Abstract
Abstract We present observations during the interval 2006–2014 of 27 day and 13.5 day periodic oscillations in the ionospheric sporadic E (Es) layer. This is a thin, dense layer composed of metallic ions in the Earth’s upper atmosphere between 90 and 130 km. Lomb–Scargle spectral and wavelet analyses reveal that these pronounced periodicities observed from ground-based ionosondes and GPS/GNSS radio occultations are associated with high-speed solar winds generated from persistent coronal holes on successive 27 day solar rotations. The 27 day and 13.5 day oscillations in the Es layers are dependent on latitude, showing a higher magnitude of periodicities at low latitudes between 0° and 15° and at high latitudes between 45° and 90° (10%–14%) than those at midlatitudes between 15° and 45° (4%–10%). The 27 day and 13.5 day oscillations in the high-latitude Es layers correlate well with the geomagnetic activity Dst and Ap indices, and these periodic oscillations become more significant at the solar maximum (2000–2003 and 2011–2014) than at the solar minimum.
Highlights
Variability in near-Earth interplanetary and terrestrial parameters is affected by the Sun
Lomb–Scargle spectral and wavelet analyses reveal that these pronounced periodicities observed from ground-based ionosondes and Global Positioning System (GPS)/Global Navigation Satellite System (GNSS) radio occultations are associated with highspeed solar winds generated from persistent coronal holes on successive 27 day solar rotations
The recurrence of geomagnetic activity is attributed to the passage of high-speed solar winds at Earth, which originate from persistent coronal holes at low heliographic latitudes on successive solar rotations (Chi et al 2018)
Summary
Variability in near-Earth interplanetary and terrestrial parameters is affected by the Sun. The Earth’s upper atmosphere and ionosphere are strongly modulated by solar activity, which exhibits 11 yr, annual, and interannual (semiannual, seasonal, 27 day, and diurnal) periods. The approximately 27 day synodic rotation period of the Sun is one prominent short-term periodic variation in the solar wind and near-Earth interplanetary parameters (Beck 2000). The recurrence of geomagnetic activity is attributed to the passage of high-speed solar winds at Earth, which originate from persistent coronal holes at low heliographic latitudes on successive solar rotations (Chi et al 2018). Lei et al (2008b) reported the ionospheric response of periodic oscillations in global mean TEC to the earthward high-speed streams of solar wind that arise from such coronal holes. Understanding the influences of solar rotation on the lower ionosphere is of vital importance to the study of the solar–terrestrial connection and possible processes that enable the solar-wind energy to impact the Earth’s atmospheric weather systems via the global electric circuit (Jánský et al 2017)
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