ALBERT

Description: Abstract An analysis of the counter‐electrojet occurrence (CEJ) during 2008–2014 is presented for the African and American sectors based on local daytime (0700–1700 LT) observations from the Communications and Navigation Outage Forecasting System (C/NOFS) vertical ion plasma drift (equivalent to vertical E×B at an altitude of about 400 km) and ground‐based magnetometers. Using quiet time (Kp≤ 3) data, differences and/or similarities between the two data sets with reference to local time and seasonal dependence are established. For the first time, it is shown that C/NOFS satellite data are consistent with magnetometer observations in identifying CEJ occurrences during all seasons. However, C/NOFS satellite data show higher CEJ occurrence rate for almost all seasons. With respect to local time, C/NOFS satellite observes more CEJ events than magnetometer observations by average of about 20% and 40% over the American and African sectors, respectively, despite both data sets showing similar trends in CEJ identification. Therefore, when a space weather event occurs, it is important to first establish the original variability nature and/or magnitude of the eastward electric field in equatorial regions before attributing the resulting changes to solar wind‐magnetosphere and ionosphere coupling processes since CEJ events can be present even during quiet conditions.

Description: Abstract Tectonic extension of continental lithosphere creates accommodation space in which sediments are deposited. Climate‐driven processes provide the mechanism by which mass is detached from hillslopes and sediments are transported into this accommodation space. These two forcings, climate and tectonics, act together to create either endorheic (internally drained) or exorheic (externally drained) rift basins. Here we use a large‐scale dynamic landscape evolution‐tectonics model to understand the contribution of tectonic processes in endorheic‐exorheic transitions. In the model, extension results in opening of an asymmetric half‐graben along a listric normal fault. Rift opening occurs in the models in wet, temperate, or semi‐arid climates where runoff and evapotranspiration are varied. Our numerical experiments show that slow rift‐opening rates, a slowing‐down of rift opening, or increase of headwater topography (e.g., upstream epeirogenic uplift), are tectonic situations that can cause a transition from an endorheic to an exorheic drainage state in a rift basin. Our results also show that wet climate conditions lead to a permanent exorheism that persists regardless of rift opening rates. In semi‐arid climates, endorheic conditions are favored, and may last for the duration of rifting except for when rift opening is very slow. These results form an interpretive framework to study endorheic and exorheic drainage systems in natural continental rifts. In the slow‐opening Rio Grande rift, the endorheic‐exorheic transition may have occurred without dramatic climate changes. Lake‐level variations in East African rift basins are predicted by our models to result from variations in climate.

Description: Abstract High‐speed solar wind streams that originate from coronal holes play an important role in space weather disturbances, especially during the declining phase of the solar cycle. Space weather forecasters attempt to find good coronal hole indices that can be used to predict high‐speed streams days in advance. Several indices related to the coronal hole area, brightness, or magnetic field expansion factor have been reported in the literature. Empirical solar wind forecast models have been developed and used in operational service by several organizations by constructing prediction functions that relate the coronal hole index to the solar wind speed. In this paper, we present a new empirical modeling method and test its validity by comparing it with a previously reported method when applied to different coronal hole indices. In total, six empirical models are tested for a long period of time (2011–2018), with a 27‐day persistence model as a comparison benchmark. The results show that while all these empirical models can capture the temporal patterns of the solar wind observations well, the new modeling method and utilization of a composite coronal hole index PCH as an input parameter indeed improves the forecast accuracy. The high‐speed streams can be predicted approximately 3 days in advance, with a probability of detection of 0.78, a positive predictive value of 0.73, and a threat score of 0.61. The uncertainty of the high‐speed stream arrival time is approximately 1 day and the uncertainty of the peak speed is approximately 80 km/s.

Description: Abstract We describe a metric that has been repeatedly applied to assess the performance of models aimed at predicting geomagnetically induced currents from Space Weather events. The used parameterization, based on the well‐known root‐mean‐square error between model and observations, is simple and intuitive. Its use is exemplified, and its advantages and disadvantages are discussed, as well as its relationship with the widely extended correlation coefficient, r. Although the use of r alone is inappropriate for purposes of evaluating the agreement between model and observations, its use is recommended to complement the described performance parameter.

Description: Abstract Coronal Mass Ejections (CMEs) cause the largest geomagnetic disturbances at Earth which impact satellites, wired communication systems and power grids. The CME Analysis Tool (CAT) is used to determine a CME's initial longitude, latitude, angular width and radial speed from coronagraph images. These are the initial conditions for the Wang‐Sheeley‐Arge (WSA) Enlil solar wind model, along with the ambient solar wind properties derived from magnetograms. However, the coronagraph imagery is limited by field of view. We have incorporated heliospheric imagery (HI) from the Solar Terrestrial Relations Observatory (STEREO) into CAT to create the CME Analysis Tool with Heliospheric Imagery (CAT‐HI). These HI images have a larger field of view, allowing tracking of CMEs to greater distances from the Sun. We have compared the performances of CAT and CAT‐HI by examining the expected arrival times of CMEs at the L1 Lagrange point and found them to be consistent. However, CAT‐HI is advantageous because it could be used to prune ensemble forecasts and issue routine updates for CME arrival time forecasts. Finally, we discuss CAT‐HI in the context of an operational mission at the L4 or L5 Lagrange points.

Description: Abstract Crustal extension is commonly thought to be accommodated by faults that strike orthogonal and obliquely to the regional trend of the minimum compressive stress (σ3). Activation of oblique faults can, however, be conceptually problematic as under Andersonian faulting, it requires preexisting crustal weaknesses, high fluid pressures, and/or stress rotations. Furthermore, measurements of incremental fault displacements, which are typically used to identify oblique faulting, do not necessarily reflect regional stresses. Here, we assess oblique faulting by calculating the stress ratio (σ3/σ1, where σ1 is the maximum compressive stress), slip tendency, and effective coefficient of friction (μs′) required to reactivate variably striking normal faults under different trends of σ3. We apply this analysis to NW and NNE striking active faults at the southern end of the Malawi Rift, where NE‐SW, ENE‐WSW, E‐W, and SE‐NW σ3 trends have previously been proposed. A uniform σ3 trend is inferred for this region as recent joints sets do not rotate along the rift. With a NE‐SW trending σ3, NW‐striking faults are well oriented, however, NNE‐striking faults require μs′ 〈 0.6 to reactivate. This is inconsistent with a lack of frictionally weak phyllosilicates detected in the fault zone rocks. With an ENE‐WSW to E‐W trending σ3, all faults can reactivate at μs′ 〉 0.55. These σ3 trends are also comparable to a focal mechanism stress inversion, regional joint orientations, and previously reported geodetically derived extension directions. We therefore conclude that unlike typical models of oblique rifting, the southern Malawi Rift consists of faults that all strike slightly oblique to σ3.

Description: Abstract Ahyi seamount, a shallow submarine volcano in the Northern Mariana Islands, began erupting on 23 April 2014. Hydroacoustic eruption signals were observed on the regional Mariana seismic network and on distant hydrophones, and National Oceanic and Atmospheric Administration (NOAA) scuba divers working in the area soon after the eruption began heard and felt underwater explosion sounds. The NOAA crew observed yellow‐orange bubble mats along the shore of neighboring Farallon de Pájaros Island, but no other surface manifestations of the eruption were reported by the crew or observed in satellite data. Here, we detail the eruption chronology and its morphologic impacts through analysis of seismic and hydroacoustic recordings and repeat bathymetric mapping. Throughout the 2‐week‐long eruption, Ahyi produced several thousand short, impulsive hydroacoustic signals that we interpret as underwater explosions as well as tremor near the beginning and end of the sequence. The initial tremor, which occurred for 2 hr, is interpreted as small phreatomagmatic explosions. This tremor was followed by a 90‐min pause before the characteristic impulsive signals began. Occasional tremor (lasting up to a few minutes) during the last 1.5 days of the eruption is interpreted as more sustained eruptive activity. Bathymetric changes show that a new crater, about 150 m deep, formed near the former summit and a large landslide chute formed on the southeastern flank. Comparing to other geophysically detected submarine eruptions, we find that the signals from the 2014 Ahyi eruption were more similar to those from other shallow or at‐surface submarine eruptions than those at deep (〉500 m) eruptions.

Description: Abstract Seismic anisotropy records past and present tectonic deformations and provides important constraints for understanding the structure and dynamics of the Earth's interior. In this work, we use tremendous amounts of high‐quality P wave arrival times from local and regional earthquakes to determine a high‐resolution tomographic model of 3‐D P wave azimuthal anisotropy down to 1,000‐km depth beneath East Asia. Our results show that trench‐parallel fast‐velocity directions (FVDs) are visible in the shallow portion of the subducting Pacific slab (〈80 km), whereas the deeper portion of the Pacific slab mainly exhibits trench‐normal FVDs, except for the stagnant slab in the mantle transition zone (MTZ) where obvious NE‐SW FVDs are revealed. The FVDs in the subslab mantle change from a subduction‐parallel trend at depths of 80–400 km to a subduction‐normal trend in the MTZ. Large‐scale low‐velocity anomalies are revealed beneath the Philippine Sea plate where the FVD is NE‐SW. The FVDs along the Izu‐Bonin arc and in a slab gap exhibit a striking anticlockwise toroidal trend. All these features may reflect complex 3‐D flows in the mantle wedge due to tearing and dehydration processes of the subducting Pacific slab. The subducting Pacific slab is split at ~300‐km depth under the Bonin arc and then penetrates into the lower mantle, whereas under East Asia the Pacific slab becomes stagnant in the MTZ and reaches the North‐South Gravity Lineament in China. The intraplate volcanoes in East Asia are caused by hot and wet upwelling flows in the big mantle wedge above the stagnant Pacific slab.

Description: Abstract We determine mass transport and structural properties of binary liquid iron alloys over a wide density (5.055–11.735 g·cm−3) and temperature range (2,500–6,500 K) using first‐principles molecular dynamics. Compositions consist of 96 at% Fe and 4 at% ϕ, where ϕ = H, C, N, O, Mg, Si, S, or Ni. Self‐diffusion coefficients (D) of Fe and ϕ range from 3.5·10−9 to 1.9·10−7 m2·s−1. Results show a relation between mean atomic radius and diffusivity ratio for the alloying element and iron: Si and Ni are “iron‐like” with similar atomic radii and D compared with those of Fe; H, C, N, O, and S are “small non‐iron‐like” with smaller atomic radii and larger D; and Mg transitions from “large non‐iron‐like” with a larger atomic radius and smaller D at low density to iron‐like under conditions of the Earth's core. The effect of pressure on D for C, N, and O is negligible for densities below ~8 g·cm−3, accompanied by an increase in average coordination numbers to ~6, and an increase in mean atomic radii. For densities above ~8 g·cm−3, diffusivities and atomic radii of these elements decrease monotonically with pressure, which is typical for the iron‐like alloying elements as well as for H, Mg, and S over the whole compression range. While atomic radius ratios move toward unity with compression, diffusivity ratios for the alloying element relative to iron tend to increase for the “non‐iron‐like” elements with density.

Description: Abstract Mass density variations can deviate from the expected behaviour caused by temperature due to changes in the composition. Such deviations can be especially significant during solar minimum conditions. Model‐data differences are typically resolved through temperature corrections while overlooking the role of errors in lower boundary composition. In this work, we use a data‐driven methodology to simultaneously estimate thermosphere composition and temperature contributions to model‐data differences. The methodology uses modal decomposition to extract high‐dimensional, reduced order basis functions for the covariance of the neutral thermospheric species and temperature. The extracted basis functions are combined with CHAMP and GRACE mass density measurements using a non‐linear least squares solver. We demonstrate the methodology using the Naval Research Laboratory's empirical MSIS (Mass Spectrometer and Incoherent Scatter) model to derive high‐dimensional basis functions. We characterize and quantify the contribution of temperature and lower boundary effects with oxygen and helium since the two species have a direct impact on drag and orbit prediction through gas‐surface interactions and mass density. We analyze the month of December in 2008, based on the work of Thayer et al. [2012], and estimate that lower boundary composition errors contribute approximately 50% of the model‐data differences.

Description: Abstract Eruptive events on the Sun have an impact on the immediate surroundings of the Earth. Through induction of electric currents, they also affect Earth‐bound structures such as the electric power transmission networks. Inspired by recent studies we investigate the correlation between the disturbances recorded in 12 years in the maintenance logs of the Czech electric‐power distributors with the geomagnetic activity represented by the K index. We find that in case of the datasets recording the disturbances on power lines at the high and very high voltage levels and disturbances on electrical substations, there is a statistically significant increase of anomaly rates in the periods of tens of days around maxima of geomagnetic activity compared to the adjacent minima of activity. There are hints that the disturbances are more pronounced shortly after the maxima than shortly before the maxima of activity Our results provide indirect evidence that the geomagnetically induced currents may affect the occurrence rate of anomalies registered on power‐grid equipment even in the mid‐latitude country in the middle of Europe. A follow‐up study that includes the modelling of geomagnetically induced currents is needed to confirm our findings.

Description: Abstract Grain size is one of the most fundamental properties of sediments. It is frequently used in paleoclimate, paleoceanographic and paleoenvironmental research as a proxy for river discharge, current and wind strength, and to identify mass flow deposits. Measuring grain‐size is, however, time‐consuming and destructive. Given the strong influence of grain size on sediment inorganic geochemistry, single element variations measured by e.g., X‐ray fluorescence (XRF) core scanning are increasingly used to estimate grain‐size variations at high resolution in sediment cores. This approach is however limited to a narrow grain‐size range since individual elements only monotonically relate to grain size over a narrow size range. Here, we present a simple, code‐free, multi‐element method based on Partial Least Square regression to predict sediment mean grain size from inorganic geochemical data over the range of sizes commonly encountered in sedimentary basins (clay to sand). The method was first tested using river sediment samples separated in eleven grain‐size fractions and it was later successfully applied to two sediment cores from the Chilean fjords. Our method only requires measuring grain size on a limited number (around ten) of selected training samples, and it allows to predict mean grain size at XRF core scanner resolution. This method has the potential to be applied to any lake or marine sediment core, provided sediment provenance, weathering, and diagenesis remain relatively stable through time, and we anticipate that it will result in a significant increase in the resolution of sediment proxy records of climate and environmental change.

Description: Abstract Dunite, harzburgite, and clinopyroxenite xenoliths from Kharchinsky volcano, Kamchatka have abundances and ratios of incompatible trace elements similar to those in arc volcanic rocks (elevated Ba/Th, La/Yb, Nd/Hf, Sr/Y). All orthopyroxenes and some clinopyroxenes in the peridotites have U‐shaped rare‐earth element patterns. Negative Ce anomalies are present in orthopyroxenes with Ce/Ce* as low as 0.01 and down to 0.22 in whole‐rock peridotite data. Ce anomaly growth is linked to increasing La/Sm and enrichments in Rb, U, Pb, and Ba over La and Ce. Isotopes (Pb, Sr, Nd, Hf) indicate pelagic sediment and hydrothermal crusts play no role in Ce anomaly development. Instead, Ce anomalies appear to be products of fluid transport and elemental scavenging under oxidizing conditions beneath the deep forearc. Textures and compositions of aluminous green spinels indicate most of the peridotites were partially melted and recrystallized at depth. Veins and pockets of amphibole reflect impregnation late in the petrogenesis of the rocks by melts similar to Kamchatka basalts. Orthopyroxenite xenoliths are fine‐grained with fibrous orthopyroxene that has high‐Mg/Mg+Fe (up to 0.96) and generally lower CaO and Al2O3 compared to peridotite orthopyroxenes, and perhaps formed by reaction of siliceous fluids with olivine. Kharchinsky xenoliths have Pb, Sr and Nd isotopes similar to Kamchatka volcanic rocks, but Hf isotopes in clinopyroxenites and gabbros are more radiogenic by 1‐3 epsilon units. Patterns in isotopic data indicate a compositional change in the source of Kamchatka volcanism within the past 20 million years.

Description: Abstract The Sun was remarkably active during the first week of September 2017 producing numerous solar flares, solar radiation storms and coronal mass ejections (CME). This activity caused disruption to terrestrial high frequency (HF, 3‐30 MHz) radio communication channels including observations with the SuperDARN HF radars. In this paper, we analyze the response of SuperDARN ground‐scatter observations and decreases in background sky noise level in response to multiple solar flares occurring in quick succession and co‐occurring with solar energetic protons and auroral activity. We estimate the attenuation in HF signal strength using an approach similar to riometry and find that the radars exhibit a nonlinear response to compound solar flare events. Additionally, we find the three different space weather drivers have varying degrees of influence on the HF signal properties at different latitudes. Our study demonstrates that in addition to monitoring high latitude convection, SuperDARN observations can be used to study the spatiotemporal evolution of disruption to HF communication during extreme space weather conditions.

Description: Abstract In this paper we present several methods to identify precursors that show great promise for early predictions of solar flare events. A data pre‐processing pipeline is built to extract useful data from multiple sources, Geostationary Operational Environmental Satellites (GOES) and Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI), to prepare inputs for machine learning algorithms. Two classification models are presented: classification of flares from quiet times for active regions and classification of strong versus weak flare events. We adopt deep learning algorithms to capture both spatial and temporal information from HMI magnetogram data. Effective feature extraction and feature selection with raw magnetogram data using deep learning and statistical algorithms enable us to train classification models to achieve almost as good performance as using active region parameters provided in HMI/Space‐Weather HMI‐Active Region Patch (SHARP) data files. Case studies show a significant increase in the prediction score around 20 hours before strong solar flare events.

Description: Abstract The total electron content (TEC) recorded at two middle‐latitude stations (Mohe and Beijing), and four low‐latitude stations (Xiamen, Guangzhou, Nanning, and Kunming) in the China sector are analyzed to study the response of the ionosphere during the sudden stratospheric warming (SSW) event in February 2018. The TEC and deviation of TEC (ΔTEC) present remarkable perturbation after the reversal of the zonal wind during the SSW period. The ΔTEC presents enhancement during the daytime and decreases after sunset, especially around the temperature peak. Results of wavelet power spectra analysis show that the ΔTEC shows intensive semidiurnal and diurnal oscillations during the SSW period. The percentage of dTEC exhibits moderate correlation with solar geophysical drivers (such as solar wind speed, F10.7, and Ap index) during the period of 11–26 February at low‐latitude stations. The significant correlation between equatorial electrojet and the percentage of dTEC monitored at low latitude indicates that the equatorial electrojet plays a key role in the anomaly perturbation and periodic oscillation of TEC, while it has a weak correlation at middle latitude.

Description: Abstract A major goal in Earth Science has been to understand how geochemical characteristics of lavas at the Earth's surface relate to the location and formation history of specific regions in the Earth's interior. For example, some of the strongest evidence for the preservation of primitive material comes from low 4He/3He ratios in ocean island basalts, but the location of the primitive helium reservoir(s) remains unknown. Here we combine whole‐mantle seismic tomography, simulations of mantle flow, and a global compilation of new and existing measurements of the 4He/3He ratios in ocean island basalts to constrain the source location of primitive 4He/3He material. Our geodynamic simulations predict the present‐day surface expression of plumes to be laterally offset from their lower mantle source locations. When this lateral offset is accounted for, a strong relationship emerges between minimum 4He/3He ratios in oceanic basalts and seismically slow regions, which are generally located within the two large low shear‐wave velocity provinces (LLSVPs). Conversely, no significant relationship is observed between maximum 208Pb*/206Pb* ratios and seismically slow regions in the lowermost mantle. These results indicate that primitive materials are geographically restricted to LLSVPs, while recycled materials are more broadly distributed across the lower mantle. The primitive nature of the LLSVPs indicates these regions are not composed entirely of recycled slabs, while complementary xenon and tungsten isotopic anomalies require the primitive portion of the LLSVPs to have formed during Earth's accretion, survived the Moon‐forming giant impact, and remained relatively unmixed during the subsequent 4.5 billion years of mantle convection.

Description: Abstract A cave monitoring study in Hatchet Bay Cave on the island of Eleuthera, Bahamas, has examined the origins of variations in oxygen and carbon isotopic and minor element composition in cave calcites. Every 3 to 8 months, between 2012 and 2016, temperature, humidity, cave air (δ13CCO2), dripwaters (δ18O and δ2H values, and Ca, Sr, and Mg concentrations), and the chemical composition of precipitating calcite (δ18O and δ13C values, and Ca, Sr, and Mg concentrations) were analyzed in two rooms in the cave. Results from the elemental analyses show that throughout the cave prior calcite precipitation (PCP) was a driver of the elemental chemistry of the precipitated calcites. In addition, cave calcites show that δ13C and δ18O values were positively correlated with Mg/Ca ratios. The Mg/Ca ratios were also positively correlated with lower calcite precipitation rates. Therefore, water/rock interactions may also influence δ13C and δ18O values and Mg/Ca ratios of the calcite. Differences were observed between the two rooms, with the Main Room of the cave exhibiting increased PCP, more ventilation, lower calcite precipitation rates, and δ18O values which were farther from equilibrium when compared to the more isolated portion of the cave. These results also validated previous interpretations from Pleistocene stalagmites collected from a nearby Bahamian cave suggesting that a positive covariation between Mg/Ca and δ13C values reflects water/rock interactions.

Description: Abstract The ferrimagnetic properties of soils are used to quantitatively reconstruct paleomonsoon precipitation from Chinese loess. Numerous magneto‐climofunctions have been established based on the magnetic proxies that are selectively sensitive to neoformation of fine‐grained superparamagnetic (SP) or single‐domain (SD) ferrimagnetic particles. Accumulating evidence has indicated that maghemite is the final product of the ferrimagnetic phases during pedogenesis in loessic soils. Quantitative estimates of abundance of maghemite of both SP and SD grains is therefore still required in developing magneto‐climofunctions. Here, we present detailed measurements on a suite of modern soil samples from the Chinese Loess Plateau to determine pedogenic ferrimagnetic mineralogy and to develop a new magneto‐climofunction based on a new parameter derived from the high‐temperature‐dependent magnetic susceptibility. Particle‐size fractionation processes combined with magnetic measurements indicate that fine‐grained SP and SD maghemite is the dominant pedogenic ferrimagnetic phases. High‐temperature dependent susceptibility measurements show that the thermally‐induced susceptibility drops between ~230°C and ~400°C during heating mainly result from the conversion of maghemite to hematite. We proposed a new parameter quantifying changes in the temperature dependence of magnetic susceptibility between 230‐400°C, "χtd ", that captures the concentration of pedogenically formed maghemite. Results show that χtd has a strong correlation with known quantities of maghemite in synthetic standard samples, and that χtd of modern soils correlates with modern mean annual precipitation (MAP) quite well (R2=0.82, n=24). The established χtd‐MAP climofunction provides a new approach to reconstructing paleorainfall during past warm interglacials from paleosols in Chinese loess.

Description: Abstract Statistical analysis of geomagnetic paleosecular variation (PSV) and time averaged field (TAF) has been largely based on global compilations of paleomagnetic data from lava flows. These show different trends in the averaged inclination anomaly (ΔI) between the two hemispheres, with small positive (〈2°) anomalies in mid‐southern latitudes and large negative (〉‐5°) anomalies in mid‐northern latitudes. To inspect the large ΔI between 20°N‐40°N we augment the global data with a new paleomagnetic dataset from the Golan‐Heights (GH), a Plio‐Pleistocene volcanic plateau in northeast Israel, located at 32°N‐33°N. The GH dataset consists of 91 lava flows sites: 40 sites obtained in the 1990s and 51 obtained in this study. The chronology of the flows is constrained by 57 40Ar/39Ar ages: 39 from previous studies and 18 from this study, which together cover most of the GH plateau. We show that the 1990s dataset might be affected by block rotations and does not fully sample PSV. The Plio‐Pleistocene pole (86.3°N, 120.8°E, N=44, k=25, α95=4.4°), calculated after applying selection criteria with Fisher precision parameter (k) ≥ 100 and number of specimens per site (n) ≥ 5 is consistent with a geocentric axial dipole field and shows smaller inclination anomaly (ΔI=‐0.4°) than predicted by global compilations and PSV models. Re‐examination of the inclination anomaly in the global compilation using different calculation methods and selection criteria suggests that inclination anomaly values are affected by: (1) inclusion of poor quality data, (2) averaging data by latitude bins and (3) the way the inclination anomaly is calculated.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: Abstract We propose an explanation to the enigmatic synrift erosional unconformities reported along the distal domain of several magma‐poor rifted margins. Using thermomechanical numerical modeling, we show that transient emersion of (future) distal domains following a phase of subsidence can be explained by asynchronous necking of first the upper mantle and subsequently the crust, without the need of prominent normal faulting caused by strain softening, mantle phase transitions, or magmatic processes. When the upper crust and upper mantle are mechanically decoupled by a weak lower crust and, in the absence of any prominent rheological heterogeneity, upper mantle, necking starts first because of the higher deviatoric stresses associated with its larger effective viscosity. Consequently, the ductile lower crustal material flows toward the necked mantle domain, delaying thinning of the overlying crust. Once the necked lithospheric mantle has locally lost most of its strength, the overdeepened Moho moves upward toward an isostatically compensated depth. This flexural rebound causes uplift and emersion of distal parts of the rift system that are composed of still relatively thick crust and triggers the necking of the overlying crust. Early necking of the upper mantle causes a transient heating event with temperatures up to 750 °C at the base of the crust in the (future) distal domain. The onset of this thermal event slightly predates emersion of the (future) distal domain. These results are consistent with field observations and thermochronological data from the fossil Alpine Tethys margins, as well as with seismic observations from several present‐day rifted margins.

Description: Abstract This paper describes a new neural network‐based approach to estimate ionospheric critical plasma frequencies (f0F2) from Global Navigation Satellite Systems (GNSS)‐vertical total electron content (TEC) measurements. The motivation for this work is to provide a method that is realistic and accurate for using GNSS receivers (which are far more commonly available than ionosondes) to acquire f0F2 data. Neural networks were employed to train vertical TEC and corresponding f0F2 observations respectively obtained from closely located GNSS receivers and ionosondes in various parts of the globe. Available data from 52 pairs of ionosonde‐GNSS receiver stations for the 17‐year period from 2000 to 2016 were used. Results from this work indicate that the relationship between f0F2 and TEC is mostly affected by the seasons, followed by the level of solar activity, and then the local time. Geomagnetic activity was the least significant of the factors investigated. The relationship between f0F2 and TEC was also shown to exhibit spatial variation; the variation is less conspicuous for closely located stations. The results also show that there is a good correlation between the f0F2 and TEC parameters. The f0F2/TEC ratio was generally observed to be lower during enhanced ionospheric ionizations in the day time and higher during reduced ionospheric ionizations in the nights and early mornings. The analysis of errors shows that the model developed in this work (known as the NNT2F2 model) can be used to estimate the f0F2 from GNSS‐TEC measurements with accuracies of less than 1 MHz. The new approach described in this paper to obtain f0F2 based on GNSS‐TEC data represents an important contribution in space weather prediction.

Description: Abstract Observations of seismic anisotropy can provide direct constraints on the character of mantle flow in subduction zones, critical for our broader understanding of subduction dynamics. Here we present over 750 new SKS splitting measurements in the vicinity of Mount St. Helens in the Cascadia subduction zone using a combination of stations from the iMUSH broadband array and Cascades Volcano Observatory network. This provides the highest density of splitting measurements yet available in Cascadia, acting as a focused “telescope” for seismic anisotropy in the subduction zone. We retrieve spatially consistent splitting parameters (mean fast direction Φ: 74°, mean delay time ∂t: 1.0 s) with the azimuthal occurrence of nulls in agreement with the fast direction of splitting. When averaged across the array, a 90° periodicity in splitting parameters as a function of back azimuth is revealed, which has not been recovered previously with single‐station observations. The periodicity is characterized by a sawtooth pattern in Φ with a clearly defined 45° trend. We present new equations that reproduce this behavior based upon known systematic errors when calculating shear wave splitting from data with realistic seismic noise. The corrected results suggest a single layer of anisotropy with an ENE‐WSW fast axis parallel to the motion of the subducting Juan de Fuca plate; in agreement with predictions for entrained subslab mantle flow. The splitting pattern is consistent with that seen throughout Cascadia, suggesting that entrainment of the underlying asthenosphere with the subducting slab is coherent and widespread.

Description: Abstract The potential field source surface (PFSS) model is widely used to derive the magnetic field of the solar corona. The only free parameter in the PFSS model is the radius of the so‐called source surface, where magnetic field lines are forced to open. The radius of this surface is typically set to 2.5 solar radii in research and operational PFSS numerical models. Here, using Global Oscillation Network Group (GONG) synoptic maps of the photospheric field, solutions of the PFSS model for various heights of the source surface are investigated for 2006–2018. In particular, numerically derived open solar magnetic flux and coronal holes are examined. Solutions of the PFSS model based on GONG synoptic maps are particularly important since they are often used to drive operational space weather forecast models. Comparisons between observations and numerical results in this paper suggest that the radius of the source surface is significantly lower than 2.5 solar radii during the active phase of solar cycle 24. The fact that the source surface location depends on the solar activity suggests that relations which associate solar wind properties with the coronal magnetic field in the PFSS‐based solar wind modes should be revisited. Furthermore, although the correction of the polar magnetic field is part of GONG synoptic map production pipeline, the results suggest that better treatment of polar fields is needed to cover observational gaps. The issue with the polar fields in GONG maps is particularly pronounced in recent years.

Description: Abstract The Kp index is a measure of the mid‐latitude global geomagnetic activity and represents short‐term magnetic variations driven by solar wind plasma and IMF. The Kp index is one of the most widely used indicators for space weather alerts and serves as input to various models, such as for the thermosphere and the radiation belts. It is therefore crucial to predict the Kp index accurately. Previous work in this area has mostly employed artificial neural networks to nowcast Kp, based their inferences on the recent history of Kp and on solar wind measurements at L1. In this study, we systematically test how different machine learning techniques perform on the task of nowcasting and forecasting Kp for prediction horizons of up to 12 hours. Additionally, we investigate different methods of machine learning and information theory for selecting the optimal inputs to a predictive model. We illustrate how these methods can be applied to select the most important inputs to a predictive model of Kp and to significantly reduce input dimensionality. We compare our best performing models based on a reduced set of optimal inputs with the existing models of Kp, using different test intervals and show how this selection can affect model performance.

Description: Abstract Recent seismic studies indicate the presence of seismic anisotropy near subducted slabs in the transition zone and uppermost lower mantle (mid‐mantle). In this study, we investigate the origin of radial anisotropy in the mid‐mantle using 3‐D geodynamic subduction models combined with mantle fabric simulations. These calculations are compared with seismic tomography images to constrain the range of possible causes of the observed anisotropy. We consider three subduction scenarios: (i) slab stagnation at the bottom of the transition zone; (ii) slab trapped in the uppermost lower mantle; and (iii) slab penetration into the deep lower mantle. For each scenario, we consider a range of parameters, including several slip systems of bridgmanite and its grain‐boundary mobility. Modeling of lattice‐preferred orientation shows that the upper transition zone is characterized by fast‐SV radial anisotropy anomalies up to −1.5%. For the stagnating and trapped slab scenarios, the uppermost lower mantle is characterized by two fast‐SH radial anisotropy anomalies of ∼+2% beneath the slab's tip and hinge. On the other hand, the penetrating slab is associated with fast‐SH radial anisotropy anomalies of up to ∼+1.3% down to a depth of 2,000 km. Four possible easy slip systems of bridgmanite lead to a good consistency between the mantle modeling and the seismic tomography images: [100](010), [010](100), [001](100), and . The anisotropy anomalies obtained from shape‐preferred orientation calculations do not fit seismic tomography images in the mid‐mantle as well as lattice‐preferred orientation calculations, especially for slabs penetrating into the deep lower mantle.

Description: Abstract Building on an earlier study that confirmed the stability of the 405‐kyr eccentricity climate cycle and the timing of the Newark‐Hartford astrochronostratigraphic polarity time scale (N‐H APTS) back to 215 Ma, we extend the magnetochronology of the Late Triassic Chinle Formation to its basal unconformity in scientific drill core PFNP‐1A from Petrified Forest National Park (Arizona, USA). The 335‐m‐thick Chinle section is imprinted with paleomagnetic polarity zones PF1r to PF10n, which we correlate to chrons E17r to E9n (~209 to 224 Ma) of the N‐H APTS. A sediment accumulation rate of ~34 m/Myr can be extended down to ~270 meters, close to the base of the Sonsela Member and the base of magnetozone PF5n, which we correlate to chron E14n that onsets at 216.16 Ma. Magnetozones PF5r to PF10n in the underlying 65‐m‐thick section of the mudstone‐dominated Blue Mesa and Mesa Redondo members plausibly correlate to chrons E13r to E9n, indicating a sediment accumulation rate of only ~10 m/Myr. Published high precision U‐Pb detrital zircon dates from the lower Chinle tend to be several million years older than the magnetochronological age model. The source of this discrepancy is unclear but may be due to sporadic introduction of juvenile zircons that get recycled. The new magnetochronological constraint on the base of the Sonsela Member brings the apparent timing of the included Adamanian‐Revueltian land vertebrate faunal zone boundary and the Zone II to Zone III palynofloral transition closer to the temporal range of the ~215 Ma Manicouagan impact structure in Canada.

Description: Abstract Using 8‐25s period Rayleigh and Love wave phase velocity dispersion data extracted from seismic ambient noise, we (i) model the 3D shear wave velocity structure of the West Antarctic crust and (ii) map variations in crustal radial anisotropy. Enhanced regional resolution is offered by the UK Antarctic Seismic Network. In the West Antarctic Rift System (WARS), a ridge of crust ~26‐30km thick extending south from Marie Byrd Land separates domains of more extended crust (~22km thick) in the Ross and Amundsen Sea Embayments, suggesting along‐strike variability in the Cenozoic evolution of the WARS. The southern margin of the WARS is defined along the southern Transantarctic Mountains (TAM) and Haag Nunataks‐Ellsworth Whitmore Mountains (HEW) block by a sharp crustal thickness gradient. Crust ~35‐40km is modelled beneath the Haag Nunataks‐Ellsworth Mountains, decreasing to ~30‐32km km thick beneath the Whitmore Mountains, reflecting distinct structural domains within the composite HEW block. Our analysis suggests that the lower crust and potentially the mid crust is positively radially anisotropic (VSH 〉 VSV) across West Antarctica. The strongest anisotropic signature is observed in the HEW block, emphasising its unique provenance amongst West Antarctica's crustal units, and conceivably reflects a ~13km thick metasedimentary succession atop Precambrian metamorphic basement. Positive radial anisotropy in the WARS crust is consistent with observations in extensional settings, and likely reflects the lattice‐preferred orientation of minerals such as mica and amphibole by extensional deformation. Our observations support a contention that anisotropy may be ubiquitous in continental crust.

Description: Abstract Quantitative estimates of natural climate variability are required to detect anthropogenic climate trends in the tropical Pacific, however instrumental records from this region are too short and scarce. Coral oxygen isotopic (δ18O) and strontium to calcium (Sr/Ca) records are often used to extend instrumental observations, however differences in the mean Sr/Ca and δ18O values of Porites spp. colonies from the same reef can introduce large uncertainties in coral‐based climate reconstructions. To quantify intercolony variability at Palmyra Atoll, we generate monthly‐resolved Sr/Ca and δ18O timeseries from five Porites spp. colonies that grew between 1980‐2010. Monthly to interannual variability in Sr/Ca and δ18O is well‐reproduced among different colonies, however we document intercolony offsets in mean Sr/Ca of ±0.09 mmol/mol (1σ) or ~1°C, and in mean δ18O of ±0.12‰ (1σ) or ~0.1°C. The sensitivity of each proxy to climate also varies across colonies, with Sr/Ca‐SST slopes ranging from ranging from ‐0.06 to ‐0.1 mmol mol‐1 °C‐1 and δ18O‐SST slopes ranging from ‐0.25 to ‐0.35 ‰°C‐1. Intercolony variability in both coral Sr/Ca and δ18O reduces the reproducibility of coral‐based δ18Osw reconstructions across overlapping colonies. Accounting for both intercolony variability and slope error suggests that SST reconstructions using Sr/Ca from a single Palmyra coral have an uncertainty of ±1.3°C (1σ), however replicating Sr/Ca records across multiple colonies can greatly reduce this uncertainty. A composite Sr/Ca record built using five modern cores, for example, offers a reduced error of ±0.6°C (1σ) in mean SST reconstructions, ~2.5 times smaller than errors associated with reconstructions from single corals.

Description: Abstract Hydrocarbon systems with declining or viscous oil production are often stimulated using enhanced oil recovery (EOR) techniques, such as the injection of water, steam and CO2, in order to increase oil and gas production. As EOR and other methods of enhancing production such as hydraulic fracturing have become more prevalent, environmental concerns about the impact of both new and historical hydrocarbon production on overlying shallow aquifers have increased. Noble gas isotopes are powerful tracers of subsurface fluid provenance and can be used to understand the impact of EOR on hydrocarbon systems and potentially overlying aquifers. In oil systems, produced fluids can consist of a mixture of oil, water and gas. Noble gases are typically measured in the gas phase; however, it is not always possible to collect gases and therefore produced fluids (which are water, oil and gas mixtures) must be analyzed. We outline a new technique to separate and analyze noble gases in multi‐phase hydrocarbon‐associated fluid samples. An offline double capillary method has been developed to quantitatively isolate noble gases into a transfer vessel, while effectively removing all water, oil, and less volatile hydrocarbons. The gases are then cleaned and analyzed using standard techniques. Air‐saturated water reference materials (n=24) were analyzed and results show a method reproducibility of 2.9% for 4He, 3.8% for 20Ne, 4.5% for 36Ar, 5.3% for 84Kr and 5.7% for 132Xe. This new technique was used to measure the noble gas isotopic compositions in six produced fluid samples from the Fruitvale Oil Field, Bakersfield, California.

Description: Abstract Geophysical data acquisition in oceanic domains is challenging, implying measurements with low and/or non‐homogeneous spatial resolution. The evolution of satellite gravimetry and altimetry techniques allows testing 3D density models of the lithosphere, taking advantage of the high spatial resolution and homogeneous coverage of satellites. However, it is not trivial to discretise the source of the gravity field at different depths. Here, we propose a new method for inferring tectonic boundaries at the crustal level. As a novelty, instead of modelling the gravity anomalies and assuming a flat Earth approximation, we model the Vertical Gravity Gradients (VGG) in spherical coordinates, which are especially sensitive to density contrasts in the upper layers of the Earth. To validate the methodology, the complex oceanic domain of the Caribbean region is studied, which includes different crustal domains with a tectonic history since Late Jurassic time. After defining a lithospheric starting model constrained by up‐to‐date geophysical datasets, we tested several a‐priory density distributions and selected the model with the minimum misfits with respect to the VGG calculated from the EIGEN‐6C4 dataset. Additionally, the density of the crystalline crust was inferred by inverting the VGG field. Our methodology enabled us not only to refine, confirm and/or propose tectonic boundaries in the study area, but also to identify a new anomalous buoyant body, located in the South Lesser Antilles subduction zone, and high density bodies along the Greater, Lesser and Leeward Antilles forearcs.

Description: Abstract On 13 March 1989, the largest magnetic storm of the last century caused widespread effects on power systems including a blackout of the Hydro‐Québec system. Since then this event has become the archetypal disturbance for examining the geomagnetic hazard to power systems. However, even 30 years on from 1989, the story of exactly what happened in March 1989 is far from complete. This paper reexamines the information available about the March 1989 event and uses this to construct a timeline and description of the space weather phenomena and how they caused the power system effects. The evidence shows that the disturbance was caused by two coronal mass ejections (CMEs): the first associated with a X4.5 flare on 10 March and the second linked to a M7.3 flare on 12 March. The arrival of the interplanetary CME shock fronts caused storm sudden commencements at 01.27 and 07.43 UT on 13 March. The transit time and speed of the first (second) interplanetary CME shock are 54.5 hr (31.5 hr) and 760 km/s (1,320 km/s). Empirical relations are used to estimate solar wind speed and southward interplanetary magnetic field, Bs, and give values of v = 980 km/s, Bs = 40 to 60 nT at the peak of the storm. Key findings are that the second storm sudden commencement occurred at the same time as the substorm that impacted the Hydro‐Québec system and indicates that external triggering of the substorm may have contributed to a faster substorm onset than might otherwise have occurred. This caused the production of larger geomagnetically induced currents that caused the Hydro‐Québec blackout. The March 1989 storm had the largest recorded value of the Dst index representing the size of the magnetic storm main phase, but the Hydro‐Québec blackout occurred early in the storm when the Dst value was less disturbed. Only later in the storm did Dst reach its peak value. At this time an expansion of the auroral oval brought disturbances to lower latitudes where they caused power system problems in the United States, United Kingdom, and Sweden.

Description: Abstract Studying spatial and temporal trends in volcanic gas compositions and fluxes is crucial to both volcano monitoring and to constrain the origin and recycling efficiency of volatiles at active convergent margins. New compositions and fluxes are here reported for Nevado del Ruiz, Galeras and Purace, the most persistently degassing volcanoes in the Colombian Arc Segment (CAS) of the Northern Volcanic Zone (NVZ). At Nevado del Ruiz, from 2014 to 2017, plume emissions showed an average molar CO2/ST ratio of 3.9 ± 1.6 (ST is total sulfur, S). Contemporary, fumarolic chemistry at Galeras progressively shifted towards low‐temperature, S‐depleted gas discharges with an average CO2/ST ratio in excess of 10 (6.0 – 46.0, 2014‐2017). This shift in volcanic gas compositions was accompanied by a concurrent decrease in SO2 emissions, confirmed on the 21 March 2017 by high‐resolution UV camera‐based SO2 fluxes of ~2.5 kg s‐1 (~213t d‐1). For comparison, SO2 emissions remained high at Nevado del Ruiz (weighted average of 8 kg s‐1) between 2014 and 2017, while Puracé maintained rather low emission levels (〈1 kg s‐1 of SO2, CO2/SO2 ≈ 14). We here estimate carbon dioxide fluxes for Nevado del Ruiz, Galeras and Puracé of ~23, 30 and 1 kg s‐1, respectively. These, combined with recent CO2 flux estimates for Nevado del Huila of ~10 kg s‐1 (~860 t d‐1), imply that this arc segment contributes about 50% to the total subaerial CO2 budget of the Andean Volcanic Belt. Furthermore, our work highlights the northward increase in carbon‐rich sediment input into the mantle wedge via slab fluids and melts that is reflected in magmatic CO2/ST values far higher than those reported for Southern Volcanic Zone (SVZ) and Central Volcanic Zone (CVZ) volcanoes. We estimate that about 20% (~1.3 Mt C/y) of the C being subducted (~6.19 Mt C/y) gets resurfaced through subaerial volcanic gas emissions in Colombia (Nevado del Ruiz ~0.7 Mt C/y). As global volcanic volatile fluxes continue to be quantified and refined, the contribution from this arc segment should not be underestimated.

Description: Abstract The OMNI database is formed by propagating the solar wind measured at around Lagrange point L1, whose result may differ from the actual solar wind in the vicinity of the bow shock nose. To test the quality of the OMNI database we cross‐correlate the 2‐hr intervals of 1‐min interplanetary magnetic field (IMF) data provided mostly by ACE and WIND spacecraft with Geotail measurements in front of the bow shock (10409 cases in 1997‐2016). We used two metrics: Pearson correlation coefficient (CC) and prediction efficiency (PE). Confirming previous studies, we found that the prediction quality of actual IMF degrades continuously with increasing distance of OMNI spacecraft from the Sun‐Earth line, with the amounts of poor and good predictions become nearly equal for RYZ ≥ 65 RE (they constitute ~12% of the entire data base). In roughly 20% of the analyzed data, low CC and PE values were the consequence of low IMF variability (a low signal to noise ratio). The remaining data set include 42% of very good data (CC ≥ 0.8), 33% of relatively good data (0.5 ≤ CC 〈 0.8 and PE ≥ 0), 10% of data having correct variability but wrong absolute values (0.5 ≤ CC 〈 0.8 and PE 〈 0), and 15% of poor data (CC 〈 0.5). We also discovered that the OMNI data are generally of a good quality when the PC index of geomagnetic activity correlates well with the solar wind‐magnetosphere coupling factor suggested by Kan and Lee (1979).

Description: Abstract We develop and test an empirical model predicting ground‐based observations of ultra‐low frequency (ULF, 1‐20 mHz) wave power across a range of frequencies, latitudes and magnetic local time sectors. This is parameterized by instantaneous solar wind speed vsw, variance in proton number density var(Np) and interplanetary southward magnetic field Bz. A probabilistic model of ULF wave power will allow us to address uncertainty in radial diffusion coefficients and therefore improve diffusion modeling of radial transport in Earth's outer radiation belt. Our model can be used in two ways to reproduce wave power; by sampling from conditional probability distribution functions or by using the mean (expectation) values. We derive a method for testing the quality of the parameterization and test the ability of the model to reproduce ULF wave power time series. Sampling is a better method for reproducing power over an extended time period as it retains the same overall distribution while mean values are better for predicting the power in a time series. The model predicts each hour in a time series better than the assumption that power persists from the preceding hour. Finally, we review other sources of diffusion coefficient uncertainty. Although this wave model is designed principally for the goal of improved radial diffusion coefficients to include in outer radiation belt diffusion based modeling, we anticipate that our model can also be used to investigate the occurrence of ULF waves throughout the magnetosphere and hence the physics of ULF wave generation and propagation.

Description: Abstract Five model compounds with representative chemical structures were selected for use in simulation experiments of pyrolytic gas production. The gas production and isotopic fractionation characteristics were observed and analyzed. Then, the factors affecting carbon isotope fractionation during natural gas generation were discussed, and a fractionation model was established and calibrated. We concluded that the final hydrocarbon gas (C1‐5) yield of octadecane, octadecylamine, octadecanoic acid, decahydronaphthalene and 9‐phenylanthracene decreased in turn with the effective hydrogen content. Compared with linear alkanes or alkyl compounds, cycloalkanes have higher thermal stability and generate gas later. The variation in the carbon isotopic composition of natural gas is primarily controlled by the following three factors. a) The thermal evolution of organic matter (OM) results in a gradually heavier isotopic composition for the main gas production stage. b) Gas inherits the isotopic composition of its parent material, and this effect is evident when the chemical structure and gas generation mechanism between parent materials are similar. c) The structure of OM determines the reaction mechanism of gas generation, which has a significant influence on the range and trend of carbon isotope fractionation in the process of methane generation. An improved chemical kinetic model can accurately characterize carbon isotope fractionation during gas generation.

Description: Abstract Benthic foraminiferal assemblages and geochemical tracers (δ18O, δ13C and 14C) have been analyzed on benthic and planktonic foraminifera from core MD77‐176, located in the northern Bay of Bengal (BoB), in order to reconstruct the evolution of intermediate circulation in the northern Indian Ocean since the last glaciation. Results indicate that during the Last Glacial Maximum (LGM), Southern Sourced Water (SSW) masses were dominant at the core site. A high relative abundance of intermediate and deep infaunal species during the LGM reflects low oxygen concentration and/or meso‐ to eutrophic deep water conditions, associated with depleted benthic δ13C values. During the Holocene, benthic foraminiferal assemblages indicate an oligo– to mesotrophic environment with well‐ventilated bottom water conditions compared with LGM. Higher values for benthic foraminifera δ13C and B‐P 14C age offsets suggest an increased contribution of North Atlantic Deep Water (NADW) to the Northern BoB during the Late Holocene compared to the LGM. Millennial‐scale events punctuated the last deglaciation, with a shift in the δ13C and the ɛNd values coincident with low B‐P 14C age offsets, providing strong evidence for an increased contribution of Antarctic Intermediate Water (AAIW) at the studied site. This was associated with enhanced upwelling in the Southern Ocean, reflecting a strong sea‐atmospheric CO2 exchange through Southern Ocean ventilation during the last deglaciation.

Description: Abstract The East Taiwan Ophiolite (ETO) occurs as blocks and thrust sheets associated with the Lichi Mélange in the Coastal Range of eastern Taiwan. The blocks consist of serpentinized harzburgite, serpentinite breccia, gabbro, dikes of dolerite and plagiogranite, pillow basalts, and red clay within a mud‐ and serpentinite‐rich mélange matrix. New U‐Pb zircon dating of a pegmatite gabbro yields a weighted mean age of 16.65±0.20 Ma. This age is earlier than the North Luzon Arc, but overlaps with the late–stage spreading of the South China Sea. ETO glassy basalt has low K2O, MgO and high CaO contents, similar to MORB. REE and trace element patterns show both N‐MORB patterns with LREE depletion and E‐MORB patterns with slight LREE enrichment. A few samples show slight depletion in Nb‐Ta, and Ti and enrichment in Rb, Ba, U and Sr, indicating a hint of subduction influence. Most ETO basalt plots within the overlapping fields of N‐MORB and BABB on Ti‐V, Cr‐Y, Nb/Yb‐ Th/Yb and Hf/3‐Th‐Ta discrimination diagrams. These geochemical compositions are emblematic of mid‐ocean ridge or back‐arc lava, like South China Sea basalt. We interpret ETO basalt and gabbro as fragments of the subducted South China Sea basement that were scrapped off and accreted to the Luzon forearc during the process of subduction initiation along the Manila Trench. Blocks of mantle material in the mélange may originate from the upper plate of the arc‐continent collision and were mixed with lower plate crustal material in a subduction channel now represented by the Lichi Mélange.

Description: Abstract Peer review remains one of the most important service activities for scientists. Through the time‐consuming process of peer review, community volunteers set the bar for the quality of science that is shared with each other and with the world. Attentive, patient, and critical review is required to maintain rigorous and accurate scientific reporting. Reviewers donate their time and effort with little incentive outside of the knowledge that they are contributing to sustain scientific rigor. Space Weather is fortunate to be able to continually rely on our reviewers to maintain a journal that receives and publishes high‐quality, high‐impact articles. We recognize the time, effort, and dedication each review requires. For this, we extend a heartfelt thank you to all of our 2018 reviewers. We sincerely appreciate your choice to respond positively to our review requests. Last year, Space Weather received 785 peer reviews from 354 individuals. The reviewers who contributed three or more reviews are recognized in italics below. Thank you all for your contributions in 2018.

Description: Abstract Magnetic properties from the Reinfjord Ultramafic Complex, in northern Norway, which formed as part of a deep magmatic conduit system, have been investigated to determine the magnetic signature of ultramafic rocks now exposed at the surface and deeper in the lower crust. The dominant carriers in these ultramafic rocks are a chrome spinel with Fe‐rich exsolution blebs, and exsolution lamellae of magnetite in clinopyroxene. Except locally, in a fault zone and in discrete small fractures, these rocks show only minor to no alteration. We infer that the magnetic oxides characterized here are representative of pristine magnetic carriers in similar rocks deeper in the crust. These oxides can be stable in lower crustal, possibly upper mantle, depths when temperatures are below the Curie temperature of magnetite, taking into account pressure effects. These ultramafic rocks are candidates for potential sources of long‐wavelength anomalies.

Description: Abstract The most recent eruption of Mt. Fuji (Japan), the VEI 5 Hōei plinian eruption (CE 1707) heavily impacted Lake Yamanaka, a shallow lake located at the foot of Mt. Fuji. Here, we discuss the influence of the Hōei eruption on the lacustrine sedimentation of Lake Yamanaka using high resolution geophysical and geochemical measurements on gravity cores. Hōei scoria fall‐out had two major impacts on Lake Yamanaka: (i) reduction of the sedimentation rate (from ~0.16 cm/yr to ~0.09 cm/yr); and (ii) the increase of in‐situ lake productivity. Sedimentation rates after the eruption were relatively low due to the thick scoria layer, trapping underlying sediments in the catchment. The lacustrine system took over more than ~170 years to begin to recover from the Hōei eruption: sedimentation recovery have been accelerated by changes in land use. Since the beginning of the 20th Century, vegetated strips delimited cultivated parcels, trapping sediment and minimizing the anthropogenic impacts on the sedimentation rate. Over the last decade, the decline of agriculture and the increase of other human activities led to an increase in the sedimentation rate (~1 cm/yr). This study highlights the effect of the grainsize of the volcanic ejecta on the sedimentation rate following a volcanic eruption. Coarse‐grained tephra are difficult to erode. Therefore, their erosion and remobilization is largely limited to intense typhoons when porous scoria deposits are saturated by heavy rains. Moreover, this study suggests that recent anthropogenic modifications of the catchment had a greater impact on the sedimentation rate than the Hōei eruption.

Description: Abstract The advantages in provenance research of U‐Pb dating different detrital minerals along with simultaneously analyzing trace elements is demonstrated in a study of sand from the mouth of the Merrimack River in New England, USA. Zircon ages record episodes of magmatism in the Early Paleozoic, peaking in the Early Devonian, followed by quiescence through the remainder of the Paleozoic and additional magmatic episodes in the Jurassic and Cretaceous. Simultaneous measurement of trace elements in zircons reveals a shift from arc magmatism to crustal melting associated with terrane collision in the Early Devonian while many Jurassic grains are clearly derived from A‐type granites. Detrital monazites and rutiles have Devonian and Permian ages. Many of the older monazites have trace element characteristics suggestive of igneous origin while Permian monazites are clearly metamorphic and record orogenesis that is absent from the detrital zircon record. Rutile grains have trace element chemistry indicative of mostly metasedimentary source rocks, and Zr thermometry indicates growth under amphibolite facies conditions. Age offsets between monazite and rutile populations provide information about the region's cooling history. Titanite grains have trace element chemistry mostly consistent with igneous origin and U‐Pb ages lining up with minor zircon age populations in the Ordovician‐Silurian and the Middle Devonian, suggesting that these magmatic episodes produced metaluminous compositions. These results show that combing trace element fingerprinting with dating and analyzing multiple detrital mineral species provide a more complete portrait of the geologic history of the sediment source region than U‐Pb dating of zircon alone.

Description: Abstract Routine in‐situ solar wind observations from L5, located 60° behind Earth in its orbit, would provide a valuable input to space‐weather forecasting. One way to ulitise such observations is to assume that the solar wind is in perfect steady state over the 4.5 days it takes the Sun to rotate 60° and thus near‐Earth solar wind in 4.5‐days time would be identical to that at L5 today. This corotation approximation is most valid at solar minimum when the solar wind is slowly evolving. Using STEREO data, it has been possible to test L5‐corotation forecasting for a few months at solar minimum, but the various contributions to forecast error cannot be disentangled. This study uses 40+ years of magnetogram‐constrained solar wind simulations to isolate the effect of latitudinal offset between L5 and Earth due to the inclination of the ecliptic plane to the solar rotational equator. Latitudinal offset error is found to be largest at solar minimum, due to the latitudinal ordering of solar wind structure. It is also a strong function of time of year; maximum at the solstices and very low at equinoxes. At solstice, the latitudinal offset alone means L5‐corotation forecasting is expected to be less accurate than numerical solar wind models, even before accounting for time‐dependent solar wind structures. Thus, a combination of L5‐corotation and numerical solar wind modelling may provide the best forecast. These results also highlight that three‐dimensional solar wind structure must be accounted for when performing solar wind data assimilation.

Description: Abstract We re‐construct the timeline of the extreme space weather event of May 1921, reviewing a wealth of reports from scientific literature, databases, newspaper reports, and reports by historians and astronomers. A series of coronal mass ejections (CMEs) bombarded Earth between 13 and 16 May, as shown by a series of sudden commencements observed across the global network of magnetometers. These CMEs produced three major periods of geomagnetic activity. The first period followed the arrival of two CMEs on 13 May. These may have cleared much density from the inner heliosphere, enabling a subsequent CME to travel quickly to Earth and cause intense activity. Continuing moderate magnetic activity following the first period may also have preconditioned the magnetosphere so it responded strongly to that later CME. This arrived late on 14 May, driving a short period of very intense activity early on 15 May, including technological impacts indicative of strong geoelectric fields. Another CME arrived early on 16 May, driving intense activity similar to that on 13 May. We show how these impacts fit with scientific observations to give a timeline that can be used in worst case studies/benchmarks. We also show that some impacts were probably coincidental with the storm, but due to more prosaic faults. This sequence of preconditioning, intense geoelectric fields and their impacts, plus coincidental faults, makes the 1921 event an excellent basis for building space weather scenarios. Such scenarios are vital scientific input to the development and implementation of policies for mitigation of severe space weather.

Description: Abstract The thermal evolution of a solid planet is governed by mantle convection and therefore the dependence of viscosity on temperature. In this study, over a span of five billion years, we investigate the effect of viscosity clipping (i.e., limiting the maximum value of the viscosity) on the thermal evolution of lunar‐sized initially hot bodies featuring decaying internal heat sources. Models with a decreasing viscosity contrast resulting from limiting the maximum viscosity to 105.5 times the initial viscosity at the core‐mantle boundary were first examined. At times determined by the initial internal heating rate, rapid cooling sets in as a result of a convective regime change from stagnant‐lid to mobile‐lid convection, followed by gradual cooling to a weakly convecting and eventually nearly conductive state. Subsequently, we employ a dynamic clipping viscosity of 105.5 times the viscosity at the core‐mantle boundary, throughout the planet's evolution. In this case, stagnant‐lid convection is the only convective regime observed. Finally, convection with an initially large viscosity contrast (1010) is modeled in both 2D and 3D spherical geometry and we find strong agreement in the thermal evolution when compared with the dynamic clipping model. Our findings show that convective regime changes due to secular cooling can occur due to implementing a fixed viscosity contrast that becomes sub‐critical with respect to obtaining a stagnant‐lid. To avoid spurious convective regime changes, the specification of a dynamic clipping viscosity can be used to emulate much higher viscosity contrasts.

Description: Abstract We report updated measurements of the integral fluxes of energetic protons, helium ions, and heavier ions as measured by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER). CRaTER is a particle telescope that has been operating aboard the Lunar Reconnaissance Orbiter since 2009. In an earlier report, we presented the methodology used to extract linear energy transfer (LET) spectra, and integral fluxes for particles with sufficient energies to fully penetrate the telescope. Results were presented for the time span from late 2009 through the end of calendar year 2014, a period that encompassed the rise of solar activity from deep solar minimum to the weak maximum of Cycle 24. Here, we update the results with data obtained from that point in time through the end of 2018, in the declining phase of Cycle 24. Fluxes obtained in the most recent data are approaching the peak levels observed in late 2009 and early 2010. The results can be used as input to models of solar modulation of Galactic Cosmic Rays, and are also relevant to human exploration of deep space.

Description: Abstract Sand‐shale mélanges from the Kodiak Accretionary Complex and Shimanto Belt of Japan record deformation during underthrusting along a paleosubduction interface in the range 150 to 350°C. We use observations from these mélanges to construct a simple kinetic model that estimates the maximum time required to seal a single fracture as a measure of the rate of fault zone healing. Crack sealing involves diffusive redistribution of Si from mudstones with scaly fabric to undersaturated fluid‐filled cracks in sandstone blocks. Two driving forces are considered for the chemical potential gradient that drives crack sealing: 1) a transient drop in fluid pressure ∆Pf , and 2) a difference in mean stress between scaly slip surfaces in mudstones and cracks in stronger sandstone blocks. Sealing times are more sensitive to mean stress than ∆Pf, with up to four orders of magnitude faster sealing. Sealing durations are dependent on crack‐spacing, silica diffusion kinetics, and magnitude of the strength contrast between block and matrix, each of which are loosely constrained for conditions relevant to the seismogenic zone. We apply the model to three active subduction zones and find that sealing rates are fastest along Cascadia and several orders of magnitude slower for a given depth along Nicaragua and Tohoku slab‐top geotherms. The model provides: 1) a framework for geochemical processes that influence subduction mechanics via crack sealing and shear fabric development and 2) demonstration that kinetically‐driven mass redistribution during the interseismic period is a plausible mechanism for creating asperities along smooth, sediment‐dominated convergent margins.

Description: Abstract We developed a fully automated magnetic field scanner dedicated to uniaxial magnetic field measurements to determine remanent magnetization intensities and their variations in sedimentary U‐channels. A fluxgate magnetometer located as close as possible to the sedimentary section is used to perform uniaxial measurements of magnetic fields generated by the isothermal remanent magnetization of the sediment. This artificial magnetization, which is known to be a powerful proxy in environmental magnetism, is produced perpendicular to the U‐channel long axis, and parallel to the fluxgate axis, using a Halbach cylinder prior to the measurement. The present magnetic scanner offers a maximal spatial resolution of 5.8 mm for point sources. A spatial resolution of 14 mm is obtained for U channel samples. The magnetic scanner presents a reliable magnetic field range over about 3 orders of magnitude allowing measurement of magnetizations that saturate the Superconducting Rock Magnetometer in its classical configuration. The estimation of remanent magnetization intensities along the U‐channel is based on a modeling approach that uses successive uniformly magnetized prisms. In lacustrine laminated sections, comparison between modeling results based on prisms of a constant thickness, on prisms determined from sedimentary facies and on prisms determined from XRF (X‐Ray Fluorescence) data helps to understand the detrital vs. diagenetic history of the sedimentary succession.

Description: Abstract Features and peculiarities of the cosmic ray intensity (CRI) and the geomagnetic activity, along with several solar plasma and interplanetary magnetic field during the period 4‐10 September 2017 are studied. The period was characterized by strong solar activity: several solar flares occurred, several halo Coronal Mass Ejections (CMEs) were ejected in space. In the near‐Earth interplanetary space, the CMEs driving shock(s) and sheath(s) were identified. At the Earth, strong Forbush decreases (FD) in CRI and geomagnetic storms (GS) were observed. Several large solar flares, one of them of very high X‐ray importance (X 9.3) and three halo CMEs were detected in the solar atmosphere. Two shock‐associated Interplanetary Coronal Mass Ejections were observed during that interval in near‐Earth space; the latter and faster one arrived even as the ejecta of earlier one was still crossing. Variations in interplanetary plasma and field parameters during, before and after the FD and GS that occurred during the considered period were examined. A detailed time‐lagged correlation analysis using data at three different temporal resolutions (hourly, 5‐min and 1‐min) was also performed. Cross‐correlations of time series of CRI with geomagnetic activity during the period 4 – 10 September 2017 are computed. This cross‐correlation analysis between CRI variability (defined as the difference of the CRI count rate between the current and the previous time step) and the Dst indicates a delay of Dst by 3‐4 hours.

Description: Abstract Ocean bottom seismometers (OBS) commonly record short duration events (SDEs), that could be described by all of these characteristics: (i) duration 〈 1 s, (ii) one single‐wave train with no identified P‐ nor S‐wave arrivals and (iii) a dominant frequency usually between 4 Hz and 30 Hz. In many areas, SDEs have been associated with gas or fluid‐related processes near cold seeps or hydrothermal vents, although fish bumps, instrumental or current‐generated noise have been proposed as possible sources. In order to address some remaining issues, this study presents results from in situ and laboratory experiments combined with observations from 2 contrasting areas, the Sea of Marmara (Turkey) and the Chilean subduction zone. The in situ experiment was conducted at the EMSO‐Molène submarine observatory (near Brest, France) and consisted in continuously monitoring two OBSs with a camera. The images revealed that no fish regularly bumped into the instruments. Laboratory experiments aimed at reproducing SDEs’ waveforms by injecting air or water in a tank filled by sand and sea‐water and monitored with an OBS. Injecting air in the sediments produced waveforms very similar to the observed SDEs, while injecting air in the water column did not, constraining the source of SDEs in the seafloor sediments. Finally, the systematic analysis of two real data sets revealed that it is possible to discriminate gas‐related SDEs from biological or sea‐state related noise from simple source parameters, such as the temporal mode of occurrence, the back azimuth and the dominant frequency.

Description: Abstract The variety of coral reefs morphologies highlights their sensitivities to several forcings; fossil reefs stack in sequences that are accordingly diverse. In order to understand their genesis and architectures, we devised a numerical approach, accounting for Quaternary sea‐level oscillations, vertical land motion, initial slope, wave erosion, and reef growth. We first test our model on the subsiding sequence of Hawaii, and on the uplifting sequence of Wangi‐Wangi (Sulawesi) that bears active barriers. We then construct a parametric study, that we analyse based on a comprehensive yet compact description of sequences as barcodes, that depict the vertical distribution of a few geometrical characteristics (number, width and height of the terraces, barriers). We find that geological factors suffice to explain the variety of architectures of reefal sequences at first order, regardless of additional ecosystemic processes. Vertical land motion and foundation slopes are the prime players, while reef growth rates only play a minor role. Barriers may develop both in uplift and subsidence mode, and their preservation attests for the erosional power. Last, we reappraise the genesis of sequences and find that sequences do not fingerprint discrete events of sea‐level oscillations but a continuous process harrowed by stochastic events: Major sea‐level fluctuations can be over‐represented by several terraces, or conversely absent; reoccupations may yield composite terraces representing multiple events. Overall, sequences shall not be regarded as stacks of reef bodies forming during sea‐level highstands, which implies that the commonly assumed bijective relationship between sea‐level highstands and terraces shall be abandoned.

Description: Abstract Current algorithms for the real‐time prediction of the Kp index use a combination of models empirically driven by solar wind measurements at the L1 Lagrange point and historical values of the index. In this study, we explore the limitations of this approach, examining the forecast for short and long lead times using measurements at L1 and Kp time series as input to artificial neural networks. We explore the relative efficiency of the solar wind‐based predictions, predictions based on recurrence, and based on persistence. Our modeling results show that for short‐term forecasts of approximately half a day, the addition of the historical values of Kp to the measured solar wind values provides a barely noticeable improvement. For a longer‐term forecast of more than two days, predictions can be made using recurrence only, while solar wind measurements provide very little improvement for a forecast with long horizon times. We also examine predictions for disturbed and quiet geomagnetic activity conditions. Our results show that the paucity of historical measurements of the solar wind for high Kp results in a lower accuracy of predictions during disturbed conditions. Rebalancing of input data can help tailor the predictions for more disturbed conditions.

Description: ABSTRACT Ion‐microprobe 206Pb/238U geochronology and trace element geochemistry of the unpolished rims and sectioned interiors of zircons from Yellowstone caldera's oldest post‐caldera lavas provide insight into the magmatic system during the prelude and aftermath of the caldera‐forming Lava Creek supereruption. The post‐caldera lavas compose the Upper Basin Member of the Plateau Rhyolite, and fall into two groups based on zircon crystallization age: early lavas with zircon ages between ~750‐550 ka and late lavas with zircon ages between ~350‐250 ka. Zircons from the early‐erupted East Biscuit Basin flow yield U‐Pb dates and trace element compositions, which when considered with the Pb isotopic compositions of their coexisting feldspars and pyroxenes, point to an isotopically distinct parental melt present during crystallization of the Lava Creek magma but untapped by the supereruption. Distinct zircon crystallization ages and Pb‐isotope compositions of major minerals between the early and late Upper Basin Member groups suggest contrasting sources in the magma reservoir. As proxies for melt evolution, the zircons indicate that Yellowstone's post‐caldera rhyolites became more evolved between mid‐ to late‐Pleistocene time, during the same interval that melting of hydrothermally‐altered wall rock and recharge by new silicic magmas changed in their relative roles. The results from this study indicate that discrete and ephemeral bodies of silicic magma, at times within a mush dominated reservoir and including during the prelude to the Lava Creek eruption, have characterized Yellowstone's subvolcanic reservoir.

Description: Abstract Studying offshore slow‐slip events (SSEs) along subduction zone interfaces is important for constraining the overall slip budget and potential for seismic slip, and the relationship with large megathrust earthquakes. Models using only onshore data increasingly lack model resolution the further from the shore the SSE occurs. In this study, we combine data from the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS) seafloor absolute pressure gauge (APG) network with daily position timeseries from New Zealand's GeoNet to create time‐dependent models of slip during the 2014 Gisborne, New Zealand SSE using the Network Inversion Filter (NIF). We compare models assuming heterogeneous vs. homogenous elastic properties to explore their influence on our models. The time‐dependent results show that slip uncertainties under the APGs drop by about 23%. We also find that the peak value of slip increases with heterogeneous elastic properties as compared to homogenous models. The inclusion of the offshore APG data in our models places more slip near the trench and detects a more defined migration of slip, especially in the heterogeneous model. These differences are important for interpreting the relationship between the SSE and associated tremor, which occurs after the peak SSE slip‐rate. Additionally, we use a static “potency bounding” technique in order to gauge the range of models that can fit the data. This analysis demonstrates that the inclusion of offshore data helps to substantially narrow the range of plausible slip models.

Description: Abstract For ~82 million years, the Hawaiian‐Emperor chain volcanoes have sampled the Pacific mantle via the Hawaiian mantle plume, providing evidence that its composition varies on a range of temporal and spatial scales. Hawaiian volcanoes from 0 to 2 Ma are divided into southwestern (Loa) and northeastern (Kea) geographic and geochemical trends that are interpreted to reflect the bilateral chemical structure of the underlying plume and its corresponding deep mantle sources. Older Hawaiian volcanoes that formed between 8 and 3 Ma record a geochemical transition between the Kea‐dominated Northwest Hawaiian Ridge (8 to 49 Ma) and the bilateral trends of the younger Hawaiian Islands. High‐precision Pb isotopic analyses conducted on 55 new shield‐stage samples from two of these key volcanoes, Kauaʻi and Waiʻanae, show that Loa‐like Pb isotopic ratios (e.g., elevated 208Pb*/206Pb*) gradually increase with decreasing age among the northern Hawaiian volcanoes and dominate for over two million years prior to the onset of the bilateral Loa and Kea geochemical trends. Distinct isotopic groups are observed across Kauaʻi and the distribution of Loa and Kea isotopic compositions is rotated relative to that observed on the younger Hawaiian Islands. Protracted Loa compositions and the atypical Loa‐Kea trend on Kauaʻi are accounted for by: 1) the arrival of a voluminous, Loa mantle heterogeneity possibly associated with anchoring of the Hawaiian plume to the Pacific Large Low Shear Velocity Province, and 2) a different orientation of the Pacific plate relative to the Loa‐Kea compositional boundary prior to 2 Ma.

Description: Abstract Analysis is made of low‐latitude ground‐based magnetometer data recording the magnetic superstorm of May 1921. By inference, the storm was driven by a series of interplanetary coronal mass ejections, one of which produced a maximum pressure on the magnetopause of ~64.5 nPa, sufficient to compress the subsolar magnetopause radius to ~5.3 Earth radii. Over the course of the storm, low‐latitude geomagnetic disturbance exhibited extreme local‐time (longitude) asymmetry that can be attributed to substorm disturbance extending to low latitudes. The storm attained an estimated maximum ‐Dst on May 15 of 907 nT ±132 nT, an intensity comparable to that of the Carrington event of 1859. The May 1921 storm interfered with and damaged telephone and telegraph systems associated with railroad systems in New York City and State. These effects were due to a combination of three factors: the localized details of geomagnetic vector disturbance, the geographic expression of the Earth's surface impedance tensor, and the configurations and physical parameters of the electrical networks of the day.

Description: No abstract is available for this article.

Description: Abstract Experiments have been conducted in which CO2 gases with varying C and O isotopic compositions and with stochastic and non‐stochastic Δ47 values have been allowed to equilibrate with phosphoric acid of two concentrations in reaction vessels of varying dimensions at temperatures of 25 and 90oC. Rates of 13C18O and 18O exchange between the CO2 and the phosphoric acid varied as a function of the length of exposure, volume of reaction vessel, acid strength, and difference of the initial Δ47 and δ18O values of the CO2 from theoretical equilibrium values. The Δ47 values were also altered by heated stainless steel surfaces such as those found within the Kiel Device and other preparation systems. These results have been used to explain variations in the differences in the fractionation between 25 and 90oC reported for calcite by different workers as well as differences in the slopes between temperature and Δ47 values produced by reacting samples at different temperatures (25 and 90oC).

Description: Abstract The Louisville Seamounts display age progressive volcanism and are thought to have formed as the Pacific plate moved over a long‐lived primary hotspot. Here we present 70 new 40Ar/39Ar age results from the Integrated Ocean Drilling Program (IODP) Sites U1372, U1375, U1376 and U1377 drilled and cored during Expedition 330 to the northern, older end of the Louisville Seamounts. The five seamounts drilled are flat‐topped guyots with ages ranging from ∼74 Ma (Canopus Guyot) to ∼51 Ma (Hadar Guyot) recovering up to ∼510 m of basaltic material beneath thin sediment interfaces. Our 40Ar/39Ar measurements reveal that throughout each drill hole most dates are constant within ∼500‐900 kyr at the 2σ confidence interval. In this study we use the new Louisville age information to compare against the Hawaiian‐Emperor trail on the Pacific Plate. The Louisville hotspot trail is low volume, dominantly alkali basalt, and seamounts have a relatively short lifespan up to ∼4 Myr, whereas the Hawaiian hotspot trail is high volume, has a tholeiitic shield‐building stage capped by an alkalic post‐shield stage, and have a lifespan up to ∼6‐7 Myr. Here we show a new approach to estimating a seamount's inception age based on the known cumulative age distributions for seamounts in the Louisville and Hawaii‐Emperor seamount trails. Based on our new 40Ar/39Ar analyses we conclude that existing absolute plate motion models misrepresent the age progression of Louisville seamounts and that the timing of the Hawaiian‐Emperor Bend and the 169°W bend in the Louisville seamounts are asynchronous by ~3.7 Myr.

Description: Abstract Introduction of new navigation signals L2C (1227.60 MHz) and L5 (1176.45 MHz) to the existing GPS (Global Positioning System) spectrum, under the modernization program of GPS offers the improvement of position accuracy. The present study aims to understand the relative robustness of the L2C and L5 signals compared to legacy L1 C/A signal during periods of scintillations in terms of durations of cycle slips encountered from an anomaly crest location, Calcutta (22.58°N, 88.38°E geographic; magnetic dip 32°N). The data analyzed in this study were recorded during the vernal equinox of 2014 (February–April), a period of high solar activity of cycle 24. Results obtained from the comparative analyses, which are perhaps one of the first from the Indian longitude sector, indicate GPS L5 to be more robust than L1 C/A and L2C in terms of occurrence and duration of cycle slips under adverse ionospheric conditions. Furthermore, loss‐of‐lock events of duration greater than 6 s are found to be more frequent for S4 ≥ 0.6. It is found that frequency sensitivity of the GPS spectrum, in terms of occurrence of cycle slips and loss of locks are in conformity with earlier results from the equatorial region but are different from the high latitudes with respect to local time of occurrence and geomagnetic activity.

Description: Abstract Between 7‐8 September 2017, Earth experienced extreme space weather events. We have combined measurements made by the IMAGE magnetometer array, ionospheric equivalent currents, GIC recordings in the Finnish natural gas pipeline, and multiple ground conductivity models to study the Fennoscandia ground effects. This unique analysis has revealed multiple interesting physical and technical insights. We show that although the 7‐8 September event was significant by global indices (Dst~150 nT), it produced an unexpectedly large peak GIC. It is intriguing that our peak GIC did not occur during the intervals of largest geomagnetic depressions, nor was there any clear upstream trigger. Another important insight into this event is that unusually large and rare GIC amplitudes (〉10 A) occurred in multiple MLT sectors and could be associated with westward and eastward electrojets. We were also successfully able to model the geoelectric field and GIC using multiple models, thus providing a further important validation of these models for an extreme event. A key result from our multiple conductivity model comparison was the good agreement between the temporal features of 1D and 3D model results. This provides an important justification for past and future uses of 1D models at Mäntsälä which is highly relevant to additional uses of this dataset. Although the temporal agreement (after scaling) was good, we found a large (factor of 4) difference in the amplitudes between local and global ground models due to the difference in model conductivities. Thus, going forward, obtaining accurate ground conductivity values are key for GIC modeling.

Description: Abstract We present three solar wind shock events that all occurred at times when Advanced Composition Explorer was near L1 and WIND was in front of the bow shock. We use a 1.5‐D MHD (magnetohydrodynamic) numerical model and the well known MVAB‐0 time‐shifting algorithm to propagate these events from Advanced Composition Explorer to the location of WIND. The results of these two methods are compared to WIND observations. We find that the 1.5‐D numerical model reproduces some important features in the WIND data that are not reflected in the time‐shifted results. We believe that 1.5‐D numerical simulations could supplement traditional time‐shifting methods in some circumstances for time‐shifting solar wind data to the bow shock.

Description: Abstract During the intense solar radio bursts on 6 September 2017, Global Navigation Satellite Systems (GNSS) signal interferences were observed at ground stations in the European longitude sector from 20°N to 70°N for all GNSS satellites in view including GPS, GLONASS, and Galileo. The solar radio noise reduced the signal‐to‐noise ratio with clear frequency dependence. The impact of the radio burst has been found at L2 and L5 frequencies, but not at L1 frequency. The ground observation of the solar radio spectrum between 1.0 and 2.0 GHz corresponds well to such frequency dependence. The maximum signal‐to‐noise ratio reduction of ‐10 dB was found when the solar radio flux was pulsating around 2,000 solar flux unit level. Precise point positioning results show that accuracy is reduced with stronger deviation for dual‐frequency solutions than for single‐frequency solutions based on L1 signal only. The positioning error refers rather to the solar extreme ultraviolet flare than to solar radio interferences. The results presented here are a clear indication of frequency‐dependent GNSS performance degradation during strong space weather events.

Description: Abstract We used data for eight magnetospheric spacecraft providing magnetic observations in various magnetospheric domains during a six‐day time period, including the June 2015 storm, and a five‐day period including the March 2015 storm. For these time intervals, containing different solar wind regimes and different activity levels, we used three types of metrics to compare predictions of all existing types of magnetospheric magnetic field models, including empirical models (TA15, TS05, and T96), a data‐adapted model (AM03), and a global magnetohydrodynamic model (Space Weather Modeling Framework/Block Adaptive Tree Solar Wind–Roe–Upwind Scheme coupled with Rice Convection Model). In total, the models are ranked in the order: AM03, TS05, TA15, Space Weather Modeling Framework, and T96. The regional scores may differ from the average ones (in particular, better scores are obtained at GEO, compared to the inner magnetosphere) and also the model effectiveness varies with activity conditions (for example, TA15 outperforms other models in quiet conditions, but TS05 leads during active times). Quite unexpectedly, although run at modest resolution, the community available global magnetohydrodynamic model closely approached the best scores of empirical statistical models during the moderate/high disturbed periods in the June event, suggesting that this kind of modeling may now compete with other type models. We also carried out the field line mapping from fixed points in the equatorial magnetosphere to the ionosphere, using different models to examine the storm time foot point excursions (which may be as large as ~10° CGLat during storm time sudden commencements) and their uncertainties, quantified by the difference between the model predictions.

Description: Abstract In this study, Global Ionosphere Specification (GIS) based on Gauss‐Markov Kalman filter assimilation of slant total electron content observed from ground‐based global positioning system receivers and space‐based radio occultation instrumentations is applied to investigate the ionospheric day‐to‐day tidal variability during the 2009 stratospheric sudden warming (SSW) period. Including the improved daily three‐dimensional global electron density distribution from GIS enables us to retrieve the daily solar tidal solution by using least squares tidal analysis. We find prominent reductions followed by enhancements in the amplitude of the solar semidiurnal migrating tide (SW2) after the peak warming, with recurrent phase variations occurring at low magnetic latitudes over a period of about 15 days. This is close to the beating period (15.13 day) between SW2 and lunar semidiurnal (M2), thus suggesting the existence of strong M2, and our results demonstrate that the intensification of M2 exists only during the SSW period. Additionally, M2 acts as the key contributor to make the semidiurnal ionospheric perturbations shift toward later local times. Our tidal analyses of daily GIS thus provide evidence for the combined impact of amplitudes and phases of the SW2 and M2 in producing semidiurnal variations in ionosphere during the 2009 SSW.

Description: Abstract In this study, the CHAMP (Challenging Minisatellite Payload satellite) and GRACE (Gravity Recovery and Climate Experiment satellite) observations and the simulations from the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model are used to investigate the impact of local time of satellite sampling on the dynamic modeling of the thermosphere. Thermosphere Ionosphere Electrodynamics General Circulation Mode simulations are sampled along the satellite orbits to obtain the synthetic observations and to reconstruct the global thermosphere. By comparing with the simulated “true” base, the relative deviations of the dynamic reconstructions are further characterized as a function of the local time of satellite sampling. It is found that the relative deviations would become relatively large when the satellite crosses the dawn‐dusk local time sectors. Our further investigation indicates that this spatial–temporal dependence would be greatly reduced, as the data from one more satellite are blended. The CHAMP and GRACE observations are also utilized to assess this local time dependence of the thermospheric forecasting.

Description: Abstract Surface charging by keV (kiloelectron Volt) electrons can pose a serious risk for satellites. There is a need for physical models with the correct and validated dynamical behavior. The 18.5‐month (2013–2015) output from the continuous operation online in real time as a nowcast of the Inner Magnetosphere Particle Transport and Acceleration Model (IMPTAM) is compared to the GOES 13 MAGnetospheric Electron Detector (MAGED) data for 40, 75, and 150 keV energies. The observed and modeled electron fluxes were organized by Magnetic Local Time (MLT) and IMPTAM driving parameters; the observed Interplanetary Magnetic Field (IMF) BZ, BY, and |B|; the solar wind speed VSW; the dynamic pressure PSW; and Kp and SYM‐H indices. The peaks for modeled fluxes are shifted toward midnight, but the ratio between the observed and modeled fluxes at around 06 MLT is close to 1. All the statistical patterns exhibit very similar features with the largest differences of about 1 order of magnitude at 18–24 MLT. Based on binary event analysis, 20–78% of threshold crossings are reproduced, but Heidke skill scores are low. The modeled fluxes are off by a factor of 2 in terms of the median symmetric accuracy. The direction of the error varies with energy: overprediction by 50% for 40 keV, overprediction by 2 for 75 keV, and underprediction by 18% for 150 keV. The revealed discrepancies are due to the boundary conditions developed for ions but used for electrons, absence of substorm effects, representations of electric and magnetic fields which can result in not enough adiabatic acceleration, and simple models for electron lifetimes.

Description: Abstract Space weather manifests in power networks as quasi‐DC currents flowing in and out of the power system through the grounded neutrals of high‐voltage transformers, referred to as geomagnetically induced currents. This paper presents a comparison of modeled geomagnetically induced currents, determined using geoelectric fields derived from four different impedance models employing different conductivity structures, with geomagnetically induced current measurements from within the power system of the eastern states of Australia. The four different impedance models are a uniform conductivity model (UC), one‐dimensional n‐layered conductivity models (NU and NW), and a three‐dimensional conductivity model of the Australian region (3DM) from which magnetotelluric impedance tensors are calculated. The modeled 3DM tensors show good agreement with measured magnetotelluric tensors obtained from recently released data from the Australian Lithospheric Architecture Magnetotelluric Project. The four different impedance models are applied to a network model for four geomagnetic storms of solar cycle 24 and compared with observations from up to eight different locations within the network. The models are assessed using several statistical performance parameters. For correlation values greater than 0.8 and amplitude scale factors less than 2, the 3DM model performs better than the simpler conductivity models. When considering the model performance parameter, P, the highest individual P value was for the 3DM model. The implications of the results are discussed in terms of the underlying geological structures and the power network electrical parameters.

Description: Abstract We review, summarize, and comment on the 2019 National Space Weather Strategy and Action Plan.

Description: Abstract Eric H. Strach (1914‐2011) studied medicine at University of Prague and graduated in 1938. Strach dedicated a great part of his life to astronomy becoming a consistent and meticulous observer. He joined the Liverpool Astronomical Association and British Astronomical Association during the 1960s and obtained two recognitions as proof of his great work in solar physics: the BAA's Merlin Medal and Gift in 1999 and Walter Goodacre Medal and Gift, 10 years later. Strach recorded four decades (1969‐2008) of systematic solar records in his observation notebooks although he started his observations from the late 1950s. In this work, we document the valuable effort made by Strach in getting four decades of solar records and the importance of this kind of long observation series for studies of space weather and climate. We present the sunspot group number series according to Strach's data and a long observation series of prominences recorded by Strach.

Description: Abstract An existing empirical model of the electron fluxes at geosynchronous orbit is extended radially outward in the equatorial plane to ~6–20 Earth radii (RE) using observations from the Research with Adaptive Particle Imaging Detectors (RAPID) instrument on the Cluster spacecraft. The new model provides electron flux predictions in the energy range ~45 eV to ~325 keV, as a function of local time and radial distance from the Earth, with geomagnetic activity parameterized by the Kp index. The model outputs include the mean and median electron fluxes along with the standard deviation and the 5th, 25th, 75th, and 95th percentiles for the given input conditions. The flux outputs from the model are tested against in‐sample observations from Cluster/RAPID and out‐of‐sample observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS)/Solid State Telescope with good prediction efficiency during quiet and active intervals, as quantified by standard methods. This new model is intended to supplement current predictive capabilities in the magnetosphere for spacecraft operations, as well as providing the necessary boundary and/or input conditions for computational/physical models of the magnetospheric system when the necessary in situ observations are unavailable. While the new model can certainly not reproduce the rapid small‐scale fluctuations inherent in spacecraft observations, it does provide a coarse capability to predict the flux of electrons close to the equatorial plane, based on radial distance, energy, local time, and geomagnetic activity, in regions where no in situ assets are available.

Description: Abstract Solar energetic protons (SEPs) can cause radiation damage to satellites. The Space Environment Prediction Center of China defines the start of a SEP event as the time when three consecutive instances of the 5‐min‐averaged integral flux of 〉10 MeV protons equal or exceed the 10 proton flux unit threshold. In this study, we analyzed the 5‐min‐averaged soft X‐ray flux and the differential and integral proton flux obtained by the Geostationary Operational Environmental Satellites for the period from January 1990 to September 2017 and developed SEP prediction models and their products. The statistical models take one or two data products and the given thresholds as the predictor and predict whether a SEP event will occur or not in the next 24 hr. The quality of the forecast models was measured by comparing the model results against certain verification metrics. Our model taking the products of 5‐min‐averaged integral flux of 〉10 MeV protons and long wavelength of soft X‐ray flux as predictors can provide a probability of detection of 0.80 (152/190), a false alarm ratio of 0.26 (53/205), and an average warning time of 2.6 hr for the correctly predicted events. In addition, the model can provide a critical success index of 0.63, a Gilbert skill score of 0.62, and a Heidke skill score of 0.76.

Description: No abstract is available for this article.

Description: Abstract The Comprehensive Assessment of Models and Events using Library Tools (CAMEL) framework leverages existing Community Coordinated Modeling Center services: Run‐on‐Request postprocessing tools that generate model time series outputs and the new Community Coordinated Modeling Center Metadata Registry that describes simulation runs using Space Physics Archive Search and Extract metadata. The new CAMEL visualization tool compares the modeled time series with observational data and computes a suite of skill scores such as Prediction Efficiency, Root‐Mean‐Square Error, and Symmetric Signed Percentage Bias. Model‐data pairs used for skill calculations are obtained considering a user‐selected maximum difference between the time of observation and the nearest model output. The system renders available data for all locations and time periods selected using interactive visualizations that allow the user to zoom, pan, and pick data values along traces. Skill scores are reported for each selected event or aggregated over all events for all participating model runs. Separately, scores are reported for all locations (satellites or stations) and for each location individually. We are building on past experiences with model‐data comparisons of magnetosphere and ionosphere model outputs from GEM2008, GEM‐CEDAR Electrodynamics Thermosphere Ionosphere, and the SWPC Operational Space Weather Model challenges. The CAMEL visualization tool is demonstrated using three validation studies: (a) Wang‐Sheeley‐Arge heliosphere simulations compared against OMNI solar wind data, (b) ground magnetic perturbations from several magnetosphere and ionosphere electrodynamics models as observed by magnetometers, and (c) electron fluxes from several ring current simulations compared to Radiation Belt Storm Probes Helium Oxygen Proton Electron instrument measurements, integrated over different energy ranges.

Description: Abstract We present evidence that variability in the STEREO‐A Heliospheric Imager (HI) data is correlated with in situ solar wind speed estimates from WIND, STEREO‐A, and STEREO‐B. For 2008–2012, we compute the variability in HI differenced images in a plane‐of‐sky shell between 20 to 22.5 solar radii and, for a range of position angles, compare daily means of HI variability and in situ solar wind speed estimates. We show that the HI variability data and in situ solar wind speeds have similar temporal autocorrelation functions. Carrington rotation periodicities are well documented for in situ solar wind speeds, but, to our knowledge, this is the first time they have been presented in statistics computed from HI images. In situ solar wind speeds from STEREO‐A, STEREO‐B, and WIND are all are correlated with the HI variability, with a lag that varies in a manner consistent with the longitudinal separation of the in situ monitor and the HI instrument. Unlike many approaches to processing HI observations, our method requires no manual feature tracking; it is automated, is quick to compute, and does not suffer the subjective biases associated with manual classifications. These results suggest we could possibly estimate solar wind speeds in the low heliosphere directly from HI observations. This motivates further investigation, as this could be a significant asset to the space weather forecasting community; it might provide an independent observational constraint on heliospheric solar wind forecasts, through, for example, data assimilation. Finally, these results are another argument for the potential utility of including a HI on an operational space weather mission.

Description: Abstract We analyse the response of different ionospheric equivalent current modes to variations in the interplanetary magnetic field (IMF) components By and Bz. Each mode comprises a fixed spatial pattern whose amplitude varies in time, identified by a month‐by‐month empirical orthogonal function separation of surface measured magnetic field variance. Here we focus on four sets of modes that have been previously identified as DPY, DP2, NBZ and DP1. We derive the cross‐correlation function of each mode set with either IMF By or Bz for lags ranging from ‐10 to +600 mins with respect to the IMF state at the bow shock nose. For all four sets of modes, the average correlation can be reproduced by a sum of up to three linear responses to the IMF component, each centered on a different lag. These are interpreted as the statistical ionospheric responses to magnetopause merging (15‐20 mins lag) and magnetotail reconnection (60 mins lag), and to IMF persistence. Of the mode sets, NBZ and DPY are the most predictable from a given IMF component, with DP1 (the substorm component) the least predictable. The proportion of mode variability explained by the IMF increases for the longer lags, thought to indicate conductivity feedbacks from substorms. In summary, we confirm the postulated physical basis of these modes and quantify their multiple reconfiguration timescales.

Description: Abstract Taking advantage of the public Global Navigational Satellite Systems (GNSS) infrastructure in South America, an operational monitoring system for the total electron content (TEC) in the ionosphere has been developed. It incorporates data in near real time, from more than 90 GNSS satellites tracked by more than 200 ground stations. In turn, the system produces every 15 min a snapshot, that is a map, of the current state of the regional ionosphere, which is immediately available online. These maps could be employed, for example, to augment positioning with single‐frequency GNSS receivers. They could also be combined with similar products in order to obtain weighted and reliable regional TEC maps, even in near real time. Most importantly, these products could be employed as data input in space environment forecasting and nowcasting models, given their very short latency of just a few minutes. In order to assess the response of the whole system to severe geomagnetic disturbances, the performance of the whole monitoring system during an actual geomagnetic storm has been investigated. The results suggest that the near‐real‐time system should be quite capable to monitor the regional TEC at a high temporal rate even under such conditions.

Description: Abstract We report an extreme erosion of the plasmasphere arising from the September 2017 storm. The cold electron density is identified from the upper limit frequency of upper hybrid resonance waves observed by the Plasma Wave Experiment instrument onboard the Exploration of energization and Radiation in Geospace/Arase satellite. The electron density profiles reveal that the plasmasphere was severely eroded during the recovery phase of the storm and the plasmapause was located at L = 1.6–1.7 at 23 UT 8 September 2017. This is the first report of deep erosion of the plasmasphere (LPP 〈 2) with the in situ observation of the electron density. The degree of the severity is much more than what is expected from the relatively moderate value of the SYM‐H minimum (−146 nT). We attempt to find a possible explanation for the observed severe depletion by using both observational evidence and numerical simulations. Our results suggest that the middle latitude electric field had penetrated from the high‐latitude storm time convection for several hours. Such an unusually long‐lasting penetration event can cause this observed degree of severity.

Description: Abstract At geosynchronous Earth orbit, the radiation belt/ring current electron fluxes with energies up to several hundred kiloelectron volts can vary widely in magnetic local time (MLT). This study aims to develop Nonlinear AutoRegressive eXogenous models using system science techniques, which account for the spatial variation in MLT. This is difficult for system science techniques, since there is sparse data availability of the electron fluxes at different MLT. To solve this problem, the data are binned from Geostationary Operational Environmental Satellites (GOES) 13, 14, and 15 by MLT, and a separate Nonlinear AutoRegressive eXogenous model is deduced for each bin using solar wind variables as the inputs to the model. These models are then conjugated into one spatiotemporal forecast. The model performance statistics for each model varies in MLT with a prediction efficiency between 47% and 75% and a correlation coefficient between 51.3% and 78.9% for the period from 1 March 2013 to 31 December 2017.

Description: Abstract An analysis of noise attenuation during 80 solar flares between 2013 and 2017 was carried out at frequencies 8–20 MHz using 34 Super Dual Auroral Radar Network radars and the EKB ISTP SB RAS radar. The attenuation was determined on the basis of noise measurements performed by the radars during the intervals between transmitting periods. The location of the primary contributing ground sources of noise was found by consideration of the propagation paths of radar backscatter from the ground. The elevation angle for the ground echoes was determined through a new empirical model. It was used to determine the paths of the noise and the location of its source. The method was particularly well suited for daytime situations, which had to be limited for the most part to only two crossings through the D region. Knowing the radio path was used to determine an equivalent vertical propagation attenuation factor. The change in the noise during solar flares was correlated with solar radiation lines measured by GOES/XRS, GOES/EUVS, SDO/AIA, SDO/EVE, SOHO/SEM, and PROBA2/LYRA instruments. Radiation in the 1 to 8 Å and near 100 Å are shown to be primarily responsible for the increase in the radionoise absorption, and by inference, for an increase in the D and E region density. The data are also shown to be consistent with a radar frequency dependence having a power law with an exponent of −1.6. This study shows that a new data set can be made available to study D and E regions.

Description: Abstract We investigate how statistical properties of the rate of change R of the surface horizontal magnetic field in the United Kingdom differ during substorm expansion and recovery phases compared with other times. R is calculated from 1‐min magnetic field data from three INTERMAGNET observatories—Lerwick, Eskdalemuir, and Hartland and between 1996 and 2014—nearly two solar cycles. Substorm expansion and recovery phases are identified from the SuperMAG Lower index using the Substorm Onsets and Phases from Indices of the Electrojet method. The probability distribution of R is decomposed into categories of whether during substorm expansion and recovery phases, in enhanced convection intervals, or at other times. From this, we find that 54–56% of all extreme R values (defined as above the 99.97th percentile) occur during substorm expansion or recovery phases. By similarly decomposing the magnetic local time variation of the occurrence of large R values (〉99th percentile), we deduce that 21–25% of large R during substorm expansion and recovery phases are attributable to the Disturbance Polar (DP)1 magnetic perturbation caused by the substorm current wedge. This corresponds to 10–14% of all large R in the entire data set. These results, together with asymptotic trends in occurrence probabilities, may indicate the two‐cell DP2 magnetic perturbation caused by magnetospheric convection as the dominant source of hazardous R 〉 600 nT/min that is potentially damaging to the U.K. National Grid. Thus, further research is needed to understand and model DP2, its mesoscale turbulent structure, and substorm feedbacks in order that GIC impact on the National Grid may be better understood and predicted.

Description: Abstract Historically, gathering data on atmospheric radiation levels during solar particle events has been difficult, as there is little or no time warning of events. Being able to accurately quantify radiation levels within the atmosphere during solar events is of significance to the aviation industry, as described in the International Civil Aviation Organization's (ICAO) Space Weather manual. Particularly during a large ground‐level enhancement (GLE) where the ionizing dose to passengers and crew can exceed the recommended general public annual dose limits, set by the International Commission for Radiological Protection (Barlett, Beck, Bilski, Bottollier‐Depois, & Lindborg, 2004, https://doi.org/10.1093/rpd/nch232), in a single flight. The Smart Atmospheric Ionizing RAdiation (SAIRA) Monitoring Network is a new system of handheld radiation detectors that can be carried on aircraft to monitor and record atmospheric radiation levels. The system operates via citizen science volunteers, who record radiation data as they travel for normal purposes. Over 30 flights have been conducted with volunteers to demonstrate that a citizen science network is possible. Volunteers have used a new Android application to record and upload data to a central server to form a database of flight measurements. The demonstration has shown that there is a willingness in public volunteers to use radiation detectors and engage in science outreach. A fully developed system will ideally provide the capability to quantify radiation levels during a solar particle event or ground‐level enhancement and the data can be used by relevant organizations to minimize potential risks.

Description: Abstract Ciomadul is the youngest volcano in the Carpathian‐Pannonian Region, Eastern‐Central Europe, which last erupted 30 ka. This volcano is considered to be inactive, however, combined evidence from petrologic and magnetotelluric data, as well as seismic tomography studies, suggests the existence of a subvolcanic crystal mush with variable melt content. The volcanic area is characterized by high CO2 gas output rate, with a minimum of 8.7 × 103 t/year. We investigated 31 gas emissions at Ciomadul to constrain the origin of the volatiles. The δ13C–CO2 and 3He/4He compositions suggest the outgassing of a significant component of mantle‐derived fluids. The He isotope signature in the outgassing fluids (up to 3.10 Ra) is lower than the values in the peridotite xenoliths of the nearby alkaline basalt volcanic field (R/Ra 5.95 Ra ± 0.01), which are representative of a continental lithospheric mantle and significantly lower than MORB values. Considering the chemical characteristics of the Ciomadul dacite, including trace element and Sr–Nd and O isotope compositions, an upper crustal contamination is less probable, whereas the primary magmas could have been derived from an enriched mantle source. The low He isotopic ratios could indicate a strongly metasomatized mantle lithosphere. This could be due to infiltration of subduction‐related fluids and postmetasomatic ingrowth of radiogenic He. The metasomatic fluids are inferred to have contained subducted carbonate material resulting in a heavier carbon isotope composition (δ13C is in the range of −1.4‰ to −4.6‰) and an increase of CO2/3He ratio. Our study shows the magmatic contribution to the emitted gases.

Description: Abstract The Talamanca Cordillera in the Central America Arc (Costa Rica‐Panama) preserves the record of the geochemical evolution from an intraoceanic arc to a juvenile continental arc in an active subduction zone, making it a testbed to explore processes that resulted in juvenile continental crust formation and explore potential mechanisms of early continental crust generation. Here we present a comprehensive set of geochronological, geochemical, and petrological data from the Talamanca Cordillera that tracks the key turning point (12–8 Ma) from the evolution of an oceanic arc depleted in incompatible elements to a juvenile continent. Most plutonic rocks from this transition and postintrusive rocks share striking similarities with average upper continental crust and Archean tonalite, trondhjemite, and granodiorite. We complement these data with seismic studies across the arc. Seismic velocities within the Caribbean Plate (basement of the arc) show a relatively uniform lateral structure consistent with a thick mafic large igneous province. Comparisons of seismic velocity profiles in the middle and lower crust beneath the active arc and remnant Miocene arc suggest a transition toward more felsic compositions as the volcanic center migrated toward the location of the modern arc. Seismic velocities along the modern arc in Costa Rica compared with other active arcs and average continental crust suggest an intermediate composition beneath the active arc in Costa Rica closer to average crust. Our geochemical modeling and radiogenic isotopes systematics suggest that input components from melting of the subducting Galapagos hotspot tracks are required for this compositional change.

Description: Abstract Several recent studies have employed variations in the concentration and isotopic composition of molybdenum as tracers of igneous processes. In this study we present new Mo concentration and δ98/95Mo data on the peculiar subduction‐related potassic magmas of the Central‐Southern Italian peninsula; the leucite‐free (lamproite‐like) rocks of the Tuscan Magmatic Province and the leucite‐bearing rocks of Mt. Vesuvius. These rocks display exotic and distinctive geochemical and isotopic features due to differences in the lithology of the subducted material in their respective mantle sources. We examine the elemental and isotopic systematics of Mo in the context of these geochemical variations. The two different associations of magmas display significantly different Ce/Mo values but surprisingly similar δ98/95Mo values (0.10–0.26‰ for Vesuvius and 0.07–0.24‰ for Tuscan Magmatic Province), which are significantly heavier than typical mid‐ocean ridge basalts. While the δ98/95Mo implicate an isotopically heavy sedimentary component recycled into their respective mantle sources, the different Ce/Mo ratios reflect contrasting elemental fractionation during sediment melting related to the lithology and consequent residual mineralogy (sulfides vs. epidote) of the subducted sedimentary material undergoing melting (Ca poor vs. Ca rich). This indicates that the heavy Mo isotopic signature of these magmas is independent of the lithology of the recycled material, which instead controls the elemental fractionation of Mo.

Description: Abstract Magma transfer from the mantle to the crust in arcs is an important step in the global cycling of elements and volatiles from Earth's interior to the atmosphere. Arc intrusive rocks dominate the total magma mass budget over extrusive rocks. However, their total volume and rate of addition is still poorly constrained, especially in continental arcs. We present lateral (forearc to backarc) and depth‐dependent (volcanics to deep crust) magma volume additions and arc‐wide magma addition rates (MARs) calculated from three continental arc crustal sections preserving magma flare‐up periods. We observe an increase in volume addition with depth and less magma added in the forearc (~15%) and backarc (~10% to 30%) compared to the main arc. Crustal‐wide MARs for each section are remarkably similar and around 0.7–0.9 km3/km2/Ma. MARs can be used to estimate CO2 fluxes from continental arcs. With initial magma CO2 contents of 1.5 wt.%, global continental arc lengths, and MARs, we calculate changes in C (Mt/year) released from continental arcs since 750 Ma. Calculated present‐day global C fluxes are similar to values constrained by other methods. Throughout the Phanerozoic, assuming equal durations of flare‐up and lull magmatism, calculated continental CO2 flux rates vary between 4 and 18 Mt C/year with highest values in the Mesozoic. These fluxes are considered minima since the intake of mantle and/or crustal carbon is not considered. Magmatic episodicity in continental arcs and changes in arc thickness and width are critical to consider when calculating MARs through time.

Description: Abstract First‐order variations in sea level exhibit amplitudes of ∼200 m over periods that coincide with those of supercontinental cycles (∼300–500 Myr). Proposed mechanisms for this sea level change include processes that change the container volume of the ocean basins and the relative elevation of continents. Here we investigate how unbalanced rates of water exchange between Earth's surface and mantle interior, resulting from fluctuations in tectonic rates, can cause sea level changes. Previous modeling studies of subduction water fluxes suggest that the amount of water that reaches sub‐arc depths is well correlated with the velocity and age of the subducting plate. We use these models to calibrate a parameterization of the deep subduction water flux, which we together with a parameterization of mid‐ocean ridge outgassing, then apply to reconstructions of Earth's tectonic history. This allows us to estimate the global water fluxes between the oceans and mantle for the past 230 Myr and compute the associated sea level change. Our model suggests that a sea level drop of up to 130 m is possible over this period and that it was partly caused by the ∼150Ma rift pulse that opened the Atlantic and forced rapid subduction of old oceanic lithosphere. This indicates that deep water cycling may be one of the more important sea level changing mechanisms on supercontinental time scales and provides a more complete picture of the dynamic interplay between tectonics and sea level change.

Description: Abstract Micrometer‐scale maps of authigenic microstructures in submarine basaltic tuff from a 1979 Surtsey volcano, Iceland, drill core acquired 15 years after eruptions terminated describe the initial alteration of oceanic basalt in a low temperature hydrothermal system. An integrative investigative approach uses synchrotron source X‐ray microdiffraction (μXRD), microfluoresence (μXRF), micro‐computed tomography (μCT), and scanning transmission electron microscopy (S/TEM) coupled with Raman spectroscopy to create finely resolved spatial frameworks that record a continuum of alteration in glass and olivine. Micro‐analytical maps of vesicular and fractured lapilli in specimens from 157.1, 137.9, and 102.6 m depth, and borehole temperatures of 83, 93.9 and 141.3 °C measured in 1980, respectively, describe the production of nanocrystalline clay mineral, zeolites, and Al‐tobermorite in diverse microenvironments. Irregular alteration fronts at 157.1 m depth resemble microchannels associated with biological activity in older basalts. By contrast, linear microstructures with little resemblance to previously described alteration features have nanocrystalline clay mineral (nontronite) and zeolite (amicite) texture. The crystallographic preferred orientation rotates around an axis parallel to the linear feature. Raman spectra indicating degraded and poorly‐ordered carbonaceous matter of possible biological origin are associated with nanocrystalline clay mineral in a crystallographically‐oriented linear microstructure in altered olivine at 102.6 m and with sub‐circular nanoscale cavities in altered glass at 137.9 m depth. Although evidence for biotic processes is inconclusive, the integrated analyses describe the complex organization of previously unrecognized mineral texture in very young basalt. They provide a foundational mineralogical reference for longitudinal, time‐lapse characterizations of palagonitized basalt in oceanic environments.

Description: Abstract We present the observational and modeling study focused on the major factors determining the spatio‐temporal structure of the high‐latitude ionospheric plasma density enhancement – the tongue of ionization (TOI) structure – during the 2015 St. Patrick's Day geomagnetic storm. We use the Global Self‐consistent Model of the Thermosphere, Ionosphere, Protonosphere (GSM TIP model) to reproduce the plasma density distribution, and the results are compared with the observational data as deduced from the ground‐based GPS TEC and in situ plasma probe measurements at different altitudes. Both the simulation and observation results show that a large‐scale TOI‐like structure of enhanced plasma density extends from the dayside mid‐latitude region towards the central polar cap along the anti‐sunward cross‐polar convection flow. We reveal an important role of the clockwise convection cells rotation for the modification of TOI structure. According to model results during the storm main phase, the neutral thermospheric composition, particularly the “tongue” in n(N2) modifies the spatial structure of TOI in such a way that: (1) the near‐pole region of enhanced plasma density is shifted to the dusk side; (2) at F region heights, the TOI is split into the dusk and dawn branches. The signature of TOI in the topside ionosphere considerably differs from that in the F region because of a lesser influence of the neutral composition changes at higher altitudes. Model results revealed that at plasmaspheric heights, the TOI structure appears in both the dawn and dusk convection cells.

Description: Abstract In this paper, a procedure for updating the International Reference Ionosphere (IRI) model by means of assimilated vertical total electron content (vTEC) measurements from a Global Navigational Satellite Systems (GNSS) receiver network is presented. This procedure stands as an additional implementation of the IRI UPdate (IRI UP) method which is based on the assimilation of ionosonde derived F2 layer ionospheric characteristics. According to this, a mathematical procedure for obtaining foF2 and M(3000)F2 values from vTEC measurements is here proposed. Mathematical relationships between F2 layer characteristics and vTEC values have been derived using South‐African co‐located ionosonde and GNSS stations. The same procedure can however be applied successfully in each region where such data are available. The goodness of the proposed IRI UP method, based on assimilated vTEC values, has been tested for several quiet and disturbed days in 2017 and 2018. IRI UP exhibits better performances than IRI for foF2, for most of the analyzed cases. Slight improvements are achieved in modeling hmF2 only for very disturbed periods in 2017. Due to the very good coverage of the terrestrial surface that GNSS receivers have achieved in recent years, we suggest that the method proposed here can be a good implementation of the IRI model for Space Weather nowcasting purposes, at least for foF2.

Description: Abstract For the purpose of building a regional (bound 20°‐60° N in latitude and 110°‐160° E in longitude) ionospheric now‐cast model, we investigated the performance of IDA4D (Ionospheric Data Assimilation Four‐Dimension) technique considering IRI (International Reference Ionosphere) model as the background. The data utilized in assimilation were slant total electron content (STEC) from twenty‐seven ground GPS (Global Positioning System) receiver stations, and NmF2 (ionospheric F2 peak density) from five ionosondes and COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) Data Analysis Archive Center. The period analyzed covered both geomagnetic quiet and disturbed days (15‐18 March, 2015). Assimilations were run under the following data combinations (cases): (1) GPS‐STEC's only; (2) GPS‐STEC's and NmF2's from five ionosondes; (3) only NmF2's from five ionosondes; and (4) GPS‐STEC's and NmF2's from both five ionosondes and COSMIC. Results showed that under case 1 the root‐mean‐square error (RMSE) in STEC reduced by 44% over the background IRI values, and on averaged over all ionosonde stations in the analysis RMSE values of foF2 (F2‐layer critical frequency) reduced by 21%. Furthermore, foF2 RMSE values under case 2 were 36% smaller than those under case 1. Under case 4, IDA4D performance improved even further in areas not covered by GPS and ionosonde measurements. Therefore, IDA4D is a potential candidate for regional ionosphere modeling that exhibits improved performance with assimilation of different data types.

Description: Abstract A certain type of deep‐sea sediment exhibits very high content of rare‐earth elements and yttrium (REY) and is therefore expected to serve as a novel resource for these industrially essential metals. In this paper, we statistically analyzed the bulk chemical composition of deep‐sea sediments collected from the western North Pacific Ocean. By applying independent component analysis (ICA) to the multi‐elemental dataset, we extracted three independent components (ICs) that can be interpreted as the influence of Mn‐oxides (IC1), REY‐enriched biogenic calcium phosphate (BCP) (IC2), and possibly a diagenetic effect involving Cu‐enrichment (IC3) on bulk sediment geochemistry. Subsequently, we selected representative samples based on the ICA result, and implemented Sr–Nd–Pb isotopic analyses of bulk sediments. The results indicate that the extremely REY‐rich mud characterized by IC2 inherits the geochemical signature of deep Pacific seawater, whereas the non‐REY‐rich mud with less diagenetic alterations, characterized by IC3, implies an influence of terrigenous dust probably from the Taklimakan Desert–Chinese loess plateau. IC1 may reflect the variation in sedimentation rates. Characteristic downhole variations of IC1 and IC3 scores imply the presence of hiatus and/or erosion of the sediment column across the REY content peak. The putative cause is an enhanced bottom current, which can physically separate coarse BCP grains with very high REY content and thus produce an extremely REY‐enriched sediment layer.

Description: Abstract Carbon dioxide draw‐down resulting from enhanced chemical weathering during orogenesis has been invoked to explain late Cenozoic global cooling. Establishing chemical weathering records from the India–Asia collision zone is important to test this hypothesis because uplift of the Tibetan Plateau is thought to be responsible for Cenozoic cooling. However, proxies for the intensity of chemical weathering can be affected by additional factors, such as sediment grain size and provenance. Here we report major element compositions and calculated chemical weathering intensity records of three size fractions (0–5, 5–20, 20–63 μm) from the Dahonggou section of the Qaidam Basin in the northeastern Tibetan Plateau, and compare those records with published provenance data from the same section. Results show that the indices of the fine (0–5 μm) fraction fractions vary in coordination with provenance shifts, but variations of the 5–20 μm and 20–63 μm fractions are less affected by provenance variations. Comparison with Upper Continental Crust reveals that some labile elements are not leached, but instead are enriched in the fine fraction, indicating that it do not faithfully record chemical weathering intensity. In addition, weathering can result in clay mineral transformation instead of elemental variations, complicating the relationship between element‐based parameters and weathering intensity. This work suggests that changes in sediment provenance must be accounted for when inferring variations in chemical weathering intensity on the basis of element‐based weathering intensity indices of the clay fraction.

Description: Abstract African basin‐and‐swell morphology is often attributed to the planform of sub‐plate mantle convection. Across North Africa, the coincidence of Neogene and Quaternary (i.e. 〈23 Ma) magmatism, topographic swells, long wavelength gravity anomalies, and slow shear wave velocity anomalies within the asthenosphere provides observational constraints for this hypothesis. Admittance analysis of topographic and gravity fields corroborates the existence of sub‐plate support. To investigate quantitative relationships between intraplate magmatism, shear wave velocity, and asthenospheric temperature, we collected and analyzed a suite of 224 lava samples from Tibesti, Jabal Eghei, Haruj, Sawda/Hasawinah and Gharyan volcanic centers of Libya and Chad. Forward and inverse modeling of major, trace, and Rare Earth elements were used for thermobarometric studies and to determine melt fraction as a function of depth. At each center, mafic magmatism is modeled by assuming adiabatic decompression of dry peridotite with asthenospheric potential temperatures of 1300–1360°C. Surprisingly, the highest temperatures are associated with the low‐lying Haruj volcanic center rather than with the more prominent Tibesti swell. Our results are consistent with earthquake tomographic models which show that the slowest shear wave anomalies within the upper mantle occur directly beneath the Haruj center. This inference is corroborated by converting observed velocities into potential temperatures, which are in good agreement with those determined by geochemical inverse modeling. Our results suggest that North African volcanic swells are primarily generated by thermal anomalies located beneath thinned lithosphere.

Description: Abstract The Yermak Plateau is one of several regions in the Arctic Ocean where paleomagnetism yields controversial results. Despite low sedimentation rates, late Pleistocene paleomagnetic excursions have been reconstructed from many cores in the region, but they are characterized by considerably longer durations when compared to established ones. Self‐reversal during maghemitization of (titano‐)magnetite has been proposed as one explanation. Rock magnetic, 14C dating, sedimentological and stable isotope (δ18O) methods were employed to three new sediment cores to put paleomagnetic results in the context of the regional stratigraphy and chronology. Coherence of lithological parameters and δ18O variations validated the ratio of anhysteretic remanent susceptibility to bulk magnetic susceptibility (κARM/κ) as a parameter for cross‐core correlation. As established by earlier studies, we use the link between glacial/interglacial cycles and κARM/κ to tune our records to a global δ18O stack, which provides age models that are independent of radicarbon ages and paleomagnetic data. Our results show that zones of negative magnetic inclination are asynchronous across the plateau. Alternating field demagnetization data revealed that negative inclinations are contained in a medium‐high coercivity (〉25‐35 mT) magnetic phase that may be the result of post‐depositional alteration of (titano‐)magnetite. We note a positive relationship between water depth and excursion duration, which may be driven by changes in water mass circulation on glacial/interglacial timescales.

Description: Abstract During the recovery of a magnetic storm, the relativistic electrons at MeV energy from the outer radiation belt will be enhanced at the geosynchronous orbit. In particular, the 〉2 MeV electrons could penetrate the surface of satellites and accumulate inside. After a long period, such an electron flux effect could cause satellites to be unable to function properly or to fail completely. Unlike previous prediction models of relativistic electrons focusing mainly on forecasting the daily value, we have developed an hourly prediction model to learn more detailed changes. In addition, due to external forcing by the solar wind, relativistic electron flux changes rapidly and is very non‐stationary during magnetic storms. We use the method of Empirical Mode Decomposition to reduce these effects. The result shows that the average prediction efficiency of hourly predictions of relativistic electrons from 2001 to 2006 is approximately 0.73. Moreover, we use this method to forecast daily fluence to validate Empirical Mode Decomposition. The prediction efficiency of daily fluence from 2001 to 2006 is 0.80, and for the period in which the relativistic electrons change particularly rapidly during 2001‐2004, the prediction efficiency is 0.79. Meanwhile, we compare with the prediction values without using Empirical Mode Decomposition. The result shows a great improvement using this method. Furthermore, it shows the non‐stationary nature of the electron flux time series has a great impact on the prediction of relativistic electrons.

Description: Abstract We have performed an extensive characterization by transmission electron microscopy (including precession electron diffraction tomography and ab initio electron diffraction refinement as well as electron energy loss spectroscopy) of anhydrous phase B (Anh‐B) formed directly from olivine at 14 GPa, 1400 °C. We show that Anh‐B, which can be considered as a superstructure of olivine, exhibits strong topotactic relationships with it. This lowers the interfacial energy between the two phases and the energy barrier for nucleation of Anh‐B which can form as a metastable phase. We have calculated the elastic and seismic properties of Anh‐B. From the elastic point of view, Anh‐B appears to be more isotropic than olivine. Anh‐B displays only a moderate seismic anisotropy quite similar to the one of wadsleyite.

Description: Abstract Slope‐gradient maps of swath bathymetry around the Hawaiian islands locate 12 shield slope breaks associated with former shorelines that are now submerged, ranging in age back to 5 Ma. The age of their drowning correlates with the waning of tholeiitic shield volcanism that ceases to repave the shoreline sometime between the beginning and the end of the late‐shield stage. Slope breaks on Mauna Loa's northeast and southwest rifts are consistent with it being in the waning stages of shield building. Superposition of shore breaks shows that the Hualālai shield is older than Mauna Kea's. We find evidence for three volcanic shields forming Ka‘ena Ridge, for a simultaneous waning of Maui‐Lāna‘i‐Kaho‘olawe shield building and the initiation of Kohala shield building by 1.3 Ma, and for Mahukona growing to just above sea level about 0.6 Ma. A contiguous shoreline slope break formed ~1.8 Ma at the end of the West Moloka‘i late‐shield stage and the beginning of the East Moloka‘i late‐shield stage. At its western end the shield dips obliquely away from, rather than toward, this slope break. Similarly, the short Hualālai slope break plunges north, which is opposite to that expected for volcanic loading to the south. Shields locally sloping away from paleo‐shorelines may be related to landslides causing flexural back‐tilting away from their unloaded footwall. The Nu‘uanu and Wailau slides and Pololū slump were mostly shield flank events that cut marginally into their former shorelines, enough to preferentially nucleate headward erosion by streams.