Traits of sub-kilometre F-region irregularities as seen with the Swarm satellites

Aol, Sharon; Buchert, Stephan; Jurua, Edward

doi:10.5194/angeo-38-243-2020

Cited by 17 publications

(9 citation statements)

References 76 publications

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“…Scintillations from ESF and EPBs have a different seasonal variation from Es as reported in previous studies [7,13,15,[39][40][41][42][43][44]. As shown Figure 5, the RO S4 at h t = 30 km can be used to map the global distribution and seasonal variation of the nighttime (20:00-02:00) as observed from the in-situ sensors as well as from the ground-based receivers.…”

Section: Equatorial Plasma Bubbles (Epbs) and Equatorial Spread-f (Esf)mentioning

confidence: 77%

Ionospheric S4 Scintillations from GNSS Radio Occultation (RO) at Slant Path

2020

Remote Sensing

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Ionospheric scintillation can significantly degrade the performance and the usability of space-based communication and navigation signals. Characterization and prediction of ionospheric scintillation can be made from the Global Navigation Satellite System (GNSS) radio occultation (RO) technique using the measurement from a deep slant path where the RO tangent height (ht) is far below the ionospheric sources. In this study, the L–band S4 from the RO measurements at ht = 30 km is used to infer the amplitude scintillation on the ground. The analysis of global RO data at ht = 30 km shows that sporadic–E (Es), equatorial plasma bubbles (EPBs), and equatorial spread–F (ESF) produce most of the significant S4 enhancements, although the polar S4 is generally weak. The enhanced S4 is a strong function of local time and magnetic dip angle. The Es–induced daytime S4 tends to have a negative correlation with the solar cycle at low latitudes but a positive correlation at high latitudes. The nighttime S4 is dominated by a strong semiannual variation at low latitudes.

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Section: Equatorial Plasma Bubbles (Epbs) and Equatorial Spread-f (Esf)mentioning

confidence: 77%

Ionospheric S4 Scintillations from GNSS Radio Occultation (RO) at Slant Path

2020

Remote Sensing

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“…The high QF values at the equinoxes and the December solstice are most likely due to the RTI, which is usually triggered at the bottom side of a rising equatorial F layer. The rate of growth of the RTI depends on the meridional wind and the eastward electric field PRE determined by the longitudinal gradient of the flux-tube-integrated conductivity (Sultan, 1996;Basu, 2002). At the June solstice, the QF values were small after sunset, as seen in Fig.…”

Section: Local Time and Seasonal Variation Of Ionospheric Irregularitiesmentioning

confidence: 92%

Simultaneous ground-based and in situ Swarm observations of equatorial F-region irregularities over Jicamarca

et al. 2020

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Abstract. Ionospheric irregularities are a common phenomenon in the low-latitude ionosphere. They can be seen in situ as depletions of plasma density, radar plasma plumes, or ionogram spread F by ionosondes. In this paper, we compared simultaneous observations of plasma plumes by the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere (JULIA) radar, ionogram spread F generated from ionosonde observations installed at the Jicamarca Radio Observatory (JRO), and irregularities observed in situ by Swarm in order to determine whether Swarm in situ observations can be used as indicators of the presence of plasma plumes and spread F on the ground. The study covered the years from 2014 to 2018, as this was the period for which JULIA, Swarm, and ionosonde data sets were available. Overall, the results showed that Swarm's in situ density fluctuations on magnetic flux tubes passing over (or near) the JRO may be used as indicators of plasma plumes and spread F over (or near) the observatory. For Swarm and the ground-based observations, a classification procedure was conducted based on the presence or absence of ionospheric irregularities. There was a strong consensus between ground-based observations of ionospheric irregularities and Swarm's depth of disturbance of electron density for most passes. Cases, where ionospheric irregularities were observed on the ground with no apparent variation in the in situ electron density or vice versa, suggest that irregularities may either be localized horizontally or restricted to particular height intervals. The results also showed that the Swarm and ground-based observations of ionospheric irregularities had similar local time statistical trends with the highest occurrence obtained between 20:00 and 22:00 LT. Moreover, similar seasonal patterns of the occurrence of in situ and ground-based ionospheric irregularities were observed with the highest percentage occurrence at the December solstice and the equinoxes and low occurrence at the June solstice. The observed seasonal pattern was explained in terms of the pre-reversal enhancement (PRE) of the vertical plasma drift. Initial findings from this research indicate that fluctuations in the in situ density observed meridionally along magnetic field lines passing through the JRO can be used as an indication of the existence of well-developed plasma plumes.

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“…The average of each segment is subtracted and the standard deviation of the residual is used as a measure of density perturbation for each 32-km interval. The r.m.s density perturbation is used as a measure for identifying density irregularity (Aol et al, 2020;Buchert et al, 2015;Xiong et al, 2016). Wan et al (2018) considered 5 × 10 10 m −3 as a threshold for density irregularity in the equatorial region as measured by Swarm.…”

Section: Irregularity Detectionmentioning

confidence: 99%

Standing Alfvén Waves Within Equatorial Plasma Bubbles

Ghadjari

Knudsen

Skone

2022

Geophysical Research Letters

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Plasma depletions in the disturbed equatorial ionosphere are known to be associated with magnetic fluctuations and Alfvén waves. Here, using data from the Swarm B satellite's vector field magnetometer and electric fields instrument at an altitude of ∼500 km, we present evidence of standing Alfvén modes trapped within strong density depletions. Fourier transforms of electric (δE) and magnetic (δB) perturbations reveal harmonic structure with anticorrelated peaks and relative phase shifts approaching ±90°, in agreement with a simple model of standing waves sampled from a moving spacecraft. The mode frequencies allow us to estimate the field‐aligned length of the bubbles, which we find to be in the range of 110–200 km. This value is much smaller than the overall field line length mapped to the two E‐region footprints, indicating that the waves we observe do not couple to the lower ionosphere.

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Traits of sub-kilometre F-region irregularities as seen with the Swarm satellites

Cited by 17 publications

References 76 publications

Ionospheric S4 Scintillations from GNSS Radio Occultation (RO) at Slant Path

Ionospheric S4 Scintillations from GNSS Radio Occultation (RO) at Slant Path

Simultaneous ground-based and in situ Swarm observations of equatorial F-region irregularities over Jicamarca

Standing Alfvén Waves Within Equatorial Plasma Bubbles

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