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A theory of strong and weak scintillations with applications to astrophysics

Citation

Lee, Lou-Chuang (1974) A theory of strong and weak scintillations with applications to astrophysics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/SP3E-6M20. https://resolver.caltech.edu/CaltechTHESIS:09212015-084744567

Abstract

The propagation of waves in an extended, irregular medium is studied under the "quasi-optics" and the "Markov random process" approximations. Under these assumptions, a Fokker-Planck equation satisfied by the characteristic functional of the random wave field is derived. A complete set of the moment equations with different transverse coordinates and different wavenumbers is then obtained from the characteristic functional. The derivation does not require Gaussian statistics of the random medium and the result can be applied to the time-dependent problem. We then solve the moment equations for the phase correlation function, angular broadening, temporal pulse smearing, intensity correlation function, and the probability distribution of the random waves. The necessary and sufficient conditions for strong scintillation are also given.

We also consider the problem of diffraction of waves by a random, phase-changing screen. The intensity correlation function is solved in the whole Fresnel diffraction region and the temporal pulse broadening function is derived rigorously from the wave equation.

The method of smooth perturbations is applied to interplanetary scintillations. We formulate and calculate the effects of the solar-wind velocity fluctuations on the observed intensity power spectrum and on the ratio of the observed "pattern" velocity and the true velocity of the solar wind in the three-dimensional spherical model. The r.m.s. solar-wind velocity fluctuations are found to be ~200 km/sec in the region about 20 solar radii from the Sun.

We then interpret the observed interstellar scintillation data using the theories derived under the Markov approximation, which are also valid for the strong scintillation. We find that the Kolmogorov power-law spectrum with an outer scale of 10 to 100 pc fits the scintillation data and that the ambient averaged electron density in the interstellar medium is about 0.025 cm-3. It is also found that there exists a region of strong electron density fluctuation with thickness ~10 pc and mean electron density ~7 cm-3 between the PSR 0833-45 pulsar and the earth.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Jokipii, J. Randolph
Thesis Committee:
  • Unknown, Unknown
Defense Date:9 December 1974
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
IBM FellowshipUNSPECIFIED
NASANGR-05-002-160
NSFGP-395-07
Alfred P. Sloan FoundationUNSPECIFIED
Record Number:CaltechTHESIS:09212015-084744567
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:09212015-084744567
DOI:10.7907/SP3E-6M20
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9161
Collection:CaltechTHESIS
Deposited By: Benjamin Perez
Deposited On:21 Sep 2015 17:53
Last Modified:21 Dec 2019 02:54

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