Using GNSS radio occultation data to derive critical frequencies of the ionospheric sporadic E layer in real time

The small-scale electron density irregularities in the ionosphere have a significant impact on the interruptions of Global Navigation Satellite System (GNSS) navigation and the accuracy of GNSS positioning techniques. The sporadic ionospheric E (Es) layer significantly contributes to the transient interruptions of signals (loss of lock) for GNSS tracking loops. These effects on the GNSS radio occultation (RO) signals can be used to derive the global location and intensity of Es layers as a complement to ground-based observations. Here we conduct statistical analyses of the intensity of Es layers, based on the scintillation index S4max from the FORMOSAT-3/COSMIC during the period 2006-2014. In comparison with simultaneous observations from an ionosonde network of five low-to-middle latitude ionosondes, the S4max indices from COSMIC, especially the small values, are linearly related to the critical frequency of Es layers (foEs). An accumulated period of less than one hour is required to derive the short-term variations in real-time ionospheric Es layers. A total of 30.22%, 69.57% and 98.13% coincident hourly foEs values have a relative difference less of than 10%, 30% and 100%. Overall, the GNSS RO measurements have the potential to provide accurate hourly observations of Es layers. Observations with S4max<0.4 (foEs<3.6 MHz), accounting for 66% of COSMIC S4 measurements, have not been used fully previously, as they are not easily visible in ground-based ionosonde data

Derivation of global ionospheric sporadic E critical frequency (foEs) data from the amplitude variations in GPS/GNSS radio occultations

The ionospheric sporadic E (Es) layer has a significant impact on the Global Positioning System (GPS)/Global Navigation Satellite System (GNSS) signals. These influences on the GPS/GNSS signals can also be used to study the occurrence and characteristics of the Es layer on a global scale. In this paper, 5.8 million radio occultation (RO) profiles from the FORMOSAT-3/COSMIC satellite mission and ground-based observations of Es layers recorded by 25 ionospheric monitoring stations and held at the UK Solar System Data Centre at the Rutherford Appleton Laboratory and the Chinese Meridian Project were used to derive the hourly Es critical frequency (foEs) data. The global distribution of foEs with a high spatial resolution shows a strong seasonal variation in foEs with a summer maximum exceeding 4.0 MHz and a winter minimum between 2.0–2.5 MHz. The GPS/GNSS RO technique is an important tool that can provide global estimates of Es layers, augmenting the limited coverage and low frequency detection threshold of ground-based instruments. Attention should be paid to small foEs values from ionosondes near the instrumental detection limits corresponding to minimum frequencies in the range 1.28–1.60 MHz

An empirical model of the ionospheric sporadic E layer based on GNSS radio occultation data

The intense plasma irregularities within the ionospheric sporadic E (Es) layers at 90–130 km altitude have a significant impact on radio communications and navigation systems. As a result, the modeling of the Es layer is very important for the accuracy, reliability, and further applications of modern real-time global navigation satellite system precise point positioning. In this study, we have constructed an empirical model of the Es layer using the multivariable nonlinear least-squares-fitting method, based on the S4max from Constellation Observing System for Meteorology, Ionosphere, and Climate satellite radio occultation measurements in the period 2006–2014. The model can describe the climatology of the intensity of Es layers as a function of altitude, latitude, longitude, universal time, and day of year. To validate the model, the outputs of the model were compared with ionosonde data. The correlation coefficients of the hourly foEs and the daily maximum foEs between the ground-based ionosonde observations and model outputs at Beijing are 0.52 and 0.68, respectively. The model can give a global climatology of the intensity of Es layers and the seasonal variations of Es layers, although the Es layers during the summer are highly variable and difficult to accurately predict. The outputs of the model can be implemented in comprehensive models for a description of the climatology of Es layers and provide relatively accurate information about the global variation of Es layers

A signature of 27-day solar rotation in the concentration of metallic ions within the terrestrial ionosphere

We present observations during the interval 2006-2014 of 27-day and 13.5-day periodic oscillations in the ionospheric sporadic E (Es) layer. This is a thin, dense layer composed of metallic ions in the Earth's upper atmosphere between 90 and 130 km. Lomb-Scargle spectral and wavelet analyses reveal that these pronounced periodicities observed from ground-based ionosondes and GPS/GNSS radio occultations are associated with high-speed solar winds generated from persistent coronal holes on successive 27-day solar rotations. The 27-day and 13.5-day oscillations in the Es layers are dependent on latitude, showing a higher magnitude of periodicities at low-latitudes between 0 {15 and high-latitudes between 45 {90 (10%{14%) than those at mid-latitudes between 15 {45 (4%{10%). The 27-day and 13.5-day oscillations in the high-latitude Es layers correlate well with the geomagnetic activity Dst and Ap indices, and these periodic oscillations become more signi cant at the solar maximum (2000{2003, and 2011{2014) than the solar minimum

Interhemispheric transport of metallic ions within ionospheric sporadic E layers by the lower thermospheric meridional circulation

Long-lived metallic ions in the Earth’s atmosphere/ionosphere have been investigated for many decades. Although the seasonal variation in ionospheric ‘sporadic E’ layers was first observed in the 1960s, the mechanism driving the variation remains a long-standing mystery. Here we report a study of ionospheric irregularities using scintillation data from COSMIC satellites and identify a large-scale horizontal transport of long-lived metallic ions, combined with the simulations of the Whole Atmosphere Community Climate Model with the chemistry of metals and ground-based observations from two meridional chains of stations from 1975–2016. We find that the lower thermospheric meridional circulation influences the meridional transport and seasonal variations of metallic ions within sporadic E layers. The winter-to-summer, meridional velocity of ions is estimated to vary between -1.08 and 7.45 m/s at altitudes of 107–118 km between 10�–60�N latitude. Our results not only provide strong support for the lower thermospheric meridional circulation predicted by a whole atmosphere chemistry-climate model, but also emphasise the influences of this winter-to-summer circulation on the large-scale interhemispheric transport of composition in the thermosphere/ionosphere

Decoupling, quantifying, and restoring aging-induced Zn-anode losses in rechargeable aqueous zinc batteries

The search for batteries beyond Li-ion that offer better performance, reliability, safety, and/or affordability has led researchers to explore a diverse array of candidates. The advantages of Zn-ion batteries reside in zinc’s relatively low reactivity, raising the prospect of a rechargeable battery with a simple aqueous electrolyte and a cheaper, safer option to the organic electrolytes that must be paired with reactive lithium. However, water still reacts with the zinc in corrosion reactions. These consume zinc, lowering the battery’s capacity, and generate gas that accumulates in the sealed cell. We diagnose the contribution of corrosion to performance decay in zinc batteries and reveal the critical role of gas accumulation in deactivating large sections of electrode, which cripples cell performance. Fortunately, electrodes can be reactivated by removal of the gas, demonstrating the importance of designing future cells that either prevent gas formation or facilitate its safe release

Well-Defined Selenium-Containing Aliphatic Polycarbonates via Lipase-Catalyzed Ring-Opening Polymerization of Selenic Macrocyclic Carbonate Monomer

The synthesis of well-defined, biodegradable selenium-containing polymers remains a formidable challenge in polymer chemistry. Herein, a selenic cyclic carbonate dimer monomer (M_Se) was developed to generate well-defined, biodegradable aliphatic polycarbonates with selenide functionality on the backbone. The monomer was synthesized via the intermolecular cyclization of di­(1-hydroxyethylene) selenide and diphenyl carbonate with lipase CA as catalysts in a mass of anhydrous toluene with very dilute monomer concentration. Then living ring-opening polymerization (ROP) was executed by solution method using the same lipase CA as catalysts. Similarly, the copolymerizations with commercial trimethylene carbonate (TMC) generated random copolymers demonstrated by ¹³C NMR, regulating the density of selenium functional groups. The resulting polymers exhibited a living polymerization characteristic, as evidenced by polymerization kinetics, predictable molecular weights, narrow molecular-weight distribution, and controlled copolymer compositions. Using hydrophilic macroinitiators (PEG), amphiphilic di/triblock copolymers could be obtained, suggesting their potential as controlled drug delivery system (DDS) and hydrogel scaffolds for tissue engineering