On the Nature of the Intraseasonal Variability of Nighttime Ionospheric Irregularities Over Taiwan

Abstract

The nature of intraseasonal (within a season) variability of the nighttime ionospheric irregularities has been studied utilizing the observation of the recently installed VHF scintillation receiver from Pingtung, Taiwan. Investigation is based on observations made in 2015 (high‐moderate solar epoch) and 2017 (low solar epoch). Detailed investigation has revealed coexistence of planetary‐scale variability (3–7 days), 10‐ to 16‐day variability, and > 25‐day variability in 2015. Interestingly, the Lomb‐Scargle frequency domain analysis indicated the variability of larger timescales to display somewhat greater amplitudes. The virtual height of the F layer, h'F, over Sanya, also indicated intraseasonal periodicities similar to S4 periodicities observed at Pingtung. Observations have also revealed that, equatorial plasma bubbles (EPBs) over Pingtung tended to occur on contiguous nights as compared to isolated occurrence, and > 60% of the EPB nights were part of two or more (up to 6) nights of contiguous occurrence. Spectral analysis revealed a quasi‐27‐day variability in the ap and AE geomagnetic indices presumably associated with the solar rotation period. The time period of geomagnetic variability corresponded with the period of dominant S4 variability, indicating that the effect of geomagnetic activity on the low‐latitude ionosphere can be periodic in nature. In 2017 (low solar flux), even with a very low occurrence of ionospheric irregularities, planetary‐scale variability was observed. The dominant period of S4 variability in the autumnal equinox was highly correlated with the periodic geomagnetic activity. Results indicate that a deeper understanding of the periodic intraseasonal variability can be imperative for extended range forecast/prediction of ionospheric irregularities.

Can Numerical Simulations of Equatorial Plasma Bubble Plume Structures be Simplified for Operational and Practical Usage?

“…Further, steep TEC gradients associated with EPBs may also adversely affect the integrity of space-based augmentation systems (SBASs) and ground-based augmentation systems (GBASs) in civil aviation (see, e.g., Yoon et al, 2017). The occurrence of EPBs follows a regular seasonality (Burke et al, 2004;Gentile et al, 2006aGentile et al, , 2006b, but there is significant day-to-day variability in EPB occurrence as well (Ogawa et al, 2006(Ogawa et al, , 2009Joshi et al, 2019), which is far more difficult to forecast (e.g., Li et al, 2021).…”

Climatology of ionospheric amplitude scintillation on GNSS signals at south American sector during solar cycle 24

“…Over the Indian sub-continent, Goswami et al (2017) found intense scintillations at the northern anomaly crest region of Calcutta during the equinoxes and Joshi et al (2019) found that scintillation variability in the autumnal equinox was highly correlated with the periodic geomagnetic activity. Sahithi et al (2019) investigated the climatology of scintillations over India at stations located around the crest and trough regions of the EIA, identifying that the probability of scintillations is higher during March equinox and December solstice, and lowest during June solstice, maximizing in the post-sunset hours.…”

Investigation of Spatiotemporal Morphology of Plasma Bubbles Based on EAR Observations

“…Prediction/forecast of EPB is considered vital as it can adversely affect the accuracy and continuity of the satellite based navigation. Intermediate scale irregularities present inside the EPB scatters the radio waves transmitted by the navigation satellites in forward direction which can result in the rapid fluctuation of the signal amplitude and phase on ground (de Lima et al, 2015;Joshi et al, 2019a;Joshi et al, 2019b;Kintner et al, 2004;Ledvina et al, 2004;Retterer, 2010;Rezende et al, 2010). Such rapid fluctuations are termed ionospheric scintillations, which can result in the signal outage and/or loss of the receiver lock on the signal.…”