bluuebunny/crossref_metadata_2025 huggingface dataset:
Net community production and calcification from 7 years of NOAA Station Papa Mooring measurements
Authors: Fassbender Andrea J. , Sabine Christopher L. , Cronin Meghan F.
Published: January 2016

Seven years of near‐continuous observations from the Ocean Station Papa (OSP) surface mooring were used to evaluate drivers of marine carbon cycling in the eastern subarctic Pacific. Processes contributing to mixed layer carbon inventory changes throughout each deployment year were quantitatively assessed using a time‐dependent mass balance approach in which total alkalinity and dissolved inorganic carbon were used as tracers. By using two mixed layer carbon tracers, it was possible to isolate the influences of net community production (NCP) and calcification. Our results indicate that the annual NCP at OSP is 2 ± 1 mol C m−2 yr−1 and the annual calcification is 0.3 ± 0.3 mol C m−2 yr−1. Piecing together evidence for potentially significant dissolved organic carbon cycling in this region, we estimate a particulate inorganic carbon to particulate organic carbon ratio between 0.15 and 0.25. This is at least double the global average, adding to the growing evidence that calcifying organisms play an important role in carbon export at this location. These results, coupled with significant seasonality in the NCP, suggest that carbon cycling near OSP may be more complex than previously thought and highlight the importance of continuous observations for robust assessments of biogeochemical cycling.
Mercury presence and speciation in the South Atlantic Ocean along the 40°S transect
Authors: Bratkič Arne , Vahčič Mitja , Kotnik Jože , Obu Vazner Kristina , Begu Ermira , Woodward E. Malcolm S. , Horvat Milena
Published: January 2016

Mercury (Hg) natural biogeochemical cycle is complex and a significant portion of biological and chemical transformation occurs in the marine environment. To better understand the presence and abundance of Hg species in the remote ocean regions, waters of South Atlantic Ocean along 40°S parallel were investigated during UK‐GEOTRACES cruise GA10. Total mercury (THg), methylated mercury (MeHg), and dissolved gaseous mercury (DGM) concentrations were determined. The concentrations were very low in the range of pg/L (femtomolar). All Hg species had higher concentration in western than in eastern basin. THg did not appear to be a useful geotracer. Elevated methylated Hg species were commonly associated with low‐oxygen water masses and occasionally with peaks of chlorophyll a, both involved with carbon (re)cycling. The overall highest MeHg concentrations were observed in the mixed layer (500 m) and in the vicinity of the Gough Island. Conversely, DGM concentrations showed distinct layering and differed between the water masses in a nutrient‐like manner. DGM was lowest at surface, indicating degassing to the atmosphere, and was highest in the Upper Circumpolar Deep Water, where the oxygen concentration was lowest. DGM increased also in Antarctic Bottom Water. At one station, dimethylmercury was determined and showed increase in region with lowest oxygen saturation. Altogether, our data indicate that the South Atlantic Ocean could be a source of Hg to the atmosphere and that its biogeochemical transformations depend primarily upon carbon cycling and are thereby additionally prone to global ocean change.
Annual cycles of phytoplankton biomass in the subarctic Atlantic and Pacific Ocean
Authors: Westberry Toby K. , Schultz Patrick , Behrenfeld Michael J. , Dunne John P. , Hiscock Michael R. , Maritorena Stephane , Sarmiento Jorge L. , Siegel David A.
Published: January 2016

High‐latitude phytoplankton blooms support productive fisheries and play an important role in oceanic uptake of atmospheric carbon dioxide. In the subarctic North Atlantic Ocean, blooms are a recurrent feature each year, while in the eastern subarctic Pacific only small changes in chlorophyll (Chl) are seen over the annual cycle. Here we show that when evaluated using phytoplankton carbon biomass (Cphyto) rather than Chl, an annual bloom in the North Pacific is evident and can even rival blooms observed in the North Atlantic. The annual increase in subarctic Pacific phytoplankton biomass is not readily observed in the Chl record because it is paralleled by light‐ and nutrient‐driven decreases in cellular pigment levels (Cphyto:Chl). Specifically, photoacclimation and iron stress effects on Cphyto:Chl oppose the biomass increase, leading to only modest changes in bulk Chl. The magnitude of the photoacclimation effect is quantified using descriptors of the near‐surface light environment and a photophysiological model. Iron stress effects are diagnosed from satellite chlorophyll fluorescence data. Lastly, we show that biomass accumulation in the Pacific is slower than that in the Atlantic but is closely tied to similar levels of seasonal nutrient uptake in both basins. Annual cycles of satellite‐derived Chl and Cphyto are reproduced by in situ autonomous profiling floats. These results contradict the long‐standing paradigm that environmental conditions prevent phytoplankton accumulation in the subarctic Northeast Pacific and suggest a greater seasonal decoupling between phytoplankton growth and losses than traditionally implied. Further, our results highlight the role of physiological processes in shaping bulk properties, such as Chl, and their interpretation in studies of ocean ecosystem dynamics and climate change.
Temperature fluctuation of the Iceland mantle plume through time
Authors: Spice Holly E. , Fitton J. Godfrey , Kirstein Linda A.
Published: January 2016

The newly developed Al‐in‐olivine geothermometer was used to find the olivine‐Cr‐spinel crystallization temperatures of a suite of picrites spanning the spatial and temporal extent of the North Atlantic Igneous Province (NAIP), which is widely considered to be the result of a deep‐seated mantle plume. Our data confirm that start‐up plumes are associated with a pulse of anomalously hot mantle over a large spatial area before becoming focused into a narrow upwelling. We find that the thermal anomaly on both sides of the province at Baffin Island/West Greenland and the British Isles at ∼61 Ma across an area ∼2000 km in diameter was uniform, with Al‐in‐olivine temperatures up to
above that of average mid‐ocean ridge basalt (MORB) primitive magma. Furthermore, by combining our results with geochemical data and existing geophysical and bathymetric observations, we present compelling evidence for long‐term (>107 year) fluctuations in the temperature of the Iceland mantle plume. We show that the plume temperature fell from its initial high value during the start‐up phase to a minimum at about 35 Ma, and that the mantle temperature beneath Iceland is currently increasing.
Geochemical behavior of dissolved manganese in the East China Sea: Seasonal variation, estuarine removal, and regeneration under suboxic conditions
Authors: Wang Zhao‐Wei , Ren Jing‐Ling , Jiang Shuo , Liu Su‐Mei , Xuan Ji‐Liang , Zhang Jing
Published: January 2016

To better understand the geochemical cycle of dissolved manganese (Mn) in the East China Sea (ECS), the distribution of dissolved Mn across the ECS was investigated during three field studies in 2011 (May, August, and November). The concentration of dissolved Mn decreased across the ECS with distance from the coast. Mn‐rich ECS shelf waters could export to the Kuroshio Waters, and had the potential to influence the northwest Pacific Ocean as well as the Japan Sea. The Kuroshio Waters were devoid of dissolved Mn, so its incursion could be tracked as it entered the ECS continental shelf region (approximately 50 m isobath). Seasonal variations of dissolved Mn in the ECS were significant, with the highest concentrations occurring in summer. Dissolved Mn in the Changjiang Estuary was nonconservative, and significant quantities were removed by net sorption onto suspended particulate matter. A model describing the sorption processes was applied to data for the Changjiang Estuary. Regeneration of dissolved Mn took place in near‐bottom waters of the suboxic zone in August 2011, following extensive consumption of oxygen. The benthic flux of dissolved Mn was estimated based on Mn concentrations in the overlying waters and the near‐bottom waters. A preliminary box model was established to develop a dissolved Mn budget for the ECS. Based on the dissolved Mn content in the ECS and the total input flux, a residence time of 76–350 days for dissolved Mn in the ECS was inferred.
CO2 flux and chemistry of El Chichón crater lake (México) in the period 2013–2015: Evidence for the enhanced volcano activity
Authors: Jácome Paz Mariana P. , Taran Yuri , Inguaggiato Salvatore , Collard Nathalie
Published: January 2016

The CO2 flux from El Chichón crater in the period from 2014 to 2015 increased by a factor of 3 (from ~260 t d−1 to ~800 t d−1) compared to the 2007–2008 data. The mechanism triggering the CO2 flux from the lake surface has changed from being dominantly diffusive to mainly advective (bubbling). The Cl concentration was steadily decreasing during the last two decades in the Na‐Cl boiling springs feeding the lake. Since 2013, for both lake and SP springs, the Cl concentration has increased up to the 2005 Cl concentration levels. A large degassing spot in the middle of the lake was found in April 2015 with a CO2 flux of more than 10,000 g m−2 d−1. These observations are the evidence of the onset of a new stage of activity within the volcano‐hydrothermal system of El Chichón volcano associated most probably with changes in the magmatic activity at depth.
Complex force history of a calving‐generated glacial earthquake derived from broadband seismic inversion
Authors: Sergeant Amandine , Mangeney Anne , Stutzmann Eléonore , Montagner Jean‐Paul , Walter Fabian , Moretti Laurent , Castelnau Olivier
Published: January 2016

The force applied to the Earth by the calving of two icebergs at Jakobshavn Isbrae, Greenland, has been quantified. The source force history was recovered by inversion of regional broadband seismograms without any a priori constraint on the source time function, in contrast with previous studies. For periods 10–100 s, the three‐component force can be obtained from distant stations alone and is proportional to the closest station seismograms. This inversion makes it possible to quantify changes of the source force direction and amplitude as a function of time and frequency. A detailed comparison with a video of the event was used to identify four forces associated with collision, then bottom‐out and top‐out rotation of the first and second icebergs, and ice mélange motion. Only the two iceberg rotations were identified in previous studies. All four processes are found here to contribute to the force amplitude and variability. Such a complete time‐frequency force history provides unique dynamical constraints for mechanical calving models.
Fault mirrors in seismically active fault zones: A fossil of small earthquakes at shallow depths
Authors: Kuo Li‐Wei , Song Sheng‐Rong , Suppe John , Yeh En‐Chao
Published: January 2016

Fault mirrors (FMs) are naturally polished and glossy fault slip surfaces that can record seismic deformation at shallow depths. They are important for investigating the processes controlling dynamic fault slip. We characterize FMs in borehole samples from the hanging wall damage zone of the active Hsiaotungshi reverse fault, Taiwan. Here we report the first documented occurrence of the combination of silica gel and melt patches coating FMs, with the silica gel resembling those observed on experimentally formed FMs that were cataclastically generated. In addition, the melt patches, which are unambiguous indicators of coseismic slip, suggest that the natural FMs were produced at seismic rates, presumably resulting from flash heating at asperities on the slip surfaces. Since flash heating is efficient at small slip, we propose that these natural FMs represent fossils of small earthquakes, formed in either coseismic faulting and folding or aftershock deformation in the active Taiwan fold‐and‐thrust belt.
Slow slip event within a gap between tremor and locked zones in the Nankai subduction zone
Authors: Takagi Ryota , Obara Kazushige , Maeda Takuto
Published: January 2016

We report on two small long‐term slow slip events (SSEs) within a gap between tremor and locked zones in the Nankai subduction zone, southwest Japan. The SSEs were detected by subtracting the steady state component and postseismic effects of large earthquakes from long‐term and high‐density Global Navigation Satellite System data. Both SSEs occurred in adjacent regions of the Bungo channel following long‐term SSEs in the Bungo channel in 2003 and 2010. The estimated slip was 1–5 cm/year that lasted at least 1–2 years after 2004 and 2011, partly accommodating plate convergence. As the low‐frequency tremor in the downdip region is activated at the same time as the Bungo channel long‐term SSE, a spatiotemporal correlation was observed between the detected SSEs and long‐term tremor activity in the downdip region. This correlation indicates along‐dip interaction of the slips on the subducting plate interface.
On the influence of cold‐water coral mound size on flow hydrodynamics, and vice versa
Authors: Cyr Frédéric , van Haren Hans , Mienis Furu , Duineveld Gerard , Bourgault Daniel
Published: January 2016

Using a combination of in situ observations and idealistic 2‐D nonhydrostatic numerical simulations, the relation between cold‐water coral (CWC) mound size and hydrodynamics is explored for the Rockall Bank area in the North Atlantic Ocean. It is shown that currents generated by topographically trapped tidal waves in this area cause large isopycnal depressions resulting from an internal hydraulic control above CWC mounds. The oxygen concentration distribution is used as a tracer to visualize the flow behavior and the turbulent mixing above the mounds. By comparing two CWC mounds of different sizes and located close to each other, it is shown that the resulting mixing is highly dependent on the size of the mound. The effects of the hydraulic control for mixing, nutrient availability, and ecosystem functioning are also discussed.
Is there a geomorphic expression of interbasin groundwater flow in watersheds? Interactions between interbasin groundwater flow, springs, streams, and geomorphology
Authors: Frisbee Marty D. , Tysor Elizabeth H. , Stewart‐Maddox Noah S. , Tsinnajinnie Lani M. , Wilson John L. , Granger Darryl E. , Newman Brent D.
Published: January 2016

Interbasin groundwater flow (IGF) can play a significant role in the generation and geochemical evolution of streamflow. However, it is exceedingly difficult to identify IGF and to determine the location and quantity of water that is exchanged between watersheds. How does IGF affect landscape/watershed geomorphic evolution? Can geomorphic metrics be used to identify the presence of IGF? We examine these questions in two adjacent sedimentary watersheds in northern New Mexico using a combination of geomorphic/landscape metrics, springflow residence times, and spatial geochemical patterns. IGF is expressed geomorphically in the landscape placement of springs and flow direction and shape of stream channels. Springs emerge preferentially on one side of stream valleys where landscape incision has intercepted IGF flow paths. Stream channels grow toward the IGF source and show little bifurcation. In addition, radiocarbon residence times of springs decrease and the geochemical composition of springs changes as the connection to IGF is lost.
Effects of sulfate aerosol forcing on East Asian summer monsoon for 1985–2010
Authors: Kim Minjoong J. , Yeh Sang‐Wook , Park Rokjin J.
Published: January 2016

We examine the effect of anthropogenic aerosol forcing on the East Asian summer monsoon (EASM) using the Community Atmosphere Model version 5.1.1. One control and two sensitivity model experiments were conducted in order to diagnose the separate roles played by sea surface temperature (SST) variations and anthropogenic sulfate aerosol forcing changes in East Asia. We find that the SST variation has been a major driver for the observed weakening of the EASM, whereas the effect of the anthropogenic aerosol forcing has been opposite and has slightly intensified the EASM over the recent decades. The reinforcement of the EASM results from radiative cooling by the sulfate aerosol forcing, which decelerates the jet stream around the jet's exit region. Subsequently, the secondary circulation induced by such a change in the jet stream leads to the increase in precipitation around 18–23°N. This result indicates that the increase in anthropogenic emissions over East Asia may play a role in compensating for the weakening of the EASM caused by the SST forcing.
Contrasting fast precipitation responses to tropospheric and stratospheric ozone forcing
Authors: MacIntosh C. R. , Allan R. P. , Baker L. H. , Bellouin N. , Collins W. , Mousavi Z. , Shine K. P.
Published: January 2016

The precipitation response to radiative forcing (RF) can be decomposed into a fast precipitation response (FPR), which depends on the atmospheric component of RF, and a slow response, which depends on surface temperature change. We present the first detailed climate model study of the FPR due to tropospheric and stratospheric ozone changes. The FPR depends strongly on the altitude of ozone change. Increases below about 3 km cause a positive FPR; increases above cause a negative FPR. The FPR due to stratospheric ozone change is, per unit RF, about 3 times larger than that due to tropospheric ozone. As historical ozone trends in the troposphere and stratosphere are opposite in sign, so too are the FPRs. Simple climate model calculations of the time‐dependent total (fast and slow) precipitation change, indicate that ozone's contribution to precipitation change in 2011, compared to 1765, could exceed 50% of that due to CO2 change.
Assimilating atmospheric observations into the ocean using strongly coupled ensemble data assimilation
Authors: Sluka Travis C. , Penny Stephen G. , Kalnay Eugenia , Miyoshi Takemasa
Published: January 2016

The local ensemble transform Kalman filter (LETKF) is used to develop a strongly coupled data assimilation (DA) system for an intermediate complexity ocean‐atmosphere coupled model. Strongly coupled DA uses the cross‐domain error covariance from a coupled‐model background ensemble to allow observations in one domain to directly impact the state of the other domain during the analysis update. This method is compared to weakly coupled DA in which the coupled model is used for the background, but the cross‐domain error covariance is not utilized. We perform an observing system simulation experiment with atmospheric observations only. Strongly coupled DA reduces the ocean analysis errors compared to weakly coupled DA, and the higher accuracy of the ocean also improves the atmosphere. The LETKF system design presented should allow for easy implementation of strongly coupled DA with other types of coupled models.
A decadally delayed response of the tropical Pacific to Atlantic multidecadal variability
Authors: Zanchettin Davide , Bothe Oliver , Graf Hans F. , Omrani Nour‐Eddine , Rubino Angelo , Jungclaus Johann H.
Published: January 2016

North Atlantic sea surface temperature anomalies are known to affect tropical Pacific climate variability and El Niño–Southern Oscillation (ENSO) through thermocline adjustment in the equatorial Pacific Ocean. Here coupled climate simulations featuring repeated idealized cycles of the Atlantic Multidecadal Oscillation (AMO) generated by nudging its tropical branch demonstrate that the tropical Pacific response to the AMO also entails a substantial decadally delayed component. The simulations robustly show multidecadal fluctuations in central equatorial Pacific sea surface temperatures lagging the AMO by about three decades and a subdecadal cold‐to‐warm transition of the tropical Pacific mean state during the AMO's cooling phase. The interplay between out‐of‐phase responses of seawater temperature and salinity in the western Pacific and associated density anomalies in local thermocline waters emerge as crucial factors of remotely driven multidecadal variations of the equatorial Pacific climate. The delayed AMO influences on tropical Pacific dynamics could help understanding past and future ENSO variability.
Near‐relativistic electron acceleration by Landau trapping in time domain structures
Authors: Mozer F.S. , Artemyev A. , Agapitov O.V. , Mourenas D. , Vasko I.
Published: January 2016

Data from the Van Allen Probes have provided the first extensive evidence of nonlinear (as opposed to quasi‐linear) wave‐particle interactions in space with the associated rapid (less than a bounce period) electron acceleration to hundreds of keV by Landau resonance in the parallel electric field of time domain structures (TDSs) traveling at high speeds (~20,000 km/s). This observational evidence is supported by simulations and discussion of the source and spatial extent of the fast TDS. This result indicates the possibility that the electrostatic fields in TDS may generate the electron seed population for cyclotron resonance interaction with chorus waves to make higher‐energy electrons.
Rainfall variations induced by the lunar gravitational atmospheric tide and their implications for the relationship between tropical rainfall and humidity
Authors: Kohyama Tsubasa , Wallace John M.
Published: January 2016

Classical tidal theory predicts that the lunar gravitational semidiurnal tide (L2) should induce perturbations in relative humidity (RH). Adiabatic expansion in divergent flow in advance of the L2 pressure minimum cools the air and reduces its saturation vapor pressure, thereby increasing the rate of condensation in saturated air parcels and causing the relative humidity (RH) of unsaturated parcels to rise. Here we detect a statistically significant L2 signature in precipitation rate (P) in a 15 year, eight times daily, global precipitation data set acquired in the Tropical Rainfall Measuring Mission. Consistent with tidal theory and with the notion that L2 modulates P mainly by perturbing RH, P varies out of phase with pressure, and it increases at a rate of about 10% per 1% increase in RH. These measurements thus provide a measure of the sensitivity of P to planetary‐scale changes in RH. Analysis of solar semidiurnal (S2) tidal statistics yields similar results.
Along‐trench variations in the seismic structure of the incoming Pacific plate at the outer rise of the northern Japan Trench
Authors: Fujie Gou , Kodaira Shuichi , Sato Takeshi , Takahashi Tsutomu
Published: January 2016

To investigate along‐trench variations in the seismic structure of the incoming oceanic plate and their effect on water transportation by the oceanic plate, we conducted a wide‐angle seismic survey of a trench‐parallel transect 270 km long on the outer rise of the northern Japan Trench. The resulting seismic structure models show that the central part of the transect is characterized by rough topography, thick oceanic crust, low seismic velocities, and high Vp/Vs ratios, suggesting pervasive fracturing and high water content (hydration) there. These observations are consistent with the presence of an ancient fracture zone associated with ridge propagation. The trenchward extension of this fracture zone corresponds to an area of low interplate seismicity, low seismic velocities, and high Vp/Vs ratio around the depth of the subduction interface. Our results suggest that this ancient scar on the oceanic plate influences along‐trench variations in interplate seismic coupling through its effect on water transportation.
Stationary mesoscale eddies, upgradient eddy fluxes, and the anisotropy of eddy diffusivity
Authors: Lu Jianhua , Wang Fuchang , Liu Hailong , Lin Pengfei
Published: January 2016

The mesoscale eddies of which parameterization is needed in coarse‐resolution ocean models include not only the transient eddies akin to baroclinic instability but also the stationary eddies associated with topography. By applying a modified Lorenz‐type decomposition to the eddy‐permitting Southern Ocean State Estimate, we show that the stationary mesoscale eddies contribute a significant part to the total eddy kinetic energy, eddy enstrophy, and the total eddy‐induced isopycnal thickness and potential vorticity fluxes. We find that beneath middepth (about 1000 m) the upgradient eddy fluxes, or so‐called “negative” eddy diffusivities, are mainly attributed to the stationary mesoscale eddies, whereas the remaining transient eddy diffusivity is positive, for which the Gent and McWilliams (1990) parameterization scheme applies well. A quantitative method of measuring the anisotropy of eddy diffusivity is presented. The effect of stationary mesoscale eddies is one of major sources responsible for the anisotropy of eddy diffusivity. We suggest that an independent parameterization scheme for stationary mesoscale eddies may be needed for coarse‐resolution ocean models, although the transient eddies remain the predominant part of mesoscale eddies in the oceans.
Dust devils in thin air: Vortex observations at a high‐elevation Mars analog site in the Argentinian Puna
Authors: Lorenz Ralph D. , Radebaugh Jani
Published: January 2016

We report in situ measurements and field observations of dust devils at ~3800–4200 m elevation in the Argentine desert plateau (Puna). These first quantitative data at elevations where the ambient atmospheric pressure is only ~600–700 mbar support the notion that large and strong dust devils may be systematically more common in low‐pressure conditions, although regional meteorology and/or surface thermophysical properties may also contribute.
Smooth 2‐D ocean sound speed from Laplace and Laplace‐Fourier domain inversion of seismic oceanography data
Authors: Blacic Tanya M. , Jun Hyunggu , Rosado Hayley , Shin Changsoo
Published: January 2016

In seismic oceanography, processed images highlight small temperature changes, but inversion is needed to obtain absolute temperatures. Local search‐based full waveform inversion has a lower computational cost than global search but requires accurate starting models. Unfortunately, most marine seismic data have little associated hydrographic data and the band‐limited nature of seismic data makes extracting the long wavelength sound speed trend directly from seismic data inherently challenging. Laplace and Laplace‐Fourier domain inversion (LDI) can use rudimentary starting models without prior information about the medium. Data are transformed to the Laplace domain, and a smooth sound speed model is extracted by examining the zero and low frequency components of the damped wavefield. We applied LDI to five synthetic data sets based on oceanographic features and recovered smoothed versions of our synthetic models, showing the viability of LDI for creating starting models suitable for more detailed inversions.
New Antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in Antarctica
Authors: Scheinert M. , Ferraccioli F. , Schwabe J. , Bell R. , Studinger M. , Damaske D. , Jokat W. , Aleshkova N. , Jordan T. , Leitchenkov G. , Blankenship D. D. , Damiani T. M. , Young D. , Cochran J. R. , Richter T. D.
Published: January 2016

Gravity surveying is challenging in Antarctica because of its hostile environment and inaccessibility. Nevertheless, many ground‐based, airborne, and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s. We present the first modern Antarctic‐wide gravity data compilation derived from 13 million data points covering an area of 10 million km2, which corresponds to 73% coverage of the continent. The remove‐compute‐restore technique was applied for gridding, which facilitated leveling of the different gravity data sets with respect to an Earth gravity model derived from satellite data alone. The resulting free‐air and Bouguer gravity anomaly grids of 10 km resolution are publicly available. These grids will enable new high‐resolution combined Earth gravity models to be derived and represent a major step forward toward solving the geodetic polar data gap problem. They provide a new tool to investigate continental‐scale lithospheric structure and geological evolution of Antarctica.
Pulsating proton aurora caused by rising tone Pc1 waves
Authors: Nomura R. , Shiokawa K. , Omura Y. , Ebihara Y. , Miyoshi Y. , Sakaguchi K. , Otsuka Y. , Connors M.
Published: January 2016

We found rising tone emissions with a dispersion of ∼1 Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over ∼30 min from 0250 UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7°N, 246.7°E, magnetic latitude 61.7°N). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all‐sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, ∼10% variations in intensity, and fine structures of 3° in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one‐to‐one correspondences with the Pc1 rising tones. This suggests that these rising tones scatter magnetospheric protons intermittently at the equatorial region. The radial motion of the magnetospheric source, of which the isolated proton aurora is a projection, can explain the central frequency increase of Pc1, but not the shorter period (tens of seconds) frequency increase of ∼1 Hz in Pc1 rising tones. We suggest that EMIC‐triggered emissions generate the frequency increase of Pc1 rising tones on the ground and that they also cause the Pc1 pearl structure, which has a similar characteristic time.
Lunar dust simulant charging and transport under UV irradiation in vacuum: Experiments and numerical modeling
Authors: Champlain A. , Matéo‐Vélez J.‐C. , Roussel J.‐F. , Hess S. , Sarrailh P. , Murat G. , Chardon J.‐P. , Gajan A.
Published: January 2016

Recent high‐altitude observations, made by the Lunar Dust Experiment (LDEX) experiment on board LADEE orbiting the Moon, indicate that high‐altitude (>10 km) dust particle densities are well correlated with interplanetary dust impacts. They show no evidence of high dust density suggested by Apollo 15 and 17 observations and possibly explained by electrostatic forces imposed by the plasma environment and photon irradiation. This paper deals with near‐surface conditions below the domain of observation of LDEX where electrostatic forces could clearly be at play. The upper and lower limits of the cohesive force between dusts are obtained by comparing experiments and numerical simulations of dust charging under ultraviolet irradiation in the presence of an electric field and mechanical vibrations. It is suggested that dust ejection by electrostatic forces is made possible by microscopic‐scale amplifications due to soil irregularities. At low altitude, this process may be complementary to interplanetary dust impacts.
Oxygen impacts on dipolarization fronts and reconnection rate
Authors: Liang Haoming , Ashour‐Abdalla Maha , Lapenta Giovanni , Walker Raymond J.
Published: January 2016

Spacecraft observations near a magnetotail X line show that oxygen (O+) ions are minor species during nonstorm substorms, but they can become major species during some of the storm time substorms. Dipolarization fronts (DFs), which are characterized by a sharp increase northward magnetic field in the magnetotail, are commonly observed during magnetospheric substorms. In this study, we investigated the O+ effects on DFs and the reconnection rate during magnetotail reconnection. We used a 2.5‐D implicit particle‐in‐cell simulation in a 2‐D Harris current sheet in the presence of H+ and O+ ions. Simulation runs with equal number densities of O+ and H+ (O+ run) and with pure H+ ion species (H+ run) were performed. Comparing the two different runs, we found that both the reconnection rate and the DF speed in the O+ run were much less than those in the H+ run. By studying the force balance and plasma composition at the DF, we found that the outflow magnetic flux and DF propagation were encumbered by the current sheet O+ inertia, which reduced the DF speed and delayed the reconnection rate in the O+ run. We also found an ambipolar electric field in the O+ run due to the different inflow and outflow speeds of O+ and electrons in the O+ diffusion region. As a result, this ambipolar electric field induced O+ drag on the convective magnetic field in the O+ diffusion region. The small reconnection rate determined in the O+ run can be attributed to the current sheet inertia and the O+ drag on the convective magnetic flux.
Comparison study of ring current simulations with and without bubble injections
Authors: Yang Jian , Toffoletto Frank R. , Wolf Richard A.
Published: January 2016

For many years, stand‐alone ring current models have been successfully producing storm time ring current enhancements without specifying explicit localized transient injections along their outer boundaries. However, both observations and simulations have suggested that the frequent burst flows or bubble injections can contribute substantially to the storm time ring current energy. In this paper, we investigate the difference in the spatial and temporal development of the ring current distribution with and without bubble injections using the Rice Convection Model‐Equilibrium. The comparison study indicates that the simulation with bubble effects smoothed out along geosynchronous orbit can predict approximately the same large‐scale ring current pressure distribution and electric potential pattern as the simulation with bubble effects included. Our results suggest that the increase of the hot plasma population along geosynchronous orbit can be envisaged as an integrated effect of bubble injections from the near‐Earth plasma sheet. However, the observed fluctuations in the plasma population and electric field can only be captured when the mesoscale injections are included in the simulation. We also confirmed again that adiabatic convection of fully populated flux tubes cannot inject the ring current from the middle plasma sheet. The paper provides a justification for using stand‐alone ring current models in the inner magnetosphere to simulate magnetic storms, without explicit consideration of bubbles and magnetic buoyancy effects inside geosynchronous orbit.
The “zebra stripes”: An effect of F region zonal plasma drifts on the longitudinal distribution of radiation belt particles
Authors: Lejosne Solène , Roederer Juan G.
Published: January 2016

We examine a characteristic effect, namely, the ubiquitous appearance of structured peaks and valleys called zebra stripes in the spectrograms of energetic electrons and ions trapped in the inner belt below L ~ 3. We propose an explanation of this phenomenon as a purely kinematic consequence of particle drift velocity modulation caused by F region zonal plasma drifts in the ionosphere. In other words, we amend the traditional assumption that the electric field associated with ionospheric plasma drives trapped particle distributions into rigid corotation with the Earth. An equation based on a simple first‐order model is set up to determine quantitatively the appearance of zebra stripes as a function of magnetic time. Our numerical predictions are in agreement with measurements by the Radiation Belt Storm Probes Ion Composition Experiment detector onboard Van Allen Probes, namely: (1) the central energy of any peak identified in the spectrum on the dayside is the central energy of a spectral valley on the night side, and vice versa; (2) there is also an approximate peak‐to‐valley inversion when comparing the spectrum of trapped electrons with that of trapped ions in the same place; and (3) the actual energy separation between two consecutive peaks (or number of stripes) in the spectrogram of a trapped population is an indicator of the time spent by the particles drifting under quiet conditions.
O+ and H+ above the polar cap: Observations and semikinetic simulations
Authors: Barghouthi I. A. , Abudayyeh H. A. , Slapak R. , Nilsson H.
Published: January 2016

A one‐dimensional direct simulation Monte Carlo model is used to study the outflow of O+ and H+ ions from 1.2 RE to 15.2 RE along two flight trajectories originating from the polar cap, namely, the central polar cap (CPC) and the cusp. To study the effect of varying geophysical conditions and to deduce the proper set of parameters, several parameters were varied, and the results were compared to corresponding data from Cluster spacecraft. First, several sets of diffusion coefficients were considered based on using diffusion coefficients calculated by Barghouthi et al. (1998), Nilsson et al. (2013), and Abudayyeh et al. (2015b) for different altitude intervals. It was found that in the central polar cap using the diffusion coefficients reported by Barghouthi et al. (1998) for altitudes lower than 3.7 RE, zero diffusion coefficients between 3.7 and 7.5 RE and diffusion coefficients from Nilsson et al. (2013) for altitudes higher than 7.5 RE provide the best fit for O+ ions. For O+ ions in the cusp the best fit was obtained for using Barghouthi et al. (1998) diffusion coefficients for altitudes lower than 3.7 RE and Nilsson et al. (2013) diffusion coefficients for altitudes higher than that. The best fit for H+ ions in both regions was obtained by using the diffusion coefficients calculated by Abudayyeh et al. (2015b). Also, it was found that along an ion's trajectory the most recent heating dominates. Second, the strength of centrifugal acceleration was varied by using three values for the ionospheric electric field, namely, 0, 50, and 100 MV/m. It was found that the value of 50 MV/m provided the best fit for both ion species in both regions. Finally, the lower altitude boundary conditions and the electron temperature were varied. Increasing the electron temperature and the lower altitude O+ parallel velocity were found to increase the access of O+ ions to higher altitudes and therefore increase the density at a given altitude. The variation of all other boundary conditions only affected the densities of the ions and not the other moments due to the overwhelming effect of wave‐particle interaction. Furthermore, varying the parameters of one ion species has no effect on the other ion species. We also compared the energy gain per ion due to wave‐particle interaction, centrifugal acceleration, and ambipolar electric field and found that wave‐particle interaction is the most important mechanism, while ambipolar electric field is relatively unimportant especially at higher altitudes.
Remote diagnostic of the hydrogen wall through measurements of the backscattered solar Lyman alpha radiation by Voyager 1/UVS in 1993–2003
Authors: Katushkina O. A. , Quémerais E. , Izmodenov V. V. , Alexashov D. B. , Sandel B. R.
Published: January 2016

We perform a new analysis of the Lyman alpha data obtained by Voyager 1 during the spatial scans in 1993–2003 while Voyager 1 was at 53–88 AU from the Sun. These data are the important source of information on the hydrogen distribution in the outer heliosphere. A sophisticated global kinetic‐MHD model of the heliospheric interface and a radiative transfer model are used for the analysis. It is shown for the first time that the ratio of the Lyman alpha intensities detected in the downwind and upwind lines of sight in the outer heliosphere is sensitive to the configuration (peak value and location) of the hydrogen wall. The hydrogen wall is a source of Doppler‐shifted backscattered Lyman alpha photons, so it can be seen from inside the heliosphere. Therefore, Voyager 1/ultraviolet spectrometer (UVS) Lyman alpha data can be used for remote sensing of the hydrogen wall. We show that our current global model of the outer heliosphere, which is consistent with many other measurements including Lyman alpha data from both Voyager 1 and 2 in 1980–1993, provides a systematically larger downwind to upwind intensity ratio compared with the UVS data in 1993–2003. In order to decrease the ratio, a higher and/or closer hydrogen wall is needed.
Traveling planetary‐scale waves in the lower thermosphere: Effects on neutral density and composition during solar minimum conditions
Authors: Sassi Fabrizio , Liu Han‐Li , Emmert John T.
Published: January 2016

The effects of breaking of traveling, planetary scale Rossby waves (TPWs) in the lower thermosphere are investigated with respect to the mixing of neutral constituents. We use numerical simulations of the Whole Atmosphere Community Climate Model, eXtended version, whose meteorology below 92 km is constrained by atmospheric specifications obtained from operational weather forecast/data assimilation system. The Fourier spectra show that the amplitude of TPWs with periods between 3 and 10 days are statistically significant in some years; the amplitude and phase of the band‐pass filtered behavior is consistent with the behavior of the 5 day wave. A wavelet analysis using the S‐transform shows that large variations with periods between 3 and 10 days can occur in relatively narrow temporal windows (20–30 days) during boreal winter. The momentum flux entering the lower thermosphere during the times of TPW amplification is shown to be large, and the amplifications of the TPWs in the thermosphere are not always associated with stratospheric sudden warming. The subtropical zonal accelerations are consistent with Rossby wave encountering a surf zone at low latitudes, resulting in wave breaking. The zonal acceleration is shown to be associated with a meridional diffusion, which is largest in the lower thermosphere where the wave activity and the wave breaking are also large. The ultimate effect on neutral density and composition is a meridional, down‐gradient mixing; although this horizontal diffusion is largest below 110 km, the effects on the composition are amplified with increasing altitude, due to the diffusive separation of the thermosphere.
Generation of magnetosonic waves over a continuous spectrum
Authors: Chen Lunjin , Sun Jicheng , Lu Quanming , Gao Xinliang , Xia Zhiyang , Zhima Zeren
Published: January 2016

Magnetosonic waves, also known as equatorial noise emission, were found to have discrete frequency structures, which is consistent with instability caused by proton ring distribution. Nonetheless, nondiscrete structure, i.e., a broadband spectrum over a continuous frequency range, has been reported. We investigate the question whether proton ring distribution can generate nondiscrete spectra for perpendicularly propagating magnetosonic waves. We propose discrete and nondiscrete characteristics of the local instability for explaining the observation of discrete, continuous, and mixed spectra. The criterion for transition from discrete and continuous instability is given, γ >∼ Ωh/2, where γ is wave growth rate and Ωh is proton cyclotron frequency. The condition is verified by particle‐in‐cell simulation using more realistic electron‐to‐proton mass ratio and speed of light than in previous studies. Such criterion of generating a continuous spectrum can be tested against simultaneous in situ measurement of wave and particle. We also find that the modes at low Ωh harmonics, including the fundamental Ωh, can be still excited through nonlinear wave‐wave coupling, even when they are neutral modes (γ = 0) according to the linear kinetic theory. Comparison with magnetosonic waves in cold plasma limit and electromagnetic ion Bernstein mode is also discussed.
Diel vertical migration of zooplankton at the S1 biogeochemical mooring revealed from acoustic backscattering strength
Authors: Inoue Ryuichiro , Kitamura Minoru , Fujiki Tetsuichi
Published: January 2016

We examined the diel vertical migration of zooplankton by using the backscatter strength obtained from moored acoustic Doppler current profilers at mooring site S1 in the North Pacific subtropical gyre. There was seasonal variability in the vertical distribution and migration of the high‐backscatter layers in that they became deeper than the euphotic zone (<100 m) in winter and were confined above this depth in other seasons. Seasonal changes in daylight hours also affected the timing of the diel migration. We found that lunar cycles affected vertical distributions of zooplankton near the surface by changing the light intensity. Physical events, such as mixed‐layer deepening and restratification and the passage of a mesoscale eddy, also affected zooplankton behavior possibly by changing food environment in the euphotic zone. Since the comparison with net samples indicated that the backscatter likely represents the bulk biomass, the accuracy of biomass estimates based on net samples could be influenced by the high temporal variability of zooplankton distributions.
Seasonal variations of seawater pCO2 and sea‐air CO2 fluxes in a fringing coral reef, northern South China Sea
Authors: Yan Hongqiang , Yu Kefu , Shi Qi , Tan Yehui , Liu Guohui , Zhao Meixia , Li Shu , Chen Tianran , Wang Yinghui
Published: January 2016

Evidence based on four field surveys conducted between July 2009 and April 2011 indicates that both sea surface partial pressures of CO2 (pCO2) and sea–air CO2 fluxes at Luhuitou fringing reef in Sanya, Hainan Island, northern South China Sea (SCS) are subject to significant seasonal variations. The diurnal variation of seawater pCO2 ranges from 264 to 579 μatm in summer, which is much larger than that in autumn (152–335 μatm), in winter (84–260 μatm), and in spring (114–228 μatm). The sea‐air CO2 flux in summer (∼9.6 mmol CO2 m−2 d−1) is also larger than that in other seasons (i.e.,∼3 mmol CO2 m−2 d−1 in spring, ∼3.5 mmol CO2 m−2 d−1 in autumn, and ∼2.7 mmol CO2 m−2 d−1 in winter). The atmospheric pCO2 in this reef shows small diurnal and seasonal variations. The integration of the time‐series pCO2 data shows that the reef area is a weak source of atmospheric CO2 at ∼0.54 mol CO2 m−2 yr−1. Further analyses indicate that the seasonal variations of the surface seawater pCO2 in Luhuitou fringing reef are mainly affected by seasonally‐dependent biological metabolic processes (organic processe and inorganic process), and that the organic process play a more important role than the inorganic process. Seasonal sea surface temperature (SST) variations and hydrodynamic processes may also have some influence on seawater pCO2 variation.
Tides in the mesopause region over Antarctica: Comparison of whole atmosphere model simulations with ground‐based observations
Authors: Akmaev R. A. , Forbes J. M. , Lübken F.‐J. , Murphy D. J. , Höffner J.
Published: January 2016

Almost a quarter century ago first optical and radar observations from the South Pole revealed rich dynamics unexpected from classical tidal theory. A strong semidiurnal wind oscillation was detected near the mesopause implying substantial deviations from the classical view that the semidiurnal variation is dominated by the migrating tide. Subsequent systematic observations exhibited large seasonal variations of both the diurnal and semidiurnal tide with dramatic reduction in amplitude from summer to winter. First numerical simulations with a realistic general circulation model extending into the lower thermosphere indicated the presence of nonmigrating tides with substantial amplitudes in the polar regions. However, direct model‐data comparisons have been limited to idealized linear models. Here whole atmosphere model (WAM) simulations for January and July are compared with available wind climatologies based on multiyear radar observations at different locations in Antarctica as well as with first summertime lidar measurements of temperature. The diurnal tide simulation agrees well with most of the independent radar and satellite wind observations in both seasons. The strong semidiurnal tide comprised of migrating and nonmigrating components is well reproduced in summer, while in winter the model tends to overestimate the amplitudes over the continental edge. Besides model validation, a self‐consistent numerical solution also enables cross validation of observations made with different instruments at different locales.