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Indian Journal of Radio & Space Physics

 

 

 

ISSN : 0367-8393

 

CODEN:IJRSAK

VOLUME 33

NUMBER 4

AUGUST  2004

 

 

CONTENTS

 

Proxies for solar EUV in cycle 23

215

R P Kane*

 

 

Effect of transverse inhomogeneous electric field and loss-cone distribution on electrostatic ion-cyclotron instability in the ionosphere

 

223

Ruchi Mishra & M S Tiwari*

 

 

Diffusion coefficient and wave amplification determination from pitch angle dependent kinetic energy of electrons

 

234

D P Singh* & U P Singh

 

 

Inter-annual variability in the dynamics and physics of the mean onset date of monsoon over Indian region

 

241

S S Naik*, L George & P S Salvekar

 

 

A logistical regression model for prediction of premonsoon convective development over Kolkata

 

252

S Dasgupta & U K De*

 

 

Association of aerosol optical depth with near surface aerosol properties in urban environment

256

K Madhavi Latha* & K V S Badarinath

 

 

Some observations on the characteristics of aerosols at traffic junctions in Pune city

260

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

 

 

Development of 20 kW amplifier at very high frequency (VHF)

267

Raghuraj Singh*, Y S S Srinivas, Pankaj Khilar, B Kadia, Sunil Dani, Dhiraj Bora & D S Bhattacharya

 

 

*Corresponding authors

 

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, August 2004, pp. 215-222

 

Proxies for solar EUV in cycle 23

R P Kane

 

For daily values in a strong 27-day sequence, lasting for more than 8 months, correlations of solar EUV with solar F10 radio emission were, sometimes, found to be lower than those with solar Mg II core-to-wing index, sometimes higher, and sometimes almost the same. Correlations of EUV with the UV Si III and Lyman-α were found to be mostly higher than those with F10 and Mg II. In contrast to the correlations for long-term changes (0.95 or more), the maximum correlations for short-term changes (daily values) were only ~0.80, implying an explained variance of only ~65%, leaving ~35% unexplained. Hence, estimates of daily EUV using F10 and Mg II as proxies could have uncertainties of several tens of percent. For intermediate and long-term changes, EUV was very highly correlated with F10, Mg II and Lyman-α (and to some extent even with sunspots) during years of low and medium sunspot activity (1996-1999) of cycle 23. The Mg II had a slight superiority over F10, but both could be considered as good proxies for EUV. However, for the sunspot maximum years 2000-2002, the EUV evolution differed from the evolutions of F10 and Mg II, so that these would be unsatisfactotry proxies for EUV.

 

Keywords: Solar EUV, Solar cycle, Solar radio emission, Sunspot

PACS No.: 96.60.Qc; 96.60.Tf; 94.20.Vv

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, August 2004, pp. 223-233

 

Effect of transverse inhomogeneous electric field and loss-cone distribution on electrostatic ion-cyclotron instability in the ionosphere

 Ruchi Mishra & M S Tiwari

 

Dispersion relation, resonant energy transferred, growth rate and marginal stability of the electrostatic ion-cyclotron wave with general loss-cone distribution function in low-b homogeneous plasma in the presence of a transverse inhomogeneous electric field are discussed by investigating the trajectories of the particles. The wave is assumed to propagate obliquely to the static magnetic field. The whole plasma is considered to consist of resonant and non-resonant particles. It is assumed that resonant particles participate in energy exchange with the wave, whereas non-resonant particles support the oscillatory motion of the wave. Effects of the steepness of the loss-cone distribution and inhomogeneity in electric field on resonant energy transferred and growth rate of the instability are discussed. It is found that the effect of transverse electric field is to stabilize the wave, whereas the inhomogeneity in electric field acts as a source of free energy for the electrostatic ion-cyclotron wave and enhances the growth rate. Effect of steepness of loss-cone is also to enhance the growth rate. The results are interpreted for the space plasma parameters appropriate to the auroral acceleration region.

 

Keywords: Ion-cyclotron instability; Electrostatic ion-cyclotron instability; Ionospheric ion-cyclotron instability; Loss-cone distribution

PACS No: 94.20.Bb; 94.20.Tt; 52.35Hr,Qz

 

 

  

Indian Journal of Radio & Space Physics

 Vol. 33, August 2004, pp. 234-240

 

Diffusion coefficient and wave amplification determination from pitch angle dependent kinetic energy of electrons

D P Singh and U P Singh

 

A new expression for diffusion coefficient D(a) is derived, which is a function of pitch angle (a) dependent kinetic energy of electrons. Pitch angle diffusion of electrons along with amplification of interacting VLF signals is studied at L= 5.1. Diffusion coefficient D(a) has been found to increase but temporal wave growth (r) and power gain (in dB) decrease with increase in pitch angle. The derived expression for D(a) is found to be convenient for numerical analysis. The results are interpreted in the light of observation/analysis of transmitted signals by Sonwalkar et al. [J Geophys Res (USA), 102 (1997) 14363]. The non-observation of 2.55-2.9 kHz signals is attributed to scarcity of suitable pitch angle anisotropy, A(Er).

 

Keywords: Diffusion coefficient, Wave amplification, Thermal anisotropy

PACS No: 94.10 Lf, 94.20 Rr, 94.30 Hn

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, August 2004, pp. 241-251

  

Inter-annual variability in the dynamics and physics of the mean onset date of monsoon over Indian region

S S Naik, L George & P S Salvekar

 

From observational and statistical studies, the mean onset date of southwest monsoon for India is 1st June with standard deviation of 8 days. In view of this, the atmospheric circulation over India and neighbourhood (EQ-25N, 50E-90E) for the mean onset date is studied using NCEP reanalyzed data from surface-300 hPa for three different years, i.e. (i) year 2000 having normal onset, (ii) year 1999, early onset (i.e. 25th May) and (iii) year 1997, late onset (i.e. 9th June). The influence of all dynamical and physical parameters for all the three years are discussed in the present study for understanding the dynamics and physics associated with onset conditions on 1st June.

 

Keywords: Atmospheric circulation, Monsoon, Monsoon onset

PACS No.: 92.60 Wc; 92.60 Jq; 92.60 Bh

IPC Code: G01W 1/02; G01W 1/10

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, August 2004, pp. 252-255

 

A logistic regression model for prediction of premonsoon convective development over Kolkata

S Dasgupta* & U K De

 

Certain parameters (both dynamic and thermodynamic) have been identified as significant for the occurrence of convective developments in the premonsoon period (March-May) in Kolkata (India). In the present paper, an attempt has been made to develop a logistic regression model for prediction of the risk of occurrence of these convective developments from a knowledge of the values of significant parameters. The model was developed on the basis of a sample of 87 days covering the premonsoon period of the year 1990. When used for the purpose of validation on the basis of data of an arbitrarily chosen year, it yielded about 80% correct predictions.

 

Keywords: Regression model; Convective development; Premonsoon prediction

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

IPC Code: GO1W 1/00; GO1W 1/10

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, August 2004, pp. 256-259

 

Association of aerosol optical depth with near surface aerosol properties in urban environment

K Madhavi Latha & K V S Badarinath

 

Changes of near surface aerosol properties and their association with aerosol optical depth studied over tropical urban environment in Hyderabad during January-May, 2003 corresponding to winter and summer seasons have been presented. Aerosol Optical Depth (AOD) has been studied using MICROTOPS-II sunphotometer and aerosol size distribution has been studied using Quartz Crystal Microbalance Particle analyzer. Results from the study suggest that the temporal variation of near surface sub-micron aerosol mass concentration and columnar aerosol optical depth at 500 nm are well correlated. Aerosol size index as well as Angstrom wavelength exponent has been found to be high during February, indicating relative dominance accumulation mode particles. During summer season Angstrom exponent values have been found to be low indicating relative dominance of coarse mode particles.

 

Keywords: Aerosol optical depth, Urban environment, Aerosol mass concentration, Aerosol size distribution

PACS No: 42.68 Jg; 92.60Mt

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, August 2004, pp. 260-266

 

Some observations on the characteristics of aerosols at traffic junctions in Pune city

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

 

Vehicular emissions are one of the potential sources of air pollution, especially in the urban regions. Pune, one of the rapidly growing cities of India, faces a severe threat from this problem. Observations of Total Suspended Particulates (TSP) and Aitken Nuclei (AN) were conducted at four traffic junctions in the city during summer (May 2000) and winter (Jan-Feb 2001). Concentrations of TSP were very high at all the traffic junctions and also the number density of AN was very high. Concentrations of all the measured constituents were more, except NH4 and Cu, at traffic junctions than those reported at Pashan, a semi-rural location, comparatively away from vehicular effects.

 

Keywords: Air pollution, Traffic junctions, Vehicular emissions, TSP, Aitken nuclei

PACS No: 82.33 Tb

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 33, August 2004, pp. 267-277

 

Development of 20 kW amplifier at very high frequency (VHF)

Raghuraj Singh, Y S S Srinivas, Pankaj Khilar, B Kadia, Sunil Dani, Dhiraj Bora  and D S Bhattacharya

 

A triode based 20 kW cw (continuous wave) amplifier has been developed and tested indigenously at 91.2 MHz and 70 MHz. The equipment will drive the pre-driver stage of 200 kW, which will, in turn drive the final stage of 1.5 MW of rf power to heat plasma in SST-1 Tokamak for 1000 s. Various aspects of design and fabrication of the amplifier are discussed in this paper.

 

Keywords: Amplifier, Very high frequency (VHF)

PACS No: 84.30 Le

IPC Code: H03F 3/191