bluuebunny/crossref_metadata_2025_split huggingface dataset:
High upward fluxes of formic acid from a boreal forest canopy
Authors: Schobesberger Siegfried , Lopez‐Hilfiker Felipe D. , Taipale Ditte , Millet Dylan B. , D'Ambro Emma L. , Rantala Pekka , Mammarella Ivan , Zhou Putian , Wolfe Glenn M. , Lee Ben H. , Boy Michael , Thornton Joel A. 
Published: August 2016

AbstractEddy covariance fluxes of formic acid, HCOOH, were measured over a boreal forest canopy in spring/summer 2014. The HCOOH fluxes were bidirectional but mostly upward during daytime, in contrast to studies elsewhere that reported mostly downward fluxes. Downward flux episodes were explained well by modeled dry deposition rates. The sum of net observed flux and modeled dry deposition yields an upward “gross flux” of HCOOH, which could not be quantitatively explained by literature estimates of direct vegetative/soil emissions nor by efficient chemical production from other volatile organic compounds, suggesting missing or greatly underestimated HCOOH sources in the boreal ecosystem. We implemented a vegetative HCOOH source into the GEOS‐Chem chemical transport model to match our derived gross flux and evaluated the updated model against airborne and spaceborne observations. Model biases in the boundary layer were substantially reduced based on this revised treatment, but biases in the free troposphere remain unexplained.
Internal structure of ex‐Typhoon Phanfone (2014) under an extratropical transition as observed by the research vessel Mirai
Authors: Katsumata Masaki , Mori Shuichi , Geng Biao , Inoue Jun 
Published: August 2016

AbstractThe internal structure of Typhoon Phanfone (2014) undergoing “extratropical transition” over ocean was captured from the research vessel Mirai. The observed time series from world first shipboard polarimetric weather radar and frequent radiosonde launches revealed both dynamic and thermodynamic structure simultaneously in detail for four phases: cirrus shield, warm front, precipitation core, and western flank. To the east of the low‐pressure center, a warm front developed along the midlatitude baroclinic zone. In the eastern vicinity of the center, remnants of the warm core worked to enhance precipitation through convergence and frontogenesis against cold ambient air. This frontogenesis and related latent heating/cooling are suggested to maintain/enhance convection in these phases. In contrast, the warm core suppressed convection in the northern/western vicinity of the low‐pressure center.
Impact of the lower atmosphere on the ionosphere response to a geomagnetic superstorm
Authors: Pedatella N. M. 
Published: August 2016

AbstractNumerical simulations in the National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) are performed to elucidate the impacts of lower atmosphere forcing on the ionosphere response to a geomagnetic superstorm. In particular, how the ionosphere variability due to the October 2003 Halloween storm would be different if it occurred in January coincident with a major sudden stratosphere warming (SSW) event is investigated. The TIE‐GCM simulations reveal that the E× B vertical drift velocity and total electron content (TEC) respond differently to the geomagnetic forcing when the lower atmosphere forcing is representative of SSW conditions compared to climatological lower atmosphere forcing conditions. Notably, the storm time variations in the E× B vertical drift velocity differ when the SSW‐induced zonal mean and tidal variability in the lower thermosphere are considered, and this is in part due to effects of the SSW on the equatorial ionosphere being potentially misinterpreted as being of geomagnetic origin. Differences in the TEC response to the geomagnetic storm can be up to 100% (∼30 TEC unit (TECU: 1 TECU = 1016 el m−2)) of the storm‐induced TEC change, and the temporal variability of the TEC during the storm recovery phase is considerably different if SSW effects are considered. The results demonstrate that even during periods of extreme geomagnetic forcing, it is important to consider the effects of lower atmosphere forcing on the ionosphere variability.
Polar cap patch transportation beyond the classic scenario
Authors: Zhang Qing‐He , Moen Jøran , Lockwood Michael , McCrea Ian , Zhang Bei‐Chen , McWilliams Kathryn A. , Zong Qiu‐Gang , Zhang Shun‐Rong , Ruohoniemi J. Michael , Thomas Evan G. , Dunlop Malcolm W. , Liu Rui‐Yuan , Yang Hui‐Gen , Hu Hong‐Qiao , Lester Mark 
Published: August 2016

AbstractWe report the continuous monitoring of a polar cap patch, encompassing its creation, and a subsequent evolution that differs from the classic behavior. The patch was formed from the storm‐enhanced density plume, by segmentation associated with a subauroral polarization stream generated by a substorm. Its initial antisunward motion was halted due to a rapidly changing of interplanetary magnetic field (IMF) conditions from strong southward to strong eastward with weaker northward components, and the patch subsequently very slowly evolved behind the duskside of a lobe reverse convection cell in afternoon sectors, associated with high‐latitude lobe reconnection, much of it fading rapidly due to an enhancement of the ionization recombination rate. This differs from the classic scenario where polar cap patches are transported across the polar cap along the streamlines of twin‐cell convection pattern from day to night. This observation provides us new important insights into patch formation and control by the IMF, which has to be taken into account in F region transport models and space weather forecasts.
Interactions between magnetosonic waves and ring current protons: Gyroaveraged test particle simulations
Authors: Fu Song , Ni Binbin , Li Jinxing , Zhou Chen , Gu Xudong , Huang Shiyong , Zhang Hui , Ge Yasong , Cao Xing 
Published: August 2016

AbstractGyroaveraged test particle simulations are implemented to quantitatively investigate interactions between linearly polarized magnetosonic waves (i.e., equatorial noises) and ring current protons inside and outside the plasmasphere at L = 4.5. For magnetosonic waves at the frequency of 33.3 Hz (fw/fcp = 6.4 at the magnetic equator, for L = 4.5), it is found that wave‐particle interactions at the resonance order corresponding to the lowest resonant proton energy (i.e., N = 6) are dominant. The interactions at other resonance orders make much less contribution. Near the equatorial loss cone at L = 4.5, magnetosonic waves produce strongest proton pitch angle diffusion at ~ 20 keV inside the plasmasphere and at ~ 100 keV outside the plasmasphere, respectively, reaching a rate above 10−6 s−1. The corresponding energy diffusion dominates over pitch angle diffusion at high pitch angles; therefore, magnetosonic waves are likely to accelerate protons at a few keV inside the plasmasphere and at ~ 10 keV outside the plasmasphere. Due to the emission equatorial confinement, the effect of transit time scattering also occurs for interactions of magnetosonic waves with ring current protons and tends to be increasingly important outside the plasmasphere, which is consistent with previous studies on interactions of magnetosonic waves with radiation belt electrons.
Seismic anisotropy of the lithosphere and asthenosphere beneath southern Madagascar from teleseismic shear wave splitting analysis and waveform modeling
Authors: Reiss M. C. , Rümpker G. , Tilmann F. , Yuan X. , Giese J. , Rindraharisaona E. J. 
Published: August 2016

AbstractMadagascar occupies a key position in the assembly and breakup of the supercontinent Gondwana. It has been used in numerous geological studies to reconstruct its original position within Gondwana and to derive plate kinematics. Seismological observations in Madagascar to date have been sparse. Using a temporary, dense seismic profile across southern Madagascar, we present the first published study of seismic anisotropy from shear wave splitting analyses of teleseismic phases. The splitting parameters obtained show significant small‐scale variation of fast polarization directions and delay times across the profile, with fast polarization rotating from NW in the center to NE in the east and west of the profile. The delay times range between 0.4 and 1.5 s. A joint inversion of waveforms at each station is applied to derive hypothetical one‐layer splitting parameters. We use finite‐difference, full‐waveform modeling to test several hypotheses about the origin and extent of seismic anisotropy. Our observations can be explained by asthenospheric anisotropy with a fast polarization direction of 50°, approximately parallel to the absolute plate motion direction, in combination with blocks of crustal anisotropy. Predictions of seismic anisotropy as inferred from global mantle flow models or global anisotropic surface wave tomography are not in agreement with the observations. Small‐scale variations of splitting parameters require significant crustal anisotropy. Considering the complex geology of Madagascar, we interpret the change in fast‐axis directions as a ~150 km wide zone of ductile deformation in the crust as a result of the intense reworking of lithospheric material during the Pan‐African orogeny. This fossil anisotropic pattern is underlain by asthenospheric anisotropy induced by plate motion.
Scaling relationships and physics for mixed heating convection in planetary interiors: Isoviscous spherical shells
Authors: Weller Matthew B. , Lenardic Adrian , Moore William B. 
Published: August 2016

AbstractWe use a suite of 3‐D numerical experiments to test and expand 2‐D planar isoviscous scaling relationships of Moore (2008) for mixed heating convection in spherical geometry mantles over a range of Rayleigh numbers (Ra). The internal temperature scaling of Moore (2008), when modified to account for spherical geometry, matches our experimental results to a high degree of fit. The heat flux through the boundary layers scale as a linear combination of internal (Q) and basal heating, and the modified theory predictions match our experimental results. Our results indicate that boundary layer thickness and surface heat flux are not controlled by a local boundary layer stability condition (in agreement with the results of Moore (2008)) and are instead strongly influenced by boundary layer interactions. Subadiabatic mantle temperature gradients, in spherical 3‐D, are well described by a vertical velocity scaling based on discrete drips as opposed to a scaling based on coherent sinking sheets, which was found to describe 2‐D planar results. Root‐mean‐square (RMS) velocities are asymptotic for both low Q and high Q, with a region of rapid adjustment between asymptotes for moderate Q. RMS velocities are highest in the low Q asymptote and decrease as internal heating is applied. The scaling laws derived by Moore (2008), and extended here, are robust and highlight the importance of differing boundary layer processes acting over variable Q and moderate Ra.
Topographic gravity modeling for global Bouguer maps to degree 2160: Validation of spectral and spatial domain forward modeling techniques at the 10 microGal level
Authors: Hirt Christian , Reußner Elisabeth , Rexer Moritz , Kuhn Michael 
Published: August 2016

AbstractOver the past years, spectral techniques have become a standard to model Earth's global gravity field to 10 km scales, with the EGM2008 geopotential model being a prominent example. For some geophysical applications of EGM2008, particularly Bouguer gravity computation with spectral techniques, a topographic potential model of adequate resolution is required. However, current topographic potential models have not yet been successfully validated to degree 2160, and notable discrepancies between spectral modeling and Newtonian (numerical) integration well beyond the 10 mGal level have been reported. Here we accurately compute and validate gravity implied by a degree 2160 model of Earth's topographic masses. Our experiments are based on two key strategies, both of which require advanced computational resources. First, we construct a spectrally complete model of the gravity field which is generated by the degree 2160 Earth topography model. This involves expansion of the topographic potential to the 15th integer power of the topography and modeling of short‐scale gravity signals to ultrahigh degree of 21,600, translating into unprecedented fine scales of 1 km. Second, we apply Newtonian integration in the space domain with high spatial resolution to reduce discretization errors. Our numerical study demonstrates excellent agreement (8 μGgal RMS) between gravity from both forward modeling techniques and provides insight into the convergence process associated with spectral modeling of gravity signals at very short scales (few km). As key conclusion, our work successfully validates the spectral domain forward modeling technique for degree 2160 topography and increases the confidence in new high‐resolution global Bouguer gravity maps.
CH4 concentrations over the Amazon from GOSAT consistent with in situ vertical profile data
Authors: Webb Alex J. , Bösch Hartmut , Parker Robert J. , Gatti Luciana V. , Gloor Emanuel , Palmer Paul I. , Basso Luana S. , Chipperfield Martyn P. , Correia Caio S. C. , Domingues Lucas G. , Feng Liang , Gonzi Siegfried , Miller John B. , Warneke Thorsten , Wilson Christopher 
Published: August 2016

AbstractThe Amazon Basin contains large wetland ecosystems which are important sources of methane (CH4). Spaceborne observations of atmospheric CH4 can provide constraints on emissions from these remote ecosystems, but lack of validation precludes robust estimates. We present the first validation of CH4 columns in the Amazon from the Greenhouse gases Observing SATellite (GOSAT) using aircraft measurements of CH4 over five sites across the Amazon Basin. These aircraft profiles, combined with stratospheric results from the TOMCAT chemical transport model, are vertically integrated allowing direct comparison to the GOSAT XCH4 measurements (the column‐averaged dry air mole fraction of CH4). The measurements agree within uncertainties or show no significant difference at three of the aircraft sites, with differences ranging from −1.9 ppb to 6.6 ppb, while at two sites GOSAT XCH4 is shown to be slightly higher than aircraft measurements, by 8.1 ppb and 9.7 ppb. The seasonality in XCH4 seen by the aircraft profiles is also well captured (correlation coefficients from 0.61 to 0.90). GOSAT observes elevated concentrations in the northwest corner of South America in the dry season and enhanced concentrations elsewhere in the Amazon Basin in the wet season, with the strongest seasonal differences coinciding with regions in Bolivia known to contain large wetlands. Our results are encouraging evidence that these GOSAT CH4 columns are generally in good agreement with in situ measurements, and understanding the magnitude of any remaining biases between the two will allow more confidence in the application of XCH4 to constrain Amazonian CH4 fluxes.
A statistical approach for isolating fossil fuel emissions in atmospheric inverse problems
Authors: Yadav Vineet , Michalak Anna M. , Ray Jaideep , Shiga Yoichi P. 
Published: August 2016

AbstractIndependent verification and quantification of fossil fuel (FF) emissions constitutes a considerable scientific challenge. By coupling atmospheric observations of CO2 with models of atmospheric transport, inverse models offer the possibility of overcoming this challenge. However, disaggregating the biospheric and FF flux components of terrestrial fluxes from CO2 concentration measurements has proven to be difficult, due to observational and modeling limitations. In this study, we propose a statistical inverse modeling scheme for disaggregating winter time fluxes on the basis of their unique error covariances and covariates, where these covariances and covariates are representative of the underlying processes affecting FF and biospheric fluxes. The application of the method is demonstrated with one synthetic and two real data prototypical inversions by using in situ CO2 measurements over North America. Inversions are performed only for the month of January, as predominance of biospheric CO2 signal relative to FF CO2 signal and observational limitations preclude disaggregation of the fluxes in other months. The quality of disaggregation is assessed primarily through examination of a posteriori covariance between disaggregated FF and biospheric fluxes at regional scales. Findings indicate that the proposed method is able to robustly disaggregate fluxes regionally at monthly temporal resolution with a posteriori cross covariance lower than 0.15 µmol m−2 s−1 between FF and biospheric fluxes. Error covariance models and covariates based on temporally varying FF inventory data provide a more robust disaggregation over static proxies (e.g., nightlight intensity and population density). However, the synthetic data case study shows that disaggregation is possible even in absence of detailed temporally varying FF inventory data.
Sensitivity of Barnes Ice Cap, Baffin Island, Canada, to climate state and internal dynamics
Authors: Gilbert A. , Flowers G. E. , Miller G. H. , Rabus B. T. , Van Wychen W. , Gardner A. S. , Copland L. 
Published: August 2016

AbstractBarnes Ice Cap is a remnant of the Laurentide Ice Sheet, which covered much of northern North America during the Last Glacial Maximum. Barnes reached a quasi‐equilibrium state ~2000 years ago and has remained similar in size since then, with a small increase during the Little Ice Age. In this study, we combine historical observations (1960–1980) with more recent satellite and airborne data (1995–2010) to drive a mass balance model coupled to a transient thermomechanical model with an adaptive mesh geometry. The model is used to characterize the current state of the ice cap and to investigate its stability as a function of climate and its own internal dynamics. On millennial time scales we show that ice flow is influenced by adjustment of an unsteady shape, by gently sloping bedrock, and by contrasting viscosities between the Pleistocene and Holocene ice. On shorter time scales, Barnes is affected by surge activity. Sensitivity tests reveal that Barnes experienced climate conditions which enabled its stability 2000 to 3000 years ago but will disappear under current climate conditions in the next millennium.
Convergence in nitrogen deposition and cryptic isotopic variation across urban and agricultural valleys in northern Utah
Authors: Hall S. J. , Ogata E. M. , Weintraub S. R. , Baker M. A. , Ehleringer J. R. , Czimczik C. I. , Bowling D. R. 
Published: August 2016

AbstractThe extent to which atmospheric nitrogen (N) deposition reflects land use differences and biogenic versus fossil fuel reactive N sources remains unclear yet represents a critical uncertainty in ecosystem N budgets. We compared N concentrations and isotopes in precipitation‐event bulk (wet + dry) deposition across nearby valleys in northern Utah with contrasting land use (highly urban versus intensive agriculture/low‐density urban). We predicted greater nitrate (NO3−) versus ammonium (NH4+) and higher δ15N of NO3− and NH4+ in urban valley sites. Contrary to expectations, annual N deposition (3.5–5.1 kg N ha−1 yr−1) and inorganic N concentrations were similar within and between valleys. Significant summertime decreases in δ15N of NO3− possibly reflected increasing biogenic emissions in the agricultural valley. Organic N was a relatively minor component of deposition (~13%). Nearby paired wildland sites had similar bulk deposition N concentrations as the urban and agricultural sites. Weighted bulk deposition δ15N was similar to natural ecosystems (−0.6 ± 0.7‰). Fine atmospheric particulate matter (PM2.5) had consistently high values of bulk δ15N (15.6 ± 1.4‰), δ15N in NH4+ (22.5 ± 1.6‰), and NO3− (8.8 ± 0.7‰), consistent with equilibrium fractionation with gaseous species. The δ15N in bulk deposition NH4+ varied by more than 40‰, and spatial variation in δ15N within storms exceeded 10‰. Sporadically high values of δ15N were thus consistent with increased particulate N contributions as well as potential N source variation. Despite large differences in reactive N sources, urban and agricultural landscapes are not always strongly reflected in the composition and fluxes of local N deposition—an important consideration for regional‐scale ecosystem models.
CH4 exchanges of the natural ecosystems in China during the past three decades: The role of wetland extent and its dynamics
Authors: Wei Da , Wang Xiaodan 
Published: August 2016

AbstractCH4 is the second largest contributor to human‐induced global warming. However, large uncertainties still exist regarding the magnitude and temporal variation of CH4 exchanges in China's natural ecosystems, especially under climate changes. In this study, we assessed its uncertainty and temporal variation during 1979–2012, by integrating a biogeochemical model, extensive in situ measurements, and various sources of wetland maps. Uncertainty analyses suggested that previous studies might have underestimated CH4 emissions, primarily due to bias in wetland extents in NE China. After that, 1 km resolution wetland maps were used to drive the model, together with a 0.1° resolution climate data set. The model showed that China's natural wetlands emitted 4.56 ± 1.24 Tg CH4 yr−1 during the 1980s, which decreased to 3.86 ± 1.09 Tg CH4 yr−1 in the 2000s, mainly due to wetland drainage in NE China. However, recent glacier‐melt‐induced wetland expansion has enhanced CH4 emissions by 28% on the Tibetan Plateau since the 1980s. The magnitude of CH4 uptake by the natural ecosystems has remained relatively stable, e.g., −2.57 ± 0.18 and −2.70 ± 0.19 Tg CH4 yr−1 in the 1980s and 2000s, respectively. In summary, the net CH4 balance of China's natural ecosystems has shown a decreasing pattern, i.e., 1.99 ± 1.42 and 1.16 ± 1.28 Tg CH4 yr−1 in the 1980s and 2000s, respectively, despite distinct regional differences between NE China and the Tibetan Plateau. Furthermore, this study emphasizes the correct representation of wetland extent and its dynamics, i.e., wetland drainage in populated regions and wetland expansion in glacier‐fed regions, in driving the decadal CH4 exchange magnitude.