bluuebunny/crossref_metadata_2025_split huggingface dataset:
Long‐Term Estimation of Diurnal Vertical E × B Drift Velocities Using C/NOFS and Ground‐Based Magnetometer Observations
Authors: Habarulema John Bosco , Dubazane Makhosonke B. , Katamzi‐Joseph Zama T , Yizengaw Endawoke , Moldwin Mark B. , Uwamahoro Jean Claude 
Published: August 2018

AbstractWe report on the development of a new mathematical expression to estimate local daytime (0700–1700 LT) vertical E × B drift in low latitudes using a combination of ground‐based magnetometer measurements and Communications and Navigation Outage Forecasting System (C/NOFS) satellite observations. The expression was developed over Jicamarca (11.8°S, 77.2°W; 0.8°N geomagnetic) and validated with Jicamarca Unattended Long‐Term studies of the Ionosphere and Atmosphere (JULIA) mode and incoherent scatter radar (ISR) measurements during the period 2008–2014. The obtained correlation coefficient (R) values computed using observed and derived vertical E × B drift velocities are 0.79 and 0.84 for ISR and JULIA, respectively when data are available during 2008–2014. Storm‐time comparison between observed and derived vertical E × B drift velocities agreed well with R of 0.92 and 0.87 during 5–8 August 2011 and 8–11 March 2012 geomagnetic storm periods for ISR and JULIA observations, respectively. Overall, we found that the developed expression is applicable in estimating vertical E × B drift response during quiet and geomagnetic storm periods. Based on these findings, we suggest that it is possible to develop accurate daytime global vertical E × B drift model over the equatorial latitude regions using inexpensive magnetometer observations and available satellite data.
Recognition of Meteor Showers From the Heights of Ionization Trails
Authors: Lukianova Renata , Kozlovsky Alexander , Lester Mark 
Published: August 2018

AbstractMeteoroids constantly enter the Earth's atmosphere, collide with atmospheric molecules, and heat and ablate in the sufficiently dense atmospheric layers at heights between 70 and 110 km. It is still a problem to recognize properties of the meteor streams among the sporadic background. The meteor radar observations at Sodankylä Geophysical Observatory (67°22′N, 26°38′E, Finland) during 2008–2017 show that meteoroids of some showers produce ionization trails at altitudes noticeably exceeding those of sporadic meteors. Using the median height of meteor trails and corresponding upper and lower quartiles as a metric, we unambiguously distinguish all northern hemisphere meteor showers with a zenithal hourly rate larger than 12, namely, the Quadrantids, Lyrids, Eta Aquariids, Arietids (or/and Daytime Zeta Perseids), Perseids, Orionids, Leonids, and Geminids. Additionally, signatures of a possible meteor stream during 26–30 January were detected, although identification of this stream is still under question. This new analysis indicates that the origin of the shower meteor trails at higher altitudes is likely due to higher speed and probably lighter or less dense meteoroids belonging to the showers.
Oscillation of the Ionosphere at Planetary‐Wave Periods
Authors: Forbes J. M. , Maute A. , Zhang X. , Hagan M. E. 
Published: August 2018

AbstractF‐region ionospheric oscillations at planetary‐wave (PW) periods (2–20 days) are investigated, with primary focus on those oscillations transmitted to the ionosphere by PW modulation of the vertically propagating tidal spectrum. Tidal effects are isolated by specifically designed numerical experiments performed with the National Center for Atmospheric Research thermosphere‐ionosphere‐electrodynamics general circulation model for October 2009, when familiar PW and tides are present in the model. Longitude versus day‐of‐month perturbations in topside F‐region electron density (Ne) of order ±30–50% at PW periods occur as a result of PW‐modulated tides. At a given height, these oscillations are mainly due to vertical oscillations in the F layer of order ±15–40 km. These vertical movements are diagnosed in terms of changes in the F2‐layer peak height, ΔhmF2, which are driven by the vertical projections of E × B drifts and field‐aligned in situ neutral winds. E × B drifts dominate at the magnetic equator, while the two sources play more equal roles between 20° and 40° magnetic latitudes in each hemisphere. The in situ neutral wind effect arises from vertical propagation of PW‐modulated tides, whereas the E × B drifts originate from dynamo‐generated electric fields produced by the E‐region component of the same wind field; the former represents a new coupling mechanism for production of ionospheric oscillations at PW periods. Roughly half the above‐mentioned variability in Ne and hmF2 is associated with zonally symmetric (S0) oscillations, which contribute at about half the level of low‐level magnetic activity during October 2009. The thermosphere‐ionosphere‐electrodynamics general circulation model simulates the S0 oscillations in Ne observed from the CHAMP satellite well during this period and reveals that S0 oscillations in E × B play a significant role in driving S0 oscillations in ΔhmF2, in addition to neutral winds.
Ab Initio Prediction of Potassium Partitioning Into Earth's Core
Authors: Xiong Zhihua , Tsuchiya Taku , Taniuchi Takashi 
Published: August 2018

AbstractPotassium partitioning between molten silicates and liquid iron alloys is the fundamental process determining its incorporation into the Earth's core. In this study, it is investigated using the method of the ab initio molecular dynamics simulation combined with the thermodynamic integration technique. Results suggest that the potassium incorporation into iron alloys positively depends on temperature, while the effect of pressure is insignificant. Moreover, the existence of oxygen in liquid iron alloys significantly enhances the potassium solubility therein, whereas sulfur and silicon only have negligible effects. Electronic structure analyses reveal that potassium remains alkali‐metallic in liquid iron alloy systems under all conditions in this study, which is distinct from the characteristics reported for solid potassium. Atomic structure analyses indicate that the oxygen coordination number around potassium atom increases with oxygen concentration in liquid iron alloys, supporting the oxygen concentration dependence of the potassium partitioning between molten silicates and liquid iron alloys. Using the obtained partitioning coefficients combined with geochemical property, the maximum potassium concentration in the Earth's core is estimated to be ~30 ppm, which would be unlikely to affect the thermal evolution of the Earth's core significantly.
Sustained Upwelling of Subsurface Iron Supplies Seasonally Persistent Phytoplankton Blooms Around the Southern Kerguelen Plateau, Southern Ocean
Authors: Schallenberg Christina , Bestley Sophie , Klocker Andreas , Trull Thomas W. , Davies Diana M. , Gault‐Ringold Melanie , Eriksen Ruth , Roden Nicholas P. , Sander Sylvia G. , Sumner Michael , Townsend Ashley T. , van der Merwe Pier , Westwood Karen , Wuttig Kathrin , Bowie Andrew 
Published: August 2018

AbstractAlthough the supply of iron generally limits phytoplankton productivity in the Southern Ocean, substantial seasonal blooms are observed over and downstream of the Kerguelen plateau in the Indian sector of the Southern Ocean. Surprisingly, of the oceanic blooms, those associated with the deeper southern plateau last much longer (~3 months) than the northern bloom (~1‐month downstream of northern plateau). In this study, iron supply mechanisms around the southern plateau were investigated, obtaining profiles of dissolved iron (<0.2 μm, dFe) to 2,000‐m deep at 25 stations during austral summer 2016. The dFe concentrations in surface waters (≤100‐m depth) ranged from below the detection limit (DL, median of 0.026 nmol/kg) to 0.34 nmol/kg near the Antarctic shelf, with almost half the data points below detection. These low and—with few exceptions—largely spatially invariant concentrations, presumably driven by seasonal drawdown of this essential micronutrient by phytoplankton, could not explain observed patterns in chlorophyll a. In contrast, dFe concentrations (0.05–1.27 nmol/kg) in subsurface waters (100–800 m) showed strong spatial variations that can explain bloom patterns around the southern Kerguelen plateau when considered in the context of frontal locations and associated frontal processes, including upwelling, that may increase the upward supply of dFe in the region. This sustained vertical dFe supply distinguishes the southern blooms from the bloom downstream of the northern Kerguelen plateau and explains their persistence through the season.
Cross‐Polarization GMF for High Wind Speed and Surface Stress Retrieval
Authors: Troitskaya Yu. , Abramov V. , Baidakov G. , Ermakova O. , Zuikova E. , Sergeev D. , Ermoshkin A. , Kazakov V. , Kandaurov A. , Rusakov N. , Poplavsky E. , Vdovin M. 
Published: August 2018

AbstractThis paper describes the construction of geophysical model function (GMF) for wind speed and surface stress retrieval at high winds from cross‐polarized radar backscatter at the water surface. The starting point is the laboratory experiment designed for the study of X‐band backscattering from water surface. In particular, it was shown that cross‐polarized normalized radar cross section (NRCS) keeps sensitivity to wind friction velocity at high winds alternatively to co‐polarized radar return. Basing on the analysis of the Doppler spectra and simultaneous measurements of parameters of surface waves, we suggest a hypothesis that at high winds the cross‐polarized backscattered signal is formed mainly due to scattering from wave breakers. The hypothesis is supported by the experimentally detected proportionality between the power of the scattered signal at cross polarization and the area swept by wave breakers. These results obtained in the laboratory environment are applied for constructing the similar dependencies for field conditions. Using the phenomenological statistical physics approach, a parameterization of active whitecap coverage fraction dependence on wind friction velocity is suggested. With the use of this parameterization, the empirical function expressing the cross‐polarized NRCS by u* is derived. Using the surface drag parameterization applicable at strong winds, this dependence is verified on the base of available data sets containing collocated satellite measurements of cross‐polarized C‐band NRCS and ground measurements of wind speed. GMFs for u* and U10 retrieval are suggested. Analysis shows that taking into account the angular dependence of cross‐polarized radar backscattered power improves the accuracy of wind speed and wind friction velocity retrieval.
Method to Estimate Water Vapor Supersaturation in the Ambient Activation Process Using Aerosol and Droplet Measurement Data
Authors: Shen Chuanyang , Zhao Chunsheng , Ma Nan , Tao Jiangchuan , Zhao Gang , Yu Yingli , Kuang Ye 
Published: August 2018

AbstractWater vapor supersaturation, as one of the most important environmental parameters during the formation of clouds or fogs, cannot be directly measured, and few studies have been carried out to estimate it in the ambient activation process. In this study, a new method to estimate the water vapor supersaturation based on the inverse application of κ‐Köhler theory is proposed. Aerosol hygroscopic parameter κ, dry particle size distributions, and wet droplet size distributions were employed and a comparison of predicted droplet number concentration with the measurement results was made to obtain the effective supersaturation during the activation process. Using this method, we acquired the supersaturations varying from 0.01% to 0.05% in a fog episode observed in the North China Plain. In this fog episode, both hydrated unactivated droplets and activated droplets play a part in the total detected droplet number concentrations with the unactivated droplets' ratio decreasing with size. The sensitivity study was also made to evaluate the effects of droplet and aerosol hygroscopic measurement errors on the supersaturation ratio estimation. Water vapor supersaturation obtained with this method can be regarded as an effective value and can be further applied to cloud analysis in the future. This method is only based on conventional measurements of aerosol and droplets and does not rely on any other data, which makes it flexible and easy to perform. Calculated supersaturations and critical diameters can also deepen the understanding of ambient activation process and corresponding interactions between aerosol and droplet characteristics.
Regional Similarities and NOx‐Related Increases in Biogenic Secondary Organic Aerosol in Summertime Southeastern United States
Authors: Liu Jun , Russell Lynn M. , Ruggeri Giulia , Takahama Satoshi , Claflin Megan S. , Ziemann Paul J. , Pye Havala O. T. , Murphy Benjamin N. , Xu Lu , Ng Nga L. , McKinney Karena A. , Budisulistiorini Sri Hapsari , Bertram Timothy H. , Nenes Athanasios , Surratt Jason D. 
Published: August 2018

AbstractDuring the 2013 Southern Oxidant and Aerosol Study, Fourier transform infrared spectroscopy (FTIR) and aerosol mass spectrometer (AMS) measurements of submicron mass were collected at Look Rock (LRK), Tennessee, and Centreville (CTR), Alabama. Carbon monoxide and submicron sulfate and organic mass concentrations were 15–60% higher at CTR than at LRK, but their time series had moderate correlations (r ~ 0.5). However, NOxhad no correlation (r = 0.08) between the two sites with nighttime‐to‐early‐morning peaks 3–10 times higher at CTR than at LRK. Organic mass (OM) sources identified by FTIR Positive Matrix Factorization (PMF) had three very similar factors at both sites: fossil fuel combustion‐related organic aerosols, mixed organic aerosols, and biogenic organic aerosols (BOA). The BOA spectrum from FTIR is similar (cosine similarity > 0.6) to that of lab‐generated particle mass from the photochemical oxidation of both isoprene and monoterpenes under high NOxconditions from chamber experiments. The BOA mass fraction was highest during the night at CTR but in the afternoon at LRK. AMS PMF resulted in two similar pairs of factors at both sites and a third nighttime NOx‐related factor (33% of OM) at CTR but a daytime nitrate‐related factor (28% of OM) at LRK. NOxwas correlated with BOA and LO‐OOA for NOxconcentrations higher than 1 ppb at both sites, producing 0.5 ± 0.1 μg/m3for CTR‐LO‐OOA and 1.0 ± 0.3 μg/m3for CTR‐BOA additional biogenic OM for each 1 ppb increase of NOx.
Investigating the Potential of Using Satellite‐Based Precipitation Radars as Reference for Evaluating Multisatellite Merged Products
Authors: Khan S. , Maggioni V. , Kirstetter P.‐E. 
Published: August 2018

AbstractThis work investigates the viability of using the Global Precipitation Mission (GPM) Dual‐frequency Precipitation Radar (DPR) as a reference for evaluating multisatellite precipitation products in locations where a ground‐based reference is not available. The Integrated Multi‐Satellite Retrievals for Global Precipitation Measurement (IMERG) version V05 products (early, late, and final) and the microwave‐only (MW) and infrared‐only (IR) components are evaluated against two reference data sets, derived from the Multi‐Radar/Multi‐Sensor System suite of products (MRMS) and the level‐2 DPR (2ADPR). The analysis focuses on a 2‐year period (2014–2015), excluding winters to evaluate liquid‐phase precipitation only. Systematic and random errors are assessed between the satellite‐based products and the MRMS‐based reference. Systematic error for the IMERG early, late, and final products and the MW component are shown to be comparable to those of 2ADPR, while the IR component exhibits a larger bias. Random errors of the IR estimates are found to be 1 order of magnitude larger than the 2ADPR random error. Thus, the hypothesis of using 2ADPR as a benchmark for quantifying uncertainties associated with IMERG holds true for evaluating random errors associated with IR precipitation estimates. Errors in the IR component are then investigated as a function of climatology and seasonality across contiguous United States. The temperate, oceanic, and subtropical climates show the best performance in terms of probability of detection and success ratio, whereas arid‐desert manifests the smallest root‐mean‐square errors. This work suggests that climatic zone‐specific error characterization model is necessary to estimate uncertainties associated with the IMERG products.
Larger Sensitivity of Precipitation Extremes to Aerosol Than Greenhouse Gas Forcing in CMIP5 Models
Authors: Lin Lei , Wang Zhili , Xu Yangyang , Fu Qiang , Dong Wenjie 
Published: August 2018

AbstractThe sensitivity of precipitation extremes (PEs; i.e., the change in PE per degree of change in global mean surface temperature) to aerosol and greenhouse gas (GHG) forcings is examined using the twentieth century historical multimodel ensemble simulations from the Coupled Model Intercomparison Program phase 5 (CMIP5). We find a robustly larger sensitivity of PE to aerosols than GHGs across all available models. The aerosol/GHG‐induced sensitivity ratios for globe‐averaged monthly maximum consecutive 5‐day precipitation (RX5day) and maximum 1‐day precipitation (RX1day) in the multimodel ensemble are 1.6 and 1.4, respectively. Over land, the corresponding ratios for RX5day and RX1day are 2.3 and 1.8, respectively. In particular, the aerosol forcing leads to several times greater sensitivity than GHG forcing in West Africa, eastern China, South and Southeast Asia, northwestern South America, and Eastern Europe. The atmospheric energy balance, dynamical adjustment, and vertical structure of forcing, all contribute to the difference in the PE sensitivity to the two forcings. It is shown that the fast response primarily contributes to the greater‐than‐one aerosol‐to‐GHG ratios of the PE sensitivities, as for the mean precipitation. This is because of a stronger rainfall suppression effect induced by the GHG atmospheric forcing. We also find that the aerosol‐to‐GHG ratios of the PE sensitivities depend on the defined extreme precipitation indices. The aerosol‐to‐GHG sensitivity ratio is larger for more loosely defined PE, and it gradually converges to one for more severely defined PE. Our results further highlight the importance of considering the anthropogenic aerosol reduction in projecting the change in PE.
The Effect of Mars‐Relevant Soil Analogs on the Water Uptake of Magnesium Perchlorate and Implications for the Near‐Surface of Mars
Authors: Primm K. M. , Gough R. V. , Wong J. , Rivera‐Valentin E. G. , Martinez G. M. , Hogancamp J. V. , Archer P. D. , Ming D. W. , Tolbert M. A. 
Published: August 2018

AbstractThe water uptake and release by perchlorate salts have been well studied since the first in situ identification of such salts in the Martian soil by the Phoenix mission in 2008. However, there have been few studies on the effect of the insoluble regolith minerals on the interaction of perchlorate with water vapor. In this work, we investigate the impact of a Mars‐relevant mineral, montmorillonite, and a Mars soil analog, Mojave Mars Simulant (MMS), on the deliquescence (transition from dry crystalline to aqueous via water vapor absorption), ice formation, and efflorescence (transition from aqueous to dry crystalline via loss of water) of pure magnesium perchlorate. We studied mixtures of magnesium perchlorate hexahydrate with either montmorillonite or MMS. Although montmorillonite and MMS are materials that may serve as nuclei for either ice nucleation or salt efflorescence, we find that these soil analogs did not affect the phase transitions of magnesium perchlorate. The salt‐mineral mixture behaved similarly, within estimated uncertainties, to pure magnesium perchlorate in all cases. Experiments were performed in both N2 and CO2 atmospheres, with no detectable difference. We use data from the Mars Science Laboratory Rover Environmental Monitoring Station instrument and the Phoenix Thermal and Electrical Conductivity Probe, as well as modeling of the shallow subsurface, to determine the likelihood of these perchlorate phase transitions occurring at Gale Crater and the northern arctic plains (Vastitas Borealis). We find that aqueous solutions are predicted in the shallow subsurface of the Phoenix landing site, but not predicted at Gale Crater.
Equation of State of SiC at Extreme Conditions: New Insight Into the Interior of Carbon‐Rich Exoplanets
Authors: Miozzi F. , Morard G. , Antonangeli D. , Clark A. N. , Mezouar M. , Dorn C. , Rozel A. , Fiquet G. 
Published: August 2018

AbstractThere is a direct relation between the composition of a host star and that of the planets orbiting around it. As such, the recent discovery of stars with unusual chemical composition, notably enriched in carbon instead of oxygen, supports the existence of exoplanets with a chemistry dominated by carbides instead of oxides. Accordingly, several studies have been recently conducted on the Si–C binary system at high pressure and temperature. Nonetheless, the properties of carbides at the pressure‐temperature conditions of exoplanets interiors are still inadequately constrained, effectively hampering reliable planetary modeling. Here we present an in situ X‐ray diffraction study of the Si–C binary system up to 200 GPa and 3,500 K, significantly enlarging the pressure range explored by previous experimental studies. The large amount of collected data allows us to properly investigate the phase diagram and to refine the Clapeyron slope of the transition line from the zinc blende to the rock salt structure. Furthermore, the pressure‐volume‐temperature equation of state is provided for the high‐pressure phase, characterized by low compressibility and thermal expansion. Our results are used to model idealized C‐rich exoplanets of end‐members composition. In particular, we derived mass‐radius relations and performed numerical simulations defining rheological parameters and initial conditions which lead to onset of convection in such SiC planets. We demonstrate that if restrained to silicate‐rich mantle compositions, the interpretation of mass‐radius relations may underestimate the interior diversity of exoplanets.
Fine Vertical Structures at the Cloud Heights of Venus Revealed by Radio Holographic Analysis of Venus Express and Akatsuki Radio Occultation Data
Authors: Imamura Takeshi , Miyamoto Mayu , Ando Hiroki , Häusler Bernd , Pätzold Martin , Tellmann Silvia , Tsuda Toshitaka , Aoyama Yuichi , Murata Yasuhiro , Takeuchi Hiroshi , Yamazaki Atsushi , Toda Tomoaki , Tomiki Atsushi 
Published: August 2018

AbstractRadio occultation (RO) is one of the most efficient techniques for studying fine vertical structures in planetary atmospheres. However, the geometrical optics (GO) method, which has been used for the analysis of RO data, suffers blurring by the finite width (Fresnel scale) of the radio ray and cannot decipher multipath propagation, which also prevents retrieval of fine structures. Here we apply Full Spectrum Inversion (FSI), which is one of the radio holographic methods, to RO data taken in Venus Express and Akatsuki missions to retrieve fine structures in Venus' cloud‐level atmosphere. The temperature profiles obtained by FSI achieve vertical resolutions of ~150 m, which is much higher than the typical resolution of 400–700 m in GO, and resolve structures in multipath regions. Thin, near‐neutral layers are found to be ubiquitous at cloud heights; we suggest here that those layers are caused by the mixing associated with the breaking of short‐wavelength gravity waves. The wavenumber spectra of small‐scale structures are consistent with the semiempirical spectrum of saturated gravity waves and show larger amplitudes at higher latitudes. Temperature profiles in the high latitudes frequently show a sharp temperature minimum near the cloud top, below which the vertical temperature gradient is near adiabat, implying that the sharp temperature minimum is created by adiabatic cooling associated with convective plumes that impinge on the overlying stable layer.