Accession Number : ADP006278

Title :   Coherence Scales of Wavefield during Propagation Through Naturally Disturbed Ionosphere in the Polar Cap, Auroral and Equatorial Regions,

Corporate Author : GEOPHYSICS LAB (AFSC) HANSCOM AFB MA

Personal Author(s) : Basu, S. ; Basu, Sunanda ; Livingston, R. C.

Report Date : 03 MAY 1990

Pagination or Media Count : 9

Abstract : Phase and intensity scintillation measurements have been made at low latitudes in the equatorial anomaly region, and at high latitudes in the auroral oval and the polar cap regions, using phase coherent transmissions at 250 MHz from stationary and near stationary satellites. The observations pertain to periods of high solar activity when intense scintillation activity is recorded at each of the above observing sites. This data set has been utilized to study the reduction of coherence times of intensity and complex amplitude scintillation with increasing strength of scattering. Estimates of coherence scales of intensity and complex amplitude scintillation at 250 MHz are provided which indicate that coherent scales of scintillation are typically of the order of hundreds of meters at high latitudes but approach values as small as tens of meters in the equatorial anomaly region. The phase spectral index in the nightside auroral oval is observed to be much steeper (p sub psi = .4) than those typically observed in the equatorial (p sub psi = 2.4) or polar cap regions (p sub psi approx. -2.3). It shows the importance of large scale phase variations in the nightside auroral oval. Under strong scatter conditions, the coherence times of complex amplitude scintillation are shown to asymptotically approach a value which is 1.4 times the coherence time of intensity scintillation. This result is consistent with the theoretical predictions for Rayleigh statistics.

Descriptors :   *IONOSPHERIC SCINTILLATION, *IONOSPHERIC PROPAGATION, VERY HIGH FREQUENCY, GLOBAL, COMPARISON, IONOSPHERIC DISTURBANCES, PHASE SHIFT.

Subject Categories : Industrial Chemistry and Chemical Processing
      Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE