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Found 5 entries in the Bibliography.
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| 2022 |
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Low-latitude plasma blobs above Africa: Exploiting GOLD and multi-satellite in situ measurements Low-latitude plasma blobs are localized density enhancements of electron density that are occasionally observed in the night-time tropical ionosphere. Two-dimensional (2D) imaging of this phenomenon has been rare and frequently restricted to Central/South America, which is densely covered with ground-based airglow imagers and Global Navigation Satellite System (GNSS) receivers. In Africa, on the contrary, no 2D image of a blob has been reported. Here we present two low-latitude blob events above Africa, one in the Northern summer and the other in winter, in the 2-dimensional Far-UltraViolet (FUV) images from the Global-scale Observations of the Limb and Disk (GOLD) mission. Additionally, multiple satellites (four spacecraft per event) on the Low-Earth-Orbit (LEO) encountered the blob events, some within the GOLD images and some outside. The LEO data support the robustness of GOLD observations and bridge time gaps between the consecutive images. Properties of the two blob events above Africa generally support the conclusions in a previous case study for Central/South America. Plasma therein exhibited higher O+ fraction and faster ion flow toward outer L-shells than the ambient. The blobs were conjugate to locally intensified Equatorial Ionization Anomaly crests without conspicuous equatorward-westward propagation. Our results demonstrate the usefulness of GOLD and multiple LEO satellites in monitoring the ionosphere above Africa, which is a fascinating laboratory of low-latitude electrodynamics but still waiting for more observatories to be deployed. Park, Jaeheung; Min, Kyoung; Eastes, Richard; Chao, Chi; Kim, Hee-Eun; Lee, Junchan; Sohn, Jongdae; Ryu, Kwangsun; Seo, Hoonkyu; Yoo, Ji-Hyeon; Lee, Seunguk; Woo, Changho; Kim, Eo-Jin; Published by: Advances in Space Research Published on: may YEAR: 2022 DOI: 10.1016/j.asr.2022.05.021 |
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Low-latitude plasma blobs have been studied since their first being reported in 1986. However, investigations on temporal evolution of a blob or on continental scale (\textgreater2,000 km) ionospheric contexts around it are relatively rare. Overcoming these limitations can help elucidate the blob generation mechanisms. On 21 January 2021, the Ionospheric Connection Explorer satellite encountered a typical low-latitude blob near the northeastern coast of South America. The event was collocated with a local enhancement in 135.6 nm nightglow at the poleward edge of an equatorial plasma bubble (EPB), as observed by the Global-scale Observations of the Limb and Disk (GOLD) imager. Total electron content maps from the Global Navigation Satellite System confirm the GOLD observations. Unlike typical medium-scale traveling ionospheric disturbances (MSTIDs), the blob had neither well-organized wavefronts nor moved in the southwest direction. Neither was the blob a monotonically decaying equatorial ionization anomaly crest past sunset. Rather, the blob varied following latitudinal expansion/contraction of EPBs at similar magnetic longitudes. The observational results support that mechanisms other than MSTIDs, such as EPBs, can also contribute to blob generation. Park, Jaeheung; Huang, Chao-Song; Eastes, Richard; Coster, Anthea; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2022 DOI: 10.1029/2021JA029992 |
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Exospheric temperature is one of the key parameters in constructing thermospheric models and has been extensively studied with in situ observations and remote sensing. The Global-scale Observations of the Limb and Disk (GOLD) at a geosynchronous vantage point provides dayglow limb images for two longitude sectors, from which we can estimate the terrestrial exospheric temperature since 2018. In this paper, we investigate climatological behavior of the exospheric temperature measured by GOLD. The temperature has positive correlations with solar and geomagnetic activity and exhibits a morning-afternoon asymmetry, both of which agree with previous studies. We have found that the arithmetic sum of F10.7 (solar) and Ap (geomagnetic) indices is highly correlated with the exospheric temperature, explaining ∼64\% of the day-to-day variability. Furthermore, the exospheric temperature has good correlation with thermospheric parameters (e.g., neutral temperature, O2 density, and NO emission index) sampled at various heights above ∼130 km, in spite of the well-known thermal gradient below ∼200 km. However, thermospheric temperature at altitudes around 100 km is not well correlated with the GOLD exospheric temperature. The result implies that effects other than thermospheric heating by solar Extreme Ultraviolet and geomagnetic activity take control below a threshold altitude that exists between ∼100 and ∼130 km. Park, Jaeheung; Evans, Joseph; Eastes, Richard; Lumpe, Jerry; van den Ijssel, Jose; Englert, Christoph; Stevens, Michael; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2022 DOI: 10.1029/2021JA030041 Aura/MLS; exospheric temperature; GOLD; ICON; swarm; TIMED/SABER |
| 2021 |
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The Thermospheric Column O/N2 Ratio More than 2 decades ago, D. J. Strickland and colleagues proposed use of the O/N2 column number density ratio as a new geophysical quantity to interpret thermospheric processes recorded in far ultraviolet (FUV) images of the Earth. This concept has enabled multiple advances in understanding the global behavior of Earth s thermosphere. Nevertheless, confusion remains about the conceptual meaning of the column density ratio, and in the application of this integral quantity. This is so even though it is now a key thermospheric measurement made by current and planned far ultraviolet remote sensing missions in pursuit of new understanding of thermospheric processes and variability. The intent here is to review the historical context of the O/N2 column density ratio, clarify its physical meaning, and resolve misunderstandings evident in the literature. Simple examples elucidate its original derivation for extracting column O/N2 ratios from measurements of the OI 135.6 nm/N2 Lyman-Birge-Hopfield (LBH) emission based on an algorithmic synthesis of model precomputations. These are organized in the form of a table lookup of column density ratio as a function of observed radiance ratios. To accommodate generalized solar-geophysical and viewing conditions, the table required to specify the number of needed parameters becomes large. Proposed as an alternative is a simplified, first principles approach to obtaining the column density ratio from the emission ratio. This new methodology is now being applied successfully to FUV measurements made from onboard the Ionospheric CONnection satellite and will be applied retrospectively to the Global Ultraviolet Imager data. Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2020JA029059 disk algorithm; far UV remote sensing; GUVI; ICON; N2 LBH bands; Oxygen 135.6 nm |
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Conjugate Photoelectron Energy Spectra Derived From Coincident FUV and Radio Measurements We present a method for estimating incident photoelectrons energy spectra as a function of altitude by combining global scale far-ultraviolet (FUV) and radio-occultation (RO) measurements. This characterization provides timely insights important for accurate interpretation of ionospheric parameters inferred from the recently launched Ionospheric Connection Explorer (ICON) observations. Quantification of photoelectron impact is enabled by the fact that conjugate photoelectrons (CPEs) directly affect FUV airglow emissions but not RO measurements. We demonstrate a technique for estimation of photoelectron fluxes and their spectra by combining coincident ICON and COSMIC2 measurements and show that a significant fraction of ICON-FUV measurements is affected by CPEs during the winter solstice. A comparison of estimated photoelectron fluxes with measured photoelectron spectra is used to gain further insights into the estimation method and reveals consistent values within 10–60 eV. Urco, J.; Kamalabadi, F.; Kamaci, U.; Harding, B.; Frey, H.; Mende, S.; Huba, J.; England, S.; Immel, T.; Published by: Geophysical Research Letters Published on: YEAR: 2021 DOI: 10.1029/2021GL095839 airglow; conjugate photolectrons; COSMIC2; energy spectra; ICON |
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