Global‐Scale Observations of the Equatorial Ionization Anomaly

Eastes, R.; Solomon, Stanley C.; Daniell, R. E.; Anderson, D. N.; Burns, A. G.; England, S.; Martinis, C. R.; McClintock, William E.

doi:10.1029/2019gl084199

Cited by 99 publications

(146 citation statements)

References 43 publications

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“…During solar minimum years, most EPBs are confined to within about ±20° magnetic latitudes (indicated by black dashed lines), and only those EPBs occurring around the Eastern Pacific, South America, and Atlantic regions in December solstice can extend to higher magnetic latitudes of about ±35° (indicated by the magenta lines). The latitudinal extent of EPBs in the Atlantic region is similar to recent observations by the Global‐scale Observations of the Limb and Disk (GOLD) imager (Eastes et al, 2019). During moderate solar flux years, the EPBs can extend to higher magnetic latitudes of about ±35°.…”

Section: Observations and Discussionsupporting

confidence: 87%

“…Recently, the National Aeronautics and Space Administration (NASA) GOLD mission has provided unprecedented observations of the day‐to‐day EIA images from western Africa to South America with rapid cadence. GOLD observed plasma depletions related to EPBs on most nights, and they display distinct spatial distributions during the October–December 2018 (Eastes et al, 2019). The EPBs tend to frequently appear with regular spacing on approximately one third of the nights, suggesting that gravity wave seeding is important (e.g., Makela et al, 2010; Takahashi et al, 2009).…”

Section: Observations and Discussionmentioning

confidence: 99%

“…The precursor waves show distinct wave patterns in equinoxes in solar minimum years, which is similar to the seasonal distribution of EPBs. This suggests that the seeding mechanism is critical and could be a necessary condition to explain the EPBs in patches and isolated clusters (Röttger, 1973) as well as periodic spacing of EPBs (e.g., Eastes et al, 2019; Makela et al, 2010). The inclusion of atmospheric wave forcing is, therefore, necessary to fully understand the global distribution of EPBs.…”

Section: Discussionmentioning

confidence: 99%

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Climatology of the Equatorial Plasma Bubbles Captured by FORMOSAT‐3/COSMIC

Chou

Pedatella

et al. 2020

JGR Space Physics

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The FORMOSAT-3/COSMIC (F3/C) satellites are used to study the climatology of equatorial plasma bubbles (EPBs) during the low to moderate solar flux years (2008)(2009)(2010)(2011)(2012)(2013). We use the F3/C total electron content to identify the presence of EPBs and investigate the background conditions for the initiation of EPBs. The results reveal that the EPB activities have strong solar dependence. The longitudinal and seasonal trends of EPBs are highly correlated to the angle between the dusk solar terminator and magnetic field lines near the magnetic equator. Asymmetries of EPBs between solstices and equinoxes exist and could be due partly to the asymmetry of equatorial ionization anomaly structures, which result in longitudinal differences as well. EPBs extend to higher altitudes and latitudes during the ascending phase of Solar Cycle 24 (2011-2013) due mainly to the increase of background electron density. However, an altitudinal asymmetry of EPBs occurs in moderate solar flux years, which is likely due to the suppression or lower growth and occurrence rates of EPBs. In addition to vertical drift, tidal forcing also contributes to the longitudinal and seasonal distributions of EPBs. Upwellings and precursor waves preceding the EPBs are observed climatologically, which likely play a vital role in initiating the EPBs. This study also reveals a vertical connection between the equatorial ionospheric irregularities and atmospheric forcing on a climatological basis.Plain Language Summary Equatorial plasma bubbles (EPBs) are an important space weather phenomenon that are often generated over the magnetic equator around twilight. They are ionospheric irregularities that can cause plasma depletions along the geomagnetic field lines, displaying geomagnetic conjugacy in both hemispheres. Since the ionospheric plasma is one of the significant error sources of the Global Navigation Satellite System (GNSS), EPBs are considered to be a primary disrupter of GNSS communication and navigation. Postsunset rise (PSSR) of the equatorial ionosphere due to vertical ion drift is often used to explain the occurrence of EPBs; however, it cannot fully explain the day-to-day variability of EPBs and the features of EPBs in patches and clusters. Mysteries abound around the EPBs and the underlying physics that initiates the EPBs remain unsolved. Here we utilize the FORMOSAT-3/COSMIC to investigate the underlying background conditions for the generation of EPBs. We find that, in addition to PSSR, symmetric equatorial ionization anomaly, as well as tidal forcing, appears to provide conditions favorable for the initiation of EPBs. Atmospheric tidal waves contribute to the longitudinal and seasonal distribution of EPBs as well. Bottomside ionospheric undulations due to atmospheric forcing are likely playing a vital role in initiating the EPBs.

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Section: Observations and Discussionsupporting

confidence: 87%

Section: Observations and Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Climatology of the Equatorial Plasma Bubbles Captured by FORMOSAT‐3/COSMIC

Chou

Pedatella

et al. 2020

JGR Space Physics

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“…The main scientific objective of GOLD is to understand the "weather" response of the Earth's thermosphere and ionosphere system to forcing from above and below, and the formation and evolution of EPBs is a primary scientific question (Eastes et al, 2017(Eastes et al, , 2019. The main scientific objective of GOLD is to understand the "weather" response of the Earth's thermosphere and ionosphere system to forcing from above and below, and the formation and evolution of EPBs is a primary scientific question (Eastes et al, 2017(Eastes et al, , 2019.…”

Section: Data Descriptionmentioning

confidence: 99%

Coordinated Ground‐Based and Space‐Based Observations of Equatorial Plasma Bubbles

Zou

Eastes

et al. 2020

JGR Space Physics

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This paper presents coordinated and fortuitous ground-based and spaceborne observations of equatorial plasma bubbles (EPBs) over the South American area on 24 October 2018, combining the following measurements: Global-scale Observations of Limb and Disk far ultraviolet emission images, Global Navigation Satellite System total electron content data, Swarm in situ plasma density observations, ionosonde virtual height and drift data, and cloud brightness temperature data. The new observations from the Global-scale Observations of Limb and Disk/ultraviolet imaging spectrograph taken at geostationary orbit provide a unique opportunity to image the evolution of plasma bubbles near the F peak height over a large geographic area from a fixed longitude location. The combined multi-instrument measurements provide a more integrated and comprehensive way to study the morphological structure, development, and seeding mechanism of EPBs. The main results of this study are as follows: (1) The bubbles developed a westward tilted structure with 10-15 • inclination relative to the local geomagnetic field lines, with eastward drift velocity of 80-120 m/s near the magnetic equator that gradually decreased with increasing altitude/latitude. (2) Wave-like oscillations in the bottomside F layer and detrended total electron content were observed, which are probably due to upward propagating atmospheric gravity waves. The wavelength based on the medium-scale traveling ionospheric disturbance signature was consistent with the interbubble distance of ∼500-800 km. (3) The atmospheric gravity waves that originated from tropospheric convective zone are likely to play an important role in seeding the development of this equatorial EPBs event.Plain Language Summary This study presents multi-instrument observations of equatorial plasma density depletions occurred on 24 October 2018 by using Global-scale Observations of Limb and Disk far ultraviolet images, Global Navigation Satellite System total electron content data, electron density measurements from Swarm satellite, ionosonde measurements, and cloud temperature data. This multi-instrument study generated an integrated and detailed image revealing both large-scale and mesoscale structures of the equatorial plasma depletion. Our results also suggest that atmospheric gravity waves originating from tropospheric convection activity could play a significant seeding role in the development of equatorial plasma bubbles. Key Points: • Combined GOLD/UV spectrograph images and ground-based TEC data revealed EPB features and development over a large geographic area • Bottomside F layer oscillations and traveling ionospheric disturbance were observed by ionosonde and detrended TEC results • Atmospheric gravity waves likely play an important role in seeding the R-T instability and the development of this EPB event Correspondence to: E. Aa,

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“…In the L1B-to-L1C processing, a small scattered light background and a variable particle radiation background are subtracted, a spectral-spatial detector flat field correction is applied, the data are converted from counts to Rayleighs (R), and binned into "superpixels" that are 0.04 nm in wavelength and 0.2°x0.2° in look direction, which projects to ~125x125 km 2 on the Earth's surface, at nadir. See Eastes et al (2017;2019), McClintock et al (2019), and the GOLD Mission website at gold.cs.ucf.edu for further information.…”

Section: Data Reduction and Displaymentioning

confidence: 99%

Global‐Scale Observations and Modeling of Far‐Ultraviolet Airglow During Twilight

et al. 2020

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1. We analyzed measurements by the Global-scale Observations of the Limb and Disk mission of far-ultraviolet emissions near the terminator.2. Airglow excitated by photoelectrons originating in the magnetically conjugate hemisphere is observed and simulated.3. The conjugate photoelectron source explains much of the twilight airglow, but losses occur in the plasmasphere and magnetosphere. AbstractThe NASA Global-scale Observations of the Limb and Disk (GOLD) ultraviolet imaging spectrograph performs observations of upper-atmosphere airglow from the sunlit disk and limb of the Earth, in order to infer quantities such as the composition and temperature of the thermosphere. To interpret the measurements, the observational and solar illumination geometry must be considered. We use forward models of upper atmosphere density and composition, photoelectron impact, airglow emissions, radiative transfer, and line-of-sight integration, to describe the expected observations, and here test those calculations against observations near the terminator, and near the limb. On the night side of the terminator, broad regions of faint airglow are seen, particularly near the winter solstice. These are caused by photoelectrons that were transported along field lines from magnetically conjugate areas in the other hemisphere, where those areas are still illuminated. We perform model calculations to demonstrate that this process is the source of the emission, and obtain good agreement with its morphology and intensity. In some regions, the observed emissions are not as intense as the model simulations. Some of the reductions in electron flux are explained by changes in magnetic field strength; in other cases, particularly at high magnetic latitude, the cause is unknown, but must occur along extended field lines as they reach into the plasma sheet. Plain Language SummaryThe NASA Global-scale Observations of the Limb and Disk (GOLD) instrument is an ultraviolet imager and spectrograph that observes light from the upper-atmosphere of the Earth, in order to infer quantities such as the composition and temperature of the thermosphere. To interpret the measurements, the observing and solar illumination geometry must be considered. We use forward models of upper atmosphere density and composition, photoelectron impact, airglow emissions, radiative transfer, and line-of-sight integration, to describe the expected observations, and here test those calculations against observations near sunrise and sunset. At night but near twilight, broad regions of faint emissions of airglow light are seen, particularly during winter. These are caused by electrons that are created by ionization on the dayside, and are then transported along field lines from magnetically conjugate areas in the other hemisphere, where those areas are still illuminated. We perform model calculations to demonstrate that this process is the source of the emission, and obtain good agreement with the observed shape and intensity. In some regions, the observed emissions are not as intense...

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Global‐Scale Observations of the Equatorial Ionization Anomaly

Cited by 99 publications

References 43 publications

Climatology of the Equatorial Plasma Bubbles Captured by FORMOSAT‐3/COSMIC

Climatology of the Equatorial Plasma Bubbles Captured by FORMOSAT‐3/COSMIC

Coordinated Ground‐Based and Space‐Based Observations of Equatorial Plasma Bubbles

Global‐Scale Observations and Modeling of Far‐Ultraviolet Airglow During Twilight

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