bluuebunny/crossref_metadata_2025 huggingface dataset:
Millennial‐scale sea surface temperature and Patagonian Ice Sheet changes off southernmost Chile (53°S) over the past ∼60 kyr
Authors: Caniupán M. , Lamy F. , Lange C. B. , Kaiser J. , Arz H. , Kilian R. , Baeza Urrea O. , Aracena C. , Hebbeln D. , Kissel C. , Laj C. , Mollenhauer G. , Tiedemann R.
Published: August 2011

Glacial millennial‐scale paleoceanographic changes in the Southeast Pacific and the adjacent Southern Ocean are poorly known due to the scarcity of well‐dated and high resolution sediment records. Here we present new surface water records from sediment core MD07‐3128 recovered at 53°S off the Pacific entrance of the Strait of Magellan. The alkenone‐derived sea surface temperature (SST) record reveals a very strong warming of ca. 8°C over the last Termination and substantial millennial‐scale variability in the glacial section largely consistent with our planktonic foraminifera oxygen isotope (δ18O) record of Neogloboquadrina pachyderma (sin.). The timing and structure of the Termination and some of the millennial‐scale SST fluctuations are very similar to those observed in the well‐dated SST record from ODP Site 1233 (41°S) and the temperature record from Drowning Maud Land Antarctic ice core supporting the hemispheric‐wide Antarctic timing of SST changes. However, differences in our new SST record are also found including a long‐term warming trend over Marine Isotope Stage (MIS) 3 followed by a cooling toward the Last Glacial Maximum (LGM). We suggest that these differences reflect regional cooling related to the proximal location of the southern Patagonian Ice Sheet and related meltwater supply at least during the LGM consistent with the fact that no longer SST cooling trend is observed in ODP Site 1233 or any SST Chilean record. This proximal ice sheet location is documented by generally higher contents of ice rafted debris (IRD) and tetra‐unsaturated alkenones, and a slight trend toward lighter planktonic δ18O during late MIS 3 and MIS 2.
A box model of the Late Miocene Mediterranean Sea: Implications from combined 87Sr/86Sr and salinity data
Authors: Topper R. P. M. , Flecker R. , Meijer P. Th. , Wortel M. J. R.
Published: August 2011

Under certain conditions the strontium isotope ratio in the water of a semi‐enclosed basin is known to be sensitive to the relative size of ocean water inflow and river input. Combining Sr‐isotope ratios measured in Mediterranean Late Miocene successions with data on past salinity, one can derive quantitative information on the Mediterranean hydrological budget at times before and during the Messinian Salinity Crisis (MSC). Previous studies obtained this hydrological budget by inverting the salinity and strontium data with steady state solutions to the conservation equations of salt, strontium and water. Here, we develop a box model with a time‐dependent set of equations to investigate the coeval evolution of salinity and Sr ratios under different water budgets, gateway restrictions and riverine Sr characteristics. Model results are compared with the salinity and strontium ratio data from the Mediterranean. With a present‐day water budget, strontium ratios in the Mediterranean never reach the observed Messinian values regardless of gateway restriction and water budget. However, a model with tripled river input, as inferred for the Late Miocene, is able to reproduce the Sr ratios observed. The onset of the MSC can be explained with a simple restriction of the gateway(s) between the Mediterranean and Atlantic. Lower Evaporite gypsum formed in a basin with less outflow to the Atlantic than modeled in previous studies because of the large Late Miocene river input. Evaporite thicknesses predicted by our model and consistent with the Messinian Sr ratios are on the low end of the thickness range inferred from seismics.
Miocene to Pliocene development of surface and subsurface temperatures in the Benguela Current system
Authors: Rommerskirchen Florian , Condon Tegan , Mollenhauer Gesine , Dupont Lydie , Schefuss Enno
Published: August 2011

The initiation of the Benguela upwelling has been dated to the late Miocene, but estimates of its sea surface temperature evolution are not available. This study presents data from Ocean Drilling Program (ODP) Site 1085 recovered from the southern Cape Basin. Samples of the middle Miocene to Pliocene were analyzed for alkenone‐based (U37K′, SSTUK) and glycerol dialkyl glycerol tetraether (GDGT) based (TEX86, TempTEX) water temperature proxies. In concordance with global cooling during the Miocene, SSTUKand TempTEXexhibit a decline of about 8°C and 16°C, respectively. The temperature trends suggest an inflow of cold Antarctic waters triggered by Antarctic ice sheet expansion and intensification of Southern Hemisphere southeasterly winds. A temperature offset between both proxies developed with the onset of upwelling, which can be explained by differences in habitat: alkenone‐producing phytoplankton live in the euphotic zone and record sea surface temperatures, while GDGT‐producing Thaumarchaeota are displaced to colder subsurface waters in upwelling‐influenced areas and record subsurface water temperatures. We suggest that variations in subsurface water temperatures were driven by advection of cold Antarctic waters and thermocline adjustments that were due to changes in North Atlantic deep water formation. A decline in surface temperatures, an increased offset between temperature proxies, and an increase in primary productivity suggest the establishment of the Benguela upwelling at 10 Ma. During the Messinian Salinity Crisis, between 7 and 5 Ma, surface and subsurface temperature estimates became similar, likely because of a strong reduction in Atlantic overturning circulation, while high total organic carbon contents suggest a “biogenic bloom.” In the Pliocene the offset between the temperature estimates and the cooling trend was reestablished.
A mechanism for brief glacial episodes in the Mesozoic greenhouse
Authors: Donnadieu Yannick , Dromart Gilles , Goddéris Yves , Pucéat Emmanuelle , Brigaud Benjamin , Dera Guillaume , Dumas Christophe , Olivier Nicolas
Published: August 2011

The Mesozoic, perhaps the longest period of warmth during the Phanerozoic Earth history, has been repeatedly affected by short‐lived cold interludes lasting about one million years. While the origin of these cold snaps has been classically attributed to a temporary atmospheric CO2 drawdown, quantified mechanisms explaining these instabilities of the carbon cycle are still lacking. Based on a climate carbon cycle model, we show that the general demise of carbonate platforms accompanying these short‐lived cold interludes is a powerful mechanism capable of generating a fast atmospheric CO2 decrease and a moderate sea level drop associated with ice sheet buildup. The temporary nature of the carbonate production decline explains the relative short time of these cold events but makes it possible to account for ice sheet waxing and waning.
THE MARTIAN ATMOSPHERIC BOUNDARY LAYER
Authors: Petrosyan A. , Galperin B. , Larsen S. E. , Lewis S. R. , Määttänen A. , Read P. L. , Renno N. , Rogberg L. P. H. T. , Savijärvi H. , Siili T. , Spiga A. , Toigo A. , Vázquez L.
Published: August 2011

The planetary boundary layer (PBL) represents the part of the atmosphere that is strongly influenced by the presence of the underlying surface and mediates the key interactions between the atmosphere and the surface. On Mars, this represents the lowest 10 km of the atmosphere during the daytime. This portion of the atmosphere is extremely important, both scientifically and operationally, because it is the region within which surface lander spacecraft must operate and also determines exchanges of heat, momentum, dust, water, and other tracers between surface and subsurface reservoirs and the free atmosphere. To date, this region of the atmosphere has been studied directly, by instrumented lander spacecraft, and from orbital remote sensing, though not to the extent that is necessary to fully constrain its character and behavior. Current data strongly suggest that as for the Earth's PBL, classical Monin‐Obukhov similarity theory applies reasonably well to the Martian PBL under most conditions, though with some intriguing differences relating to the lower atmospheric density at the Martian surface and the likely greater role of direct radiative heating of the atmosphere within the PBL itself. Most of the modeling techniques used for the PBL on Earth are also being applied to the Martian PBL, including novel uses of very high resolution large eddy simulation methods. We conclude with those aspects of the PBL that require new measurements in order to constrain models and discuss the extent to which anticipated missions to Mars in the near future will fulfill these requirements.
An accurate and efficient algorithm for Faraday rotation corrections for spaceborne microwave radiometers
Authors: Singh Malkiat , Bettenhausen Michael H.
Published: August 2011

Faraday rotation changes the polarization plane of linearly polarized microwaves which propagate through the ionosphere. To correct for ionospheric polarization error, it is necessary to have electron density profiles on a global scale that represent the ionosphere in real time. We use raytrace through the combined models of ionospheric conductivity and electron density (ICED), Bent, and Gallagher models (RIBG model) to specify the ionospheric conditions by ingesting the GPS data from observing stations that are as close as possible to the observation time and location of the space system for which the corrections are required. To accurately calculate Faraday rotation corrections, we also utilize the raytrace utility of the RIBG model instead of the normal shell model assumption for the ionosphere. We use WindSat data, which exhibits a wide range of orientations of the raypath and a high data rate of observations, to provide a realistic data set for analysis. The standard single‐shell models at 350 and 400 km are studied along with a new three‐shell model and compared with the raytrace method for computation time and accuracy. We have compared the Faraday results obtained with climatological (International Reference Ionosphere and RIBG) and physics‐based (Global Assimilation of Ionospheric Measurements) ionospheric models. We also study the impact of limitations in the availability of GPS data on the accuracy of the Faraday rotation calculations.
Realistic implementation of ellipsoidal reflector antennas to produce near‐field focused patterns
Authors: Chou H.‐T. , Kuo L.‐R. , Chou H.‐H. , Hung K.‐L. , Nepa P.
Published: August 2011

The radiation characteristics of ellipsoidal reflector antennas in the near zone of antenna aperture are investigated using Physical Optics (PO) approximations. This antenna has potential applications in the near‐field communications because its radiation focuses in the near zone. Analytical formulations to predict the radiation efficiency and exhibit field phenomena are developed. Its applications as a RFID reader antenna at 2.4 GHz are demonstrated by numerical simulations and measurements over a realistic implementation of offset reflector fed by a microstrip patch antenna. Both numerical and experimental studies are performed to validate this antenna design.
Using TEC and radio scintillation data from the CITRIS radio beacon receiver to study low and midlatitude ionospheric irregularities
Authors: Siefring Carl L. , Bernhardt Paul A. , Koch Douglas E. , Galysh Ivan J.
Published: August 2011

Unique data on ionospheric plasma irregularities from the Naval Research Laboratory Scintillation and TEC Receiver in Space (CITRIS) instrument is presented. CITRIS is a multiband receiver that recorded Total Electron Content (TEC) and radio scintillations from Low‐Earth Orbit (LEO) on STPSat1. The 555 ± 5 km altitude 35° inclination orbit covers low and midlatitudes. The measurements require propagation from a transmitter to a receiver through the F region plasma. CITRIS used both 1) satellite beacons in LEO and 2) the French sponsored global network of ground‐based Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) beacons. This paper is both a brief review of the CITRIS experiment and the first combined TEC and scintillation study of ionospheric irregularities using a satellite‐borne beacon receiver. It primarily focuses on CITRIS/DORIS observations and is a case study of the ionospheric irregularities and associated scintillation characteristics at 401.25 MHz during the 2008 equinox solar minimum. In addition, CITRIS was operated in a complementary fashion with the Communication/Navigations Outages Forecasting System (C/NOFS) satellite during C/NOFS' first year of operations and comparison with measured C/NOFS irregularity characteristics are made. Several types of irregularities have been studied including Spread–F and the newly discovered dawn‐side depletions.
Rates and timing of vertical‐axis block rotations across the central Sierra Nevada‐Walker Lane transition in the Bodie Hills, California/Nevada
Authors: Rood Dylan H. , Burbank Douglas W. , Herman Scott W. , Bogue Scott
Published: August 2011

We use paleomagnetic data from Tertiary volcanic rocks to address the rates and timing of vertical‐axis block rotations across the central Sierra Nevada‐Walker Lane transition in the Bodie Hills, California/Nevada. Samples from the Upper Miocene (∼9 Ma) Eureka Valley Tuff suggest clockwise vertical‐axis block rotations between NE‐striking left‐lateral faults in the Bridgeport and Mono Basins. Results in the Bodie Hills suggest clockwise rotations (R ± ΔR, 95% confidence limits) of 74 ± 8° since Early to Middle Miocene (∼12–20 Ma), 42 ± 11° since Late Miocene (∼8–9 Ma), and 14 ± 10° since Pliocene (∼3 Ma) time with no detectable northward translation. The data are compatible with a relatively steady rotation rate of 5 ± 2° Ma−1 (2σ) since the Middle Miocene over the three examined timescales. The average rotation rates have probably not varied by more than a factor of two over time spans equal to half of the total time interval. Our paleomagnetic data suggest that block rotations in the region of the Mina Deflection began prior to Late Miocene time (∼9 Ma), and perhaps since the Middle Miocene if rotation rates were relatively constant. Block rotation in the Bodie Hills is similar in age and long‐term average rate to rotations in the Transverse Ranges of southern California associated with early transtensional dextral shear deformation. We speculate that the age of rotations in the Bodie Hills indicates dextral shear and strain accommodation within the central Walker Lane Belt resulting from coupling of the Pacific and North America plates.
Miocene south directed low‐angle normal fault evolution on Kea Island (West Cycladic Detachment System, Greece)
Authors: Iglseder Christoph , Grasemann Bernhard , Rice A. Hugh N. , Petrakakis Konstantin , Schneider David A.
Published: August 2011

New structural, petrologic, and thermochronologic data from Kea, West Cyclades, define a crustal‐scale ductile shear zone and ductile/brittle low‐angle normal fault (LANF) system. Both the greenschist‐facies shear zone forming the footwall and the overlying LANF zone formed during constrictional strains, with a consistent top‐to‐SW‐S shear sense, with increasing finite strains toward higher structural levels but decreasing temperatures from footwall to hanging wall. The tectonostratigraphy comprises a ∼450 m thick footwall of shallowly dipping schists and calcite marbles representing the Intermediate Unit of the Attic‐Cycladic Crystalline (ACC). Above the footwall is a ∼60 m thick highly strained LANF zone, consisting of phyllonites, cataclastic schists, ultramylonitic calcite marbles, (proto) mylonitic calcite marbles, and cohesive cataclasites that arch over the whole island. These fault rocks exhibit multistage LANFs, evolving from ductile to brittle conditions. An up to ∼50 m thick brecciated limestone and dolostone sequence forms the unmetamorphosed hanging wall which is most probably part of the Upper Unit of the ACC. Multiequilibrium P‐T estimates on chlorite‐white mica pairs in the footwall yield 7–5.5 kbar/360°C–450°C for inclusions in albite and epidote, 5.5–3 kbar/400°C–350°C for the main foliation, and 3–2 kbar/350°C–280°C in localized shear bands (C and C′ foliations). The40Ar/39Ar white mica footwall cooling ages demonstrate that greenschist‐facies retrogression occurred between ∼21 and 17 Ma. Localized, late decimeter thick shear zones were active and dynamically recrystallized before ∼15 to 13 Ma. The LANF on Kea, together with similar structures in South Attica and the West Cyclades define the West Cycladic Detachment System, characterized by ductile to brittle top‐SW‐S shear sense.
Cretaceous reactivation of the Deokpori Thrust, Taebaeksan Basin, South Korea, constrained by K‐Ar dating of clayey fault gouge
Authors: Zwingmann Horst , Han Raehee , Ree Jin‐Han
Published: August 2011

The Deokpori Thrust, juxtaposing the early Paleozoic Yeongwol‐type Joseon Supergroup (Yeongwol Group) against the Duwibong‐type Joseon Supergroup (Taebaek Group) in the Okcheon belt, is an important regional structure in the Phanerozoic tectonic evolution of Korea. Although the initiation of the thrust has recently been conjectured to occur during the Middle Jurassic Daebo tectonic event in a continental magmatic arc setting, its movement history has never been studied. We report timing of brittle reactivation of the thrust obtained from K‐Ar dating of fault gouges in the core of the Deokpori Thrust zone. K‐Ar illite age data of fault gouges suggest reactivation of the thrust at ca. 72 Ma after a contact metamorphism around 94 Ma. Our result is the first documentation of the reactivation of a major Jurassic ‘Daebo’ structure and the reactivation may represent a significant contractional tectonic event during the Late Cretaceous in the Korean Peninsula.
Clay mineralogy and thermal history of the Neogene Vinchina Basin, central Andes of Argentina: Analysis of factors controlling the heating conditions
Authors: Collo Gilda , Dávila Federico M. , Nóbile Julieta , Astini Ricardo A. , Gehrels George
Published: August 2011

The Vinchina Foreland Basin, western Argentina, contains a ∼7 km thick nonmarine stratigraphy, chronologically constrained within the Mio‐Pliocene (circa 19–3.4 Ma), and where distribution of Illite/Smectite interstratified phases has shown a progressive smectite‐illitization progress (R0 → R1 → R3), is consistent with an incipient burial history. R0 represents randomly mixed‐layered illite/smectite normally found at shallow depths, as this ordering is not stable at ∼120°C. In the Vinchina Basin, however, the R0 is still persistent at ∼7 km depth, and its appearance even in the deepest levels is consistent with previous interpretations of low burial temperatures based on thermochronologic studies of detrital apatites. The maximum paleotemperature estimation and basin depth imply geothermal gradient as low as ∼15°C/km, which allowed an estimate of heat flow values between 33 and 42 mW/m2, that would rise to between ∼40 and 51 mW/m2 when the sedimentation rate (thermal blanketing) is taken into account. These values were only reported for cold basins and represent a paleothermal state of a refrigerated lithosphere. We suggest the central Andes were dominated since the Miocene by heat transfer derived mostly from crustal contributions with a minimum input from the asthenosphere. This refrigerated lithosphere is typical of segments affected by flat subduction. Preliminary thermal models based on previous geodynamic approaches support our conclusions.
Improved understanding and prediction of the hydrologic response of highly urbanized catchments through development of the Illinois Urban Hydrologic Model
Authors: Cantone Joshua , Schmidt Arthur
Published: August 2011

What happens to the rain in highly urbanized catchments? That is the question that urban hydrologists must ask themselves when trying to integrate the hydrologic and hydraulic processes that affect the hydrologic response of urban catchments. The Illinois Urban Hydrologic Model (IUHM) has been developed to help answer this question and improve understanding and prediction of hydrologic response in highly urbanized catchments. Urban catchments are significantly different than natural watersheds, but there are similarities that allow features of the pioneering geomorphologic instantaneous unit hydrograph concept developed for natural watersheds to be adapted to the urban setting. This probabilistically based approach is a marked departure from the traditional deterministic models used to design and simulate urban sewer systems and does not have the burdensome input data requirements that detailed deterministic models possess. Application of IUHM to the CDS‐51 catchment located in the village of Dolton, Illinois, highlights the model's ability to predict the hydrologic response of the catchment as well as the widely accepted SWMM model and is in accordance with observed data recorded by the United States Geological Survey. In addition, the unique structure and organization of urban sewer networks make it possible to characterize a set of ratios for urban catchments that allow IUHM to be applied when detailed input data are not available.
Determinants of residential water consumption: Evidence and analysis from a 10‐country household survey
Authors: Grafton R. Quentin , Ward Michael B. , To Hang , Kompas Tom
Published: August 2011

Household survey data for 10 countries are used to quantify and test the importance of price and nonprice factors on residential water demand and investigate complementarities between household water‐saving behaviors and the average volumetric price of water. Results show (1) the average volumetric price of water is an important predictor of differences in residential consumption in models that include household characteristics, water‐saving devices, attitudinal characteristics and environmental concerns as explanatory variables; (2) of all water‐saving devices, only a low volume/dual‐flush toilet has a statistically significant and negative effect on water consumption; and (3) environmental concerns have a statistically significant effect on some self‐reported water‐saving behaviors. While price‐based approaches are espoused to promote economic efficiency, our findings stress that volumetric water pricing is also one of the most effective policy levers available to regulate household water consumption.
Experimental investigation of nonequilibrium capillarity effects: Fluid viscosity effects
Authors: Goel Gaurav , O'Carroll Denis M.
Published: August 2011

Numerical models have been widely used to simulate multiphase flow in porous media for a variety of applications (e.g., NAPL migration in subsurface aquifers, carbon sequestration, agriculture, paper production, and petroleum reservoir development). The relationship between the difference in phase pressures and saturation is used as one of the important constitutive relationships in numerical models. Theoretical studies have suggested that this relationship should include a damping coefficient or capillarity coefficient () on the basis of thermodynamic considerations. A literature review suggests that the magnitude of this capillarity coefficient varies by over three orders of magnitude. While recent experimental studies have explored the effect of porous medium properties, effect of domain size, hysteresis, and the imposed boundary conditions on the magnitude of , there has been no experimental study investigating the impact of fluid viscosity on . This study reports on a series of primary drainage experiments conducted under both static and dynamic conditions in F70 silica sand. Fluid pairs used included water and silicone oil with two differing viscosities and slightly different densities (used as model nonaqueous phase liquids) in addition to air. Water saturation and both wetting and nonwetting phase pressures were measured in a custom‐built aluminum column using EC‐5 probes and tensiometers at three levels. Results show a strong dependence of the magnitude of the capillarity coefficient on effective fluid viscosity. This implies that consideration should be given for the inclusion of a capillarity coefficient in modeling tools used to simulate multiphase flow when fluids saturations are changing rapidly and when fluids have a large viscosity ratio.
Separation of river network–scale nitrogen removal among the main channel and two transient storage compartments
Authors: Stewart Robert J. , Wollheim Wilfred M. , Gooseff Michael N. , Briggs Martin A. , Jacobs Jennifer M. , Peterson Bruce J. , Hopkinson Charles S.
Published: August 2011

Transient storage (TS) zones are important areas of dissolved inorganic nitrogen (DIN) processing in rivers. We assessed sensitivities regarding the relative impact that the main channel (MC), surface TS (STS), and hyporheic TS (HTS) have on network denitrification using a model applied to the Ipswich River in Massachusetts, United States. STS and HTS connectivity and size were parameterized using the results of in situ solute tracer studies in first‐ through fifth‐order reaches. DIN removal was simulated in all compartments for every river grid cell using reactivity derived from Lotic Intersite Nitrogen Experiment (LINX2) studies, hydraulic characteristics, and simulated discharge. Model results suggest that although MC‐to‐STS connectivity is greater than MC‐to‐HTS connectivity at the reach scale, at basin scales, there is a high probability of water entering the HTS at some point along its flow path through the river network. Assuming our best empirical estimates of hydraulic parameters and reactivity, the MC, HTS, and STS removed approximately 38%, 21%, and 14% of total DIN inputs during a typical base flow period, respectively. There is considerable uncertainty in many of the parameters, particularly the estimates of reaction rates in the different compartments. Using sensitivity analyses, we found that the size of TS is more important for DIN removal processes than its connectivity with the MC when reactivity is low to moderate, whereas TS connectivity is more important when reaction rates are rapid. Our work suggests a network perspective is needed to understand how connectivity, residence times, and reactivity interact to influence DIN processing in hierarchical river systems.
Quantifying the role of climate and landscape characteristics on hydrologic partitioning and vegetation response
Authors: Voepel Hal , Ruddell Benjamin , Schumer Rina , Troch Peter A. , Brooks Paul D. , Neal Andrew , Durcik Matej , Sivapalan Murugesu
Published: August 2011

There is no consensus on how changes in both temperature and precipitation will affect regional vegetation. We investigated controls on hydrologic partitioning at the catchment scale across many different ecoregions, and compared the resulting estimates of catchment wetting and vaporization (evapotranspiration) to remotely sensed indices of vegetation greenness. The fraction of catchment wetting vaporized by plants, known as the Horton index, is strongly related to the ratio of available energy to available water at the Earth's surface, the aridity index. Here we show that the Horton index is also a function of catchment mean slope and elevation, and is thus related to landscape characteristics that control how much and how long water is retained in a catchment. We compared the power of the components of the water and energy balance, as well as landscape characteristics, to predict Normalized Difference Vegetation Index (NDVI), a surrogate for vegetation productivity, at 312 Model Parameter Estimation Experiment (MOPEX) catchments across the United States. Statistical analysis revealed that the Horton index provides more precision in predicting maximum annual NDVI for all catchments than mean annual precipitation, potential evapotranspiration, or their ratio, the aridity index. Models of vegetation productivity should emphasize plant‐available water, rather than just precipitation, by incorporating the interaction of climate and landscape. Major findings related to the Horton index are: (1) it is a catchment signature that is relatively constant from year‐to‐year; (2) it is related to specific landscape characteristics; (3) it can be used to create catchment typologies; and (4) it is related to overall catchment greenness.
Determination of dimensional flow fields in hydrogeological settings via the MRT lattice‐Boltzmann method
Authors: Hilpert Markus
Published: August 2011

In this paper we demonstrate how the single and multiple‐relaxation‐time (MRT) lattice‐Boltzmann (LB) method can be used to simulate hydrogeological flows under standard conditions. We explain in detail how real‐world hydrogeological flow problems, which are formulated in terms of dimensional boundary and initial conditions, can be related to the nondimensional LB world, in which both the lattice spacing and the time step are nondimensional and typically set to unity. We first demonstrate the method in two examples where analytical solutions are known: steady state and transient flow of water in a square duct where fluid inertia is either negligible or not, respectively. Finally we simulate the flow of water in a sand where inertial forces are not negligible. For steady state flow we also present equations for calculating the permeability. Moreover, we demonstrate and advocate the usage of Richardson's extrapolation, which allows one to estimate LB modeling results for an infinite numerical resolution that include uncertainty intervals. For pressure‐driven simulations of steady state creeping flow, we show how one can improve the numerical convergence behavior by performing “light‐water” simulations at a lower Reynolds number while still predicting the correct velocity field.
Catchment hydrological responses to forest harvest amount and spatial pattern
Authors: Abdelnour Alex , Stieglitz Marc , Pan Feifei , McKane Robert
Published: August 2011

Forest harvest effects on streamflow generation have been well described experimentally, but a clear understanding of process‐level hydrological controls can be difficult to ascertain from data alone. We apply a new model, Visualizing Ecosystems for Land Management Assessments (VELMA), to elucidate how hillslope and catchment‐scale processes control stream discharge in a small Pacific Northwest catchment. VELMA is a spatially distributed ecohydrology model that links hydrological and biogeochemical processes within watersheds. The study site is WS10 of the H.J. Andrews LTER, a 10 ha forested catchment clearcut in 1975. Simulated and observed daily streamflow are in good agreement for both the pre‐ (1969–1974) and postharvest (1975–2008) periods (Nash‐Sutcliffe efficiency = 0.807 and 0.819, respectively). One hundred scenarios, where harvest amounts ranged from 2% to 100% were conducted. Results show that (1) for the case of a 100% clearcut, stream discharge initially increased by ∼29% or 345 mm but returned to preclearcut levels within 50 years, and (2) annual streamflow increased at a near linear rate of 3.5 mm year−1 for each percent of catchment harvested, irrespective of location. Thereafter, to assess the impact of harvest location on stream discharge, 20 harvest scenarios were simulated, where harvest amount was fixed at 20% but harvest location varied. Results show that the streamflow response is strongly sensitive to harvest distance from the stream channel. Specifically, a 20% clearcut area near the catchment divide resulted in an average annual streamflow increase of 53 mm, whereas a 20% clearcut near the stream resulted in an average annual streamflow increase of 92 mm.
Probing the integration of land use and watershed planning in a shifting governance regime
Authors: Plummer Ryan , de Grosbois Danuta , de Loë Rob , Velaniškis Jonas
Published: August 2011

Effective governance that contributes to the integration of water management and land use planning is essential for successful protection of drinking water sources and, ultimately, provision of safe drinking water. In many jurisdictions, land use planning and watershed management occur on separate tracks. This article examines the prospects for integration of these two critical processes. A multicase study approach is used, focusing on the specific objective of protection of drinking water sources. Experiences in three case study watershed regions in Ontario, Canada (Grand River, Upper Thames, and Lake Simcoe), were analyzed. The goal was to identify the extent to which source water protection components and indicators are expressed in land use and watershed‐based planning documents. Similarities and differences among the watershed regions are distinguished through a cross‐case analysis. The results suggest that a shifting governance regime for drinking water safety in Ontario is contributing to integration between land use and water management. However, proactive and ongoing efforts are required to ensure that integration occurs and that barriers to integration are addressed. Timely guidelines, incentive‐based tools, up‐to‐date and accurate information, and adequate financial resources are essential.
Surface storage dynamics in large rivers: Comparing three‐dimensional particle transport, one‐dimensional fractional derivative, and multirate transient storage models
Authors: Anderson Eric J. , Phanikumar Mantha S.
Published: August 2011

Large rivers are major conduits for sediment and nutrient transport and play an important role in global biogeochemical cycles. While smaller rivers received attention in recent decades for hyporheic exchange and nutrient uptake, fewer studies have focused on the dynamics of surface storage zones in large rivers. We investigate transport dynamics in the St. Clair River, an international river straddling the U.S.–Canadian border, using a combination of modeling and dye tracer studies. We describe a calibrated three‐dimensional hydrodynamic model to generate (synthetic) breakthrough data to evaluate several classes of 1‐D solute transport models for their ability to describe surface storage dynamics. Breakthrough data from the 3‐D particle transport model exhibited multimodal behavior and complex dynamics that could not be described using a single first‐order exchange coefficient—an approach often used to describe surface storage in transient storage models for small rivers. The 1‐D models examined include multirate transient storage (MRTS) models in which storage zones were arranged either in series or parallel as well as 1‐D models based on fractional derivatives. Results indicate that for 1‐D models to describe data adequately, the timing of solute pulses that correspond to various in‐channel features such as sandbars, islands or meander bends should be taken into account. As a result, the MRTS model with storage zones arranged in series (i.e., exchange rates triggered sequentially) provided the best description of the data. In contrast, fractional derivative models that assume storage zones were arranged in parallel failed to capture the multimodal nature of the breakthrough curves.
Quantifying the relative contribution of the climate and direct human impacts on mean annual streamflow in the contiguous United States
Authors: Wang Dingbao , Hejazi Mohamad
Published: August 2011

Both climate change and human activities are known to have induced changes to hydrology. Consequently, quantifying the net impact of human contribution to the streamflow change is a challenge. In this paper, a decomposition method based on the Budyko hypothesis is used to quantify the climate (i.e., precipitation and potential evaporation change) and direct human impact on mean annual streamflow (MAS) for 413 watersheds in the contiguous United States. The data for annual precipitation, runoff, and potential evaporation are obtained from the international Model Parameter Estimation Experiment (MOPEX), which is often assumed to only include gauges unaffected by human interferences. The data are split into two periods (1948–1970 and 1971–2003) to quantify the change over time. Although climate is found to affect MAS more than direct human impact, the results show that assuming the MOPEX data set to be unaffected by human activities is far from realistic. Climate change causes increasing MAS in most watersheds, while the direct human‐induced change is spatially heterogeneous in the contiguous United States, with strong regional patterns, e.g., human activities causing increased MAS in the Midwest and significantly decreased MAS in the High Plains. The climate‐ and human‐induced changes are found to be more severe in arid regions, where water is limited. Comparing the results to a collection of independent data sets indicates that the estimated direct human impacts on MAS in this largely nonurban set of watersheds might be attributed to several human activities, such as cropland expansion, irrigation, and the construction of reservoirs.
What determines drying rates at the onset of diffusion controlled stage‐2 evaporation from porous media?
Authors: Shokri N. , Or D.
Published: August 2011

Early stages of evaporation from porous media are marked by relatively high evaporation rates supplied by capillary liquid flow from a receding drying front to vaporization surface. At a characteristic drying front depth, hydraulic continuity to the surface is disrupted marking the onset of stage‐2 evaporation where a lower evaporative flux is supported by vapor diffusion. Observations suggest that in some cases the transition is accompanied by a jump in the vaporization plane from the surface to a certain depth below. The resulting range of evaporation rates at the onset of stage‐2 is relatively narrow (0.5–2.5 mm d−1). The objective is to estimate the depth of the vaporization plane that defines vapor diffusion length at the onset of stage‐2. The working hypothesis is that the jump length is determined by a characteristic length of connected clusters at the secondary drying front that obeys a power law with the system's Bond number. We conducted evaporation experiments using sands and glass beads of different particle size distributions and extracted experimental data from the literature for model comparison. Results indicate the jump length at the end of stage‐1 was affected primarily by porous media properties and less so by boundary conditions. Results show power law relationships between the length of the vaporization plane jump and Bond number with an exponent of −0.48 in good agreement with the percolation theory theoretical exponent of −0.47. The results explain the origins of a relatively narrow range of evaporation rates at the onset of stage‐2, and provide a means for estimating these rates.
A homogenous daily rainfall record for the Radcliffe Observatory, Oxford, from the 1820s
Authors: Burt T. P. , Howden N. J. K.
Published: August 2011

A record of daily rainfall totals from 1827 at the Radcliffe Observatory, Oxford, United Kingdom, is presented. Changing instrumentation over the period and homogenization of the record are described. Brief analysis of the record is provided, including reference to the monthly record from 1767. Most heavy falls of rain occur in summer. The twentieth century tendency toward wetter winters was not accompanied by any significant increase in heavy falls of rain. There were very few heavy falls in summer during the 1990s but a large number in autumn. Preliminary analysis suggests that there are more heavy downpours in summers when there is reduced storminess in the North Atlantic region.
Toward a robust method for subdaily rainfall downscaling from daily data
Authors: Beuchat X. , Schaefli B. , Soutter M. , Mermoud A.
Published: August 2011

Compared to daily rainfall data, observed subdaily rainfall times are rare and often very short. For hydrologic modeling, this problem is often addressed by generating synthetic hourly rainfall series, with rainfall generators calibrated on relevant rainfall statistics. The required subdaily rainfall statistics are traditionally derived from daily rainfall records by assuming some temporal scaling behavior of these statistics. However, as our analyzes of a large data set suggest, the mathematical form of this scaling behavior might be specific to individual gauges. This paper presents, therefore, a novel approach that bypasses the temporal scaling behavior assumption. The method uses multivariate adaptive regression splines; it is learning‐based and seeks directly relationships between target subdaily statistics and available predictors (including (supra‐) daily rainfall statistics and external information such as large‐scale atmospheric variables). A large data set is used to investigate these relationships, including almost 340 hourly rainfall series coming from gauges spread over Switzerland, the USA and the UK. The predictive power of the new approach is assessed for several subdaily rainfall statistics and is shown to be superior to the one of temporal scaling laws. The study is completed with a detailed discussion of how such reconstructed statistics improve the accuracy of an hourly rainfall generator based on Poisson cluster models.
Role of channel and floodplain cross‐section geometry in the basin response
Authors: Mejia A. I. , Reed S. M.
Published: August 2011

We investigate the role of cross‐section geometry in flow routing by developing an analytical framework based on the instantaneous response function (IRF) and relationships of river basin geomorphology. The cross‐section geometry is included explicitly within the framework by assuming a power law cross section that is, in turn, used to derive expressions for the at‐a‐site hydraulic geometry. The analysis performed using the Illinois River basin indicates that the cross‐section geometry takes on different roles depending on whether flows are in the channel or floodplain. The cross‐section geometry where width dominates over depth (width dominant), i.e., the at‐a‐site width‐depth ratio increases with increasing depth, tends to produce a larger network celerity and dispersion for the channel, and the trend reverses for the high floodplain flows. We found that the cross‐section geometry can influence the relative contribution of hydrodynamic and kinematic dispersion. For the channel, the depth‐dominant cross section produces a lower hydrodynamic dispersion than the width‐dominant cross section and vice versa for the floodplain. We found that the nonlinear dependence of the IRF on effective rainfall, expressed in the IRF time to peak and peak flow, may vary depending on the cross‐section geometry, with the nonlinearity decreasing for the width‐dominant cross sections. Additionally, the effect of cross‐section geometry on the basin response can alter the relative contribution of the stream network and hillslopes to the basin dispersion. The derived framework has potential as an a priori tool for incorporating channel and floodplain geometry into distributed rainfall‐runoff models.
Tropospheric distribution and variability of N2O: Evidence for strong tropical emissions
Authors: Kort E. A. , Patra P. K. , Ishijima K. , Daube B. C. , Jiménez R. , Elkins J. , Hurst D. , Moore F. L. , Sweeney C. , Wofsy S. C.
Published: August 2011

Measurements of atmospheric N2O spanning altitudes from the surface to 14 km, and latitudes from 67°S to 85°N, show high concentrations in the tropics and subtropics, with strong maxima in the middle and upper troposphere. The pattern varies significantly over time scales of a few weeks. Global simulations do not accurately capture observed distributions with latitude, altitude, or time. Inversion results indicate strong, episodic inputs of nitrous oxide from tropical regions (as large as 1 Tg N‐N2O over 9 weeks) are necessary to produce observed vertical and latitudinal distributions. These findings highlight strong tropical sources of N2O with high temporal variability, and the necessity of using full vertical profile observations in deriving emissions from atmospheric measurements.
Methane observations from the Greenhouse Gases Observing SATellite: Comparison to ground‐based TCCON data and model calculations
Authors: Parker Robert , Boesch Hartmut , Cogan Austin , Fraser Annemarie , Feng Liang , Palmer Paul I. , Messerschmidt Janina , Deutscher Nicholas , Griffith David W. T. , Notholt Justus , Wennberg Paul O. , Wunch Debra
Published: August 2011

We report new short‐wave infrared (SWIR) column retrievals of atmospheric methane (XCH4) from the Japanese Greenhouse Gases Observing SATellite (GOSAT) and compare observed spatial and temporal variations with correlative ground‐based measurements from the Total Carbon Column Observing Network (TCCON) and with the global 3‐D GEOS‐Chem chemistry transport model. GOSAT XCH4 retrievals are compared with daily TCCON observations at six sites between April 2009 and July 2010 (Bialystok, Park Falls, Lamont, Orleans, Darwin and Wollongong). GOSAT reproduces the site‐dependent seasonal cycles as observed by TCCON with correlations typically between 0.5 and 0.7 with an estimated single‐sounding precision between 0.4–0.8%. We find a latitudinal‐dependent difference between the XCH4 retrievals from GOSAT and TCCON which ranges from 17.9 ppb at the most northerly site (Bialystok) to −14.6 ppb at the site with the lowest latitude (Darwin). We estimate that the mean smoothing error difference included in the GOSAT to TCCON comparisons can account for 15.7 to 17.4 ppb for the northerly sites and for 1.1 ppb at the lowest latitude site. The GOSAT XCH4 retrievals agree well with the GEOS‐Chem model on annual (August 2009 – July 2010) and monthly timescales, capturing over 80% of the zonal variability. Differences between model and observed XCH4 are found over key source regions such as Southeast Asia and central Africa which will be further investigated using a formal inverse model analysis.
Fast draining lakes on the Greenland Ice Sheet
Authors: Selmes N. , Murray T. , James T. D.
Published: August 2011

The rapid drainage of supraglacial lakes around the ablation zone of the Greenland Ice Sheet forms an important link between water at the surface and the ice sheet base, allowing surface meltwater to reach the bed and hence increase glacial velocity. The conduits formed by lake drainages may remain open during the remainder of the melt season providing a pathway for further meltwater to reach the base. We investigated the drainage behavior of lakes from all regions of the Greenland Ice Sheet for the period 2005–2009. We mapped the evolution of 2600 lakes from 3704 MODIS images detecting a mean of 263 drainage events per year, of which 61% occurred in the south‐west region. Only 1% of lake drainages occurred in the rapidly thinning south‐east region. Our results show marked differences between the hydrology of the different regions of the ice sheet, with few lake drainages occurring in the regions where the highest dynamic mass loss is occurring. In the south‐west and north‐east, lake drainages are common and could impact glacier dynamics; in the south‐east they are rare and are thus unlikely to do so.