Indian Journal of Radio & Space Physics

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(CODEN : IJRSAK        ISSN : 0367-8393)

VOLUME 35

NUMBER 4

AUGUST 2006

 

CONTENTS

 

Guest Editorial: Global warming, global dimming and bright sky

        D K Chakrabarty*

 

225

Nocturnal variations of F-region vertical ionization velocities near the magnetic equator

        O S Oyekola,* Akinremi Ojo & Jolasun Akinrimisi

 

 

227

 

Power spectral studies of VHF ionospheric scintillations near the crest of the equatorial anomaly in India

        K N Iyer, M N Jivani, M A Abdu, H P Joshi* & Malini Aggarwal

 

 

234

HF Doppler radar observations of vertical and zonal plasma drifts–Signature of a plasma velocity vortex in evening F-region

        C V Sreehari, C Bhuvanendran & S R Prabhakaran Nayar*

 

 

242

A new research approach of electromagnetic theory and its applications

        Zhang Jia-tian* & Li Ying-le

 

249

Year-to-year variation of ozone hole over Schirmacher region of East Antarctica: A synopsis of four-year measurement

        Sachin D Ghude*, S L Jain, Pavan S Kulkarni, Ashok Kumar & B C Arya

 

 

253

Characteristics of brightness temperature with respect to rain rate over ocean and land and its implication on rain rate retrieval

        Diganta K Sarma, Mahen Konwar, Sanjay Sharma*, Jyotirmoy Das & Srimanta Pal

 

 

259

Supercell storm at Kolkata, India and neighbourhood–Analysis of thermodynamic conditions, evolution, structure & movement

        Vivek Sinha & Devendra Pradhan*

 

 

270

Retrieval of the vertical temperature profile of atmosphere from MST radar backscattered signal

        I M L Das* & Pramod Kumar

 

 

280

Study of temperature and moisture profiles retrieved from microwave and hyperspectral infrared sounder data over Indian regions

        Devendra Singh* & R C Bhatia

 

 

286

Equilateral triangular microstrip antenna for circular polarization dual-band operation

Rajesh K Vishwakarma*, J A Ansari & M K Meshram

293

_______________________

*Authors for correspondence

 

 


Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 227-233

 

Nocturnal variations of F-region vertical ionization velocities near
the magnetic equator

O S Oyekola & Akinremi Ojo

Department of Physics, University of Ibadan, Ibadan, Nigeria

E-mail: osoyekola@yahoo.com

and

Jolasun Akinrimisi

Department of Physics, University of Lagos, Lagos, Nigeria

Received 1 November 2005; revised 3 March 2006; accepted 14 July 2006

F-region vertical plasma drifts at the magnetic equatorial station, Ibadan (7.4 °N, 3.9 °E; 6 °S dip) are inferred from the time variation of the hourly-recorded ionosonde virtual height () of F-layer data; obtained during 1957/58 International Geophysical Year (IGY) period under geomagnetically quiet and disturbed nights. Prominent nocturnal vertical drift characteristics are presented at African longitudinal sector. Seasonal effects appeared to be pronounced during undisturbed and disturbed nighttime conditions. Also, pre-reversal peak velocity obviously varies considerably with season. In addition, pre-reversal peak velocity exhibits significant variability with 10.7 cm Solar Flux Index and average Zurich monthly sunspot numbers. Furthermore the threshold parameters, such as, E × B vertical drifts and virtual height (h'F) required to cause spread-F irregularities are determined to be approximately 30 m/s and 400 km, respectively. Results obtained by the authors are in good accord with those for other low-latitude regions that employ other observational techniques. There are several likely processes responsible for the quiet and disturbed times plasma drift variability in the night hours at equatorial regions.

Keywords: Equatorial ionosphere, Pre-reversal velocity, Solar parameter

PACS No: 92.20.Ji

 

 

Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 234-241

 

Power spectral studies of VHF ionospheric scintillations near the crest of the equatorial anomaly in India

K N Iyer1, M N Jivani2, M A Abdu3, H P Joshi1 & Malini Aggarwal1

1Department of Physics, Saurashtra University, Rajkot 360 005, India

2Department of Electronics, Saurashtra University, Rajkot 360 005, India

3Instituto Nacional de Pesquisas Espaciais – INPE, São Jose dos Campos, SP,12201-970, Brazil

Received 6 December 2005; revised 15 May 2006; accepted 11 July 2006

Scintillation of VHF (250 MHz) signals from FLEETSAT (73oE) was recorded at the equatorial anomaly crest location, Rajkot, in India during 1991-93. The irregularity parameters: S4 index, and fade rate and spectral parameters: spectral slope and upper roll off frequency, fu are derived and their variation with time of night and with solar activity studied. S4 index and fade rate increase with solar activity. The spectral slope does not show any systematic dependence on solar activity but fu increases with solar activity. These results, when interpreted in terms of Fresnel size, indicate a shifting of irregularity spectrum towards longer scales in low solar activity period. The temporal variation of these parameters, after the irregularity generation phase, also indicate preponderence of large (kilometer) scale irregularities around midnight—post-midnight period, consistent with earlier simultaneous radar and scintillation observations at Jicamarca. The solar activity dependence of S4 index is interpreted as due to the variation of background F-region plasma density variations. The results suggest that when strong scattering causes strong scintillations, fu is not representative of the Fresnel scale.

Keywords: Power spectra, Ionospheric scintillations, Equatorial anomaly

PACS No.: 94.20.Ww

 

Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 242-248

 

 

HF Doppler radar observations of vertical and zonal plasma drifts–Signature of a plasma velocity vortex in evening F-region

 

C V Sreehari1, C Bhuvanendran2 & S R Prabhakaran Nayar1

1Department of Physics, University of Kerala, Trivandrum 695 581, Kerala, India

e-mail: srp@md2.vsnl.net.in

2 Department of Physics, Devaswom Board College, Sasthamcotta, Kollam 690 521, Kerala, India

Received 28 July 2005; revised 23 January 2006; accepted 14 April 2006

The simultaneous vertical and zonal plasma drift measurements using an HF Doppler radar system around March equinox of 1995 at the magnetic equatorial station, Trivandrum, India (8.33°N, 77°E, dip 0.4°N) are analyzed to evaluate the vector plasma drift at the F-region. It is found that the pre-reversal enhancement in vertical drift and the direction change of zonal drift from westward to eastward occur almost simultaneously. The velocity vector in the vertical-zonal plane, the resultant of vertical and zonal velocities, exhibits a gradual rotation in the evening time. The characteristics of velocity vector clearly promulgate the existence of a plasma velocity vortex in the equatorial F-region during post-sunset period.

Keywords: Equatorial ionosphere, HF Doppler radar, Vertical drift, Pre-reversal enhancement, Zonal drift, Plasma drift vortex

PACS No: 94.20.Ww

 

 

Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 249-252

 

 

A new research approach of electromagnetic theory and its applications

 

Zhang Jia-tian

School of Electronic Engineering, Xian Shiyou University, Xian 710 065, China

and

Li Ying-le

Scientific Research Office, Xianyang Normal College, Xianyang, 712 000, China

E-mail: liyinglexidian@yahoo.com.cn

Received 18 August 2005; revised 5 December 2005; accepted 15 February 2006

A new research approach of electromagnetic theory is presented. The relations of electromagnetic parameters in the scale-transformation coordinate system and in the original coordinate system are presented. The applied fields of the scale-transformation theory are introduced. The result obtained with the scale-transformation theory is in agreement with that in the literature. The method presented in this paper has the characteristics of briefness and is of convenience in engineering.

Keywords:   Scale-transformation, Electromagnetic parameter, Electromagnetic scattering.

PACS No.:  41. 20Jb; 94.30 Bg; 94. 20 Bb


Indian Journal of Radio Space Physics

Vol. 35, August, 2006, pp. 253-258

 

 

Year-to-year variation of ozone hole over Schirmacher region of East Antarctica: A synopsis of four-year measurement

Sachin D Ghude*, S L Jain, Pavan S Kulkarni, Ashok Kumar & B C Arya

Radio & Atmospheric Sciences Division, National Physical Laboratory

Dr K S Krishnan Marg, New Delhi 110 012, India

E-mail: sljain@mail.nplindia.ernet.in

Received 5 August 2005; revised 15 October 2005; accepted 12 July 2006

During the 16th, 21st, 22nd and 23rd Indian Antarctic expedition conducted in 1997, 2002-03 and 2004 respectively, measurement of columnar ozone have been made using MICROTOPS II Sun-photometer from the Indian station Maitri (70º 45' S, 11º 44' E). It is found that the ozone hole depth fluctuated from year-to-year. The minimum columnar ozone observed over Maitri was 135 (±9.3) DU, 185 (±12) DU, 126 (±9.7) DU and 159.8 (±8.8) DU during spring 1997, 2002, 2003 and 2004, respectively. Ozone concentration below 220 DU (nominal ozone threshold value) during Antarctic spring (day 225–365) over Maitri has been observed to be 45.1 %, 20.7 %, 62.7 % and 60 % in 1997, 2002, 2003 and 2004, respectively. The chemical loss of ozone (total ozone values below 220 DU) over Maitri during 2003 (day 225–365) was found to increase by a factor of 0.4 when compared to 1997, and by a factor of 2 when compared to 2002. The observations at Maitri also showed an event of major stratospheric warming during 2002. The ozone hole in the year 2002 was not found to be deep and further recovered quite early when compared to 1997, 2003 and 2004.

Keywords: Antarctica, Ozone hole, Sudden stratospheric warming, Planetary waves, Polar vortex

PACS No.: 92.70.Cp; 93.30.Ca; 94.10.Dy

 

 

Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 259-269

 

 

Characteristics of brightness temperature with respect to rain rate over ocean and land and its implication on rain rate retrieval

Diganta Kumar Sarma, Mahen Konwar & Sanjay Sharma

 Department of Physics, Kohima Science College, Kohima, Nagaland 797 002, India

e-mail: sanjay_sharma11@hotmail.com

and

Jyotirmoy Das & Srimanta Pal

 Electronics & Communication Sciences Unit, Indian Statistical Institute, Kolkata 700 035, India

Received 9 May 2005; revised 30 January 2006; accepted 23 March 2006

This paper studies the characteristics of brightness temperature (BT) with respect to rain rate over ocean and land and its subsequent implication on rainfall retrieval utilizing artificial neural network (ANN). The BTs data are obtained from Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). Variations of BT with rain rate are compared for all the nine channels over ocean and land, and over ocean 10.67 GHz is found to be most sensitive to rain rate.  For 37.0 GHz channels, emission effect is not noticed over land, but it is prominent over ocean for lower value of rain rate. Over land, lower frequency channels (Nos 1-4) are least sensitive to rain rate. From a quantitative comparison of the 85.5 GHz channels over ocean and land, BT difference of ~10 K is observed. It is also observed that polarization difference between the BTs for this frequency channel is more over ocean. A difference of ~10 K and ~3 K are noticed over ocean and land, respectively. Neural networks are trained over ocean and land to give rain rate as output. The nine channel BTs from TMI are considered as input for training the networks. The collocated near-surface rainfall rate data from TRMM precipitation radar are considered as target. Correlation values of 0.92 and 0.82 are observed for validation set over ocean and land, respectively, with root mean square error (rmse) values of 2.26 mm/h and 3.54 mm/h. It is observed that rain rate retrieval is better over land after discarding the lower frequency channels. The ANN retrieved rain rate is compared with TMI rain rate and correlations of 0.71 and 0.57 are observed over ocean and land, respectively.

Keywords: Brightness temperature, Rain rate, Rain rate retrieval, Precipitation radar, Artificial neural network.

PACS No.: 92.60 Jq; 92.60. Ry; 92.60 Nv

IPC Code: G01S 13/95; G06 T 1/40

 

Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 270-279

 

 

Supercell storm at Kolkata, India and neighbourhood¾Analysis of thermodynamic conditions, evolution, structure & movement

 

Vivek Sinha

Aerodrome Meteorological Office, Netaji Subhas Chander Bose International Airport, Kolkata 700 052, India

Devendra Pradhan

Cyclone Detection Radar, New Secretariat Building, 1 K S Ray Road, Kolkata 700 001, India

(Email: pradhan_dev1960@yahoo.com)

Received 5 August 2005; revised 13 March 2006; accepted 7 April 2006

On 12th March 2003 a very severe thunderstorm traversed across the Gangetic West Bengal in India and adjoining areas of Bangladesh. Documentation and analysis of the thermodynamic condition of the atmosphere and evolution, structure and movement of the storm as tracked by the Doppler radar is presented in this paper. One particular cell of the system lasted for over 12 h. Based on the internal structure, reflectivity, duration and weather pattern on the ground, it has been concluded that the particular cell was a supercell.

Keywords:   Bulk Richardson number, Convective inhibition energy, Storm relative helicity, Surface rainfall intensity, Vertically integrated liquid, Weak echo region, Vertical profiles of radar reflectivity

PACS No:   92.60.Wc; 84.40.Xb

 

 

Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 280-285

 

Retrieval of the vertical temperature profile of atmosphere from MST radar backscattered signal

 

I M L Das1,2 & Pramod Kumar2

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

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

E-mail: drimldas@yahoo.com

Received 28 September 2004; revised 1 February 2006; accepted 20 February 2006

The vertical temperature profile of the tropical lower atmosphere has been reconstructed from the backscattered signal received by Indian MST radar located at Gadanki (13.47°N, 79.2°E). The reconstructed temperature profile compares well with the altitude variation of temperature obtained from the simultaneously launched radiosonde flight.

Keywords: Vertical temperature profile, MST radar, Tropical lower atmosphere, Backscattered signal

PACS No.: 92.60.Ry; 92.60.Ta; 92.60.Ek

IPC Code: G01S13/95; G01S13/02


Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 286-292

 

 

Study of temperature and moisture profiles retrieved from microwave and hyperspectral infrared sounder data over Indian regions

Devendra Singh & R C Bhatia

India Meteorological Department, Lodhi Road, New Delhi 110 003

Received 27 July 2005; revised 10 March 2006; accepted 4 April 2006

The neural network technique has been used to retrieve atmospheric temperature and moisture profiles using Advanced Microwave Sounding Unit (AMSU) measurements onboard National Oceanic Atmospheric Administration (NOAA K, L and M) satellites over Indian region in real time. In the present study, an attempt has been made to inter-compare these profiles, which are being generated from two different sets of spectral wavelengths-one from infrared and the other from microwave. These inter-comparisons have been made for the month of January and August 2004. It has been found that in general, the temperature and moisture profiles retrieved using microwave data at India Meteorological Department (IMD), New Delhi, are comparable with the temperature and moisture profiles from advanced infrared sounder (AIRS) data.

Keywords: Temperature profile, Moisture profile, Infrared data, Microwave, Spectral wavelength, Neural network.

PACS No.: 92.60.Jq; 92.60Wc

IPC Code: G06T1/40; G01W1/02

 

 

Indian Journal of Radio & Space Physics

Vol. 35, August 2006, pp. 293-296

 

 

Equilateral triangular microstrip antenna for circular polarization

dual-band operation

 

Rajesh K Vishwakarma1, J A Ansari2  & M K Meshram1

1Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005 (UP), India

2J K Institute of Applied Physics, Allahabad University, Allahabad 221 002 (UP), India

E-mail: rkv_786@yahoo.com,

Received 26 August 2005; revised 23 May 2005; accepted 14 July 2006

Experimental investigations were conducted on the equilateral triangular microstrip antenna to examine the radiation characteristic with two-layer triangular patch antenna. The two-layer triangular patch at both the frequencies 3.0 and 3.5 GHz radiate maximum power, VSWR, return loss, etc, which depended heavily on two-layer triangular microstrip patch antenna. It is shown to be possible to design two-layer equilateral triangular patch antenna for dual-band operation with reasonably good circular polarization.

Keywords: Microstrip antenna, Triangular antenna, Dual-band antenna, Circular polarization

PACS No: 84.40.Ba, 75.50 Gg

IPC Code: H01Q9/ 00; H01Q21/ 00; H01Q23/ 00