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Indian Journal of Radio & Space Physics

 

 

 

 

ISSN : 0367-8393

 

CODEN:IJRSAK

VOLUME 33

NUMBER 3

JUNE 2004

 

 

CONTENTS

 

Distortion of a 27-day sequence of solar indices

149

R P Kane*

 

 

Characteristics of VHF scintillations in the Indian equatorial and low latitude stations

158

D S V V D Prasad, P S Brahmanandam, K Venkateswarlu, K Niranjan & P V S Rama Rao*

 

 

Effect of volcanic aerosols on stratospheric ozone at Kodaikanal

170

Meena Jain* & Namita Kundu

 

 

Rain attenuation and performance deterioration of a communication link at Ka band over Indian tropical eastern region

 

176

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

 

 

Double knife edge diffraction propagation studies over irregular terrain

180

M V S N Prasad*, S V Bhaskara Rao, T Rama Rao, S K Sarkar & Suresh Sharma

 

 

Variations in the concentrations of ionic species in rain events at Pune

185

D M Chate*, P S P Rao, G A Momin, P D Safai, K Ali, S Tiwari & P S Praveen

 

 

Attenuation of ULF-VLF seismo-electromagnetic signals and their propagation to long distances

 

189

Raj Pal Singh, Birbal Singh*, Vinod Kumar Kushwah & Ram Vir Singh Chauhan

 

 

Estimation of dielectric constant of soil from the given texture at microwave frequency

 

196

O P N Calla*, Vivek Ranjan, Chetan Bohra, Gangadhar L Naik, Waseem Hasan & Harmeet Singh Bali

 

 
Notes

 

Percentage contribution of atmospheric minor constituents on marine lower tropospheric ozone

 

201

P K Jana, S C Nandi & S K Midya*

 

 

 

__________

 

*Corresponding authors

 

 


 

Indian Journal of Radio & Space Physics

Vol. 33, June 2004, pp. 149-157

 

Distortion of a 27-day sequence of solar indices

 R P Kane

 

The interval 20 Feb.- 4 July 1998 had strong ~27-day oscillations, almost simultaneously, in various solar indices. Counting 20 Feb. 1998 as day number 1, the peaks occurred near day numbers 4, (27) 31, (18) 49, (27) 76, (8) 84, (24) 108, (27) 135, where the numbers in parantheses are the spacings in days. The first two peaks had a separation of 27 days, but the next peak was only 18 days away, heralding probably the commencement of a new, second sequence. The next peak was 27 days away which was the part of this second sequence, but the peak next to that was only 8 days away, indicating that the second sequence terminated. However, the next peaks were such that they fitted nicely as if the first sequence restarted (4, 31, 58 missed, 84, 108, 135), indicating that some sequences can remain dormant for a cycle or two and then reappear. The peaks at 4, 31, 49, 76, 84, 108, 135 were qualitatively the same for several solar indices, but their quantitative evolution was different for different indices.

 

Keywords: Solar activity, Solar indices

PACS No.: 96.60.Ly; 96.60.Qc

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, June 2004, pp. 158-169

  

Characteristics of VHF scintillations in the Indian equatorial and low latitude stations

 D S V V D Prasad, P S Brahmanandam, K Venkateswarlu, K Niranjan & P V S Rama Rao*

 

The VHF scintillation data from three different locations, namely, Pondicherry (11°N, 78°E, dip 7.6°N), a near- equatorial station, and Waltair (17.7°N, 83.3°E, dip 20°N) and Mumbai (19°N, 73°E, dip 25°N), the two anomaly crest region stations, are considered for the study of some typical characteristic features and geophysical effects on the occurrence of VHF scintillations both on short and long term basis. The data pertaining to the period of increasing sunspot years of 1998 and 1999 from the three different locations are considered for these studies. The percentage occurrences of scintillations revealed that the occurrence is more at the equatorial station, Pondicherry, compared to those at the two off-equatorial stations, Waltair and Mumbai. The onset of scintillations, in most cases, is found to occur first at the equatorial station, and later at the two off-equatorial stations. However, there are some occasions when the occurrence of scintillations is first seen at Waltair and Mumbai without their prior occurrence at the equatorial station, Pondicherry. These cases are believed to be associated with the generation of irregularities at the anomaly crest regions. Further, it is found that the scintillation occurrence increases as the sunspot number increases at all the three stations with increasing latitude, suggesting the widening of the scintillation activity belt with the increase of solar activity. The suppression effects of magnetic activity on the occurrence of scintillations seem to be more evident during the pre-midnight hours than during post-midnight hours.

 

Keywords : VHF scintillations, Magnetic activity, Sunspot number, Ionospheric irregularities

PACS No.: 94.20Rr; 94.20.Vv; 94.20.Ji


 

 

Indian Journal of Radio & Space Physics

 Vol. 33, June 2004, pp. 170-175

 

Effect of volcanic aerosols on stratospheric ozone at Kodaikanal

 Meena Jain & Namita Kundu

 

Nimbus 7 SBUV data (average of zonal means for 5-10°N and 10-15°N) and Dobson data over Kodaikanal (10° N latitude) for the period 1979-1994 have been analysed to study the effect of El-Chichon and Pinatubo volcanic eruptions on ozone quasi-biennial oscillation (QBO). The ozone QBO has been found to be disturbed up to the height of 34 km following both the eruptions and the effect persisted even after one year of the event. The impact of El-Chichon volcanic eruption on ozone shows a depletion up to 34 km with maximum effect at 29 km, whereas the impact following Pinatubo eruption shows ozone depletion up to 29 km above which an increase in ozone is observed. The cause of depletion below about 27 km is due to well known heterogeneous chemistry. The cause of ozone depletion above 27 km following the two major eruptions has been investigated. The percentage change in ozone has been estimated after taking the warming due to aerosol into consideration. The theoretically calculated and the observed percentage deviations of ozone show good agreement in the case of El-Chichon eruption, while for Pinatubo eruption the calculated values show more negative values.

 

Keywords: Ozone, QBO, El-Chichon eruption, Pinatubo eruption, Ozone depletion

PACS No.: 92.60.Mt; 94.10.Fa; 92.60.Sz

IPC Code: G 01 W 1/00; G 01 W 1/17

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, June 2004, pp. 176-179

 

Rain attenuation and performance deterioration of a communication link
at Ka band over Indian tropical eastern region

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

 

Experimentally measured values of radiowave attenuation due to rains in Ka band are not available over the Indian subcontinent. In this paper an attempt has been made to present measured values of attenuation at 18 GHz taken during rainy conditions. Using rapid response rain gauge having integration time 10 s, simultaneous rain intensity measurements were carried out. The communication link operating at 18 GHz was monitored in eastern India and the signal intensity measured. The deterioration of the link in relation to measured signal level during rainy periods has also been discussed. Such types of measured values are useful to design future communication links in Ka band (17.3-31 GHz) over India.

 

Keywords: Rain attenuation, rain intensity, Indian tropical region, Ka band

PACS No: 94.10.-s

IPC Code: G 01 W 1/14; G 01 S 13/95


 

 

Indian Journal of Radio & Space Physics

 Vol. 33, June 2004, pp. 180-184

 

Double knife edge diffraction propagation studies over irregular terrain

 M V S N Prasad1, S V Bhaskara Rao2, T Rama Rao3, S K Sarkar1 & Suresh Sharma4

 

Mountain cliffs constituting knife edges influence radio wave propagating from VHF to microwave frequencies. The diffraction phenomena caused by these single or multiple knife edges are a dominant propagation mechanism that has to be taken into account in planning TV, FM networks, cellular radio, microwave network, etc., in mountainous regions. In order to investigate the above mechanism field strength measurements were conducted over five double knife edge paths and the measured signal levels are compared with several prediction techniques. The deviations of the prediction techniques and their suitability are presented in this paper. It is seen that out of all the prediction methods Giovanelli’s method gives best agreement with the observed results.

 

Keywords: Knife edge diffraction, Field strength measurements, Path loss, Prediction techniques

PACS No.: 92.60.Ta; 94.10.Gb; 84.40.Ua

IPC Code : H 04 H 1/00; H 04 B 7/00; G 01 S 1/08

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, June 2004, pp. 185-188

 

Variations in the concentrations of ionic species in rain events at Pune

D M Chate, P S P Rao, G A Momin, P D Safai, K Ali, S Tiwari & P S Praveen

 

In the present work, evolutions of the concentrations of major neutralizing agents (Ca2+ and NH4+) and acidic species (SO42‑ and NO3) are computed with Slinn's model using the initial number concentrations of particle size distributions measured at Pune during 1998-1999. Theoretically predicted ionic concentrations are compared with observed ionic concentrations in the sequential samples collected in the rain events at Pune. Also, equivalent ratios [(SO42‑ + NO3)/(Ca2+ + NH4+)] are computed theoretically to study the neutralizing capacity of the atmosphere during precipitation events and compared them with observed ones. The variation of observed equivalent ratios with accumulated rain (mm) indicated that acidic components are always neutralized with neutralizing species.

 

Keywords: Ionic species, Rain events, Ionic concentration, Particle size distributions

PACS No: 92.60.Hp; 92.60.Ls; 94.10.Fa

IPC Code: G O1 W 1/14; G O1 W 1/16

 
 

 

Indian Journal of Radio & Space Physics

 Vol. 33, June 2004, pp.189-195

 

Attenuation of ULF-VLF seismo-electromagnetic signals
and their propagation to long distances

Raj Pal Singh, Birbal Singh, Vinod Kumar Kushwah & Ram Vir Singh Chauhan

 

Using a two-layer crust model between the source region and earth surface, the attenuation of seismo-electromagnetic signals is calculated. Results show that attenuation of Ultra Low Frequency (ULF) signals is very low and they can penetrate the crustal region to enter the atmosphere and ionosphere over the epicentral area of the earthquakes. However, the attenuation increases steeply in the crust for the ELF and VLF ranges of signals. These results are utilized to discuss the propagation mechanism of VLF signals (f = 3 kHz), which are recorded at Agra by employing a borehole antenna during the periods of Chamoli earthquakes in India and large magnitude earthquakes in Afghanistan. It is suggested that these VLF signals propagate upward and find windows of very low conductivity in the skin layer through which they get transmitted to the atmosphere. They then propagate to the observing station at Agra through earth-ionosphere waveguide.

 

Keywords: ULF signal, VLF signal, ELF signal, Seismo-electromagnetic signal, Signal propagation

PACS No: 91.30 Px

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, June 2004, pp. 196-200

  

Estimation of dielectric constant of soil from the given texture at microwave frequency

 O P N Calla and Vivek Ranjan1, Chetan Bohra1 & Gangadhar L Naik2, and

Waseem Hasan & Harmeet Singh Bali

 

Value of the dielectric constant of a given sample of soil has been estimated from its known texture by multiplying the given texture with the constants at different microwave frequencies. The model is tested for four samples of soil: one sample from Uttar Pradesh and three samples from Kashmir in India.

 

Keywords: Dielectric constant, Soil, Microwave frequency

PACS No: 95.75 Rs; 84.40 Xb

IPC Code: G 01 N 33/24


 

 

Indian Journal of Radio & Space Physics

 Vol. 33, June 2004, pp. 201-205

 

Percentage contribution of atmospheric minor constituents on marine lower tropospheric ozone

P K Jana & S C Nandi, and S K Midya*

 

A critical analysis has been made on contribution of atmospheric minor constituents on the formation of oceanic ozone at the lower troposphere. Altitudinal distributions of these constituents are also presented.

 

Keywords: Minor constituents, Atmospheric minor constituents, Troposphere, Ozone

PACS No: 94.10.Fa

IPC Code: G 01 W 1/00