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|Title:||Annual & Semi-annual Periodicities in IEC at Low Latitudes|
|Authors:||Bhuyan, P K|
Tyagi, T R
|Abstract:||The variations of the annual and semi-annual periodicities in ionospheric electron content (IEC) are investigated by harmonically analyzing the monthly median values for three Indian locations during the low solar activity period of 1975-76 and through half a solar cycle (1 975-80) for Delhi. Results are presented as a function of local time. The phase and amplitude of the annual and semi-annual components exhibit geomagnetic solar cycle and local time dependence. Semi-annual maxima occur in April and October at all the locations and irrespective of solar activity condition which may be attributed to similar changes in atomic oxygen concentration controlIing the production of ionization. The annual maximum shows systematic changes in phase and amplitude as a function of latitude and local time. During low solar activity, the winter phase is evident only near the dip equator. Away from the equator the occurrence of the annual maximum changes from summer to winter as the sunspot activity increase. Another feature observed is the near absence of these periodicities during nighttime. In addition to atmospheric composition changes, F-region plasma transport controlled by E B drifts is likely to be the main contributor to these observed periodicities at low latitudes.|
|ISSN:||0975-105X (Online); 0367-8393 (Print)|
|Appears in Collections:||IJRSP Vol.14(2&3) [April & June 1985]|
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