An improved method to retrieve electron density profiles from Global Positioning System (GPS) radio occultation (RO) data is presented and applied to Constellation Observing System for Meteorology, ...Ionosphere, and Climate (COSMIC) observations. The improved inversion uses a monthly grid of COSMIC F region peak densities (NmF2), which are obtained via the standard Abel inversion, to aid the Abel inversion by providing information on the horizontal gradients in the ionosphere. This lessens the impact of ionospheric gradients on the retrieval of GPS RO electron density profiles, reducing the dominant error source in the standard Abel inversion. Results are presented that demonstrate the NmF2 aided retrieval significantly improves the quality of the COSMIC electron density profiles. Improvements are most notable at E region altitudes, where the improved inversion reduces the artificial plasma cave that is generated by the Abel inversion spherical symmetry assumption at low latitudes during the daytime. Occurrence of unphysical negative electron densities at E region altitudes is also reduced. Furthermore, the NmF2 aided inversion has a positive impact at F region altitudes, where it results in a more distinct equatorial ionization anomaly. COSMIC electron density profiles inverted using our new approach are currently available through the University Corporation for Atmospheric Research COSMIC Data Analysis and Archive Center. Owing to the significant improvement in the results, COSMIC data users are encouraged to use electron density profiles based on the improved inversion rather than those inverted by the standard Abel inversion.
Key Points
Develop new inversion for COSMIC electron density profiles
New inversion reduces the impact of horizontal gradients on the Abel inversion
Inversion improves results in the E and F region ionosphere
The Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC)/Formosa Satellite 3 (FORMOSAT‐3) is a six‐satellite radio occultation mission that was launched in mid‐April, 2006. ...The close proximity of the COSMIC satellites provides a unique opportunity to estimate the precision of the radio occultation remote sensing technique from closely collocated occultations (<10 km separation of tangent points). The RMS difference of refractivity between 10 and 20 km altitude is less than 0.2%, which is approximately twice better than previous estimates obtained from CHAMP and SAC‐C collocated occultations, apparently, due to smaller separation of the occultation pairs and due to parallel occultation planes. In the lower troposphere, the maximal RMS is ∼0.8% at 2 km altitude and decreases abruptly to ∼0.2% between 6 and 8 km altitude. The RMS difference of electron density in the ionosphere between 150 and 500 km altitude for collocated occultations is about 103 cm−3.
This investigation focuses on sodium biphosphate (Na2HPO4) as corrosion inhibitor for construction steel. All the tests are carried out in a solution that simulates the composition of the pores in ...chloride-contaminated carbonated concrete. The carbonated solution (CS) contained Na2CO3 (0.0015mol L−1), NaHCO3 (0.03mol L−1) and NaCl (0.1mol L−1), resulting in Cl−/OH−=10000. Inhibited solutions (IS20, IS60 and IS100) incorporated 20, 60, and 100 mmol L−1 Na2HPO4 respectively. These were labeled IS20, IS60 and IS100 respectively and result in HPO42−/Cl− = 0.2, 0.6, and 1. Cyclic voltammograms and anodic polarization curves were complemented with micro-Raman spectroscopy and XPS, to evaluate the surface film composition. The results show that chloride contamination promotes active corrosion. When phosphate ions are incorporated, steel becomes passive with a more positive corrosion potential (Ecorr), and pitting presents as the predominant form of localized corrosion. Raman spectra show a broad band, centred in 982 cm−1, suggesting that phosphates incorporate to the passive film. Phosphates are also present in the corrosion products. The surface film becomes more protective to pitting for the highest biphosphate content. However, after pitting no repassivation was detected. After over one month in immersion, steel remains passive in the condition IS100, with inhibition efficiency higher than 99%. In contrast, in the case of IS60 and IS20, pitting was detected.
It can be concluded that phosphate ions are good candidates to be used as corrosion inhibitors for steel in chloride-contaminated concrete.
This letter reports for the first time the simulated error distribution of radio occultation (RO) electron density profiles (EDPs) from the Abel inversion in a systematic way. Occultation events ...observed by the COSMIC satellites are simulated during the spring equinox of 2008 by calculating the integrated total electron content (TEC) along the COSMIC occultation paths with the "true" electron density from an empirical model. The retrieval errors are computed by comparing the retrieved EDPs with the "true" EDPs. The results show that the retrieved NmF2 and hmF2 are generally in good agreement with the true values, but the reliability of the retrieved electron density degrades in low latitude regions and at low altitudes. Specifically, the Abel retrieval method overestimates electron density to the north and south of the crests of the equatorial ionization anomaly (EIA), and introduces artificial plasma caves underneath the EIA crests. At lower altitudes (E- and F1-regions), it results in three pseudo peaks in daytime electron densities along the magnetic latitude and a pseudo trough in nighttime equatorial electron densities.
This study investigates the underlying physics of equatorial plasma bubbles (EPBs) on 11 December 2019, under solar minimum conditions. The Global‐scale Observations of the Limb and Disk (GOLD) ...ultraviolet nightglow images exhibit a periodic distribution of reduced emissions related to EPBs. Remarkably, FORMOSAT‐7/COSMIC‐2 (F7/C2) observes a significant altitudinal difference of ~45 km in the bottomside ionosphere between two nearly collocated electron density profiles before the onset of EPBs, indicating the presence of an upwelling. Distinct ionospheric perturbations are also observed in F7/C2 and ground‐based Global Positioning System observations, suggesting that gravity waves may contribute to the upwelling. Simulations with SAMI3/ESF are further carried out to evaluate the upwelling growth and pre‐reversal enhancement (PRE) effect on EPB development. Simulations reveal that the crests of upwellings show a localized uplift of ~50 km, and EPBs only develop from the crest of upwellings. The uplift altitude of upwellings is comparable to the F7/C2 observations and the post‐sunset rise in moderate solar conditions. The polarization electric field (Ep) developed within the upwellings can drive vertical Ep × B drifts of ~32–35 m/s, which are comparable to the PRE vertical E × B drifts. We find that the PRE alone cannot drive EPBs without upwelling growth, but it can facilitate the upwelling growth. Observations and simulations allow us to conclude that upwelling growth could play a vital role in the formation of EPBs.
Plain Language Summary
Equatorial plasma bubbles (EPBs) are a crucial nighttime space weather phenomenon that can cause severe radio waves scintillations from the Global Navigation Satellite System. Scientists presumed that the post‐sunset rise (PSSR) of the ionosphere due to vertical drift is the primary driver of EPBs. However, the linkage becomes weak on a daily basis; the PSSR cannot explain the morphology and day‐to‐day variability of EPBs. In this study, we used the recently launched FORMOSAT‐7/COSMIC2 (F7/C2) satellite and Global‐scale Observations of the Limb and Disk (GOLD) to investigate the nature behind the EPBs. GOLD observed EPBs with regular spacing over the Atlantic Ocean region on 11 December 2019. We found a distinct local uplift in the bottomside ionosphere between the nearly collocated F7/C2 electron density profiles before the onset of EPBs, indicating an upwelling. Gravity waves likely contribute to the formation of the upwelling and subsequent development of EPBs. A theoretical ionosphere model is further used to evaluate the upwelling growth and post‐sunset vertical drift effect on EPB development. This study reveals the importance of atmospheric waves on the formation of upwelling and subsequent EPB development.
Key Points
Periodic EPBs and an upwelling are observed by GOLD and FORMOSAT‐7/COSMIC2 during solar minimum
The localized upwelling uplifts the bottomside ionosphere by ~45 km
The vertical Ep × B drift generated by upwellings in the bottomside ionosphere are comparable to the pre‐reversal enhancement
THE COSMIC/FORMOSAT-3 MISSION Anthes, R. A.; Bernhardt, P. A.; Chen, Y. ...
Bulletin of the American Meteorological Society,
03/2008, Letnik:
89, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The radio occultation (RO) technique, which makes use of radio signals transmitted by the global positioning system (GPS) satellites, has emerged as a powerful and relatively inexpensive approach for ...sounding the global atmosphere with high precision, accuracy, and vertical resolution in all weather and over both land and ocean. On 15 April 2006, the joint Taiwan–U.S. Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)/Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3, hereafter COSMIC) mission, a constellation of six microsatellites, was launched into a 512-km orbit. After launch the satellites were gradually deployed to their final orbits at 800 km, a process that took about 17 months. During the early weeks of the deployment, the satellites were spaced closely, offering a unique opportunity to verify the high precision of RO measurements. As of September 2007, COSMIC is providing about 2000 RO soundings per day to support the research and operational communities. COSMIC RO data are of better quality than those from the previous missions and penetrate much farther down into the troposphere; 70%–90% of the soundings reach to within 1 km of the surface on a global basis. The data are having a positive impact on operational global weather forecast models.
With the ability to penetrate deep into the lower troposphere using an advanced open-loop tracking technique, the COSMIC RO instruments can observe the structure of the tropical atmospheric boundary layer. The value of RO for climate monitoring and research is demonstrated by the precise and consistent observations between different instruments, platforms, and missions. COSMIC observations are capable of intercalibrating microwave measurements from the Advanced Microwave Sounding Unit (AMSU) on different satellites. Finally, unique and useful observations of the ionosphere are being obtained using the RO receiver and two other instruments on the COSMIC satellites, the tiny ionosphere photometer (TIP) and the tri-band beacon.
Development of radio‐holographic inversion methods that solve for multipath propagation of radio occultation signals in the moist lower troposphere resulted in significant reduction of inversion ...errors of the bending angle and refractivity. Still, inversion errors depend on the length of recorded radio occultation signals, additive noise, and some tunable inversion parameters. These errors have components with nonzero mean (biases) and thus must be understood and quantified for weather and climate applications. In this study a physical explanation of the above mentioned inversion biases is given and their magnitude is evaluated (about 1% in the tropical lower troposphere). Assuming data with 50 Hz sampling rate and a noise level that is typical for the COSMIC GPS radio occultation observations, this magnitude can be considered as the measure of uncertainty of radio holographic inversions below ∼5 km in the moist tropical troposphere.
Magnesium alloys such as AZ91D, has been presented as potential material for temporary implant material since it has a mechanical performance suitable with bone tissue and also degrades in time. The ...fast degradation at early times of AZ91D alloy could be retarded applying bioactive sol-gel glass coatings. In this work, two compositions of known bioactive silica-glasses (58S and 68S) were synthetized by sol-gel method and deposited by dip coating to the magnesium substrates. The glasses were produced without using any nitrate precursor, avoiding the presence of remaining residual in the coatings that could be not beneficial to the body. The coatings presented an excellent bioactive response after immersion in Hanks' balanced salt solution (HBSS) at 37 °C, showing apatite related deposits after 72 h immersion detected by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Corrosion behaviour has been also analyzed, 58S presented as better protective features after 17 days of immersion. Cell attachment and proliferation tests demonstrate that both 58S and 68S coatings on AZ91D magnesium alloy are suitable as temporary implant materials.
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•Nitrate free bioactive glasses can be deposited on AZ91 magnesium alloy.•Sol-gel glass like coatings reduce corrosion of AZ91 in early stages immersion.•58S and 68S coatings generate in vitro bioactivity and cell attachment.
Previous studies report unexpected electron density reductions, termed “plasma caves,” located underneath the equatorial ionization anomaly (EIA) crests. A radio occultation (RO) observation ...simulation experiment has been built to evaluate possible biases introduced by the spherical symmetry assumption in the standard (Abel) RO inversion processes. The experiment simulates the electron density profiles and reconstructs the plasma structure of the EIA at low latitudes, where the horizontal gradient is most significant. The reconstruction shows that artificial plasma caves are created underneath the EIA crests along with three density enhancements in adjacent latitudes. The artifact appears mainly below 250 km altitudes and becomes pronounced when the EIAs are well developed. Above that altitude, the two EIA features in the original (truth) model, the International Reference Ionosphere (IRI‐2007), and in the inversion are similar, but the inversion reconstructs less distinct EIA crests with underestimation of the electron density. A simple correction has been introduced by multiplying the ratio between the truth and inversion with actual FORMOSAT‐3/COSMIC observations. This initial correction shows that the artificial plasma caves are mitigated. Results also reveal that the RO technique is not suitable to detect or rule out possible existence of the plasma caves.
This paper shows the deposition of superhydrophobic PTFE (polytetrafluoroethylene) films on FTO (fluorine doped tin oxide) coated glass slides, employing the electrospray technique, using a ...commercial PTFE particle suspension in water. Water contact angles as high as 167° were measured on the PTFE surface. Water drop sliding angles at 2° show a very low contact angle hysteresis. Scanning electron and atomic force microscopy images show the typical rough micro/nanostructure required for superhydrophobicity.
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