New Science College, Rewa 486 001 (MP), India

E-mail: rkt84@rediffmail.com

and

Pankaj K Shrivastava

Department of Physics, Government Model Science College, Rewa 486 001 (MP), India

E-mail: pankaj_in_2001@rediffmail.com

Received 31 March 2006; revised 17 July 2006; accepted 20 February 2007

The relationship between cosmic rays and coronal index of solar activity (CI) for the periods of negative (A < 0), mixed and positive (A > 0) polarities of the general magnetic field of sun has been analysed. In cosmic ray modulation, sunspot numbers are being generally used as a reliable solar parameter. In this analysis, coronal index has been used as a new solar parameter for long-term cosmic ray modulation. Negative and high correlations are found between CI and cosmic rays for the A > 0 epochs and A < 0 epochs of solar magnetic field. Significant differences are found between A > 0 and A < 0 epochs of solar magnetic field. Correlations are found to be poor during the mixed polarity years.

Keywords: Cosmic rays, Solar activity, Coronal index

PACS No.: 96.40, 96.60

 

Indian Journal of Radio & Space Physics

Vol. 36, April 2007, pp. 91-102

Some features of plasma bubble induced scintillations during the
AICPITS campaigns of 1991

 

P N Vijayakumar1, T R Tyagi1, Lakha Singh1, H Chandra2, G D Vyas2, *D R K Rao3, B M Pathan3, A Iype3,
B Ramsekaran4, A Naidu5, S M Sadique6, K N Iyer7, K N Pathak7, A K Gwal8, Sushil Kumar8, R P Singh9,
U P Singh9, Birbal Singh10, Pawan Kumar10, G N Navneeth11, P V S Koparkar11, P V S Ramarao12,
P T Jaychandran12, P Sriram12, R Sethuraman13, A Dasgupta14, K Basu14 & R G Rastogi2

1 Radio Science Division, National Physical Research Laboratory, New Delhi 110 012

2 Physical Research Laboratory, Ahmedabad 380 009

3 Indian Institute of Geomagnetism, New Panvel, Navi Mumbai 410 218

4 Department of Physics, Aditnar College, Tiruchendur 628 215

5 Department of Physics, JNTU College, Anantpur 515 022

6 Goa University, Bambolim, , Goa 403 005

7 Department of Physics, Saurashtra University, Rajkot 360 005

8 Department of Physics, Barkatullah University, Bhopal 462 026

9 Department of Physics, Banaras Hindu University, Varanasi 221 005

10 Department of Physics, RBS College, Agra 283 105

11 Department of Physics, Nagpur University, Nagpur 440 010

12 Department of Physics Andhra University, Waltair 530 003

13 Hindusthan College of Engineering, Chinglepet 603 103

14 Institute of Radio Physics & Electronics, Calcutta University, Calcutta, 700 009

Received 28 September 2006; revised received 12 December 2006; accepted 3 January 2007

The VHF scintillations were recorded at a chain of low-latitude stations in India as part of the All India Coordinated Programme of Ionospheric and Thermospheric Studies (AICPITS), using the 244 MHz radio beacon from the geo-stationary satellite FLEETSAT which was located at 73° E longitude. Data collected during the second campaign of September-October 1991 and analyzed jointly by the participating investigators are presented. The onset times of scintillation at pairs of stations at similar latitude but different longitudes can be used to estimate the eastward drift of the scintillation patches and its E-W extent. The maximum monthly mean occurrence for September 1991 is about 35% at Trivandrum and Tiruchendur, the stations close to dip equator. Occurrence is maximum for stations Annamalainagar, Payyanur and Anantpur (50 %), located slightly north of the dip equator. It decreases further north to 30 % at Nuzvid, Bombay, 20 % near anomaly crest region, 10 % at Agra and 8 % at Delhi, which is the northern most edge of the present observations. The occurrence frequency is slightly less than that observed during the campaign of March 1991. For the sake of completeness some very interesting features and dynamical characteristics of plasma bubble induced scintillations are included here based on digital records of scintillations made at Delhi during the two equinox data campaigns in March-April 1991 and September-October 1991.

Keywords: Plasma bubble, VHF scintillations, AICPITS, Equinox data campaigns

PACS: 94.20.Vv; 94.20.Bb; 94.20.Ji

 

 

Indian Journal of Radio & Space Physics

Vol. 36, April 2007, pp. 103-113

 

Observations of ULF/ELF anomalies detected by DEMETER satellite
prior to earthquakes

S Bhattacharya, S Sarkar, A K Gwal & M Parrot1

Space Science Laboratory, Department of Physics, Barkatullah University, Bhopal 462 026 (MP), India

Email: shourabhbhattacharya@rediffmail.com

1LPCE/CNRS, 3A Avenue da le Recherche Scientifique, 45071, Orleans Cedex 2, France

 

Received 17 March 2006; revised 17 November 2006; accepted 26 February 2007

Seismo-electromagnetic effects refer to the electric and magnetic field perturbations found during the course of earthquakes. Furthermore, in the range of electromagnetic emissions, stress is laid on the ultra low frequency (ULF) and extremely low frequency (ELF), due to their reasonably higher penetration depth as compared to the other higher frequencies. The emissions are observed prior to moderate and strong earthquakes. One of the most promising diagnostic tools for studying the electromagnetic anomalies is using satellite based technique. Some important electric field variations observed prior to two individual earthquakes are discussed in this paper, one in Arunachal Pradesh, India (28.87°N, 94.60°E, 20:06:42 hrs UTC) measuring 5.9 and the other in the west coast of Columbia (6.86°N, 77.8°W, 20:50:46 hrs UTC) measuring a stronger 6.2 on the Richter scale. The anomalies are reported to occur in the ULF/ELF range. The observations have been detected prior to both the events using the low altitude satellite DEMETER (height ≈710 km), which is aimed at studying the ionospheric perturbations related to earthquakes and volcanic eruptions.

Keywords: DEMETER, Ultra low frequency, Extremely low frequency, Earthquake

PACS No.: 91.30.Px

 

Indian Journal of Radio & Space Physics

Vol. 36, April 2007, pp. 114-127

 

Rainfall retrieval from TRMM radiometric channels using artificial neural networks

Rajesh Kumar 1, I M L Das1,2, R M Gairola3, A Sarkar3, Vijay K Agarwal3

1M N Saha Centre of Space Studies, Institute of Interdisciplinary Studies, University of Allahabad, Allahabad 211 002, India

2Department of Physics, University of Allahabad, Allahabad 211 002, India

3Meteorology and Oceanography Group, Space Application Centre, Indian Space Research Organization, Ahmedabad 380 015, India

Received 29 May 2006; revised 11 December 2006; accepted 13 February 2007

An algorithm for the retrieval of rainfall has been developed from the radiometric measurements of TRMM microwave Imager (TMI) of Tropical Rainfall Measuring Mission (TRMM) satellite using multilayer feed forward Artificial Neural Network (ANN) over different oceanic and land regions of India and its neighborhoods. The “back propagation with momentum” has been used as a learning algorithm for the ANN architecture. The inputs to the ANN are TMI-brightness temperatures (TB) and the output TMI-rain rates, to demonstrate its capability to retrieve rain rates within limited computer time and with reasonable accuracy. The training data has been split up randomly in three parts, viz. training, validation and test data sets. The performance of the network is evaluated for independent data sets (which were not included in the training) after training and cross validation. Instantaneous precipitation estimates demonstrate very high correlation coefficients with the observed rainfall. Although the rainfall estimation using ANN are influenced by many factors such as the representativeness and sufficiency of the training dataset, the generalization capability of the network to new data sets, seasonal and location changes, it is found that the model can still be used for the retrieval of precipitation at high spatial and temporal resolutions. The ANN is shown to quickly reproduce the results of a long time series of data. The ANN derived rain rates have been compared with the estimates obtained from non-linear multivariate regression (MR) techniques using the identical set of data. It has been found that the ANN method, in general, is far superior to the MR technique in its ability to reproduce rainfall intensity in very short time.

Keywords: Artificial neural network, Brightness temperature, Multivariate regression, Multilayered feed forward

PACS No: 92.60.Jq; 84.35.+i

 

 

Indian Journal of Radio & Space Physics

Vol. 36, April 2007, pp. 128-144

 

Annual cycle of surface meteorological and solar energy parameters over Orissa

 

G N Mohapatra, U S Panda & P K Mohanty

Department of Marine Sciences, Berhampur University, Berhampur 760 007, Orissa, India

Email: pratap_mohanty@yahoo.com

Received 21 November 2005; revised 17 April 2006; accepted 16 January 2007

Surface meteorological and solar energy parameters over Orissa are studied using observed data from India Meteorological Department (IMD) and National Aeronautics and Space Administration Surface meteorology and Solar Energy (NASA SSE) data set. The observed data are mostly on surface meteorological parameters over 17 meteorological stations over Orissa. SSE data set, Release 3, is a satellite and reanalysis derived 10 year climatology (July 1983-June 1993) available on global grid mesh of 1° and consisting of both surface meteorological and solar energy parameters. The usefulness of NASA data set for the Orissa regions are examined by comparing it with IMD data. Comparative views of the annual cycle of both the data sets reveal the intensities and periods of extremes and their relative agreements /disagreements in the course of the annual cycle. Closeness of fit and coherence between the two data sets are examined through scatter plots and cross-spectral analysis, respectively. The results show a better goodness of fit between IMD and NASA data set in air temperature and lowest standard error of estimate in wind speed. Cross-spectrum analysis shows very good coherence between IMD and NASA data in the annual and semi-annual bands but lesser coherence in the intra-seasonal band. The results suggest that NASA data, when used in conjunction with good quality observed data, can make it possible to assess the renewable energy potential of different districts in Orissa, besides its use for weather and climate study.

Key words: Annual cycle, Insolation, Coherence, Albedo, Solar energy

PACS No: 92.60.-e; 96.60.-j

 

Indian Journal of Radio & Space Physics

Vol. 36, April 2007, pp. 145-152

Implementation of multilayer ferrite radar absorbing coating with genetic algorithm for radar cross-section reduction at X-band

 

Ramesh C Parida, D Singh & N K Agarwal

Department of Electronics and Computer Engineering, Indian Institute of Technology Roorkee,
Roorkee (U.A.) 247 667

E-mail:dharmfec@iitr.ernet.in

Received 21 March 2006; revised 18 September 2006; accepted 11 December 2006

Genetic algorithm (GA) approach has been analyzed to optimize the thickness of various layers as well as selection of suitable ferrite material for better absorption and reduction of radar cross-section (RCS) at X-band frequency. For this purpose, the available ferrite materials with frequency-dependent permittivities ε(f) and permeabilities μ(ƒ) have been used as data base. An empirical relationship has been developed between µ and f as well as ε and f for application of GA to select the proper ferrite material at particular frequency range for minimum reflection or maximum absorption and reduction of RCS. The GA has advantage that, with fitness function, it places an upper bound on the total thickness of the coating as well as on the number of layers contained in the coating. This greatly simplifies manufacturing of absorber in the form of sheet by coating ferrite material. Four-layer coating with different thickness and different ferrite materials has been simulated by GA and the results obtained with GA have been synthesized on aluminum plate. The paint for coating over aluminum sheet has been prepared by mixing the known ferrite powders (used in data base) with glass epoxy resin with suitable amount of hardener. The absorption has been measured by absorber testing device (ATD) method and RCS has been measured by monostatic radar measurements at X-band (8-12 GHz) in anechoic chamber. The absorption and RCS were measured after each layer of coating. A considerable amount of reduction of RCS and absorption is observed as compared to the plain aluminum sheet at X-band.

Keywords:   Absorber testing device, Radar cross-section, Genetic algorithm

PACS No.:  85.40Sz; 84.40Xb; 81.05 Zx

IPC Code: G01 S13/02; G01 S13/04