PLANETARY WAVE EFFECT ON IONOSPHERIC ABSORPTION

A relationship is examined between quasi-periodic fluctuations in abso rption data at ionospheric altitudes and wave perturbations in wind da ta at tropospheric, stratospheric and lower mesospheric heights at Ind ian latitudes. The spectral analyses using Maximum Entropy Method (MEM ) reveal almost the same band of periodicities in both the parameters. The important band of frequencies of 6-8 days and between 20-25 days in wind data are found to propagate up to mesospheric heights and are well reflected in absorption data. These fluctuations in absorption da ta are thought to be due to the vertical propagation of Rossby waves o n different time scales. The correlation coefficient between absorptio n and wind data are found to be of the order of 0.5 to 0.75 at 95% con fidence level in most of the cases at a lag of 1 to 5 days with lower stratospheric zonal winds. The lag reduces considerably when the corre lation coefficient was computed at 60 km altitude using rocket data. A nother important finding is that when the QBO is in the easterly phase the long-period band preferably shows a predominance of 20-25 days, w hile during the westerly phase of the QBO, this band of periods extend s to 30-45 days, which is consistently observed in quasi-periodic fluc tuations of both absorption and wind data. This may have possible impl ications of coupling between the stratosphere and mesosphere through t he QBO. (C) 1997 Elsevier Science Ltd. All rights reserved.