Indian Journal of Radio & Space Physics

(CODEN : IJRSAK    ISSN : 0367-8393)

 

VOLUME 31

NUMBER 4

AUGUST 2002

 

CONTENTS

 

Calculated electron flux and densities at 10-1000 eV in the dayside Martian ionosphere : Comparison with MGS and Viking results

 

173

S A Haider & K I Oyama

 

 

Numerical simulation of magnetic reconnection and plasmoid dynamics in the geotail

183

Manashi Roy & G S Lakhina

 

 

Solar causes of geomagnetic storms

190

Santosh Kumar & Mahendra Pratap Yadav

 

 

Application of SCORE algorithm to improve GPS accuracy in low latitude regions

197

A D Sarma, V Venkata Rao & G Sasi Bhushana Rao

 

Environmental impact on electrical parameter and gaseous concentrations

201

S S Kandalgaonkar, M I R Tinmaker, M K Kulkarni & Asha Nath

 

 

Validation of IRS P4 MSMR data over the central Bay of Bengal during

  July-August 1999

 

210

K Jossia Joseph, C V K Prasada Rao, P V Hareesh Kumar & N Mohan Kumar

 

Role of weight percentage of H2SO4 in homogeneous heteromolecular nucleation

216

N Singh, M S Chauhan & Y K Singh

 

 

A typical hexagonal ferrite from industrial waste for microwave energy

  absorption at Ku-band

 

225

  M R Meshram, Nawal K Agrawal, Bharoti Sinha & P S Misra

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Indian Journal of Radio & Space Physics

Vol.31, August 2002, pp.173-182

 

 

Calculated electron flux and densities at 10-1000 eV in the dayside Martian ionosphere:
Comparison with MG S and Viking results

S A Haider* & K I Oyama

Institute of Space and Astronautical Science, Kanagawa, Japan

Received 16 July 2001; accepted 8 February 2002

 

The photoelectron flux, ion production rates and electron densities are calculated in the energy range of 10-1000 eV for the dayside Martian ionosphere at solar zenith angle 70o in order to compare electron reflectometer measurements made by Mars Global Surveyor (MGS). These calculations are made by using analytical yield spectrum approach and one-dimensional continuity momentum equations in the presence of horizontal magnetic field where the vertical transport of electrons is inhibited. Using this method, ion and electron densities were also calculated in the absence of horizontal magnetic field at solar zenith angle 45o for all energy ranges. These results are compared with radio occultation measurements made by Viking and other reports which have used one-, two- and three-dimensional models. It is found that the calculated photoelectron flux and density at energy range 10 -1000 eV are in good agreement with the measurements in absence of ionization peaks as observed by electron reflectometer experiment onboard MGS. Above 200 km, the observed horizontal magnetic field of 50 nT is found to be sufficient to explain the electron density measured by electron reflectometer experiment. Below this altitude, there is no effect of horizontal magnetic field in the dayside ionosphere of Mars. The present calculation suggests that X-ray ionization is an important process in the upper ionosphere of Mars at energy greater than 90 eV and the 10-90 eV electron population is controlled by photoionization and photoelectron impact ionizations. The total electron energy population in the dayside ionosphere of Mars is mainly governed by 10-90 eV electron population. The two- and three-dimensional models are not able to reproduce the electron density measured by MGS and Viking. The present one-dimensional model can explain the upper ionosphere of Mars in the presence of precise intensity of magnetic anomaly whose location coincides with the location of electron density measurements.

 

 

Indian Journal of Radio & Space Physics

Vol. 31, August 2002, pp. 183-189

 

Numerical simulation of magnetic reconnection and plasmoid
dynamics in the geotail

 

Manashi Roy & G S Lakhina

Indian Institue of Geomagnetism Colaba, Mumbai 400 005

Received 16 August 2001; revised 26 November 2001; accepted 14 February 2002

The time evolution of the geotail is represented by a set of single fluid magnetohydrodynamic (MHD) equations. The initial equilibrium is allowed to be destroyed by a finite, but very small electric resistivity, so that the fluid is still an almost ideal MHD system. The subsequent evolution of the geotail is investigated by a two-dimensional numerical code. The onset of reconnection and formation of magnetic island-like structures called plasmoids are reproduced. The velocity pattern and the size of plasmoid are investigated under different initial conditions and are compared with actual observations in space.

 

Indian Journal of Radio & Space Physics

Vol. 31, August 2002, pp. 190-196

 

Solar causes of geomagnetic storms

Santosh Kumar

Department of PG Studies & Research in Physics and Electronics, R D University, Jabalpur (MP) 482 001

and

Mahendra Pratap Yadav

Govt. Tilak PG College, Katni (MP) 483 501

Received 7 June 2001; revised 27 September 2001; accepted 18 January 2002

Two hundred ninety nine geomagnetic storms (GMSs) of moderate, moderately severe and severe type with Ap 20 have been investigated for the period 1978-99 and their possible interplanetary and solar causes are looked upon. Solar features like Ha, X-ray solar flares and active prominences and disappearing filaments (APDFs) have been found to occur more in lower heliographic latitudinal zones and produce larger number of GMSs at various locations on the earth. No significant correlation between magnitude of GMSs and importance of Ha and X-ray solar flares and APDFs has been observed. Maximum number of GMSs is associated with importance SF of each Ha and X-ray solar flares. On the basis of the statistical sampling of four putative solar causes of GMSs on the earth, the causes are identified leading to magnetic disturbance with Ap 20. The Ha, X-ray solar flares are more plausible causes of GMSs. However, a very few GMSs have been observed without being associated with either of these four solar features. The occurrence of disturbed days varies with seasons. Further, monthly distribution of disturbed days shows a cyclic variation having two peaks during the solar cycle.

 

Indian Journal of Radio & Space Physics

Vol. 31, August 2002, pp. 197-200

 

Application of SCORE algorithm to improve GPS accuracy in low latitude regions

 

A D Sarma & V Venkata Rao

R & T Unit for Navigational Electronics, Osmania University, Hyderabad 500 007

and

G Sasi Bhushana Rao

Airports Authority of India, Hyderabad Airport, Hyderabad 500 016

Received 16 July 2001; revised 22 January 2002; accepted 6 March 2002

The performance of global positioning system (GPS) is limited by several sources of errors. Receiver system pseudorange error is one such error. A self-calibration of pseudorange error (SCORE) algorithm, which was proposed recently to correct it and used at midlatitude regions, has been applied in this paper for low latitude regions. The results are promising and have shown marked improvement in GPS position accuracy.

 

Indian Journal of Radio & Space Physics

Vol. 31, August 2002, pp. 201-209

 

Environmental impact on electrical parameter and gaseous concentrations

S S Kandalgaonkar, M I R Tinmaker, M K Kulkarni & Asha Nath

Indian Institute of Tropical Meteorology, Pune 411 008

Received 30 May 2001; revised 5 November 2001; accepted 30 April 2002

Ground-based observations of electric field, Aitken nuclei (AN) and concentrations of trace gases in fair weather conditions are made at four locations having different environmental status (oceanic, hill-top, semi-urban and industrial). The influence of concentration of Aitken nuclei and trace gases on atmospheric electric field at these locations is examined and an attempt is made to obtain the effective attachment coefficients and mean life time of small ions at the locations. The results show that, in clean and relatively less polluted regions, the diurnal as well as monthly variation of fair weather electric field is significantly (0.1 and 0.01%) correlated with Aitken nuclei concentration. An examination of gaseous concentrations suggests that the electric field gets adversely affected in the regions which are enriched with SO2 loading and particulate matter from the industries. The values of attachment coefficient and mean lifetime of small ions obtained in the present set of study reveal that the environmental status is an important factor to affect the air pollutants which, in turn, affect the electric field.

 

Indian Journal of Radio & Space Physics

Vol. 31, August 2002, pp. 210-215

 

Validation of IRS P4 MSMR data over the central Bay of Bengal during July-August 1999

K Jossia Joseph, C V K Prasada Rao, P V Hareesh Kumar & N Mohan Kumar,

Naval Physical and Oceanographic Laboratory, Thrikkakara, Kochi 682 021

Received 16 July 2001; revised 18 December 2001; accepted 3 April 2002

Validations of satellite-derived sea surface temperature (SST) and wind speed (WS) were carried out with sea-truth measurements obtained from moored data buoy and ship during July-August 1999. The SST sensed by multi-frequency scanning microwave radiometer (MSMR) showed significant departures from sea-truth measurements. The difference in SST (sea-truth MSMR) was negative and large during daytime and vice versa during nighttime. Sea-truth measurements of wind speed indicated that they were always lower (2-5 ms -1) than the MSMR winds. The derived correction factors reduced the biases of satellite data.

 

 

Indian Journal of Radio & Space Physics

Vol. 31, August 2002, pp. 216-224

 

Role of weight percentage of H2SO4 in homogeneous heteromolecular nucleation

 

N Singh, M S Chauhan & Y K Singh

Department of Physics, Nehru College, Chhibramau (U P) 209 721

Received 30 October 2000; revised 6 March 2002; accepted 29 May 2002

Heteromolecular homogeneous nucleation of sulphuric acid (H2SO4) has been considered for different mass fractions as the function of number of water molecules as well as H2SO4 molecules. The calculations have been made for critical radius, free energy of formation of critical nucleus as the function of weight percentage of H2SO4. The calculated values have been compared with those for HCl and HNO3. The pH values of solution of H2SO4 and H2O have been calculated. The results show that pH of H2SO4 solution decreases with the decrease in water molecules for a given value of H2SO4 molecules. It has also been inferred that the pH has positive values for weight percentage of H2SO4 < 10, while it is negative for weight percentages 10

 

Indian Journal of Radio & Space Physics

Vol.31, August 2002, pp.225-229

 

A typical hexagonal ferrite from industrial waste for microwave energy absorption at Ku-band

 

M R Meshram, Nawal K Agrawal & Bharoti Sinha

Department of Electronics & Computer Engineering, Indian Institute of Technology, Roorkee 247 667

 

and

 

P S Misra

Department of Metallurgical & materials Engineering, Indian Institute of Technology, Roorkee, 247 667

 

Received 4 June 2001 ; revised 11 February 2002; accepted 22 March 2002

The development of ferrite, using iron oxide as an industrial waste material, has been described. The developed ferrite powder [Ba(Co-Ti)d Fe(11.9-d)Mn0.15O19] , 60% by weight, was dispersed in epoxy resin to form a paint. This paint was coated on conducting aluminum sheet to study absorption characteristics of EM wave at Ku-band. It is found that the single layer absorbing paint exhibits broad-band characteristics from 12 to 18 GHz with minimum absorption of 6 dB and maximum absorption of 13.6 dB at 15 GHz for a coating thickness of 2.3 mm. It is also found that, addition of small quantity of carbon and iron powder, 10% by weight, in the developed ferrite powder provides broad-band characteristics with a minimum absorption of 10.1 dB from 15.5 to 18 GHz for a thickness of 1.76 mm.