Abstract
Using the equations of the wind shear theory of sporadic- E and the ionosonde measured values of fbE S and f 0E , it is shown possible to deduce the ‘effective wind shears’ (in the E-region) defined as U′ eff = U′ ( kv im iα ) −, where v i, m i , and α are the collision frequency, mean mass and recombination coefficient, respectively, of the ions forming into E S layers, and k is a constant, and U′ is the vertical shear of the eastward neutral wind. Using the above method, the daily, seasonal and solar cycle variations of these ‘effective wind shears’ are obtained at nine stations. Daily and seasonal variations of large amplitude, and also smaller but significant solar cycle variations are present at all stations, thereby indicating a strong solar control of these ‘effective wind shears.’ In addition, a latitudinal change in the occurrence times of the maximum wind shears is observed. Assuming that the variations in v i and α are small, and assuming further that internal gravity waves are the source of the wind shears, two possible interpretations of the results are discussed. In one, the variations in the (wave) propagation conditions in the mesosphere and lower thermosphere are considered to cause the deduced wind shear variations. In the second, the possibility of gravity waves being generated by non-linearities in tidal winds is considered, and in such a case, the variations in the tidal wind amplitudes can cause corresponding variations in the strength of the gravity wave shears.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call