bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleoceanographic changes in the Eastern Equatorial Pacific over the last 10 Myr
Authors: Seki Osamu , Schmidt Daniela N. , Schouten Stefan , Hopmans Ellen C. , Sinninghe Damsté Jaap S. , Pancost Richard D.
Published: July 2012

To examine the Late Neogene evolution of tropical Pacific oceanography, we determined multiple geochemical proxy records for temperature (U37K′and TEX86Hindices) and primary productivity (algal biomarkers and diol indices) in sediments recovered at ODP Site 1241 in the East Equatorial Pacific (EEP) spanning a record of the last 10 Myr. The TEX86Htemperatures are lower than those recorded by U37K′indices, exhibiting large fluctuations and suggesting strong warming during the Mid Pliocene Warm Period (MPWP; 4.5–3.2 Ma) and significantly colder temperature during the Late Miocene cooling period (7–5 Ma) and after the Middle Pliocene Warm Period (MPWP). Such variations could reflect changes in the EEP thermocline temperatures, but we suggest that they instead reflect changes in the depth of export production of glycerol dialkyl glycerol tetraether lipids in response to changes in the upper ocean structure. A combination of temperature records, inferred to represent different and likely varying depths in the water column, as well as algal biomarker records for export production and ecosystem structure, suggest that both productivity and inference upwelling were reduced in the EEP during warmer periods, such as the MPWP and prior to 7 Ma. In contrast, stronger upwelling conditions and associated increased productivity likely prevailed from 7 to 5 Ma and for the past 3 Myr, both corresponding to globally cool intervals. A further increase in EEP productivity occurred at ca 1.8 Ma, coincident with the development of the E‐W Pacific SST gradient. These results confirm previous work that protracted El Niño–like conditions prevailed during warmer intervals of the Pliocene before ultimately descending into the current climate state.
Bayesian parameter uncertainty modeling in a macroscale hydrologic model and its impact on Indian river basin hydrology under climate change
Authors: Raje D. , Krishnan R.
Published: July 2012

Macroscale hydrologic models (MHMs) were developed to study changes in land surface hydrology due to changing climate over large domains, such as continents or large river basins. However, there are many sources of uncertainty introduced in MHM hydrological simulation, such as model structure error, ineffective model parameters, and low‐accuracy model input or validation data. It is hence important to model the uncertainty arising in projection results from an MHM. The objective of this study is to present a Bayesian statistical inference framework for parameter uncertainty modeling of a macroscale hydrologic model. The Bayesian approach implemented using Markov Chain Monte Carlo (MCMC) methods is used in this study to model uncertainty arising from calibration parameters of the Variable Infiltration Capacity (VIC) MHM. The study examines large‐scale hydrologic impacts for Indian river basins and changes in discharges for three major river basins with distinct climatic and geographic characteristics, under climate change. Observed/reanalysis meteorological variables such as precipitation, temperature and wind speed are used to drive the VIC macroscale hydrologic model. An objective function describing the fit between observed and simulated discharges at four stations is used to compute the likelihood of the parameters. An MCMC approach using the Metropolis‐Hastings algorithm is used to update probability distributions of the parameters. For future hydrologic simulations, bias‐corrected GCM projections of climatic variables are used. The posterior distributions of VIC parameters are used for projection of 5th and 95th percentile discharge statistics at four stations, namely, Farakka, Jamtara, Garudeshwar, and Vijayawada for an ensemble of three GCMs and three scenarios, for two time slices. Spatial differences in uncertainty projections of runoff and evapotranspiration for years 2056–2065 for the a1b scenario at the 5th and 95th percentile levels are also projected. Results from the study show increased mean monthly discharges for Farakka and Vijayawada stations, and increased low, mid and high duration flows at Farakka, Jamtara and Vijayawada for the future. However, it is seen that uncertainty introduced due to choice of GCM, is larger than that due to parameter uncertainty for the VIC MHM. The largest effects of runoff predictive uncertainty due to uncertainty in VIC parameters are seen in the Himalayan foothills belt, and the high‐precipitation Northeast region of the country. It is demonstrated through the study that it is relevant and feasible to provide Bayesian uncertainty estimates for macroscale models in projection of large‐scale and regional hydrologic impacts.
Dual‐permeability model for flow in shrinking soil with dominant horizontal deformation
Authors: Coppola Antonio , Gerke Horst H. , Comegna Alessandro , Basile Angelo , Comegna Vincenzo
Published: July 2012

In this study, a dual‐permeability approach is discussed for modeling preferential flow in shrinking soils by accounting for shrinking effects on macropore and matrix domain hydraulic properties. Conceptually, the soil is treated as a dual‐permeability bulk porous medium consisting of two dynamic interacting pore domains: (1) the fracture (from shrinkage) pore domain and (2) the aggregate (interparticles plus structural) or matrix pore domain. The model assumes that the swell‐shrink dynamics is represented by the inversely proportional volume changes of the fracture and matrix domains, while the overall porosity of the total soil, and hence the layer thickness, remains constant. This assumption can be justified for soils with dominant horizontal soil deformation in the swelling‐shrinkage process (shrinkage geometry factor,rs> 3). The swell‐shrink dynamics was included in a one‐dimensional dual‐permeability model in which water flow in both domains was described with the Richards' equation. Swell‐shrink dynamics was incorporated in the model partly by changing the coupled domain‐specific hydraulic properties according to the shrinkage characteristics of the matrix and partly by allowing the fractional contribution of the two domains to change with the pressure head. As a first step, the hysteresis in the swell‐shrink dynamics was not included. We also assumed that the aggregate behavior and its hydraulic properties depend only on the average aggregate water content and not on its internal real distribution. The model proved, describing successfully effects of shrinkage on the spatial and temporal evolution of water contents measured in a silty loam soil in the field.
Spatial and temporal phosphorus distribution changes in a large wetland ecosystem
Authors: Zapata‐Rios Xavier , Rivero Rosanna G. , Naja Ghinwa M. , Goovaerts Pierre
Published: July 2012

Long‐ and short‐term changes in the spatial distribution of surface water phosphorus concentrations were assessed for the Everglades wetland (USA) from 12 years of monitoring data. Changes in phosphorus spatial distributions, before and after implementation of measures to reduce phosphorus, including stormwater treatment areas (STAs) and best management practices (BMPs), were used to evaluate the effect of the remediation strategies in the naturally oligotrophic wetland. Results showed a clear spatial and temporal gradient in phosphorus concentrations, with highest total phosphorus (TP) reaching 200μg/L in the northern Water Conservation Areas (WCAs) because of canal inflow from the Everglades Agricultural Area (EAA). Long‐term records of TP concentrations from 1995 to 2007 showed declines in Water Conservation Area WCA1 during the dry season (−5.1%). Short‐term changes (2003–2007) showed increasing trends in TP concentrations elsewhere in the Everglades, mainly in the southern areas: WCA3 and Everglades National Park (ENP). From 2003 to 2007, phosphorus increased by 7.4% per year in the ENP during the dry season. The area of the Everglades that exceeded the 10μg/L surface water TP concentration ecological threshold was quantified and showed a long‐term overall decline. However, except for the ENP, more than 65% of the Everglades surface area exceeded the 10μg/L water quality threshold in 2007. During recent years, ENP and WCA3 surface areas that exceeded the alternative 15μg/L annual geometric mean slightly increased, confirming the need to closely monitor these two regions.
Loading effect of water table variation and density effect on tidal head fluctuations in a coastal aquifer system
Authors: Wang Xuejing , Li Hailong , Wan Li , Liu Futian , Jiang Xiaowei
Published: July 2012

Water table variation will result in considerable variation of the weight of the pore water, which has loading effects on the groundwater flow in the underlying confined aquifer. Here we present an analytical solution on such a loading effect in a coastal aquifer system consisting of an unconfined aquifer, a confined aquifer, and an impermeable layer between them, with the two lower layers extending under the sea. The solution generalizes several existing ones in the literature. The water table variation's loading effects tend to enhance the amplitude and to reduce the phase shift of the tide‐induced head fluctuation. These effects become considerable when the tidal loading coefficient is large, the aquifer's offshore extending length is long, and the unconfined aquifer has large values of hydraulic conductivity and specific yield. Numerical examination indicated that the assumption of ignoring the density variation causes an error not greater than 2.5% of the tidal amplitude.
Identifying distinct thermal components of a creek
Authors: Boughton David A. , Hatch Christine , Mora Ethan
Published: July 2012

Statistical and heat budget methods for analyzing temperature dynamics of creeks are limited by the ability to resolve thermal processes and fine‐grained thermal structures, respectively. Here we describe a hybrid method that identifies distinct thermal components in a stream's heat budget using only temperature data and an algorithm that employs mutual information to “unmix” signals in the temperature data. Spatial resolution is limited only by the number of temperature‐logging sensors, which can be quite high for distributed‐temperature sensors. Process resolution is at the level of thermal components, defined as distinct collections of heat flux elements sharing coordinated (nonindependent) dynamics. Inference can be used to relate thermal components to meteorological forcing and structural heterogeneity in the fluvial system and to suggest novel hypotheses for further testing with targeted heat budget studies. Applying the method to a small, arid‐land creek produced two novel hypotheses: (1) lateral conduction of heat from adjacent dry land (bed, terraces) appeared to cause a substantial heating of the stream, augmented by off‐channel flow paths, and (2) riparian vegetation was associated with a subtraction of heat from the stream at a rate proportionate to solar insolation, exceeding the maximum decoupling effect of shade by at least 2°C at midday, and suggesting upwelling heat flux from water to tree canopy proportional to sunlight. The method appears useful for generating new hypotheses, for selecting informative sites for detailed heat budgets, for determining the dimensionality of heat budgets in natural streams, and more broadly for associating thermal components to fluvial structure and processes.
2012 AGU medal, award, and prize recipients
Authors: McPhaden Mike , Fine Rana
Published: July 2012

The Honors and Recognition Committee is very pleased to present the 2012 AGU medalists, awardees, and prize recipients. These individuals are recognized for their outstanding contributions to the advancement of Earth and space science and for their service to the scientific community. They have distinguished themselves through their extraordinary achievements and are role models for future generations of scientists. We look forward to recognizing the accomplishments of these esteemed colleagues at an honors ceremony to be held on 5 December 2012 at the Fall Meeting in San Francisco, Calif. This year's honorees are also listed on AGU's Web site at http://sites.agu.org/honors.
Clay anomaly responsible for Mexican slow slip earthquakes
Authors: Schultz Colin
Published: July 2012

Over the past decade, seismologists have uncovered a previously unknown class of earthquakes. Known as slow slip earthquakes (SSEs), these events are marked by their long duration; periodic or repetitive nature; and substantial, though harmless, increases in the velocity of intersecting tectonic plates. In southern Mexico the subduction of the Cocos plate under the North American tectonic plate has been found to harbor SSEs that last for up to a year. Compared to traditional earthquakes, which occur because of a sudden lurch between two frictionally locked plates, SSEs have been traced to the deeper rock underlying this locked layer. The rock properties that lend this deeper layer to the occurrence of SSEs, however, are poorly known. Measuring how seismic waves propagate through the varying rock layers of the south Mexican fault, Song and Kim identify the properties of rock that make this particular system susceptible to slow slip earthquakes.
Large‐scale observations of flows in the ionosphere
Authors: Balcerak Ernie
Published: July 2012

At midlatitudes in the ionosphere, just below the auroral region, narrow channels of strong westward flow have been observed. These flows, known as subauroral polarization streams (SAPS), are driven by pressure gradients in near‐Earth space and are a manifestation of the coupling between the upper atmosphere and the magnetosphere. To better understand these flows, Clausen et al. measured the flow velocities inside SAPS using the new midlatitude chain of Super Dual Auroral Radar Network (SuperDARN) instruments. The observations, which lasted for 3 hours and covered the entire North American continent, are the first large‐scale simultaneous observations of the velocity structure of SAPS.
Groundwater depletion contributes to sea level rise
Authors: Balcerak Ernie
Published: July 2012

Groundwater depletion is contributing substantially to sea level rise and will likely continue to do so over the next several decades, according to a new study by Wada et al. Much of the groundwater extracted for irrigation, drinking, and other uses does not wind up back in the ground but instead evaporates to the atmosphere and then returns to the surface as precipitation, which eventually makes its way to the oceans and leads to sea level rise. The authors reconstructed past groundwater depletion and its contribution to global sea level change and developed new projections for the 21st century based on models. They found that the contribution of groundwater depletion to global sea level increased from 0.035 millimeter per year in 1900 to 0.57 millimeter per year in 2000 and is projected to increase to 0.82 millimeter per year by 2050.
Physical controls of rift interaction identified
Authors: Schultz Colin
Published: July 2012

Valleys formed by lithospheric rifting—which cut into the surface of every continent and even the faces of other planets—are distinctive markers of tectonic activity. Rifts form from a structurally weak segment of the brittle upper crust when stress‐induced fracturing causes lengthening and spreading over hundreds of thousands of years. Rift valleys, known as graben, can extend for thousands of kilometers and spread at rates up to a few centimeters per year. Where multiple individual rift systems come together, tectonic plates can be cut in two or new crust formation regions can arise. Whether separate rifts in close proximity will lead to one of these more consequential outcomes or stagnate as a series of valleys and peaks depends on the physical properties of the rifts, brittle crust, and viscous lower layers of the lithosphere.
Understanding ionospheric instabilities eludes current approaches
Authors: Bhattacharya Atreyee
Published: July 2012

Ionized gases are heavily concentrated in the ionosphere's F zone, the region between 200 and 500 kilometers in altitude, which is critical for transmitting long‐distance radio signals on Earth. However, instabilities in the F region plasma, which can last from seconds to hours and can be spread over centimeters to tens of kilometers, disrupt transmission of radio signals. The plasma instabilities, restricted to the equatorial region following sunset, are called equatorial spread F (ESF). Earth‐based instruments perceive ESF events as “twinkling” radio signals. ESF events, first detected in the 1930s, affect the performance and reliability of space‐borne and ground‐based electronic systems; they can disrupt satellite operations and related communications and navigation systems.
Changing El Niño could reshape Pacific Ocean biology
Authors: Schultz Colin
Published: July 2012

Over the past few decades, scientific understanding of El Niño has grown increasingly complex. Traditionally viewed as a periodic warming focused largely in the eastern equatorial Pacific Ocean, El Niño is associated with reduced productivity in South American fisheries and changing temperature, pressure, and rainfall patterns around the world. In the 1990s, however, researchers started to notice a new kind of El Niño, one where anomalous ocean temperatures were concentrated mainly in the central equatorial Pacific Ocean. This previously unknown mode of variability, now termed the Central Pacific (CP) El Niño, in contrast to the classical Eastern Pacific (EP) El Niño, has increased in frequency and intensity over the past 30 years. Some scientists expect CP El Niños to become the dominant El Niño variant in response to global warming, so understanding their differing effects is a pressing concern.
Langmuir circulation inhibits near‐surface water turbulence
Authors: Schultz Colin
Published: July 2012

In the surface ocean, breaking waves are a major source of air bubbles and turbulent kinetic energy. During the presence of a consistent surface wind, these wave‐generated bubbles, along with other surface material like seaweed or foam, can be drawn into long rows along the surface. Driving this organization is Langmuir circulation, a phenomenon in which the wind and waves cause surface waters to rotate helically, moving like a wire wrapped around a pole in the windward direction. These spiral currents oscillate between clockwise and counterclockwise rotations, such that in some places the surface waters are pushed together and in others they are pulled apart. Researchers have previously found that at sites of convergence the bubbles produced by breaking waves are pushed to depths of 15 meters or more, with important implications for air‐sea gas mixing and other processes.
Peat‐based climate reconstructions run into murky waters?
Authors: Bhattacharya Atreyee
Published: July 2012

Peatlands are globally important ecosystems that serve as archives of past environmental change. Peatlands form over thousands of years from the accumulation of decaying plants and hold water, or in some cases, purely rainwater. Therefore, external processes, such as climate, as well as internal processes, such as the rates of peat growth and decay, control the water table in peatlands. However, throughout the previous century and particularly over the past decade, paleoclimatologists have increasingly relied on reconstructions of the water table in rain‐fed peatlands to infer changes in rainfall through the Holocene period (the past ∼12,000 years), ignoring the potentially important role of internal processes.
Diagenetic alteration of magnetic minerals in Labrador Sea sediments (IODP Sites U1305, U1306, and U1307)
Authors: Kawamura Noriko , Ishikawa Naoto , Torii Masayuki
Published: July 2012

In order to reveal the potential effects of early diagenesis on magnetic minerals in deep‐sea sediments, we studied early diagenetic zones and magnetic mineral characteristics of Lower Pliocene hemipelagic sediment samples from IODP Sites U1305, U1306, and U1307 on Eirik Drift, Labrador Sea. All samples analyzed were unlithified silty clay sediments recovered by a piston corer from depths down to 200 meters composite depth (mcd). Based on shipboard interstitial‐water geochemistry, we divided the sediment column from each site into six early diagenetic zones. Magnetite (Fe3O4) was present at all analyzed depths, whereas maghemite (γFe2O3) was found only above the iron reduction zone. We attribute this to associated changes in interstitial redox conditions, which induced preferential dissolution of maghemitized surfaces on magnetite grains. Mineral magnetic results indicate a general down‐hole change in mean grain size of magnetic minerals. At Site U1307, which has relatively low organic carbon contents, the diagenetic zones occur at greater depths than at the other studies sites. This suggests that interstitial oxygen levels at this site remained high enough to degrade organic matter through oxic bacterial activity, and that detrital magnetic minerals have been preserved even at depth.
Coal maturation by frictional heat during rapid fault slip
Authors: Kitamura Manami , Mukoyoshi Hideki , Fulton Patrick M. , Hirose Takehiro
Published: July 2012

The detection of frictional heating effects along faults provides key insight into the dynamics of earthquakes and faulting. Thermal maturity of organic matter has been considered a possible fault‐thermometer that records the frictional heat signature of ancient earthquakes. However, whether or not organic matter can mature on the order of seconds, typical earthquake rise time, remains uncertain. Here we present the results of experiments aimed at revealing coal maturation by frictional heat generated at slip velocities representative of natural earthquakes of up to 1.3 m/s. Our results show that coal can mature coseismically in ∼11 seconds at temperatures induced by frictional heat ranging from 26 to 266°C. Even with a temperature rise to only 28.7°C over 15 m displacement in ∼3.2 hours, coal can slightly mature within a shear localized zone. The commonly used kinetic model of vitrinite maturation cannot predict the experimental results. A kinetic model involving the effect of flash temperature at grain contacts and mechanochemical effects on reaction kinetics is necessary to better estimate heat generation along a fault.
Seasonal hydrological loading in southern Alaska observed by GPS and GRACE
Authors: Fu Yuning , Freymueller Jeffrey T. , Jensen Tim
Published: July 2012

We compare vertical seasonal loading deformation observed by continuous GPS stations in southern Alaska and modeled vertical displacements due to seasonal hydrological loading inferred from GRACE. Seasonal displacements are significant, and GPS‐observed and GRACE‐modeled seasonal displacements are highly correlated. We define a measure called the WRMS Reduction Ratio to measure the fraction of the position variations at seasonal periods removed by correcting the GPS time series using a seasonal model based on GRACE. The median WRMS Reduction Ratio is 0.82 and the mean is 0.73 ± 0.26, with a value of 1.0 indicating perfect agreement of GPS and GRACE. The effects of atmosphere and non‐tidal ocean loading are important; we add the AOD1B de‐aliasing model to the GRACE solutions because the displacements due to these loads are present in the GPS data, and this improves the correlations between these two geodetic measurements. We find weak correlations for some stations located in areas where the magnitude of the load changes over a short distance, due to GRACE's limited spatial resolution. GRACE models can correct seasonal displacements for campaign GPS measurements as well.
The influence of ENSO on global terrestrial water storage using GRACE
Authors: Phillips T. , Nerem R. S. , Fox‐Kemper Baylor , Famiglietti J. S. , Rajagopalan B.
Published: July 2012

The influence of the El Nino/Southern Oscillation (ENSO) on terrestrial water storage is analyzed for the time period 2003–2010 using monthly estimates of continental water storage from the Gravity Recovery and Climate Experiment (GRACE). Peak correlation between NOAA's Multivariate ENSO Index (MEI) and the measured mass anomaly timeseries shows an R2 of 0.65 for the Amazon Basin and Borneo in Southeast Asia. By including a Hilbert transformation of the MEI to account for time lag, the R2is improved to 0.76. Tropical regions show strong negative correlation with the MEI and arid regions are positively correlated. GRACE is able to detect all the significant known ENSO teleconnection patterns around the globe, including Alaska and Antarctica. In addition, a significant correlation suggests some of Greenland's recent mass loss could be ENSO‐related.
Trends in record‐breaking temperatures for the conterminous United States
Authors: Rowe Clinton M. , Derry Logan E.
Published: July 2012

In an unchanging climate, record‐breaking temperatures are expected to decrease in frequency over time, as established records become increasingly more difficult to surpass. This inherent trend in the number of record‐breaking events confounds the interpretation of actual trends in the presence of any underlying climate change. Here, a simple technique to remove the inherent trend is introduced so that any remaining trend can be examined separately for evidence of a climate change. As this technique does not use the standard definition of a broken record, our records* are differentiated by an asterisk. Results for the period 1961–2010 indicate that the number of record* low daily minimum temperatures has been significantly and steadily decreasing nearly everywhere across the United States while the number of record* high daily minimum temperatures has been predominantly increasing. Trends in record* low and record* high daily maximum temperatures are generally weaker and more spatially mixed in sign. These results are consistent with other studies examining changes expected in a warming climate.
An avenue of eddies: Quantifying the biophysical properties of mesoscale eddies in the Tasman Sea
Authors: Everett J. D. , Baird M. E. , Oke P. R. , Suthers I. M.
Published: July 2012

The Tasman Sea is unique ‐ characterised by a strong seasonal western boundary current that breaks down into a complicated field of mesoscale eddies almost immediately after separating from the coast. Through a 16‐year analysis of Tasman Sea eddies, we identify a region along the southeast Australian coast which we name ‘Eddy Avenue’ where eddies have higher sea level anomalies, faster rotation and greater sea surface temperature and chlorophylla anomalies. The density of cyclonic and anticyclonic eddies within Eddy Avenue is 23% and 16% higher respectively than the broader Tasman Sea. We find that Eddy Avenue cyclonic and anticyclonic eddies have more strongly differentiated biological properties than those of the broader Tasman Sea, as a result of larger anticyclonic eddies formed from Coral Sea water depressing chl. aconcentrations, and for coastal cyclonic eddies due to the entrainment of nutrient‐rich shelf waters. Cyclonic eddies within Eddy Avenue have almost double the chlorophylla (0.35 mg m−3) of anticyclonic eddies (0.18 mg m−3). The average chlorophyll a concentration for cyclonic eddies is 16% higher in Eddy Avenue and 28% lower for anticyclonic eddies when compared to the Tasman Sea. With a strengthening East Australian Current, the propagation of these eddies will have significant implications for heat transport and the entrainment and connectivity of plankton and larval fish populations.
Response of low‐latitude ionosphere to medium‐term changes of solar and geomagnetic activity
Authors: Kutiev Ivan , Otsuka Yuichi , Pancheva Dora , Heelis Rod
Published: July 2012

The paper presents the medium‐term quasi periodic (∼9–27 day) response of middle and low‐latitude ionosphere to solar [F10.7) and geomagnetic (Kp‐index) forcing. The ionospheric response is examined by wavelet analysis of the relative deviations of TEC over Japan for the period of time 2000–2008. It is found that the ∼27‐day rTEC oscillations correlate well with the same oscillations of the solar index F10.7 particularly in the solar maximum and its early declining phase (2001–2005). During the declining phase of solar activity (for example, year of 2005) the Kp‐index variability exhibits additionally strong oscillations with periods 13.5‐ and 9‐days. Similar oscillations are found in rTEC as well but they do not follow the geomagnetic forcing as faithfully as those associated with F10.7. During solar minimum the quasi periodic rTEC variability is shaped mainly by the recurrent geomagnetic activity. An attempt is made to investigate the latitudinal dependence of the ∼9–27‐day rTEC response over Japan as well as the phase relationship between the forcing and response.
Spatial distribution of Kelvin‐Helmholtz instability at low‐latitude boundary layer under different solar wind speed conditions
Authors: Li W. Y. , Guo X. C. , Wang C.
Published: July 2012

Using the PPMLR‐MHD global simulation model, we examined the Kelvin‐Helmholtz (K‐H) instability at the low‐latitude boundary layer (LLBL) under northward interplanetary magnetic field (IMF) conditions with various solar wind speeds (400, 600, and 800 km/s). The spatial distribution of the K‐H wave power in the equatorial plane shows two distinct power populations, referring to the two modes of K‐H surface waves. The spatial evolution of K‐H instability at the boundary layer is classified into four phases: quasi‐stable, exponential growth, linear growth, and nonlinear phases. The boundary layer is quasi‐stable near the subsolar point region. The K‐H instability starts at about 30° longitude, and grows exponentially with a spatial growth rate of 0.28∼0.87 RE−1until ∼45° longitude where the vortices fully develop. At larger longitudes, the instability grows linearly, while the vortices grow in size. From ∼80° longitude to the distant magnetotail, the K‐H instability develops nonlinearly and the vortices roll up. The wave frequency, wavelength, and phase speed are given at various spatial points. Model results show that the higher solar wind speed generates K‐H waves with higher frequency under the northward IMF, and the wavelengths and the phase speeds increase with the increase of the longitude. Moreover, we made a comparison of the K‐H wave periods on Earth's, Mercury's and Saturn's magnetopauses by a proposed prediction method.
Bounce‐averaged approach to radial diffusion modeling: From a new derivation of the instantaneous rate of change of the third adiabatic invariant to the characterization of the radial diffusion process
Authors: Lejosne Solène , Boscher Daniel , Maget Vincent , Rolland Guy
Published: July 2012

In this paper, a new approach for the derivation of the instantaneous rate of change of the third adiabatic invariant is introduced. It is based on the tracking of the bounce‐averaged motion of guiding centers with assumptions that are only kept to the necessary conditions for definition and conservation of the first two adiabatic invariants. The derivation is first given in the case of trapped equatorial particles drifting in a time varying magnetic field in the absence of electrostatic potential. It is then extended to more general cases including time varying electric potentials and non‐equatorial particles. Finally, the general formulation of the third adiabatic invariant time derivative is related to the description of the radial diffusion process occurring in the radiation belts. It highlights the links that exist between previous theoretical works with the objective of a better understanding of the radial diffusion process. A theoretical validation in the specific case of equatorial particles drifting in a magnetic field model whose disturbed part is limited to the first terms of a spherical expansion is also presented.
Spin crossover equation of state and sound velocities of (Mg0.65Fe0.35)O ferropericlase to 140 GPa
Authors: Chen Bin , Jackson Jennifer M. , Sturhahn Wolfgang , Zhang Dongzhou , Zhao Jiyong , Wicks June K. , Murphy Caitlin A.
Published: July 2012

We have determined the elastic and vibrational properties of periclase‐structured (Mg0.65Fe0.35)O (“FP35”), a composition representative of deep mantle “pyrolite” or chondrite‐pyroxenite models, from nuclear resonant inelastic x‐ray scattering (NRIXS) and x‐ray diffraction (XRD) measurements in diamond‐anvil cells at 300 K. Combining within situXRD measurements, the Debye sound velocity of FP35 was determined from the low‐energy region of the partial phonon density of states (DOS) obtained from NRIXS measurements in the pressure range of 70 to 140 GPa. In order to obtain an accurate description of the equation of state (EOS) for FP35, separate XRD measurements were performed up to 126 GPa at 300 K. A new spin crossover EOS was introduced and applied to the fullP‐Vdata set, resulting in a zero‐pressure volumeV0 = 77.24 ± 0.17 Å3, bulk modulus K0= 159 ± 8 GPa and its pressure‐derivativeK′0= 4.12 ± 0.42 for high‐spin FP35 andK0,LS = 72.9 ± 1.3 Å3, K0,LS = 182 ± 17 GPa with K′0,LSfixed to 4 for low‐spin FP35. The high‐spin to low‐spin transition occurs at 64 ± 3 GPa. Using the spin crossover EOS and Debye sound velocity, we derived the shear (VS) and compressional (VP) velocities for FP35. Comparing our data with previous results on (Mg,Fe)O at similar pressures, we find that the addition of iron decreases both VP and VS, while elevating their ratio (VP/VS). Small amounts (<10%) of low‐spin FP35 mixed with silicates could explain moderate reductions in wave speeds near the core mantle boundary (CMB), while a larger amount of FP35 near the CMB would not allow a large structure to maintain neutral buoyancy.
Searching for single domain magnetite in the “pseudo‐single‐domain” sedimentary haystack: Implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations
Authors: Roberts Andrew P. , Chang Liao , Heslop David , Florindo Fabio , Larrasoaña Juan C.
Published: July 2012

Magnetic hysteresis measurements of sediments have resulted in widespread reporting of “pseudo‐single‐domain”‐like magnetic properties. In contrast, the ideal single domain (SD) properties that would be expected to be responsible for high quality paleomagnetic records are rare. Determining whether SD particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment. We apply a range of such techniques and find that SD particles are much more common than has been reported in the literature and that magnetite magnetofossils (the inorganic remains of magnetotactic bacteria) are widely preserved at depth in a range of sediment types, including biogenic pelagic carbonates, lacustrine and marine clays, and possibly even in glaci‐marine sediments. Thus, instead of being rarely preserved in the geological record, we find that magnetofossils are widespread. This observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments. Magnetofossils also have grain sizes that are substantially smaller than the 1–15μm size range for which there is reasonable empirical support for relative paleointensity studies. The different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies. This issue needs much closer attention. Despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years, much remains to be understood about how they become magnetized.
Relative importance of pelagic and sediment respiration in causing hypoxia in a deep estuary
Authors: Bourgault D. , Cyr F. , Galbraith P. S. , Pelletier E.
Published: July 2012

Oxygen depletion in the 100‐m thick bottom layer of the deep Lower St. Lawrence Estuary is currently thought to be principally caused by benthic oxygen demand overcoming turbulent oxygenation from overlying layers, with pelagic respiration playing a secondary role. This conception is revisited with idealized numerical simulations, historical oxygen observations and new turbulence measurements. Results indicate that a dominant sediment oxygen demand, over pelagic, is incompatible with the shape of observed oxygen profiles. It is further argued that to sustain oxygen depletion, the turbulent diffusivity in the bottom waters should be ≪10−4 m2 s−1, consistent with direct measurements but contrary to previous model results. A new model that includes an Arrhenius‐type function for pelagic respiration and a parameterization for turbulence diffusivity is developed. The model demonstrates the importance of the bottom boundary layer in reproducing the shape of oxygen profiles and reproduces to within 14% the observed change in oxygen concentration in the Lower St. Lawrence Estuary. The analysis indicates that turbulent oxygenation represents about 8% of the sum of sediment and pelagic oxygen demand, consistent with the low turbulent oxygenation required to maintain oxygen depletion. However, contrary to previous hypotheses, it is concluded that pelagic oxygen demand needs to be five time larger than sediment oxygen demand to explain hypoxia in the 100‐m thick bottom layer of the Lower St. Lawrence Estuary.
Long‐range transport of Saharan dust over northwestern Europe during EUCAARI 2008 campaign: Evolution of dust optical properties by scavenging
Authors: Bègue N. , Tulet P. , Chaboureau J.‐P. , Roberts G. , Gomes L. , Mallet M.
Published: July 2012

The evolution of dust optical properties is illustrated in this paper through a case of long‐range transport of Saharan dust over northwestern Europe during the European Integrated Project on Aerosol‐Cloud‐Climate and Air Quality Interactions (EUCAARI) experimental campaign in 2008. This spread of dust over northwestern Europe is investigated by combining satellite, airborne, ground‐based observations and the non‐hydrostatic meso‐scale model Meso‐NH. The total dust amount emitted during the study period is estimated to 185 Tg. The analysis of the removal processes reveals that only 12.5 Tg is lost by dry deposition, and that wet deposition is the main process of dust removal (73 Tg). The observed aerosol optical thickness ranged from 0.1 to 0.5 at the wavelength of 440 nm, with a maximum value close to 1 is found over the Netherlands (51.97°N, 4.93°E). Over that site, the main dust layer is located between 2.5 and 5.2 km above sea level (asl), moreover dust was also present at 0.9 km asl. The nephelometer measurements on board the ATR‐42 aircraft revealed a strong wavelength dependence of the scattering coefficient over the Netherlands. The Angström exponent is greater than 0.5, whereas usually it approaches zero in presence of Saharan dust. This is due to high precipitation scavenging efficiency for the coarse mode, particularly below 4 km. Our results confirm that atmospheric conditions govern the life cycle of dust microphysical phenomena, providing conditions for transformation processes during transport, and removal of particles from the atmosphere.
Validation of upper mesospheric and lower thermospheric temperatures measured by the Solar Occultation for Ice Experiment
Authors: Stevens Michael H. , Deaver Lance E. , Hervig Mark E. , Russell James M. , Siskind David E. , Sheese Patrick E. , Llewellyn Edward J. , Gattinger Richard L. , Höffner Josef , Marshall B. T.
Published: July 2012

Temperature observations in the polar mesosphere and lower thermosphere are critical for studies of polar mesospheric cloud (PMC) formation and variability. The Solar Occultation for Ice Experiment (SOFIE) on NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite has been measuring temperatures in the polar atmosphere nearly continuously since 2007. We herein present an improved SOFIE temperature data set and validate it against a variety of satellite and ground‐based observations. We find that when taking all comparisons together, SOFIE temperatures are in agreement with independent observations to within reported systematic uncertainties from 15 to 88 km altitude. Between 88 and 95 km SOFIE temperatures have a warm bias that peaks between 10 and 15 K in the Arctic summer and 20–30 K in the Antarctic summer. Much of the warm bias is likely related to uncertainties in prescribed atomic oxygen densities that are required for the SOFIE temperature retrieval.
High precision, absolute total column ozone measurements from the Pandora spectrometer system: Comparisons with data from a Brewer double monochromator and Aura OMI
Authors: Tzortziou Maria , Herman Jay R. , Cede Alexander , Abuhassan Nader
Published: July 2012

We present new, high precision, high temporal resolution measurements of total column ozone (TCO) amounts derived from ground‐based direct‐sun irradiance measurements using our recently deployed Pandora single‐grating spectrometers. Pandora's small size and portability allow deployment at multiple sites within an urban air‐shed and development of a ground‐based monitoring network for studying small‐scale atmospheric dynamics, spatial heterogeneities in trace gas distribution, local pollution conditions, photochemical processes and interdependencies of ozone and its major precursors. Results are shown for four mid‐ to high‐latitude sites where different Pandora instruments were used. Comparisons with a well calibrated double‐grating Brewer spectrometer over a period of more than a year in Greenbelt MD showed excellent agreement and a small bias of approximately 2 DU (or, 0.6%). This was constant with slant column ozone amount over the full range of observed solar zenith angles (15–80°), indicating adequate Pandora stray light correction. A small (1–2%) seasonal difference was found, consistent with sensitivity studies showing that the Pandora spectral fitting TCO retrieval has a temperature dependence of 1% per 3°K, with an underestimation in temperature (e.g., during summer) resulting in an underestimation of TCO. Pandora agreed well with Aura‐OMI (Ozone Measuring Instrument) satellite data, with average residuals of <1% at the different sites when the OMI view was within 50 km from the Pandora location and OMI‐measured cloud fraction was <0.2. The frequent and continuous measurements by Pandora revealed significant short‐term (hourly) temporal changes in TCO, not possible to capture by sun‐synchronous satellites, such as OMI, alone.
A one‐dimensional eco‐geomorphic model of marsh response to sea level rise: Wind effects, dynamics of the marsh border and equilibrium
Authors: Tambroni N. , Seminara G.
Published: July 2012

In this study we investigate the long term evolutionary trend of tidal marshes and their possible tendency to approach equilibrium. We account of the dynamic interaction between the marsh and its adjacent environment, allowing for both variations of marsh elevation and displacement of the marsh boundary. We thus consider a 1‐D configuration consisting of a tidal channel merging into a 1‐D marsh. Starting from some initial configuration of the channel we model how a salt marsh forms at the landward end of the channel and determine the long term evolution of the channel ‐ marsh configuration under different scenarios of relative sea level rise. Previously established results on the morphodynamic evolution of a tidal channel are extended accounting for the effects of vegetation and wind driven sediment resuspension in regions where tidal stresses are too weak to mobilize sediments. Results suggest that, for sufficiently low rates of relative sea level rise the marsh platform may be able to reach an equilibrium elevation, provided wind resuspension is able to maintain a sufficiently large sediment concentration close to the marsh boundary. This is in general agreement with recent results based on zero dimensional modeling. However, we find that the marsh boundary is unstable, as progradation or retreat is generally experienced depending on a delicate balance between tidal transport and transport driven by wind setup. In this sense, actual morphodynamic equilibrium is a rather exceptional and unstable state.
Evapotranspiration along an elevation gradient in California's Sierra Nevada
Authors: Goulden M. L. , Anderson R. G. , Bales R. C. , Kelly A. E. , Meadows M. , Winston G. C.
Published: July 2012

We combined observations from four eddy covariance towers with remote sensing to better understand the altitudinal patterns of climate, plant phenology, Gross Ecosystem CO2Uptake, and Evapotranspiration (ET) around the Upper Kings River basin in the southern Sierra Nevada Mountains. Precipitation (P) increased with elevation to ∼500 m, and more gradually at higher elevations, while vegetation graded from savanna at 405 m to evergreen oak and pine forest to mid‐montane forest to subalpine forest at 2700 m. CO2uptake and transpiration at 405 m peaked in spring (March to May) and declined in summer; gas exchange at 1160 and 2015 m continued year‐round; gas exchange at 2700 m peaked in summer and ceased in winter. A phenological threshold occurred between 2015 and 2700 m, associated with the development of winter dormancy. Annual ET and Gross Primary Production were greatest at 1160 and 2015 m and reduced at 405 m coincident with less P, and at 2700 m coincident with colder temperatures. The large decline in ET above 2015 m raises the possibility that an upslope redistribution of vegetation with climate change could cause a large increase in upper elevation ET. We extrapolated ET to the entire basin using remote sensing. The 2003–11 P for the entire Upper Kings River basin was 984 mm y−1 and the ET was 429 mm y−1, yielding a P‐ET of 554 mm y−1, which agrees well with the observed Kings River flow of 563 mm y−1. ET averaged across the entire basin was nearly constant from year to year.
Experimental and numerical investigation of saltwater intrusion dynamics in flux‐controlled groundwater systems
Authors: Chang Sun Woo , Clement T. Prabhakar
Published: July 2012

Sea level rise and reduction of groundwater fluxes due to changes in rainfall patterns are the two major climate change–induced hydrological variables that can severely affect saltwater intrusion in coastal aquifers. In this study we use a combination of laboratory experiments and numerical simulations to study the impacts of changes in one of these climate change–induced hydrological variables, groundwater flux, on saltwater intrusion process. We have completed experiments in a laboratory‐scale model to study the changes in two types of groundwater fluxes—areal recharge flux and regional flux. The experimental results were modeled using the numerical code SEAWAT. The transient data sets reported in this study are useful benchmarks for testing numerical models that employ flux‐type boundary conditions. Also, based on the experimental observations, we hypothesize that when the fluxes are perturbed, it would require relatively less time for a salt wedge to recede from an aquifer when compared to the time required to advance into the aquifer. This rather counterintuitive hypothesis implies that saltwater intrusion and receding processes are asymmetric and the timescales associated with these processes will be different. We use a combination of laboratory and numerical experiments to test this hypothesis and use the resulting data set to explain the reason for the difference in intrusion rates.