are measured along x and y axes which are normal to the propagation direction with the x axis in the plane containing the propagation direction and the magnetic field line (Figure A-l); is the angle between the propagation direction and the field line. The phase correlation function has an anisotropic Gaussian form similar to the correlation function of the electron density except the axial ratio of the ellipses of equal correlation is now rather than The rms phase fluctuation for an extended irregular medium is given by: where is the radio wavelength, is classical electron radius, is the angle from zenith at the irregularities, and is the thickness of the irregularity layer. A. 4 PHASE AND AMPLITUDE FLUCTUATIONS AND THEIR SPATIAL AND TEMPORAL CORRELATION FUNCTIONS ON AN OBSERVATIONAL PLANE The phase deviations of the wavefront emerging from the irregular medium described above will lead also to amplitude fluctuations as the wave propagates 3 away from the screen. Using diffraction theory Bowhill has derived expressions to describe the statistical properties of the wave field at a distant point for the general case where the source and the observational point are located at finite distance from the diffracting screen. The results are summarized in a convenient form in a recent report by Evans. . The spatial correlation functions of amplitude and phase and rms fluctuations in amplitude (divided by mean amplitude) and phase Q0) are defined by:
RkJQdWJsaXNoZXIy MTU5NjU0Mg==