NISCAIR Online Periodicals Repository Collection: IJRSP Vol.35(4) [August 2006]

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

Sat, 29 Jul 2006 22:58:59 GMT

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

Authors: Sinha, Vivek; Pradhan, Devendra

Abstract: On 12^th 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.

Page(s): 270-279

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

Sat, 29 Jul 2006 22:58:59 GMT

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

Authors: Ghude, Sachin D; Jain, S L; Kulkarni, Pavan S; Kumar, Ashok; Arya, B C

Abstract: During the 16^th, 21^st, 22^nd and 23^rd 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.

Page(s): 253-258

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

Sat, 29 Jul 2006 22:58:59 GMT

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

Authors: Oyekola, O S; Ojo, Akinremi

Abstract: 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 (h'F) 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.

Page(s): 227-233

Equilateral triangular microstrip antenna for circular polarization dual-band operation

Sat, 29 Jul 2006 22:58:59 GMT

Title: Equilateral triangular microstrip antenna for circular polarization dual-band operation

Authors: Vishwakarma, Rajesh K; Ansari, J A; Meshram, M K

Abstract: 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.

Page(s): 293-296