bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solar‐Driven Variation in the Atmosphere of Uranus
Authors: Aplin K. L. , Harrison R. G. 
Published: December 2017

AbstractLong‐term measurements (1972–2015) of the reflectivity of Uranus at 472 and 551 nm display variability that is incompletely explained by seasonal effects. Spectral analysis shows that this nonseasonal variability tracks the 11 year solar cycle. Two mechanisms could cause solar modulation: (a) nucleation onto ions or electrons created by galactic cosmic rays (GCR) or (b) UV‐induced aerosol color changes. Ion‐aerosol theory is used to identify expected relationships between reflectivity fluctuations and GCR flux, tested with multiple regression and compared to the linear response predicted between reflectivity and solar UV flux. The statistics show that 24% of the variance in reflectivity fluctuations at 472 nm is explained by GCR ion‐induced nucleation, compared to 22% for a UV‐only mechanism. Similar GCR‐related variability exists in Neptune's atmosphere; hence, the effects found at Uranus provide the first example of common variability in two planetary atmospheres driven through energetic particle modulation by their host star.
Topographical and Local Time Dependence of Large Stationary Gravity Waves Observed at the Cloud Top of Venus
Authors: Kouyama T. , Imamura T. , Taguchi M. , Fukuhara T. , Sato T. M. , Yamazaki A. , Futaguchi M. , Murakami S. , Hashimoto G. L. , Ueno M. , Iwagami N. , Takagi S. , Takagi M. , Ogohara K. , Kashimura H. , Horinouchi T. , Sato N. , Yamada M. , Yamamoto Y. , Ohtsuki S. , Sugiyama K. , Ando H. , Takamura M. , Yamada T. , Satoh T. , Nakamura M. 
Published: December 2017

AbstractThe existence of large stationary gravity waves was discovered during Akatsuki's first observation sequence in 2015. In this study, the further detection of large stationary gravity waves in brightness temperature images over a 1.5 year period is reported. The waves periodically appeared mostly above four specific highland regions in the low latitudes when these regions were in the local afternoon. The wave amplitudes attenuated after the wave locations passed beyond the evening terminator, and the locations of the waves tended to slowly drift eastward over their lifetimes. The appearances of stationary waves depend not only on surface topography but also on latitude and local time, suggesting that solar heating during the daytime and atmospheric structure affected by solar heating may control the excitation and propagation of stationary waves.
Tracking the Subsurface Signal of Decadal Climate Warming to Quantify Vertical Groundwater Flow Rates
Authors: Bense V. F. , Kurylyk B. L. 
Published: December 2017

AbstractSustained ground surface warming on a decadal time scale leads to an inversion of thermal gradients in the upper tens of meters. The magnitude and direction of vertical groundwater flow should influence the propagation of this warming signal, but direct field observations of this phenomenon are rare. Comparison of temperature‐depth profiles in boreholes in the Veluwe area, Netherlands, collected in 1978–1982 and 2016 provided such direct measurement. We used these repeated profiles to track the downward propagation rate of the depth at which the thermal gradient is zero. Numerical modeling of the migration of this thermal gradient “inflection point” yielded estimates of downward groundwater flow rates (0–0.24 m a−1) that generally concurred with known hydrogeological conditions in the area. We conclude that analysis of inflection point depths in temperature‐depth profiles impacted by surface warming provides a largely untapped opportunity to inform sustainable groundwater management plans that rely on accurate estimates of long‐term vertical groundwater fluxes.
Ionospheric Bow Waves and Perturbations Induced by the 21 August 2017 Solar Eclipse
Authors: Zhang Shun‐Rong , Erickson Philip J. , Goncharenko Larisa P. , Coster Anthea J. , Rideout William , Vierinen Juha 
Published: December 2017

AbstractDuring solar eclipses, the Moon's shadow causes a large reduction in atmospheric energy input, including not only the stratosphere but also the thermosphere and ionosphere. The eclipse shadow has a supersonic motion which is theoretically expected to generate atmospheric bow waves, similar to a fast‐moving river boat, with waves starting in the lower atmosphere and propagating into the ionosphere. However, previous geographically limited observations have had difficulty detecting these weak waves within the natural background atmospheric variability, and the existence of eclipse‐induced ionospheric waves and their evolution in a complex coupling system remain controversial. During the 21 August 2017 eclipse, high fidelity and wide coverage ionospheric observations provided for the first time an oversampled set of eclipse data, using a dense network of Global Navigation Satellite System receivers at ∼2,000 sites in North America. We show the first unambiguous evidence of ionospheric bow waves as electron content disturbances over central/eastern United States, with ∼1 h duration, 300–400 km wavelength and 280 m/s phase speed emanating from and tailing the totality region. We also identify large ionospheric perturbations moving at the supersonic speed of the maximum solar obscuration which are too fast to be associated with known gravity wave or large‐scale traveling ionospheric disturbance processes. This study reveals complex interconnections between the Sun, Moon, and Earth's neutral atmosphere and ionosphere and demonstrates persistent coupling processes between different components of the Earth's atmosphere, a topic of significant community interest.
The 2017 Mw 8.2 Chiapas, Mexico, Earthquake: Energetic Slab Detachment
Authors: Ye Lingling , Lay Thorne , Bai Yefei , Cheung Kwok Fai , Kanamori Hiroo 
Published: December 2017

AbstractOn 8 September 2017, a great (Mw 8.2) normal faulting earthquake ruptured within the subducting Cocos Plate ~70 km landward from the Middle American Trench beneath the Tehuantepec gap. Iterative inversion and modeling of teleseismic and tsunami data and prediction of GPS displacements indicate that the steeply dipping rupture extended ~180 km to the northwest along strike toward the Oaxaca coast and from ~30 to 70 km in depth, with peak slip of ~13 m. The rupture likely broke through the entire lithosphere of the young subducted slab in response to downdip slab pull. The plate boundary region between the trench and the fault intersection with the megathrust appears to be frictionally coupled, influencing location of the detachment. Comparisons of the broadband body wave magnitude (mB) and moment‐scaled radiated energy (ER/M0) establish that intraslab earthquakes tend to be more energetic than interplate events, accounting for strong ground shaking observed for the 2017 event.
Do Southern Ocean Cloud Feedbacks Matter for 21st Century Warming?
Authors: Frey W. R. , Maroon E. A. , Pendergrass A. G. , Kay J. E. 
Published: December 2017

AbstractCloud phase improvements in a state‐of‐the‐art climate model produce a large 1.5 K increase in equilibrium climate sensitivity (ECS, the surface warming in response to instantaneously doubled CO2) via extratropical shortwave cloud feedbacks. Here we show that the same model improvements produce only a small surface warming increase in a realistic 21st century emissions scenario. The small 21st century warming increase is attributed to extratropical ocean heat uptake. Southern Ocean mean‐state circulation takes up heat while a slowdown in North Atlantic circulation acts as a feedback to slow surface warming. Persistent heat uptake by extratropical oceans implies that extratropical cloud biases may not be as important to 21st century warming as biases in other regions. Observational constraints on cloud phase and shortwave radiation that produce a large ECS increase do not imply large changes in 21st century warming.
Energy Flow Exciting Field‐Aligned Current at Substorm Expansion Onset
Authors: Ebihara Y. , Tanaka T. 
Published: December 2017

AbstractAt substorm expansion onset, upward field‐aligned currents (FACs) increase abruptly, and a large amount of electromagnetic energy starts to consume in the polar ionosphere. A question arises as to where the energy comes from. Based on the results obtained by the global magnetohydrodynamics simulation, we present energy flow and energy conversion associated with the upward FACs that manifest the onset. Our simulations show that the cusp/mantle region transmits electromagnetic energy to almost the entire region of the magnetosphere when the interplanetary magnetic field is southward. Integral curve of the Poynting flux shows a spiral moving toward the ionosphere, probably suggesting the pathway of electromagnetic energy from the cusp/mantle dynamo to the ionosphere. The near‐Earth reconnection initiates three‐dimensional redistribution of the magnetosphere. Flow shear in the near‐Earth region results in the generation of the near‐Earth dynamo and the onset FACs. The onset FACs are responsible to transport the electromagnetic energy toward the Earth. In the near‐Earth region, the electromagnetic energy coming from the cusp/mantle dynamo is converted to the kinetic energy (known as bursty bulk flow) and the thermal energy (associated with high‐pressure region in the inner magnetosphere). Then, they are converted to the electromagnetic energy associated with the onset FACs. A part of electromagnetic energy is stored in the lobe region during the growth phase. The release of the stored energy, together with the continuously supplied energy from the cusp/mantle dynamo, contributes to the energy supply to the ionosphere during the expansion phase.
Negative Potential Solitary Structures in the Magnetosheath With Large Parallel Width
Authors: Holmes J. C. , Ergun R. E. , Newman D. L. , Wilder F. D. , Sturner A. P. , Goodrich K. A. , Torbert R. B. , Giles B. L. , Strangeway R. J. , Burch J. L. 
Published: December 2017

AbstractWe report multispacecraft observations by the Magnetospheric MultiScale (MMS) mission of large (80–155 λDe parallel to B) electrostatic solitary waves (ESWs). Observations of the same ESWs at different positions and times enable unprecedented accuracy in determining the size, velocity, and evolution of these nonlinear structures. This particular event is a short series of negative potential solitary waves in the magnetosheath. The observed structures differ in amplitude and speed, merging or colliding with one another. A Vlasov simulation supports initial wave growth by a cold feature in the electron distribution function. Such cold electrons are likely the result of mixing between the cold magnetospheric and warm magnetosheath plasma along a reconnection separatrix. ESW speed and perpendicular size are inconsistent with ion phase space holes. Solving Poisson's equation for the measured potential, we find a reduction in electron density rather than an enhancement expected from an electron soliton. These ESWs have an unusual combination of properties on both ion and electron scales, likely supported by a complex electron distribution in the nonlinear state.
Revisiting Slow Slip Events Occurrence in Boso Peninsula, Japan, Combining GPS Data and Repeating Earthquakes Analysis
Authors: Gardonio B. , Marsan D. , Socquet A. , Bouchon M. , Jara J. , Sun Q. , Cotte N. , Campillo M. 
Published: December 2017

AbstractSlow slip events (SSEs) regularly occur near the Boso Peninsula, central Japan. Their time of recurrence has been decreasing from 6.4 to 2.2 years from 1996 to 2014. It is important to better constrain the slip history of this area, especially as models show that the recurrence intervals could become shorter prior to the occurrence of a large interplate earthquake nearby. We analyze the seismic waveforms of more than 2,900 events (M≥1.0) taking place in the Boso Peninsula, Japan, from 1 April 2004 to 4 November 2015, calculating the correlation and the coherence between each pair of events in order to define groups of repeating earthquakes. The cumulative number of repeating earthquakes suggests the existence of two slow slip events that have escaped detection so far. Small transient displacements observed in the time series of nearby GPS stations confirm these results. The detection scheme coupling repeating earthquakes and GPS analysis allow to detect small SSEs that were not seen before by classical methods. This work brings new information on the diversity of SSEs and demonstrates that the SSEs in Boso area present a more complex history than previously considered.
Spatiotemporal Patterns and Synoptics of Extreme Wet‐Bulb Temperature in the Contiguous United States
Authors: Raymond C. , Singh D. , Horton R. M. 
Published: December 2017

AbstractExtremes of wet‐bulb temperature (WBT)—jointly reflecting temperature and specific humidity—have seen relatively little study in terms of climatology, despite their demonstrated relevance for health and economic impacts. In this study, we uncover and characterize distinct spatiotemporal patterns of WBT extremes in the contiguous United States for the 1981–2015 period, focusing on identifying and making a first pass at understanding regional differences. We find that anomalies of specific humidity are of greater importance than those of temperature in controlling extreme WBT in most of the contiguous U.S., particularly for southern and arid regions. Composites of extreme‐WBT days for each region reveal coherent sea‐surface temperature anomalies and midlevel and upper ‐level geopotential‐height anomalies that differ considerably between regions, particularly in terms of the resulting low‐level temperature and moisture fields. These findings suggest that the primary factors controlling the timing and intensity of WBT extremes, while ultimately forced by synoptic‐scale weather patterns, vary spatially according to both local geography and baseline climate. We demonstrate this conclusion by showing how regional features such as late‐summer WBT extremes in the Southwest and southern Great Plains derive primarily from spatial and temporal variations in moist low‐level flows.
Characterizing Stratospheric Polar Vortex Variability With Computer Vision Techniques
Authors: Lawrence Zachary D. , Manney Gloria L. 
Published: December 2017

AbstractComputer vision techniques are used to characterize the Arctic stratospheric polar vortex in 38 years of reanalysis data. Such techniques are typically applied to analyses of digital images, but they represent powerful tools that are more widely applicable: basic techniques and considerations for geophysical applications are outlined herein. Segmentation, descriptive, and tracking algorithms are combined in the Characterization and Analysis of Vortex Evolution using Algorithms for Region Tracking (CAVE‐ART) package, which was developed to comprehensively describe dynamical and geometrical evolution of polar vortices. CAVE‐ART can characterize and track multiple vortex regions through time, providing an extensive suite of region, moments, and edge diagnostics for each. CAVE‐ART is valuable for identifying vortex‐splitting events including, but not limited to, previously cataloged vortex‐split sudden stratospheric warmings. An algorithm for identifying such events detects 52 potential events between 1980 and 2017; of these, 38 are subjectively classified as distinct “split‐like” events. The algorithm based on CAVE‐ART is also compared with moment‐based methods previously used to detect split events. Furthermore, vortex edge‐averaged wind speeds from CAVE‐ART are used to define extreme weak and strong polar vortex events over multiple vertical levels; this allows characterization of their occurrence frequencies and extents in time and altitude. Weak and strong events show distinct signatures in CAVE‐ART diagnostics: in contrast to weak events, strong vortices are more cylindrical and pole centered, and less filamented, than the climatological state. These results from CAVE‐ART exemplify the value of computer vision techniques for analysis of geophysical phenomena.
Mechanistic Processes Controlling Persistent Changes of Forest Canopy Structure After 2005 Amazon Drought
Authors: Shi Mingjie , Liu Junjie , Zhao Maosheng , Yu Yifan , Saatchi Sassan 
Published: December 2017

AbstractThe long‐term impact of Amazonian drought on canopy structure has been observed in ground and remote sensing measurements. However, it is still unclear whether it is caused by biotic (e.g., plant structure damage) or environmental (e.g., water deficiency) factors. We used the Community Land Model version 4.5 (CLM4.5) and radar backscatter observations from SeaWinds Scatterometer on board QuikSCAT (QSCAT) satellite to investigate the relative role of biotic and environmental factors in controlling the forest canopy disturbance and recovery processes after the 2005 Amazonian drought. We validated the CLM4.5 simulation of the drought impact and the recovery of leaf carbon (C) pool, an indicator of canopy structure, over southwestern Amazonia with QSCAT backscatter observations, which are sensitive to canopy structure change. We found that the leaf C pool simulated by CLM4.5 recovered to the 2000–2009 mean level (343 g C m−2) in 3 years after a sharp decrease in 2005, consistent with the QSCAT observed slow recovery. Through sensitivity experiments, we found that the slow C recovery was primarily due to biotic factors represented by the canopy damage and reduction of plant C pools. The recovery of soil water and the coupling between water and C pools, which is an environmental factor, only contributes ~24% to the leaf C recovery. The results showed (1) the strength of scatterometer backscatter measurements in capturing canopy damage over tropical forests and in validating C cycle models and (2) the biotic factors play the dominant role in regulating the drought induced disturbance and persistent canopy changes in CLM4.5.
Derivation and Solution of the Omega Equation Associated With a Balance Theory on the Sphere
Authors: Dostalek John F. , Schubert Wayne H. , DeMaria Mark 
Published: December 2017

AbstractThe quasi‐geostrophic omega equation has been used extensively to examine the large‐scale vertical velocity patterns of atmospheric systems. It is derived from the quasi‐geostrophic equations, a balanced set of equations based on the partitioning of the horizontal wind into a geostrophic and an ageostrophic component. Its use is limited to higher latitudes, however, as the geostrophic balance is undefined at the equator. In order to derive an omega equation which can be used at all latitudes, a new balanced set of equations is developed. Three key steps are used in the formulation. First, the horizontal wind is decomposed into a nondivergent and an irrotational component. Second, the Coriolis parameter is assumed to be slowly varying, such that it may be moved in and out of horizontal derivative operators as necessary to simplify the derivation. Finally, the mass field is formulated from the nondivergent wind field. The resulting balanced set of equations and the omega equation derived from them take a similar form to the quasi‐geostrophic equations, yet are valid over the whole sphere. A method of solution to the global omega equation using vertical normal modes and spherical harmonics is presented, along with a middle‐latitude and low‐latitude example.
The Heterogeneous Impacts of Groundwater Management Policies in the Republican River Basin of Colorado
Authors: Hrozencik R. A. , Manning D. T. , Suter J. F. , Goemans C. , Bailey R. T. 
Published: December 2017

AbstractGroundwater is a critical input to agricultural production across the globe. Current groundwater pumping rates frequently exceed recharge, often by a substantial amount, leading to groundwater depletion and potential declines in agricultural profits over time. As a result, many regions reliant on irrigated agriculture have proposed policies to manage groundwater use. Even when gains from aquifer management exist, there is little information about how policies affect individual producers sharing the resource. In this paper, we investigate the variability of groundwater management policy impacts across heterogeneous agricultural producers. To measure these impacts, we develop a hydroeconomic model that captures the important role of well capacity, productivity of water, and weather uncertainty. We use the model to simulate the impacts of groundwater management policies on producers in the High Plains aquifer of eastern Colorado and compare outcomes to a no‐policy baseline. The management policies considered include a pumping fee, a quantity restriction, and an irrigated acreage fee. We find that well capacity and soil type affect policy impacts but in ways that can qualitatively differ across policy type. Model results have important implications for the distributional impacts and political acceptability of groundwater management policies.
A Field‐Scale Sensor Network Data Set for Monitoring and Modeling the Spatial and Temporal Variation of Soil Water Content in a Dryland Agricultural Field
Authors: Gasch C. K. , Brown D. J. , Campbell C. S. , Cobos D. R. , Brooks E. S. , Chahal M. , Poggio M. 
Published: December 2017

AbstractWe describe a soil water content monitoring data set and auxiliary data collected at a 37 ha experimental no‐till farm in the Northwestern United States. Water content measurements have been compiled hourly since 2007 by ECH2O‐TE and 5TE sensors installed at 42 locations and five depths (0.3, 0.6, 0.9, 1.2, and 1.5 m, 210 sensors total) across the R.J. Cook Agronomy Farm, a Long‐Term Agro‐Ecosystem Research Site stationed on complex terrain in a Mediterranean climate. In addition to soil water content readings, the data set includes hourly and daily soil temperature readings, annual crop histories, a digital elevation model, Bt horizon maps, seasonal apparent electrical conductivity, soil texture, and soil bulk density. Meteorological records are also available for this location. We discuss the unique challenges of maintaining the network on an operating farm and demonstrate the nature and complexity of the soil water content data. This data set is accessible online through the National Agriculture Library, has been assigned a DOI, and will be maintained for the long term.
The Importance of Bank Storage in Supplying Baseflow to Rivers Flowing Through Compartmentalized, Alluvial Aquifers
Authors: Rhodes Kimberly A. , Proffitt Tiffany , Rowley Taylor , Knappett Peter S. K. , Montiel Daniel , Dimova Natasha , Tebo Daniel , Miller Gretchen R. 
Published: December 2017

AbstractAs water grows scarcer in semiarid and arid regions around the world, new tools are needed to quantify fluxes of water and chemicals between aquifers and rivers. In this study, we quantify the volumetric flux of subsurface water to a 24 km reach of the Brazos River, a lowland river that meanders through the Brazos River Alluvium Aquifer (BRAA), with 8 months of high‐frequency differential gaging measurements using fixed gaging stations. Subsurface discharge sources were determined using natural tracers and End‐Member Mixing Analysis (EMMA). During a 4 month river stage recession following a high stage event, subsurface discharge decreased from 50 m3/s to 0, releasing a total of 1.0 × 108 m3 of water. Subsurface discharge dried up even as the groundwater table at two locations in the BRAA located 300–500 m from the river remained ∼4 m higher than the river stage. Less than 4% of the water discharged from the subsurface during the prolonged recession period resembled the chemical fingerprint of the alluvial aquifer. Instead, the chemistry of this discharged water closely resembled high stage “event” river water. Together, these findings suggest that the river is well connected to rechargeable bank storage reservoirs but disconnected from the broader alluvial aquifer. The average width of discrete bank storage zones on each side of the river, identified with Electrical Resistivity Tomography (ERT), was approximately 1.5 km. In such highly compartmentalized aquifers, groundwater pumping is unlikely to impact the exchange between the river and the alluvium.