Study of solar flux dependency of the winter anomaly in GPS TEC
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In literature, ionospheric winter anomaly refers to a higher daytime electron density (NmF2) at the F2 peak in winter than in summer that has a well-established mechanism for its formation. A number of researchers have extrapolated the same feature to total electron content (TEC) and have looked for a similar trend in TEC. The present work is a reassessment of the winter anomaly in TEC during different levels of solar flux. For this, we have analyzed TEC data for the period 2005–2012 using dual-frequency GPS receivers at three low-latitude and two mid-latitude stations in the Asian region. This period encompasses the declining and the lowest phase of solar cycle 23, and also the rising phase of solar cycle 24. The results of the study show that if the solar flux in a particular year is higher in winter (December) than in summer (June), only then the winter anomaly in TEC is observed. Thus, our research shows that the winter anomaly is not a consistent feature during all phases of solar activity at the chosen low as well as mid latitudes. If indeed a physical mechanism is responsible for the winter anomaly in TEC, then the anomaly must be observed during different phases of solar activity. To ascertain this, we have also studied the variation of solar-flux-independent TEC determined at a constant level of solar flux. While the semiannual oscillation in solar flux-independent TEC is a consistent feature, the winter anomaly is absent throughout the period 2005–2012. Hence, TEC is not a pertinent parameter to look for the winter anomaly.
KeywordsGlobal positioning system (GPS) Total electron content (TEC) Winter anomaly Low-latitude ionosphere Mid-latitude ionosphere
This work is supported from research grant received from the Council of Scientific and Industrial Research (CSIR), New Delhi, India under Emeritus Scientist Scheme (Sanction number 21(954)/13/EMR-II).
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