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The intensity scintillation index (S4) exhibits a linear frequency dependence derived from a power law phase screen model, with the exponent determined by the phase spectral index (p). However, it is well known that a departure from linearity occurs as S4 increases and saturates under strong scatter conditions. Additionally, statistical errors over a finite time window can also cause the scintillation statistic to deviate from the power law dependence on frequency. This paper presents a parametric analysis on the deviation in the S4 frequency dependence from the power law form. This investigation focuses on the contribution of statistical uncertainty in S4 calculations to the deviation in the frequency dependence according to the selected parameters: S4 and Fresnel frequency (fF). The deviation is determined by comparing p estimates calculated from the power law relationship of S4 at different L‐band frequencies with those inferred from a model‐fitting method using a multi‐frequency global navigation satellite system scintillation data set. The results show the well‐known departure from linearity as S4 increases, and reveal increasing deviations with decreasing fF. The spectral analysis indicates that the variability at the lowest frequencies of intensity spectra contributes to the statistical errors in S4 calculations due to the finite time window, particularly when scintillations are dominated by low‐frequency contributions at low fF. Simulation results of scintillation realizations show much lower deviations with a 30‐min compared to 1‐min window. This suggests a 1‐min window can be too short for reliable S4 calculations due to statistical uncertainty, especially at low fF. Plain Language Summary: The S4 index is a widely used measure to quantify scintillation strength. The relationship between S4 values at different signal frequencies is theoretically expected to follow a linearity. However, this simple relationship is only valid under certain conditions, and the calculation of S4 with a finite time window can introduce uncertainty that causes deviations from the expected frequency dependence. In this study, we analyze the uncertainty in the relationship between S4 values at different frequencies, considering the specific scintillation conditions. Our observations confirm two main findings: (a) a well‐known departure from linearity at high levels of scintillation, and (b) deviations caused by statistical uncertainty due to large‐scale fluctuations over a finite time window for S4 calculations. We validate these findings through simulations that cover a wide range of scintillation scenarios. Key Points: Deviation/departure of S4 frequency dependence from the power law form was parametrically investigated via global navigation satellite system scintillation observationsIn addition to the well‐known departure at high S4, larger deviations in the S4 frequency dependence were observed at lower fFSimulation shows lower deviations with a 30‐min S4 window rather than 1‐min due to statistical uncertainty depending on the window length [ABSTRACT FROM AUTHOR]

Sanitary landfills and uncontrolled dumpsites are plastic wastes (PWs) reservoirs containing ∼60% of all the plastics ever made, amounting to 5,000 × 106 tons as of 2017. The distribution, long-term behavior, and release of macro- and microplastics (MPs) from disposal sites are critical to global plastics pollution, but are poorly understood and lack systematic assessments. We review comprehensively the available knowledge in the three aspects herein. The spatial and temporal distribution of PW in 616 municipal solid waste (MSW) samples retrieved from 275 disposal sites in 56 countries are summarized. The weight percentages of PW (%PW) generally decrease with increasing year of disposal and disposal depth. Other influential factors are disposal duration and country income level. The %PW values in different disposal sites show high regionality and spatial variability and heterogeneity. Disposal sites mostly have harsh temperature and stress, reactive liquids, and microbial activities, which are conducive to long-term processes of PW and MPs. The major processes are chemical degradation, dissolution, leaching and adsorption, biological degradation, mechanical wearing, pneumatic and hydrological transport and deposition, and conglomeration. PW leaves disposal sites via recycling, scavenging, mining, wind and surface runoff, coastal erosion and flooding, and slope failure. The release and removal pathways of PW from disposal sites have been recognized only qualitatively. In addition, the sources, presences, and secondary generation of MPs in disposal sites have been studied occasionally, whereas the transport and fate of MPs within and from disposal sites remain largely unstudied. [ABSTRACT FROM AUTHOR]

A newly released, novel ionospheric data set of global gridded vertical total electron content (VTEC) is introduced in this paper. This VTEC data set, provided by Los Alamos National Laboratory (LANL), is derived from very high frequency (VHF; defined as 30–300 MHz) broadband radio‐frequency (RF) measurements of lightning made by U.S. Department of Defense sensing systems on board Global Positioning System (GPS) satellites. This paper presents the new data set (LANL VTEC), discusses the errors inherent in VHF TEC estimation due to ionospheric dispersion, and compares the LANL VTEC to two community standard VTEC gridded products: Jet Propulsion Laboratory's Global Ionospheric Model (JPL GIM) and the CEDAR community's Open Madrigal VTEC gridded measurements of L‐band GNSS (global navigation satellite systems) TEC. We find that the LANL VTEC data have an offset of 3 TECU from CEDAR Madrigal GNSS VTEC and a full‐width‐half‐maximum (FWHM) of 6 TECU. In comparison, the offset between LANL VTEC and the JPL GIM model is −3 TECU, but with a FWHM of 5 TECU. We also compare to Jason‐3 VTEC measurements over the ocean, finding an offset of less than 0.5 TECU and an FWHM of <5 TECU. Because this technique uses a completely different methodology to determine TEC, the sources of errors are distinct from the typical ground‐based GNSS L‐band (GHz) TEC measurements. Also, because it is derived from RF lightning signals, this data set provides measurements in regions that are not well covered by ground‐based GPS measurements, such as over oceans and over central Africa. Plain Language Summary: The ionosphere is a region of the atmosphere that is very important in communications between ground and satellite. For that reason, decades of scientific effort have been put toward developing models of the ionosphere so that we can more accurately predict what the state of the ionosphere is at any given location and time. A general product produced by many of these models is the vertical total electron content (VTEC), which is the vertically integrated electron density at a particular location at a particular time. The majority of these models use measurements of TEC from ground‐based receivers or instruments, meaning that abundant measurements that go into the models often lack data from over the oceans or in technologically limited regions of the world (e.g., Africa). Here, we present a new VTEC data set that is derived from lightning strokes detected with U.S. Department of Defense sensing systems on GPS satellites. Because the data set uses naturally occurring lightning for its source, it does not have the same limitations as ground‐based TEC measurements and can provide an additional source of validation data for ionospheric models. We introduce the data set and compare it with community‐accepted VTEC models and measurements. Key Points: New global gridded vertical total electron content (VTEC) data set derived from radio‐frequency measurements from lightning emissions during the entire year of 2018 has been releasedVTEC product adds new global coverage in areas with few global navigation satellite systems receivers (ocean and continental Africa)The VTEC values, generated from very high frequency radio‐frequency data, show bias in Madrigral data set and differences to Jet propulsion laboratory's global ionospheric model model‐derived VTEC [ABSTRACT FROM AUTHOR]

Significant polar topside total electron content (topTEC) enhancement (PTTE) above 1,336 km altitude is reported for the first time. The results are based on GPS measurements during 2008–2019 from NASA's Jason‐2 satellite with zenith‐oriented antennas. The observations show increasing topTEC toward the southern polar cap at geomagnetic latitudes poleward of 65°S, where TEC values are normally very low. A case study for the 2013 St. Patrick's Day storm indicates that the enhancement can exceed 5.5 TEC units above the dayside ambient state, corresponding to 78% increase. Comparisons with COSMIC/FORMOSAT‐3 topTEC measurements above 800 km altitude confirm that PTTE events are observed from both Jason‐2 and COSMIC on the same day. Our statistical analysis of the Jason‐2 data in the southern polar region reveals that PTTE mostly occurs on the dayside, with a seasonal preference of southern summer, and preferentially during geomagnetically disturbed days but can also occur during quiet days. PTTE during storm days shows increased occurrence, magnitude, and deviation from the mean in the cusp region compared with quiet days. Our case analysis indicates that PTTE is observed simultaneously with the effect of tongue of ionization. This suggests that the during storms, dayside F region plasma moving poleward following the antisunward plasma convection may also be part of the PTTE source, and the plasma upflow driven by the polar wind may act to cause PTTE. Plain Language Summary: Significant polar topside total electron content (topTEC) enhancement (PTTE) above 1,336 km altitude is reported for the first time. The results are based on GPS measurements from NASA's Jason‐2 satellite during 2008–2018. The observations show increasing topside TEC toward the southern polar cap where TEC values are normally very low. Comparisons with COSMIC/FORMOSAT‐3 topside TEC measurements confirm that PTTE events are observed from both Jason‐2 and COSMIC on the same day. Our statistical analysis reveals that PTTE mostly occurs in the southern cusp and dayside polar cap, with a seasonal preference of summer, and preferentially during geomagnetically disturbed days but can also occur during quiet days. PTTE during storm days shows increased occurrence, magnitude, and deviation from the mean in the cusp region compared with quiet days. Our case analysis indicates that PTTE is observed simultaneously with the effect of tongue of ionization. This suggests that the during storms, dayside F region plasma moving poleward following the antisunward plasma convection may also be part of the PTTE source, and the plasma upflow driven by the polar wind may act to cause PTTE. Key Points: NASA's Jason‐2 satellite zenith‐viewing GPS total electron content (TEC) measurements spanning 2008–2018 are analyzedSignificant increases of TEC above 1,336 km altitude in the southern polar region are reported for the first timeThe polar topside TEC enhancement (PTTE) appears preferentially during geomagnetic storms and during summer [ABSTRACT FROM AUTHOR]

Radar sounding from aircraft or ground-coupled radars has long provided scientists with a powerful technique to sound through ice layers to retrieve local depth and layering structure. More recently, it has been used to detect shallow aquifers in warm, dry, and desert regions. At Mars, a long-wavelength radar sounding from low orbit altitudes has produced global maps that reveal the presence of ice layering at all latitudes and glacial deposits on the flanks of volcanoes. Until now, sounding from the earth orbit at wavelengths long enough to penetrate ice sheets and arid sand was thought to be infeasible, because of the electromagnetic properties of the ionosphere. In this paper, we show that a radar sounding at frequencies as low as 45 MHz is, in fact, theoretically possible under viewing conditions that occur often enough to be practical. This conclusion opens up a previously unutilized portion of the electromagnetic spectrum for large-scale, spaceborne remote sensing of subsurface features on the earth. [ABSTRACT FROM PUBLISHER]

This paper presents a characterization of L-band ionospheric scintillation observed at a single site in the Arctic auroral zone, and an analysis of GPS-based point positioning error caused by carrier phase data degradation during scintillation. Observed amplitude and phase scintillations of L1CA, L2C, and L5 signals during auroral electrojet activities driven by space weather disturbances show the following three types: continuous, intermittent, and spike (sudden intensity drop). The relations of scintillation strength between different signals are derived for carrier phase, signal intensity, and code-carrier divergence fluctuations, showing precise linear relation, de-correlation, and different linear fitting slope, respectively. These relations can help predict phase scintillation behavior of one signal from measurements of another, except for amplitude scintillation. Experiments of precise point positioning show that phase data degradation due to scintillation can cause significant positioning error increase if the scintillation effects are not considered carefully in GNSS data processing and design of positioning approaches. Copyright © 2017 Institute of Navigation [ABSTRACT FROM AUTHOR]