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High resolution radio spectroscopy of continuum radio bursts at decameter wavelengths from the sun a thesis submitted for the degree of Doctor of Philosophy in the faculty of science, Bangalore University, Bangalore Subramanian, K.R. [Ph.D Thesis]

By: Contributor(s): Material type: TextTextPublication details: Bangalore Indian Institute of Astrophysics 1992Description: 207pSubject(s): Online resources: Dissertation note: Doctor of Philosophy Indian Institute of Astrophysics, Bangalore 1992 Summary: Observations of solar radio bursts at decameter wavelengths with high time, frequency and sensitivity are presented. The time and intensity characteristics of type IIIb burst observed at 25 MHz are compared with those of type III burst which follows the type IIIb burst. A theoretical model which accounts for the various aspects of these bursts is proposed. The time profile of isolated and type III associated type III bursts are compared. It is observed that while there exists a correlation between exciter duration and decay constant for isolated Type III bursts, it absent in the case of type III bursts The Gauribidanur radio telescope operating at a frequency of 34.5 MHz and an eight channel filter bank spectrograph are described. Fine structures in the radio emission of the sun observed with the above system are presented. Observations on the pulsation pattern in the time profile of short duration solar radio bursts, are presented. These pulsations are found to be present in the saturation phase of the burst. A tentative physical model to explain the observed characteristics is proposed. From the bandwidth and drift rate of slowly drifting spike b0rsts,the strength of the magnetic field at 1.5 solar radii is determined. From the time profiles of diffuse echo bursts, the distance between the plasma layers corresponding to frequencies 17.25 MHz and 34.5 MHz is derived. To study solar radio bursts over wide bandwidth a broadband array operating in the frequency range of 30 to 70 MHz was designed and constructed. Using this array and a four channel spectral receiver, low frequency radio spectrum of the continuum emission from the undisturbed sun is determined for 24 days over the period 1985 May - Sept. It is found that the spectral index varied from + 1.6 to + 3.6 during this period. It is suggested that the large positive spectral indices are due to the existence of temperature gradients in the outer corona. Temporal and spectral characteristics of microbursts observed in the frequency range of 38 to 65 MHz are compared with those of normal type III rad i,o ,bursts. It is shown that the microbursts are low frequency extension of the brightness temperature spectrum of type III bursts.
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Item type Current library Shelving location Call number Status Date due Barcode
Thesis & Dissertations Thesis & Dissertations IIA Library-Bangalore General Stacks 043:523.985/ SUB (Browse shelf(Opens below)) Available 15392

Thesis Supervisors Ch. V. Sastry and M. N. Anandaram

Doctor of Philosophy Indian Institute of Astrophysics, Bangalore 1992

Observations of solar radio bursts at decameter wavelengths with high time, frequency and sensitivity are presented. The time and intensity characteristics of type IIIb burst observed at 25 MHz are compared with those of type III burst which follows the type IIIb burst. A theoretical model which accounts for the various aspects of these bursts is proposed. The time profile of isolated and type III associated type III bursts are compared. It is observed that while there exists a correlation between exciter duration and decay constant for isolated Type III bursts, it absent in the case of type III bursts
The Gauribidanur radio telescope operating at a frequency of 34.5 MHz and an eight channel filter bank spectrograph are described. Fine structures in the radio emission of the sun observed with the above system are presented. Observations on the pulsation pattern in the time profile of short duration solar radio bursts, are presented. These pulsations are found to be present in the saturation phase of the burst. A tentative physical model to explain the observed characteristics is proposed. From the bandwidth and drift rate of slowly drifting spike b0rsts,the strength of the magnetic field at 1.5 solar radii is determined. From the time profiles of diffuse echo bursts, the distance between the plasma layers corresponding to frequencies 17.25 MHz and 34.5 MHz is derived.
To study solar radio bursts over wide bandwidth a broadband array operating in the frequency range of 30 to 70 MHz was designed and constructed. Using this array and a four channel spectral receiver, low frequency radio spectrum of the continuum emission from the undisturbed sun is determined for 24 days over the period 1985 May - Sept. It is found that the spectral index varied from + 1.6 to + 3.6 during this period. It is suggested that the large positive spectral indices are due to the existence of temperature gradients in the outer corona. Temporal and spectral characteristics of microbursts observed in the frequency range of 38 to 65 MHz are compared with those of normal type III rad i,o ,bursts. It is shown that the microbursts are low frequency extension of the brightness temperature spectrum of type III bursts.

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