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F ‐layer irregularities as determined by backscatter studies at 19 MHz over half of a solar cycle
Author(s) -
Basu Sunanda,
Vesprini Robert L.,
Aarons Jules
Publication year - 1974
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/rs009i003p00355
Subject(s) - sporadic e propagation , backscatter (email) , latitude , atmospheric sciences , sunspot , solar cycle , physics , f region , magnetic field , radar , astrophysics , ionosphere , geophysics , solar wind , astronomy , telecommunications , quantum mechanics , computer science , wireless
A continuous series of backscatter observations at 19 MHz made at Plum Island, Massachusetts, 56°N invariant latitude, over nearly half a solar cycle is utilized to derive occurrence characteristics of ground backscatter propagated by means of F ‐layer reflection, 1 F , as well as those of aspect‐sensitive field‐aligned echoes from the F layer, FAE( F ). Neither field‐aligned E ‐layer echoes nor ground backscatter propagated by means of sporadic E were found to produce any noticeable blanketing of the radar signal for this frequency and radar location. The 1 F propagation showed marked sunspot cycle and azimuthal dependence and was strongest in winter and weakest in summer. Under quiet magnetic conditions FAE( F ) was primarily a sunset phenomenon, occurring usually at delays of 7 to 10 msec, with a marked sunspot cycle dependence. Some daytime activity was observed at longer delays of 20 to 22 msec which could be explained in terms of F ‐layer field alignment after one intermediate ground reflection. The occurrence of FAE( F ) during magnetic storms showed a seasonal variation in agreement with the well‐known storm behavior of f 0 F 2 at these latitudes. In general, however, the occurrence of FAE( F ) increased monotonically with increasing magnetic activity until the threshold of K Fr = 4 was reached, beyond which the depletion in the F ‐layer background ionization caused it to decrease, with complete cut‐off occurring irrespective of season during very disturbed conditions, K Fr ≥ 7. With the aid of ray traces, the occurrence statistics of both 1 F and FAE( F ) are interpreted and discussed in terms of the geometry of the probing radar, the various factors controlling F ‐layer propagation, and the extent of the F ‐layer irregularity region.