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|Title:||Long period oscillations of zonal wind in lower and middle atmosphere over Thumba: Power spectrum analysis for inter-annual variations and other features|
|Authors:||Jain, A R|
Rangarajan, G K
|Abstract:||Long period oscillations such as quasi-biennial (QBO), annual (AO) and semi-annual (SAO) oscillation over Thumba (8.5° N) are fond to show considerable variation from year to year. Long series of data (1971-1986) available for Thumba is used to quantify these inter-annual variations using the technique of complex demodulation. Inspite of the large inter-annual variation the height profile of AO and SAO retains their basic characteristics. The inter-annual variations of AO amplitude at tropospheric heights are smallest (2Sd 5ms-1, where Sd is the standard deviation) and are well correlated with solar activity. Inter-annual variations of SAO near stratopause height are largest (2Sd ~ 12 ms-1) and are inversely correlated with solar activity. Method of maximum entropy (MEM) is used for studying the variability of QBO period with altitude and also for detecting the presence of additional spectral line in the data. The QBO period shows considerable height variations with largest value of ~ 31 month near 40 km altitude and with smaller values above and below this altitude. An oscillation with a period of ~ 14 month is identified between 18 and 50 km. The characteristics of this oscillation tend to suggest that it is an independent oscillation. To understand the solar activity dependence of AO, SAO and QBO, and the height variation of QBO, simultaneous study of equatorial wave activity over long period has been recommended.|
|ISSN:||0975-105X (Online); 0367-8393 (Print)|
|Appears in Collections:||IJRSP Vol.20(6) [December 1991]|
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