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The Gulf Coast province provides an array of scientific dilemmas ranging from the origin of the gulf itself to the causes and effects of long-lasting circulation of hot, deep waters throughout the thick sedimentary section. The nature of the underlying crust and superjacent sediments and their contained waters; the precise timing of rifting; depositional history and diagenesis of the sedimentary sequence; fluid dynamics; geochemistry; hydrocarbon generation and migration; thermal history, including unusually high thermal gradient; and the fluid pressure regime in the deep sedimentary section are too poorly understood to permit quantitative analysis of processes that are of enormous scientific and practical importance. The area centered on DeWitt and Victoria counties, Texas, on the southeastern extension of the San Marcos arch, is probably the best location for a deep borehole to investigate these important phenomena and problems. The arch extends southeastward from exposed Grenville-age basement rocks of the Llano uplift and separates the deep South Texas and Houston embayment salt basins. Seaward of the Llano uplift, highly deformed and slightly metamorphosed rocks of the Ouachita-Marathon orogen have been intersected beneath Cretaceous sediments. The inferred edge of continental crust underlies an extensive Lower Cretaceous reef trend southeast of known Ouachita orogen rocks. Rapid thickening of Tertiary and possibly of Cretaceous sediments southeast of the shelf edge, together with geophysical indications of a relatively shallow Moho, suggests that “transitional continental crust” underlies sediments basinward of the inferred edge of continental crust. This transitional crust, the ultimate objective for a proposed deep well, could be rifted Grenville basement, buried rocks of the Ouachita trend, an island arc related to the Ouachita trend, or exotic continental basement related to a proto-South American continent. To achieve optimum results to guarantee adequate basement penetration, a borehole should be designed to penetrate a relatively thin succession of lower Mesozoic synrift, graben-fill sediments seaward of the shelf edge. Because of expected high temperatures and pressures, new technologies will need to be developed to successfully drill and test the well.

The series of 12 papers that follows this brief introduction is part of the “New Views of the Moon” initiative started by NASA's Curation and Analysis Planning Team for Extraterrestrial Materials (CAPTEM) in 1998 [cf. Jolliff and Ryder, 1998]. This initiative strives to integrate the various facets of lunar investigations, such as remotely sensed surface data (e.g., spectral reflectance, gamma-ray, etc.), geophysics, sample analysis, and space weathering. The ensuing special section of 12 papers is the third that has been published in Journal of Geophysical Research (JGR)-Planets as part of this lunar science initiative and is the result of topical sessions at the 31st Lunar and Planetary Science Conference in 2000. The first, published in 2000 (JGR, 105 (E2), 4173–4368) [Jolliff, 2000], contained 11 papers as a result of the initial “New Views” workshop that was held in Houston in 1998 [Jolliff and Ryder, 1998].

In 1946 the great geologist R.A. Daly published an important paper in which he discussed a great many problems concerning the Moon and its features and origin. His paper was almost completely ignored by the scientists of the day and was “lost” for nearly half a century. The present paper marks an attempt to outline Daly's contributions to the interpretation of these lunar problems, in particular the origin of the Moon. One of the major ideas, which probably was the incentive for him to write the paper, was that the Moon was born as a result of a very early glancing collision of the Earth and a planet-sized body. Other subjects covered are the origin of the craters from Earth fragments, although meteoritic impact is also presented; the nature of the maria as lava from the body of the Moon; and origin of the lines of small craters as produced by gas escaping from the Moon. Daly rejected all non impact models for crater origin except for the tiny gas-made aligned pits. He vigorously stated that the Moon was largely created from the body of the Earth and discussed three methods by which this could be accomplished, one internal and two external, before settling on the glancing collision model. Daly clearly was the pioneer in presenting the impact model of the origin of the Moon. Much later, works by others have modified the hypothesis, but this is only natural evolution. Two other “lost” papers will be mentioned to show that this is an all too frequent occurrence. In 1893 Gilbert wrote a milestone paper that was generally unrecognized for more than 50 years. He espoused the impact theory of the origin of lunar basins and craters. He was wrong about the mechanism involved, but he was right about the impact idea. Similarly, Opik in 1916 showed that impact craters must be formed by explosions due to the high energies of striking meteorites. He showed that such impacts, even at low angles of fall would result in circular craters, thus correcting Gilbert, whom he did not mention. His paper also “disappeared” for many years. Early recognition and understanding of these three papers would have advanced lunar studies by many years.

This special issue of the Journal of Geophysical Research is remarkable in bringing together papers relating to the coupled ocean-atmosphere system, with emphasis on the western tropical Pacific region, and in doing so, temporarily reuniting the “Oceans” and the “Atmospheres” sections of the journal. In the western Pacific, the so-called “warm pool,” containing the world's warmest open ocean surface waters is found. Here vigorous and complex air-sea interactions are occurring on time scales ranging from intradiurnal to interannual, and on spatial scales ranging from a few kilometers (individual convective clouds), to the westerly wind burst which interacts with the ocean over thousands of kilometers, and to the 30- to 60-day oscillation, which is global in scale but which is most energetic in the warm-pool region. Understanding these interactions is extremely important for modeling and prediction of both short- and long-term climate variability [TOGA COARE Panel, 1990], since the deep convection over the warm pool provides the strongest heating source of the global upper troposphere.

The proposition that mid-plate (‘hot spot‘) magmatism is strongly discouraged by a combination of thick lithosphere and rapid plate motion is examined empirically on a global basis and found to be inadequate. Although hot spots perhaps tend to ‘avoid’ cratonic areas, the nonrandom worldwide distribution of hot spots appears primarily to reflect the state of the sublithospheric mantle. Plate thickness or speed is of lesser importance. The high level of African mid-plate volcanism since 25 m.y. B.P. appears to be part of a global pattern controlled by events in the mantle rather than a result of the Africa plate coming to rest over sublithospheric thermal sources about 40 m.y. B.P.

Historical notes. In 1893 the Norwegian explorer Fridtjof Nansen started on an Arctic Ocean expedition in his brand new wooden ship the Fram, which was to be allowed to freeze into the arctic ice pack and then hopefully to drift with her crew still aboard across the entire arctic basin. It was to be a test of Nansen's theory of a polar current and would allow numerous scientific observations to be made. It took the Fram 3 years finally to drift across the top of the world. She reached a latitude of 85° 57″N, a record not surpassed until the nuclear submarine Nautilus reached the north pole in 1958 by going under the arctic ice pack.

The papers in this special section were solicited at the IUTAM Symposium on Mixing in Stratified Fluids, held in Margaret River, Western Australia, from August 25 to 29, 1985. Each participant was invited to contribute a manuscript for the special section, and, as is seen in the following pages, we ended up with 18 contributions. Of these, four are reviews which should form a valuable long-term reference work. The aim of the symposium was to draw together progress in the general area of mixing in stratified fluids. In particular, it was perceived that there existed a need to bring together engineers, oceanographers, and fluid mechanicians in order to assess our ability to predict the vertical and horizontal fluxes of mass, momentum, and energy in a stratified fluid in a geophysical context. With this in mind the symposium was divided into four 1-day sessions. Each session covered a particular topic, and each topic was introduced by a general review of the subject.

Based on 1 year of data from the double-probe electric field instrument on Isee 1, a survey of occurrence of micropulsations near and inside the plasmapause has been made. The observed pulsations are classified as Pc 3 and Pi 2. In addition one single event of Pc 1 is observed. Pc 3 events are common during the local day, with a maximum percentage of occurrence as high as 72 in the morning hours. They occur on all frequencies in the Pc 3 band, but the most dominant frequencies are 30–50 mHz (20–33-s period), and the amplitudes range from 0.1 to 4–5 mV/m peak to peak. The strongest Pc 3 events are nearly linearly polarized. Based on the azimuth angle of the polarization, the orientation is usually either radial from the earth or east-west. The direction of rotation for the electric field vector is most often left-handed in the morning sector and right-handed in the afternoon sector. The Pi 2 events are concentrated on the local nightside. The amplitude for these pulsations is typically of the order of 2 mV/m peak to peak but can range as high as 20 mV/m peak to peak. These pulsation events are usually composed of several frequency components, with the dominant frequency most often in the band 10–16 mHz (62–100-s period).

Anthropogenic emissions of trichloromethane (CHCl3, chloroform) in 1990 have been estimated with a variety of methods specific to the source category. The largest source category for CHCl3 was found to be pulp and paper manufacturing, responsible for an estimated 30±8 Gg yr−1 reactive chlorine in the form of CHCl3. Water treatment of various types was estimated to contribute another 19±12 Gg. Manufacturing facilities of products other than pulp or paper and other relatively minor sources were estimated to emit an additional 13±5 Gg yr−1, for a total of 62±25 Gg yr−1 reactive chlorine in the form of CHCl3. The global flux of chlorodifluoromethane (HCFC-22) is well characterized from industrial and regulatory data to have been 195 Gg in 1990, equivalent to 80±0.6 Gg yr−1 as active chlorine. The fluxes of reactive chlorine from CHCl3 and HCFC-22, distributed globally in a 1° latitude times 1° longitude grid, revealed areas highest in emissions.

[1] This short paper contains a discussion on the use of Langley plots for Sun photometer and Brewer spectroradiometer calibration in the presence of a diurnal aerosol cycle. It is shown that with Langley plots alone, it is impossible to correctly identify or remove atmospheric variations having a 24-hour periodicity with an extreme at local noon. Therefore experimentalists must either be able to exclude such a periodicity using additional measurements, or approach different calibration techniques such as the approximation by linear sections.

Wood smoke in the atmosphere often accounts for 20–30% of the ambient fine-particle concentrations. In communities where wood is burned for home heating, wood smoke can at times contribute the majority of the atmospheric fine-particle burden. Chemical mass balance receptor models that use organic compounds as tracers can be used to determine the contributions of different emission sources, including wood smoke, to atmospheric fine-particle samples. In order for organic chemical tracer techniques to be applied to communities across the United States, differences in wood smoke composition that arise from differences in the type of wood burned in various regions must be understood. A continental-scale accounting of particulate organic compound emissions from residential wood combustion has been constructed which helps to quantify the regional differences in wood smoke composition that exist between different parts of the United States. Data from a series of source tests conducted on 22 North American wood species have been used to assemble a national inventory of emissions for more than 250 individual organic compounds that are released from wood combustion in fireplaces and wood stoves in the United States. The emission rates of important wood smoke markers, such as levoglucosan, certain substituted syringols and guaiacols, and phytosterols vary greatly with wood type and combustor type. These differences at the level of individual wood type and combustion conditions translate into regional differences in the aggregate composition of ambient wood smoke. By weighting the source test results in proportion to the availability of firewood from specific tree species and the quantities of wood burned in each locale, it is possible to investigate systematic differences that exist between wood smokes from different regions of North America. The relative abundance of 10 major wood smoke components averaged over the emissions inventory in different regions of the United States is computed and then used to illustrate the extent to which wood smoke composition differs from region to region in North America.

Author(s): Rutz, JJ; Shields, CA; Lora, JM; Payne, AE; Guan, B; Ullrich, P; O’Brien, T; Leung, LR; Ralph, FM; Wehner, M; Brands, S; Collow, A; Goldenson, N; Gorodetskaya, I; Griffith, H; Kashinath, K; Kawzenuk, B; Krishnan, H; Kurlin, V; Lavers, D; Magnusdottir, G; Mahoney, K; McClenny, E; Muszynski, G; Nguyen, PD; Prabhat, M; Qian, Y; Ramos, AM; Sarangi, C; Sellars, S; Shulgina, T; Tome, R; Waliser, D; Walton, D; Wick, G; Wilson, AM; Viale, M | Abstract: Atmospheric rivers (ARs) are now widely known for their association with high-impact weather events and long-term water supply in many regions. Researchers within the scientific community have developed numerous methods to identify and track of ARs—a necessary step for analyses on gridded data sets, and objective attribution of impacts to ARs. These different methods have been developed to answer specific research questions and hence use different criteria (e.g., geometry, threshold values of key variables, and time dependence). Furthermore, these methods are often employed using different reanalysis data sets, time periods, and regions of interest. The goal of the Atmospheric River Tracking Method Intercomparison Project (ARTMIP) is to understand and quantify uncertainties in AR science that arise due to differences in these methods. This paper presents results for key AR-related metrics based on 20+ different AR identification and tracking methods applied to Modern-Era Retrospective Analysis for Research and Applications Version 2 reanalysis data from January 1980 through June 2017. We show that AR frequency, duration, and seasonality exhibit a wide range of results, while the meridional distribution of these metrics along selected coastal (but not interior) transects are quite similar across methods. Furthermore, methods are grouped into criteria-based clusters, within which the range of results is reduced. AR case studies and an evaluation of individual method deviation from an all-method mean highlight advantages/disadvantages of certain approaches. For example, methods with less (more) restrictive criteria identify more (less) ARs and AR-related impacts. Finally, this paper concludes with a discussion and recommendations for those conducting AR-related research to consider.

Over the past 3–4 decades, coincident with global warming and atmospheric CO2 increase, Arctic sea ice has significantly decreased in its extent as well as in thickness. When extrapolating this alarming trend, the central Arctic Ocean might become ice-free during summers within about the next 2–5 decades. Paleoclimate records allow us to better understand the processes controlling modern climate change and distinguish between natural and anthropogenic forcing. In this context, detailed studies of the earlier Earth history characterized by a much warmer global climate with elevated atmospheric CO2 concentrations are important. The main focus of this review paper is the long-term late Mesozoic-Cenozoic Arctic Ocean climate history from Greenhouse to Icehouse conditions, with special emphasis on Arctic sea ice history. Starting with some information on the Cretaceous Arctic Ocean climate, this paper will concentrate on selected results from Integrated Ocean Drilling Program (IODP) Expedition 302 (Arctic Ocean Coring Expedition (ACEX)), the first scientific drilling in the permanently ice-covered Arctic Ocean, dealing with the Cenozoic climate history. While these results from ACEX were unprecedented, key questions related to the Cenozoic Arctic climate history remain unanswered, largely due to the major mid-Cenozoic hiatus (if existing) and partly to the poor recovery of the ACEX record. Following-up ACEX and its cutting-edge science, a second scientific drilling on Lomonosov Ridge with a focus on the reconstruction of the continuous and complete Cenozoic Arctic Ocean climate history has currently been proposed and scheduled as IODP Expedition 377 for 2021.

Coronal Mass Ejections (CMEs) are the key drivers of strong to extreme space weather storms at the Earth that can have drastic consequences for technological systems in space and on ground. The ability of a CME to drive geomagnetic disturbances depends crucially on the magnetic structure of the embedded flux rope, which is thus essential to predict. The current capabilities in forecasting in advance (at least half a day before) the geoeffectiveness of a given CME is however severely hampered by the lack of remote-sensing measurements of the magnetic field in the corona and adequate tools to predict how CMEs deform, rotate, and deflect during their travel through the coronal and interplanetary space as they interact with the ambient solar wind and other CMEs. These problems can lead not only to overestimation or underestimation of the severity of a storm, but also to forecasting "misses" and "false alarms" that are particularly difficult for the end-users. In this paper, we discuss the current status and future challenges and prospects related to forecasting of the magnetic structure and orientation of CMEs. We focus both on observational- and modeling-based (first principle and semiempirical) approaches and discuss the space- and ground-based observations that would be the most optimal for making accurate space weather predictions. We also cover the gaps in our current understanding related to the formation and eruption of the CME flux rope and physical processes that govern its evolution in the variable ambient solar wind background that complicate the forecasting. Plain Language Summary Coronal Mass Ejections (CMEs) are gigantic magnetized plasma clouds that are frequently expelled from the Sun. Practically all strong and extreme space weather disturbances in the near-Earth space environment are caused by CMEs that propagate in a few days from the Sun to the Earth. Space weather disturbances are related to various harmful effects to modern technology both in space and on ground which can lead to substantial economic losses. Forecasting the CME properties at least half a day before their impact on Earth is thus essential for our society. Our ability to provide accurate predictions of space weather consequences of CMEs is however currently quite modest. The key challenges are related to observational and modeling limitations, and complex evolution CMEs may experience as they propagate from Sun to Earth. This paper discusses the current status and future prospect in forecasting key CME properties using both observations and simulations.

Terrestrial gamma ray flashes (TGFs) are sub‐millisecond bursts of high energetic gamma radiation associated with intracloud flashes in thunderstorms. In this paper we use the simultaneity of lightning detections by World Wide Lightning Location Network to find TGFs in the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) data that are too faint to be identified by standard search algorithms. A similar approach has been used in an earlier paper, but here we expand the data set to include all years of RHESSI + World Wide Lightning Location Network data and show that there is a population of observationally weak TGFs all the way down to 0.22 of the RHESSI detection threshold (three counts in the detector). One should note that the majority of these are “normal” TGFs that are produced further away from the subsatellite point (and experience a 1/r 2 effect) or produced at higher latitudes with a lower tropoause and thus experience increased atmospheric attenuation. This supports the idea that the TGF production rate is higher than currently reported. We also show that compared to lightning flashes, TGFs are more partial to ocean and coastal regions than over land., Key Points We show that there is a fluence distribution of TGFs down to 0.22 of the detection threshold, and we do not see a cutoff in the RHESSI TGF distributionWe find that there are six times as many TGFs inside of RHESSI's field of view, than can be identified by current search algorithmsWe find that observationally weak TGFs largely originate at larger radial distances and higher latitudes from the subsatellite point

Solar energetic particles are one of the main sources of particle radiation seen in space. In the first part of September 2017 the most active solar period of cycle 24 produced four large X-class flares and a series of (interplanetary) coronal mass ejections, which gave rise to radiation storms seen over all energies and at the ground by neutron monitors. This paper presents comprehensive cross comparisons of in situ radiation detector data from near-Earth satellites to give an appraisal on the state of present data processing for monitors of such particles. Many of these data sets have been the target of previous cross calibrations, and this event with a hard spectrum provides the opportunity to validate these results. As a result of the excellent agreement found between these data sets and the use of neutron monitor data, this paper also presents an analytical expression for fluence spectrum for the event. Derived ionizing dose values have been computed to show that although there is a significant high-energy component, the event was not particularly concerning as regards dose effects in spacecraft electronics. Several sets of spacecraft data illustrating single event effects are presented showing a more significant impact in this regard. Such a hard event can penetrate thick shielding; human dose quantities measured inside the International Space Station and derived through modeling for aircraft altitudes are also presented. Lastly, simulation results of coronal mass ejection propagation through the heliosphere are presented along with data from Mars-orbiting spacecraft in addition to data from the Mars surface.

Paper 1 in this series (Lockwood et al., 2018a, https://doi.org/10.1029/2018SW001856) showed that the power input into the magnetosphere Pα is an ideal coupling function for predicting geomagnetic “range” indices that are strongly dependent on the substorm current wedge and that the optimum coupling exponent α is 0.44 for all averaging timescales, τ, between 1 min and 1 year. The present paper explores the implications of these results. It is shown that the form of the distribution of Pα at all averaging timescales τ is set by the interplanetary magnetic field orientation factor via the nature of solar wind‐magnetosphere coupling (due to magnetic reconnection in the dayside magnetopause) and that at τ = 3 hr (the timescale of geomagnetic range indices) the normalized Pα (divided by its annual mean, that is, τ=3hr/τ=1yr) follows a Weibull distribution with k of 1.0625 and λ of 1.0240. This applies to all years to a useful degree of accuracy. It is shown that exploiting the constancy of this distribution and using annual means to predict the full distribution gives the probability of space weather events in the largest 10% and 5% to within uncertainties of magnitude 10% and 12%, respectively, at the one sigma level.

The total solar eclipse over the continental United States on 21 August 2017 offered a unique opportunity to study the dependence of the ionospheric density and morphology on incident solar radiation at different local times. The Super Dual Auroral Radar Network (SuperDARN) radars in Christmas Valley, Oregon, and Fort Hays, Kansas, are located slightly southward of the line of totality; they both made measurements of the eclipsed ionosphere. The received power of backscattered signal decreases during the eclipse, and the slant ranges from the westward looking radar beams initially increase and then decrease after totality. The time scales over which these changes occur at each site differ significantly from one another. For Christmas Valley the propagation changes are fairly symmetric in time, with the largest slant ranges and smallest power return occurring coincident with the closest approach of totality to the radar. The Fort Hays signature is less symmetric. In order to investigate the underlying processes governing the ionospheric eclipse response, we use a ray-tracing code to simulate SuperDARN data in conjunction with different eclipsed ionosphere models. In particular, we quantify the effect of the neutral wind velocity on the simulated data by testing the effect of adding/removing various neutral wind vector components. The results indicate that variations in meridional winds have a greater impact on the modeled ionospheric eclipse response than do variations in zonal winds. The geomagnetic field geometry and the line-of-sight angle from each site to the Sun appear to be important factors that influence the ionospheric eclipse response. National Aeronautics and Space Administration (NASA)National Aeronautics & Space Administration (NASA) [NNX17AH70G]; National Science Foundation (NSF)National Science Foundation (NSF) [AGS-1552188, AGS-1341925, AGS-1934997, AGS-1341918, AGS-1935110]; Virginia Space Grant Consortium (VSGC) 2015-2016 Undergraduate Research Fellowship; 2017-2018 VSGC Graduate Research Fellowship; 2018-2019 VSGC Graduate Research Fellowship Published version Funding for this research was provided by National Aeronautics and Space Administration (NASA) grant NASA #NNX17AH70G, National Science Foundation (NSF) grant NSF #AGS-1552188, a Virginia Space Grant Consortium (VSGC) 2015-2016 Undergraduate Research Fellowship, and 2017-2018 and 2018-2019 VSGC Graduate Research Fellowships. The ray tracing results presented in this paper were obtained using the HF propagation toolbox, PHaRLAP, created by Dr. Manuel Cervera, Defence Science and Technology Organisation, Australia(manuel.cervera@dsto.defence.gov.au). Funding for operations of U.S. SuperDARN radars is provided by NSF grants AGS-1341925 and AGS-1934997 (for Dartmouth College) and AGS-1341918 and AGS-1935110 (for Virginia Tech). Data analysis and visualizations in this paper were generated by employing several free open-source software packages including matplotlib (Hunter, 2007), iPython (Perez & Granger, 2007), SciPy (Virtanen et al., 2020), NumPy (van derWalt et al., 2011), and DaViTPy (Ribeiro et al., 2020), among others. Note that DaViTPy was depreciated upon the release of pyDARN (Schmidt et al., 2020) in May 2020, after the work presented in this paper was completed. Also, we acknowledge the contributions of New Jersey Institute of Technology Eclipse Team (especially Joshua Vega, Joshua Katz, and Nathaniel Frissell) to our initial development of supporting Matlab functions for the use of SAMI3 output files with PHaRLAP.

The mid Miocene represents an important target for paleoclimatic study because the atmospheric CO2 concentration ranged from near modern values to ∼800 ppm, while a large, dynamic Antarctic ice sheet was likely to have been present throughout much of this interval. In this special issue, Modestou et al. (2020) (doi.org/10.1029/2020PA003927) reconstruct deep ocean warmth based on the clumped isotopic composition of benthic foraminifera, a technique that allows the ice volume and thermal components of the benthic oxygen isotope stack to be separated. These data reveal a very warm deep ocean while simultaneously suggesting that continental ice volume may, at times, have been greater than today. Here, I review these results in the context of recent developments in geochemical proxies and ice sheet modeling, and explore how the presence of a large Miocene ice sheet could be reconciled with CO2 at least as high as present. More broadly, I argue that many of the 'paradoxes' that pepper the paleoclimate literature result as much from our imperfect understanding of the proxies, as from our understanding of the climate system. Robust proxies with a well‐understood mechanistic basis, as employed by Modestou et al. (2020), as well as advances in model‐data comparability usher in a new era of palaeoclimate research; an exciting future of untangling Earth's myriad past climate states awaits., Plain Language Summary: Reconstructing climate variation in Earth's geologic past informs us of the broad features of warm climates, which is relevant to preparing for climate change over the coming centuries. Moreover, these data can be compared to state‐of‐the‐art climate models, which provides a test of the degree to which our models can reproduce warm climate states. A paper recently published in this journal applies a new method in order to reconstruct the temperature of the deep ocean in the middle Miocene (between 17 and 12 million years ago), when the atmospheric CO2 concentration was naturally similar to or higher than it is today. Coupled with decades of previous study, these exciting results depict an unfamiliar world characterized by a warm deep ocean, and yet a large ice sheet was present on Antarctica. Both models and data agree that the Antarctic ice sheet in the Miocene was highly responsive to changes in the atmospheric CO2 concentration, a clear cause of concern in the context of ongoing anthropogenic climate change., Key Points: The importance of a paper by Modestou et al. (2020) is explained, which reports middle Miocene benthic foraminifera clumped isotope data. Ways in which a large Antarctic ice sheet can be reconciled with a warm deep ocean and moderately high CO2 are explored. More broadly, I argue that recent advances in proxy methodology are resulting in ever increasing confidence in paleoclimate reconstructions.

In this paper we report the first close, high-resolution observations of downward-directed terrestrial gamma-ray flashes (TGFs) detected by the large-area Telescope Array cosmic ray observatory, obtained in conjunction with broadband VHF interferometer and fast electric field change measurements of the parent discharge. The results show that the TGFs occur during strong initial breakdown pulses (IBPs) in the first few milliseconds of negative cloud-to-ground and low-altitude intracloud flashes, and that the IBPs are produced by a newly-identified streamer-based discharge process called fast negative breakdown. The observations indicate the relativistic runaway electron avalanches (RREAs) responsible for producing the TGFs are initiated by embedded spark-like transient conducting events (TCEs) within the fast streamer system, and potentially also by individual fast streamers themselves. The TCEs are inferred to be the cause of impulsive sub-pulses that are characteristic features of classic IBP sferics. Additional development of the avalanches would be facilitated by the enhanced electric field ahead of the advancing front of the fast negative breakdown. In addition to showing the nature of IBPs and their enigmatic sub-pulses, the observations also provide a possible explanation for the unsolved question of how the streamer to leader transition occurs during the initial negative breakdown, namely as a result of strong currents flowing in the final stage of successive IBPs, extending backward through both the IBP itself and the negative streamer breakdown preceding the IBP., Comment: Typo fixed and reference added. Manuscript is 36 pages. Supplemental Information is 42 pages. This paper is to be published in the Journal of Geophysical Research: Atmospheres. Online data repository: Open Science Framework DOI: 10.17605/OSF.IO/Z3XDA

We acknowledge and thank the Wind and ACE teams for the solar wind data and NASA GSFC's Space Physics Data Facility's CDAWeb service for data availability (https://cdaweb.gsfc.nasa.gov/index.html/). The results presented in the paper also rely on the SC list made available by the International Service on Rapid Magnetic Variations (https://www.obsebre.es/en/rapid) and published by the Observatorio de l'Ebre in association with the International Association of Geomagnetism and Aeronomy (IAGA) and the International Service of Geomagnetic Indices (ISGI). We thank the involved national institutes, the INTERMAGNET network and the ISGI. The authors would like to thank A. A. Samsonov for helpful discussions. This work has also used the interplanetary shock catalog compiled by Oliveira, Arel, et al. (2018), including those intervals identified Wang et al. (2010), and Dr. J. C. Kasper for the Wind (https://www.cfa.harvard.edu/shocks/wi_data/) and ACE data (https://www.cfa.harvard.edu/shocks/ac_master_data/), and also by the ACE team (https://www‐ssg.sr.unh.edu/mag/ace/ACElists/obs_list.html#shocks). It may be found in the supporting information of Oliveira, Arel, et al. (2018). A. W. S. and I. J. R. were supported by STFC Consolidated Grant ST/S000240/1 and NERC grants NE/P017150/1 and NE/V002724/1. C. F. was supported by the NERC Independent Research Fellowship NE/N014480/1 and STFC Consolidated Grant ST/S000240/1. D. M. O. was supported by NASA through grant HISFM18‐HIF (Heliophysics Innovation Fund). The analysis in this paper was performed using python, including the pandas (McKinney, 2010), numpy (van der Walt et al., 2011), scikit‐learn (Pedregosa et al., 2011), scipy (Virtanen et al., 2020) and matplotlib (Hunter, 2007) libraries. Detailed documentation for the models can be found at https://scikit‐learn.org/, while the specific implementations of the models used in this work are: sklearn.linear_model.LogisticRegression, sklearn.naive_bayes.GaussianNB, sklearn.gaussian_process.GaussianProcessClassifier, sklearn.ensemble.RandomForestClassifier. Funding Information: National Aeronautics and Space Administration (NASA). Grant Number: HISFM18‐HIF Natural Environment Research Council (NERC). Grant Numbers: NE/P017150/1, NE/V002724/1, NE/N014480/1 RCUK | Science and Technology Facilities Council (STFC). Grant Number: ST/S000240/1

The intercalibration between a broadband and a hyperspectral satellite Earth observation system requires the convolution of the hyperspectral data with the spectral response functions (SRFs) of the corresponding broadband channels. There are two potential issues associated with the convolution procedure. First, the finite resolution of a hyperspectral spectrum, that is, the deviation from the highly accurate line-by-line monochromatic radiances, will contribute to convolution errors. The magnitude of the errors depends on the spectral resolution and the SRF shape of the hyperspectral instrument. This type of the convolution error has not been well recognized, and there is a lack of corresponding discussion in most published papers. Although it is small as compared with the instrument accuracy of existing hyperspectral sounders, the error is deemed to be signicant when it is compared with the stringent calibration requirement imposed by future climate missions like the Climate Absolute Radiance and Refractivity Observatory (CLARREO). Second, some broadband channels are insufficiently covered by the hyperspectral data, causing spectral gaps that lead to convolution errors. Although several methods have been developed to fill the spectral gaps and hence compensate for the second type of convolution error, the correction accuracy may still need improvement especially when a large spectral gap needs to be lled. This paper presents a methodology to accurately quantify and compensate for both types of convolution errors. This methodology utilizes the available hyperspectral information to correct the scene-dependent convolution errors due to either the limited spectral resolution or spectral gaps. We use simulations to characterize the intercalibration errors between the Moderate resolution Imaging Spectroradiometer (MODIS) and current operational infrared sounders. We demonstrate that convolution errors can be effectively removed to meet the highly accurate intersatellite calibration requirement proposed by the Climate Absolute Radiance and Refractivity Observatory. Our methodology is also validated using real satellite data for the intercalibration between Aqua MODIS and Aqua Atmospheric Infrared Sounders (AIRS). Our study demonstrates that the accurate characterization and correction for the convolution errors greatly reduces the scene-dependent and spectrally dependent errors, being critical to the consistency check between Infrared Atmospheric Sounding Interferometer (IASI) and AIRS using the double-difference method. The convolution correction also facilitates the evaluation for other intercalibration errors (e.g., the drift of MODIS SRFs). Our derived SRF shift values from MODIS-AIRS (after convolution error corrections) and from MODIS-IASI intercalibration are consistent with each other. We further extend the methodology to study the calibration of a broadband channel which is either completely or largely uncovered bya hyperspectral measurement.The large spectral gap-filling methodology is validated by demonstrating the accurate prediction of the MODIS radiance of band 29 using the Cross-track Infrared Sounder spectra, with the real IASI spectral data being used as the reference.

A companion paper by Fritts et al. [2017a] employed an anelastic numerical model to explore the dynamics of gravity waves (GWs) encountering a mesospheric inversion layer (MIL) having a moderate static stability enhancement and a layer of weaker static stability above. That study revealed that MIL responses, including GW transmission, reflection, and instabilities, are sensitive functions of GW parameters. This paper expands on two of the Fritts et al. [2017a] simulations to examine GW instability dynamics and turbulence in the MIL, forcing of the mean wind and stability environments by GW, instability, and turbulence fluxes, and associated heat and momentum transports. These direct numerical simulations resolve turbulence inertial-range scales and yield the following results: GW breaking and turbulence in the MIL occur below where they would otherwise due to enhancements of GW amplitudes and shears in the MIL, 2D GW and instability heat and momentum fluxes are ~20-30 times larger than 3D instability and turbulence fluxes, mean fields are driven largely by 2D GW and instability dynamics rather than 3D instabilities and turbulence, 2D and 3D heat fluxes in regions of strong turbulence yield small departures from initial T(z) and N2(z) profiles, hence do not yield nearly adiabatic “mixed” layers, and our MIL results are consistent with the relation between the turbulent vertical velocity variance and energy dissipation rate proposed by Weinstock [1981] for the limited intervals evaluated.

This paper addresses whether geomagnetic activity challenged the reliability of the electric power system during part of the declining phase of solar cycle 23. Operations by National Grid in England and Wales are examined over the period of 11 March 2003 through 31 March 2005. This paper examines the relationship between measures of geomagnetic activity and a metric of challenged electric power reliability known as the net imbalance volume (NIV). Measured in megawatt hours, NIV represents the sum of all energy deployments initiated by the system operator to balance the electric power system. The relationship between geomagnetic activity and NIV is assessed using a multivariate econometric model. The model was estimated using half-hour settlement data over the period of 11 March 2003 through 31 December 2004. The results indicate that geomagnetic activity had a demonstrable effect on NIV over the sample period. Based on the parameter estimates, out-of-sample predictions of NIV were generated for each half hour over the period of 1 January to 31 March 2005. Consistent with the existence of a causal relationship between geomagnetic activity and the electricity market imbalance, the root-mean-square error of the out-of-sample predictions of NIV is smaller; that is, the predictions are more accurate, when the statistically significant estimated effects of geomagnetic activity are included as drivers in the predictions.

Single-column model simulations of mixed-phase altocumulus clouds were shown to have a strong vertical-resolution sensitivity in Part I of this paper. Coarse resolution models were unable to simulate the long-lived supercooled-liquid-layer at cloud top, typically only 200-m thick. In this paper, the sensitivity to vertical resolution is investigated using idealized simulations. Vertical gradients of ice water mixing ratio and temperature near cloud top are found to be inadequately represented at coarse-resolution. The vertical discretization using grid-box mean values, rather than the full vertical profile, leads to biased calculations of mixed-phase microphysical process rates and affects the diagnosis of thin liquid-water layers. As a result the liquid-water layer becomes quickly glaciated and altocumulus cloud lifetime is underestimated. Similar impacts are expected for mixed-phase boundary layer clouds commonly observed at high latitudes. A novel parameterization is introduced that accounts for the vertical gradients of ice water mixing ratio and temperature in the microphysics calculations and the diagnosis of liquid near cloud top. It substantially improves the representation of altocumulus layers in coarse vertical-resolution single-column model simulations and reduces the bias identified in Part I. The new parameterization removes the large underestimate in supercooled water content caused by the resolution sensitivity for temperatures warmer than −30∘C. Given the radiative importance of mixed-phase altocumulus clouds, their underestimation by numerical weather prediction models and their potential to act as a negative climate feedback, there is a need to re-evaluate the global climate sensitivity by implementing the findings in these two papers in a climate model.

The Global Navigation Satellite System (GNSS) beacon has been widely used in ionospheric monitoring. The Chinese Beidou Navigation Satellite System (BDS) started to operate in 2012, with three kinds of constellations: the medium Earth orbit (MEO), the inclined geosynchronous satellite orbit (IGSO) and the geosynchronous Earth orbit (GEO). A compact, portable and low power GNSS observation instrument which is named BG2 GNSS ionospheric monitor was developed at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). It is capable of tracking BDS, Global Positing System (GPS) and GLONASS signals with a sampling rate up to 5 Hz. To use the unique BDS GEO signals for ionospheric monitoring, the Beidou Ionospheric Observation Network (BION) utilizing the BG2 GNSS ionospheric monitor was established recently in China with a total of 31 sites. This paper describes the development of the GNSS ionospheric monitor, the construction of the network, data processing, and preliminary scientific research. As demonstrated in the following paper, the BDS GEO total electron content (TEC) data has shown unique value in some specific ionospheric studies due to the fact that it is not influenced by the mixed effect of spatial and temporal ionospheric variability as observed with other GNSS signals. As a part of the BION, the Septentrio PolaRx5s mutli-constellation GNSS ionospheric scintillation monitor will be installed at 14 observation sites at low latitude of China in the near future.

This paper is the primary deliverable of the very first NASA Living With a Star Institute Working Group, Geomagnetically Induced Currents (GIC) Working Group. The paper provides a broad overview of the current status and future challenges pertaining to the science, engineering, and applications of the GIC problem. Science is understood here as the basic space and Earth sciences research that allows improved understanding and physics-based modeling of the physical processes behind GIC. Engineering, in turn, is understood here as the “impact” aspect of GIC. Applications are understood as the models, tools, and activities that can provide actionable information to entities such as power systems operators for mitigating the effects of GIC and government agencies for managing any potential consequences from GIC impact to critical infrastructure. Applications can be considered the ultimate goal of our GIC work. In assessing the status of the field, we quantify the readiness of various applications in the mitigation context. We use the Applications Readiness Level (ARL) concept to carry out the quantification.

In this paper the contribution of turbulence into the electrification of thunderstorms, snowstorms, and dust storms is investigated for the first time. A model of large-scale electric field generation in a weakly conducting medium, containing two types of particles charging by collisions, is used. Thunderstorm and snowstorm electrification are considered in detail in this paper; dust storm electrification is also considered, despite being substantially different from the two other cases, to demonstrate the universality of the proposed method. A comparison of the results with the experimental data for thunderstorms, blizzards, and dust storms is carried out. It is found that the situation is notably different for inductive and noninductive charge separations. For inductive charge separation there is a range of thunderstorm and snowstorm parameters (conductivity and the particle radii being the most important factors) for which the electric field grows exponentially with time. This effect can make the inductive mechanism dominant near the breakdown field in turbulent zones of thunderclouds. For noninductive (or triboelectric) charge separation caused by intense velocity fluctuations, the electric field strength grows only linearly with time. The most substantial effect of turbulence on noninductive charging is expected to occur in snowstorms and dust storms, whereas noninductive turbulent charging has a little impact on the thunderstorm electrification.

Savanna fires contribute significantly to global aerosol loading and hence to the earth's radiative budget. Modelling of the climatic impact of these aerosols is made difficult due to a lack of knowledge of their size distribution. Australia is the third largest source of global carbon emissions from biomass burning, with emissions dominated by tropical savanna fires. Despite this, only a few previous studies have reported emission factors of trace gases from this important ecosystem and there are no previous published emission factors for the aerosol properties reported here for Australian savanna fires. In June 2014, the SAFIRED campaign (Savanna Fires in the Early Dry season) took place in the northern territory of Australia, with the purpose of investigating emissions and aging of aerosols from Australian savanna fires. This paper presents observed enhancement ratios and inferred emission factors of trace gases (CO2, CO, CH4, N2O and gaseous elemental mercury), particles over different size modes (Aitken and accumulation) and speciated aerosols components (organics, sulfate, nitrate, ammonium and chloride). Nine smoke events were identified from the data using large enhancements in CO and/or aerosol data to indicate biomass burning event. The results reported in this paper include the first emission factors for Aitken and accumulation mode aerosols from savanna fires, providing useful size information to enable better modelling of the climatic impact of this important source of global aerosols.

This paper describes space weather impacts to the satellite infrastructure as perceived by satellite industry stakeholders. The information was gathered through in-person and remote meetings with both satellite operators and manufacturers. The paper describes current impacts, industry processes for managing and mitigating impacts, costs, and industry needs and requirements. Lastly, we suggest potential improvements and solutions to problem areas based on our observation of the industry processes including 1) Improved tools for quick anomaly attribution, 2) Training, and 3) Coordinated information sharing.

During recent decades, the use of probabilistic forecasting methods has increased markedly. However, these predictions still need improvement in uncertainty quantification and predictability analysis. For this reason, the main aim of this paper is to develop tools for quantifying uncertainty and predictability of wind speed over the Iberian Peninsula. To achieve this goal, several spread indexes extracted from an ensemble prediction system are defined in this paper. Subsequently, these indexes were evaluated with the aim of selecting the most appropriate for the characterization of uncertainty associated to the forecasting. Selection is based on comparison of the average magnitude of ensemble spread (ES) and mean absolute percentage error (MAPE). MAPE is estimated by comparing the ensemble mean with wind speed values from different databases. Later, correlation between MAPE and ES was evaluated. Furthermore, probability distribution functions (PDFs) of spread indexes are analyzed to select the index with greater similarity to MAPE PDFs. Then, the spread index selected as optimal is used to carry out a spatiotemporal analysis of model uncertainty in wind forecasting. The results indicate that mountainous regions and the Mediterranean coast are characterized by strong uncertainty, and the spread increases more rapidly in areas affected by strong winds. Finally, a predictability index is proposed for obtaining a tool capable of providing information on whether the predictability is higher or lower than average. The applications developed may be useful in the forecasting of wind potential several days in advance, with substantial importance for estimating wind energy production.

The primary goal of this paper is to introduce two new surface reflectivity climatologies. The two databases contain the Lambertian-equivalent reflectivity (LER) of the Earth's surface, and they are meant to support satellite retrieval of trace gases and of cloud and aerosol information. The surface LER databases are derived from the Global Ozone Monitoring Experiment (GOME)-2 and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instruments and can be considered as improved and extended descendants of earlier surface LER climatologies based on the Total Ozone Mapping Spectrometer (TOMS), GOME-1, and Ozone Monitoring Instrument (OMI) instruments. The GOME-2 surface LER database consists of 21 wavelength bands that span the wavelength range from 335 to 772 nm. The SCIAMACHY surface LER database covers the wavelength range between 335 and 1670 nm in 29 wavelength bands. The two databases are made for each month of the year, and their spatial resolution is 1° × 1°. In this paper we present the methods that are used to derive the surface LER; we analyze the spatial and temporal behavior of the surface LER fields and study the amount of residual cloud contamination in the databases. For several surface types we analyze the spectral surface albedo and the seasonal variation. When compared to the existing surface LER databases, both databases are found to perform well. As an example of possible application of the databases we study the performance of the Fast Retrieval Scheme for Clouds from the Oxygen A-band (FRESCO) cloud information retrieval when it is equipped with the new surface albedo databases. We find considerable improvements. The databases introduced here can not only improve retrievals from GOME-2 and SCIAMACHY but also support those from other instruments, such as TROPOspheric Monitoring Instrument (TROPOMI), to be launched in 2017.

The paramo ecoregion of Ecuador contains extensive peatlands that are known to contain carbon (C) dense soils capable of long-term C storage. Although high-altitude mountain peatlands are typically small when compared to low altitude peatlands, they are abundant across the Andean landscape and are likely a key component in regional C cycling. Since efforts to quantify peatland distribution and C stocks across the tropical Andes have been limited due to the difficulty in sampling remote areas with very deep peat, there is a large knowledge gap in our quantification of the current C pools in the Andean mountains, which limits our ability to predict and monitor change from high rates of land use and climate change. In this paper we tested if ground penetrating radar (GPR), combined with manual coring and C analysis could be used for estimating C stocks in peatlands of the Ecuadorian paramo. Our results indicated that GPR was successful in quantifying peat depths and carbon stocks. Detection of volcanic horizons like tephra layers allowed further refinement of variability of C stocks within the peat column, while providing information on the lateral extent of tephras at high (cm scale) resolution that may prove very useful for the correlation of time-stratigraphic markers between sediments in alpine peatlands. In conclusion, this paper provides a methodological basis for quantifying C stocks in high altitude peatlands and to infer changes in the physical properties of soils that could be used as proxies for C content or paleoclimate reconstructions.

It has been discussed that lightning flashes emit high-energy electrons, positrons, photons, and neutrons with single energies of several tens of MeV. In the first part of this paper we study the absorption of neutron beams in the atmosphere. We initiate neutron beams of initial energies of 350 keV, 10 MeV, and 20 MeV at source altitudes of 4 km and 16 km upward and downward and see that in all these cases neutrons reach ground altitudes and that the cross-section areas extend to several km2. We estimate that for terrestrial gamma-ray flashes approximately between 10 and 2000 neutrons per ms and m2 are possibly detectable at ground, at 6 km, or at 500 km altitude. In the second part of the paper we discuss a feedback model involving the generation and motion of electrons, positrons, neutrons, protons, and photons close to the vicinity of lightning leaders. In contrast to other feedback models, we do not consider large-scale thundercloud fields but enhanced fields of lightning leaders. We launch different photon and electron beams upward at 4 km altitude. We present the spatial and energy distribution of leptons, hadrons, and photons after different times and see that leptons, hadrons, and photons with energies of at least 40 MeV are produced. Because of their high rest mass hadrons are measurable on a longer time scale than leptons and photons. The feedback mechanism together with the field enhancement by lightning leaders yields particle energies even above 40 MeV measurable at satellite altitudes.

Extreme space weather due to coronal mass ejections has the potential to cause considerable disruption to the global economy by damaging the transformers required to operate electricity transmission infrastructure. However, expert opinion is split between the potential outcome being one of a temporary regional blackout and of a more prolonged event. The temporary blackout scenario proposed by some is expected to last the length of the disturbance, with normal operations resuming after a couple of days. On the other hand, others have predicted widespread equipment damage with blackout scenarios lasting months. In this paper we explore the potential costs associated with failure in the electricity transmission infrastructure in the U.S. due to extreme space weather, focusing on daily economic loss. This provides insight into the direct and indirect economic consequences of how an extreme space weather event may affect domestic production, as well as other nations, via supply chain linkages. By exploring the sensitivity of the blackout zone, we show that on average the direct economic cost incurred from disruption to electricity represents only 49% of the total potential macroeconomic cost. Therefore, if indirect supply chain costs are not considered when undertaking cost-benefit analysis of space weather forecasting and mitigation investment, the total potential macroeconomic cost is not correctly represented. The paper contributes to our understanding of the economic impact of space weather, as well as making a number of key methodological contributions relevant for future work. Further economic impact assessment of this threat must consider multiday, multiregional events.

This paper describes the development of the United States National Space Weather Program (NSWP) from early interests in space environmental phenomena and their impact through the culmination of the program in 2015. Over its 21-year run, the NSWP facilitated substantial improvements in the capabilities of federal space weather services and fostered broad and enduring partnerships with industry and the academic community within the US and internationally. Under the management of the Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM) a coalition of ten federal agencies worked together from 1994 to 2015 to advance national space weather enterprise. The paper describes key events and accomplishments of the NSWP interagency partnership while recognizing the great achievements made by the individual agencies. In order to provide context, the paper also discusses several important events outside the NSWP purview. Some of these external events influenced the course of the NSWP, while others were encouraged by the NSWP partnership. Following the establishment of the Space Weather Operations, Research, and Mitigation Task Force of the National Science and Technology Council in the White House and the deactivation of the NSWP Council, the agencies now play a supporting role in the national effort as the Federal engagement in the National Space Weather Partnership graduates to a higher level.

Estimating the impact of radiation transport through cloud sides on the global energy budget is hampered by the lack of a fast radiation scheme suitable for use in global atmospheric models that can represent these effects in both the shortwave and longwave. This two-part paper describes the development of such a scheme, which we refer to as the Speedy Algorithm for Radiative Transfer through Cloud Sides (SPARTACUS). The principle of the method is to add extra terms to the two-stream equations to represent lateral transport between clear and cloudy regions, which vary in proportion to the length of cloud edge as a function of height. The present paper describes a robust and accurate method for solving the coupled system of equations in both the shortwave and longwave in terms of matrix exponentials. This solver has been coupled to a correlated-k model for gas absorption. We then confirm the accuracy of SPARTACUS by performing broadband comparisons with fully 3-D radiation calculations by the Monte Carlo model “MYSTIC” for a cumulus cloud field, examining particularly the percentage change in cloud radiative effect (CRE) when 3-D effects are introduced. In the shortwave, SPARTACUS correctly captures this change to CRE, which varies with solar zenith angle between −25% and +120%. In the longwave, SPARTACUS captures well the increase in radiative cooling of the cloud, although it is only able to correctly simulate the 30% increase in surface CRE (around 4 W m−2) if an approximate correction is made for cloud clustering.

Current weather and climate models neglect 3-D radiative transfer through cloud sides, which can change the cloud radiative effect (CRE) significantly. This two-part paper describes the development of the SPeedy Algorithm for Radiative TrAnsfer through CloUd Sides (SPARTACUS) to capture these effects efficiently in a two-stream radiation scheme for use in global models. The present paper concerns the longwave spectral region, where not much work has been done previously, although the limited previous work has suggested that radiative transfer through cloud sides increases the longwave surface CRE of shallow cumulus by around 30%. To assist the development of a longwave capability for SPARTACUS, we use a reference case of an isolated, isothermal, optically thick, cubic cloud in vacuum, for which 3-D effects increase CRE by exactly 200%. It is shown that for any cloud shape, the 3-D effect can be represented in SPARTACUS provided that correct account is made for (1) the effective zenith angle of diffuse radiation emitted from a cloud, (2) the spatial distribution of fluxes in the cloud, (3) cloud clustering that enhances the interception of emitted radiation by neighboring clouds, and (4) radiative smoothing leading to the effective cloud edge length being less than the measured value. We find empirically that the circumference of an ellipse fitted to a horizontal cross section through a cumulus cloud provides a good estimate of the radiatively effective cloud edge length, which provides some guidance to how cloud observations could be analyzed to extract their most important properties for radiation.

Results from a recent graduate student survey found unsurprisingly that Solar and Space Physics (S&SP) PhD graduate students almost all aspire to have research careers in Solar and Space Physics. This study reports on the research career persistence over the first decade of the new millennium for S&SP PhDs. We used publication of science citation indexed articles as the indicator for persistence in a research career. We found that nearly two thirds (64%) of PhDs who graduated between 2001 and 2009 published refereed papers in 2012 or 2013, while 17% of PhDs never published another paper beyond the year they received their PhD. The remaining 19% of PhDs stopped publishing within three years of receiving their PhD. We found no gender difference between research persistence. We also found that though there is statistically no difference on persistence of publishing research between graduates of the largest programs compared to all other programs, there are significant differences between individual programs. This study indicates that a majority of S&SP PhDs find research careers but that a significant fraction pursue careers where publishing in science citation indexed journals is not required. Graduate programs, advisors, and potential graduate students can use these data for career planning and developing mentoring programs that meet the career outcomes of all of their graduates.

Northern rivers connect a land area of approximately 20.5 million km2 to the Arctic Ocean and surrounding seas. These rivers account for ~10% of global river discharge and transport massive quantities of dissolved and particulate materials that reflect watershed sources and impact biogeochemical cycling in the ocean. In this paper, multiyear data sets from a coordinated sampling program are used to characterize particulate organic carbon (POC) and particulate nitrogen (PN) export from the six largest rivers within the pan-Arctic watershed (Yenisey, Lena, Ob', Mackenzie, Yukon, Kolyma). Together, these rivers export an average of 3055 × 109 g of POC and 368 × 109 g of PN each year. Scaled up to the pan-Arctic watershed as a whole, fluvial export estimates increase to 5767 × 109 g and 695 × 109 g of POC and PN per year, respectively. POC export is substantially lower than dissolved organic carbon export by these rivers, whereas PN export is roughly equal to dissolved nitrogen export. Seasonal patterns in concentrations and source/composition indicators (C:N, δ13C, Δ14C, δ15N) are broadly similar among rivers, but distinct regional differences are also evident. For example, average radiocarbon ages of POC range from ~2000 (Ob') to ~5500 (Mackenzie) years before present. Rapid changes within the Arctic system as a consequence of global warming make it challenging to establish a contemporary baseline of fluvial export, but the results presented in this paper capture variability and quantify average conditions for nearly a decade at the beginning of the 21st century.