bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of hydrology and effluent quality on the management of woodchip pads for overwintering cattle. I. Development of monitoring methodology and sampling strategies
Authors: JACKSON D. R. , SMITH K. A.
Published: August 2012

Woodchip pads can be a sustainable alternative to the overwintering of stock on grassland or in conventional housing and can offer benefits in improved animal performance, improved health and environmentally sustainable options for the management of animal excreta (dung, urine and the resulting effluent). Novel flow measuring equipment was developed to monitor effluent drainage from two woodchip pads sited on commercial farms in the UK, one in Powys (Wales, UK) and the other in Leicestershire (England, UK). Observations were made over 8 months in 2009/10. The aim was to assess both hydrological characteristics and nutrient fluxes. Flow monitoring, based on the use of tipping bucket or the principles of an overshot water wheel, was required to be capable of diverting a sample into a storage tank for sub-sampling and subsequent analysis. Estimates of pad outputs through evaporation and sub-surface drainage accounted for 0·98–1·01 of total inputs from precipitation and animal excreta, with evaporation and pad drainage representing 0·47–0·63 and 0·34–0·51 of total inputs, respectively. The resulting scientific information is of value in the synthesis of guidelines for design, construction and management of woodchip pads. Detailed analysis of flow and precipitation data, coupled with column absorption studies to evaluate moisture retention in the woodchip matrix, were used to consider the development of modelling approaches, with the potential to predict drainage outputs across a range of geographical, weather and pad management situations.
Characteristics and drivers of global NDVI‐based FPAR from 1982 to 2006
Authors: Peng Dailiang , Zhang Bing , Liu Liangyun , Fang Hongliang , Chen Dongmei , Hu Yong , Liu Lingling
Published: August 2012

Fraction of Absorbed Photosynthetically Active Radiation (FPAR) is a state parameter in most ecosystem productivity models and is also the key terrestrial product. In this study, Normalized Difference Vegetation Index (NDVI) from Advanced Very High Resolution Radiometer (AVHRR) Global Inventory Modeling and Mapping Studies (GIMMS) was used to estimate FPAR from 1982 to 2006, using an intermediate model. Our research focused on the analysis of long‐term global FPAR interannual trend patterns and driving forces involving climate and land cover changes. Results showed that interannual trend and spatial distribution patterns of global FPAR were independent of the changes in AVHRR instruments, and differed by season dynamics and vegetation types. Compared with other seasons, the period during JJA (June–August) exhibited more areas with decreasing FPAR and greater reduction range. For FPAR interannual trend, a wholly different correlation pattern was observed between temperature and precipitation, especially for arid and semi‐arid regions. A significant influence of extreme droughts such as those associated with El Nino/Southern Oscillation (ENSO) on FPAR variability was found. The result also revealed the increasing and decreasing interannual trend of FPAR corresponding to the afforestation in the Three North Shelterbelts Program in China and deforestation in tropical forests in Southeast Asia. Driving factor analysis indicated that the climate and land cover changes had an interactive effect on the FPAR annual anomalous variation.
A global model for the uptake of atmospheric hydrogen by soils
Authors: Morfopoulos C. , Foster P. N. , Friedlingstein P. , Bousquet P. , Prentice I. C.
Published: August 2012

A simple process‐based model for the consumption of atmospheric hydrogen (H2) has been developed. The model includes a description of diffusion and biological processes which together control H2flux into the soil. The model was incorporated into the LPJ‐WHyMe Dynamic Global Vegetation Model, and used to simulate H2 fluxes over the 1988–2006 period. The model results have been confronted with field and laboratory measurements. The model reproduces observed seasonal cycles of H2 uptake at different sites and shows a realistic sensitivity to changes in soil temperature and soil water content in comparisons with field and laboratory measurements. A recent study, based on 3D atmospheric model inversion, found an increase of the global H2 sink from soils, with a trend of −0.77 Tg a−2 for the 1992–2004 period (fluxes are negative as soils act as a sink for atmospheric H2). For the same period, however, our process‐based model calculates a trend of only −0.04 Tg a−2. Even when forced with drastic changes in soil water content, soil temperature and snow cover depth, our model is unable to reproduce the trend found in the inversion‐based study, questioning the realism of such a large trend.
The first in situ observation of Kelvin‐Helmholtz waves at high‐latitude magnetopause during strongly dawnward interplanetary magnetic field conditions
Authors: Hwang K.‐J. , Goldstein M. L. , Kuznetsova M. M. , Wang Y. , Viñas A. F. , Sibeck D. G.
Published: August 2012

We report the first in situ observation of high‐latitude magnetopause (near the northern duskward cusp) Kelvin‐Helmholtz waves (KHW) by Cluster on January 12, 2003, under strongly dawnward interplanetary magnetic field (IMF) conditions. The fluctuations unstable to Kelvin‐Helmholtz instability (KHI) are found to propagate mostly tailward, i.e., along the direction almost 90° to both the magnetosheath and geomagnetic fields, which lowers the threshold of the KHI. The magnetic configuration across the boundary layer near the northern duskward cusp region during dawnward IMF is similar to that in the low‐latitude boundary layer under northward IMF, in that (1) both magnetosheath and magnetospheric fields across the local boundary layer constitute the lowest magnetic shear and (2) the tailward propagation of the KHW is perpendicular to both fields. Approximately 3‐hour‐long periods of the KHW during dawnward IMF are followed by the rapid expansion of the dayside magnetosphere associated with the passage of an IMF discontinuity that characterizes an abrupt change in IMF cone angle,ϕ = acos
, from ∼90° to ∼10°. Cluster, which was on its outbound trajectory, continued observing the boundary waves at the northern evening‐side magnetopause during sunward IMF conditions following the passage of the IMF discontinuity. By comparing the signatures of boundary fluctuations before and after the IMF discontinuity, we report that the frequencies of the most unstable KH modes increased after the discontinuity passed. This result demonstrates that differences in IMF orientations (especially inϕ) are associated with the properties of KHW at the high‐latitude magnetopause due to variations in thickness of the boundary layer, and/or width of the KH‐unstable band on the surface of the dayside magnetopause.
Saturn's inner magnetospheric convection pattern: Further evidence
Authors: Thomsen M. F. , Roussos E. , Andriopoulou M. , Kollmann P. , Arridge C. S. , Paranicas C. P. , Gurnett D. A. , Powell R. L. , Tokar R. L. , Young D. T.
Published: August 2012

Observations of the radial locations of satellite absorption microsignatures in energetic particle data at Saturn have suggested the existence of an average convection pattern, fixed in local time, that is superimposed on the dominant near‐corotation of the inner magnetosphere. Such a pattern should have additional observational consequences, and we use several different Cassini data sets to test these expectations. These include day/night asymmetries in the A‐ring absorption signature of high‐energy particles and total electron density, day/night asymmetries in plasma ion and electron temperatures, and day/night asymmetries in energetic‐particle phase‐space densities. For L > 4, the observations are found to be consistent with expectations based on the suggested convective drifts in a global noon‐to‐midnight electric field, such that particles drift outward on the dawn side of the magnetosphere and inward on the dusk side, resulting in drift orbits with an outward offset toward noon. The different data sets yield similar estimates of the required radial offsets, ∼0.5–1 Rs in the region inside L = 10. The corresponding convection electric field appears to decrease with increasing radial distance, from ∼0.3 mV/m near Tethys to ∼0.1 mV/m beyond Dione. The source of such an electric field remains a puzzle, but whatever the source, it appears to be a dominant factor in the circulation of plasma in Saturn's inner magnetosphere. For L < 4, the observations are not fully consistent with such a global convection field, and other explanations for A‐ring absorption asymmetries are needed.
Macroholes in stalagmites and the search for lost water
Authors: Zisu Nurit Shtober , Schwarcz Henry P. , Konyer Norman , Chow Tom , Noseworthy Michael D.
Published: August 2012

Fluid microinclusions in stalagmites have provided samples of paleowaters present during the growth of the stalagmite, but only in microliter amounts. Genty et al. (2002) discovered much larger water‐filled macroinclusions in some stalagmites. Using computerized tomographic (CT) X‐ray‐scanning and magnetic resonance imaging (MRI) we searched for such macroinclusions in 21 stalagmites from diverse localities in North and Central America and the Caribbean. We show that most stalagmites contained numerous mm to cm‐sized internal cavities (macroholes). These do not penetrate the outer surfaces which in most cases are deceptively unblemished. Some stalagmites have up to 10% average internal porosity. Two types of macroholes are distinguishable: axial holes formed during growth due to slower calcite accumulation at the axial drip site; off‐axis holesformed penecontemporaneously with growth in discrete layers; these cut previous growth laminae showing that they are post‐depositional. Using MRI on uncut, apparently sealed specimens, we find that very few of these cavities contain significant quantities of water although they were clearly formed while the stalagmite was being continuously bathed by drip water. Presumably, the water has escaped post‐depositionally, through micro fissures, extensive connected hole system, crystal boundaries or other defects.
Estimation of daily cloud‐free, snow‐covered areas from MODIS based on variational interpolation
Authors: Xia Qing , Gao Xiaogang , Chu Wei , Sorooshian Soroosh
Published: August 2012

NASA's MODIS global snow‐covered area (SCA) products are one of the mission's major objectives that frequently contain cloud hindrances, which degrade their practical usability. Many techniques have been developed to mitigate the problem but with no assurance of eliminating all of the clouds. An image‐processing algorithm with its kernel based on the variational interpolation theorem is developed to automatically obtain cloud‐free dynamic SCA maps from MODIS. Two cases consisting of “accumulation” and “melting” phases are processed and validated using observations at 121 ground‐snow sensors over the Sierra Nevada Mountains in California. The results show that the algorithm cleared all the cloud hindrance over the period of study. In terms of accuracy, the retrieved cloud‐free snow cover for the accumulation case had an average omission error of around 22.5% and average commission error of around 2.1%, as compared to all available ground sensors. These high percentages of errors basically came from the input data of Terra and Aqua, which had omission errors of 14.3% and 20.2% (and the commission errors of ∼0.5%), respectively. For the melting case, when there were fewer clouds and hence more sensors available, the errors of omission and commission between the algorithm and direct observations from Terra and Aqua were close to each other (5.7–5.0% for omission and 0% for commission).
The effective elastic thickness of the continental lithosphere: Comparison between rheological and inverse approaches
Authors: Tesauro Magdala , Audet Pascal , Kaban Mikhail K. , Cloetingh Sierd
Published: August 2012

Following the release of global continental effective elastic thickness (Te) maps obtained using different approaches, we now have the opportunity to provide better constraints onTe.We improve previous estimates ofTederived from thermo‐rheological models of lithospheric strength (orTer) using new equations that consider variations of the Young's Modulus in the lithosphere. These new values are quantitatively compared with those obtained from an inverse approach (orTei) based on a comparison of the spectral coherence between topography and gravity anomalies with the flexural response of an equivalent elastic plate to loading. The two models show in general a good agreement, having equal means (at the 95% significance level) in about half of the continental areas. In other regionsTeiexceedsTerin about 65% of the data points, showing thatTeiprovides an upper bound onTe.The two data sets have a similar range, but demonstrate different distributions.Terhas a bimodal distribution, with the two peaks representative of the cratons and of the areas outside of them. In contrast,Teihas more uniform distribution without predominant peaks. Our models show higher similarities in the Meso‐Cenozoic orogens than in the Archaean and Proterozoic shields and platforms, due to the methods employed. For the regions with the most robust determinations ofTerandTei, the relationship between them is close to linear. The results of this work can be used for further studies on the mechanical properties of the lithosphere.
High fluid pressures and high fluid flow rates in the Megasplay Fault Zone, NanTroSEIZE Kumano Transect, SW Japan
Authors: Moore J. Casey , Barrett Myles , Thu Moe Kyaw
Published: August 2012

Annular pressure while drilling data shows high fluid overpressures at Site C0001 in part of the megasplay fault zone of the NanTroSEIZE transect across the subduction zone of SW Japan. Mostly standard annular pressures while drilling occur at three other sites, including two penetrating major faults. The two holes at Site C0001 show a step up to lithostatic annular pressure at about 500 mbsf, following initial indicators of overpressure at about 375 mbsf (meters below seafloor). The annular pressure remains high and increasing to total depth of 1000 mbsf. Seismic lines through the site show bright reflectors in the zone of initial annular pressure increase. Borehole images, sonic velocities, and resistivity all suggest a zone of fractures, from about 490 to 630 mbsf. A hydraulic model of the fluid system explains the observed pressures by influx of formation fluid at about 500 mbsf. The combination of a natural influx of 3300 l/m plus 2200 l/m from the drilling system can explain the observed annular pressures. The highly fractured zone that bleeds fluids to the borehole may be sealed by a localized zone of compressive stress or by overlying gas hydrates.
Kinematic interpretation of the 3D shapes of metamorphic core complexes
Authors: Le Pourhiet Laetitia , Huet Benjamin , May Dave A. , Labrousse Loic , Jolivet Laurent
Published: August 2012

Metamorphic Core Complexes form dome shaped structures in which the ductile crust is exhumed beneath a detachment fault. The 3D dome geometry, inferred by mapping the schistosity in the exhumed crust, can be either elongated normal to the stretching direction or along it. In the first case, the domes are interpreted as having formed during extension. However, in the second case, they are interpreted either as strike‐slip, transpressive or constrictive extensional structures, depending on the geodynamic context. Numerical models of metamorphic core complexes published to date are all two‐dimensional and therefore, theoretically only apply to domes which are elongated normal to the stretching direction. Here, we explore by means of 3D thermomechanical modeling, the impact of 3D kinematic extensional boundary conditions on the shape of metamorphic core complexes. We examine the impact of a transtensional step over and of horsetail splay fault kinematics on the dynamics of exhumation, finite strain and P‐T paths, and compare them to cylindrical 3D models. We show, for the first time, that domes formed in transtensional step over, or at the tip of propagating strike‐slip faults, display a finite strain field which can be interpreted as characteristic of a transpressive domes, although no shortening was applied in the far‐field. Applying our models to the Cyclades, we propose that the coeval formation of domes elongated normal and parallel to the stretching during the Miocene can be the result of horsetail splay fault kinematics, which could correspond to the formation of a tear in the Aegean slab.
Constraining cloud lifetime effects of aerosols using A‐Train satellite observations
Authors: Wang Minghuai , Ghan Steven , Liu Xiaohong , L'Ecuyer Tristan S. , Zhang Kai , Morrison Hugh , Ovchinnikov Mikhail , Easter Richard , Marchand Roger , Chand Duli , Qian Yun , Penner Joyce E.
Published: August 2012

Aerosol indirect effects have remained the largest uncertainty in estimates of the radiative forcing of past and future climate change. Observational constraints on cloud lifetime effects are particularly challenging since it is difficult to separate aerosol effects from meteorological influences. Here we use three global climate models, including a multi‐scale aerosol‐climate model PNNL‐MMF, to show that the dependence of the probability of precipitation on aerosol loading, termed the precipitation frequency susceptibility (Spop), is a good measure of the liquid water path response to aerosol perturbation (λ), as both Spop and λ strongly depend on the magnitude of autoconversion, a model representation of precipitation formation via collisions among cloud droplets. This provides a method to use satellite observations to constrain cloud lifetime effects in global climate models. Spopin marine clouds estimated from CloudSat, MODIS and AMSR‐E observations is substantially lower than that from global climate models and suggests a liquid water path increase of less than 5% from doubled cloud condensation nuclei concentrations. This implies a substantially smaller impact on shortwave cloud radiative forcing over ocean due to aerosol indirect effects than simulated by current global climate models (a reduction by one‐third for one of the conventional aerosol‐climate models). Further work is needed to quantify the uncertainties in satellite‐derived estimates ofSpop and to examine Spopin high‐resolution models.
Evidence of sudden rupture of a large asperity during the 2008 Mw7.9 Wenchuan earthquake based on strong motion analysis
Authors: Zhang Guohong , Vallée Martin , Shan Xinjian , Delouis Bertrand
Published: August 2012

We investigate the rupture process of the 12 May 2008 Wenchuan earthquake using the records of 26 strong‐motion stations, located 20–120 km from the seismic fault and with a good azimuthal coverage. The wave velocity model required to conduct this analysis has been validated against aftershocks, for which the point source hypothesis is a very good approximation. The inversion of the main shock rupture process confirms the slip distribution and the average rupture velocity (∼3 km/s) previously determined. However, a very peculiar behavior is clearly resolved by the extensive data set used in this study: the major slip area of the Wenchuan earthquake, located at 20–50 km North‐East of the epicenter, is shown to break almost simultaneously, 25 s after earthquake initiation. This implies that slip in this part of the fault cannot be understood by simple stress release at the rupture front. A more likely interpretation is the presence of a strong asperity, which could break only when it was completely surrounded by stress increase, resulting in a delayed but brutal rupture.
Gravity wave momentum flux spectra observed from satellite in the summertime subtropics: Implications for global modeling
Authors: Ern M. , Preusse P.
Published: August 2012

The spectral distribution in terms of horizontal and vertical wavenumber is deduced for gravity wave (GW) momentum flux observations from space for the first time. The paper focuses on High Resolution Dynamics Limb Sounder (HIRDLS) observations in the subtropics and compares spectra over particularly strong deep convective forcing with a background inferred from regions of less momentum flux. The deep convective spectra are strongly enhanced at high horizontal wavenumbers over a wide range of vertical wavenumbers and phase speeds. The observations indicate that GWs generated by deep convection are an important contribution on top of the background spectrum due to other GW sources (at least about 20–30% on zonal average is from convective GWs). The implications for global modeling are discussed.
Why is the areoid like the residual geoid?
Authors: Burke Kevin , Werner Stephanie C. , Steinberger Bernhard , Torsvik Trond H.
Published: August 2012

The equipotential figures of Earth (residual geoid), and of Mars (areoid) are characterized by pairs of elevated and pairs of depressed antipodal equatorial regions. Elevated regions of the residual geoid lie vertically above the two Large Low Shear Wave Velocity Provinces (LLSVPs) on the Core Mantle Boundary (CMB). There is evidence that the LLSVPs are dense, physicochemically distinct, and have been stable in their positions with respect to each other and to the Earth's spin axis for at least ∼550 My. The final event in the planetary‐scale development of the Earth's structure was the moon‐forming event and the comparable event on Mars is thought by many to have been the Borealis basin‐forming impact. We attribute the formation of the LLSVPs and postulated comparable masses underlying the elevated regions of the areoid on the CMB of Mars, to the immediate after‐effects of those two giant impacts.
Space‐based observations of megacity carbon dioxide
Authors: Kort Eric A. , Frankenberg Christian , Miller Charles E. , Oda Tom
Published: August 2012

Urban areas now house more than half the world's population, and are estimated to contribute over 70% of global energy‐related CO2emissions. Many cities have emission reduction policies in place, but lack objective, observation‐based methods for verifying their outcomes. Here we demonstrate the potential of satellite‐borne instruments to provide accurate global monitoring of megacity CO2 emissions using GOSAT observations of column averaged CO2 dry air mole fraction (XCO2) collected over Los Angeles and Mumbai. By differencing observations over the megacity with those in nearby background, we observe robust, statistically significant XCO2 enhancements of 3.2 ± 1.5 ppm for Los Angeles and 2.4 ± 1.2 ppm for Mumbai, and find these enhancements can be exploited to track anthropogenic emission trends over time. We estimate that XCO2 changes as small as 0.7 ppm in Los Angeles, corresponding to a 22% change in emissions, could be detected with GOSAT at the 95% confidence level.
How much do precipitation extremes change in a warming climate?
Authors: Shiu Chein‐Jung , Liu Shaw Chen , Fu Congbin , Dai Aiguo , Sun Ying
Published: August 2012

Daily data from reanalyses of the European Centre for Medium‐Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) are analyzed to study changes in precipitation intensity with respect to global mean temperature. The results are in good agreement with those derived from the Global Precipitation Climatology Project (GPCP) data by Liu et al. (2009), providing an independent verification for large changes in the precipitation extremes: about 100% increase for the annual top 10% heavy precipitation and about 20% decrease for the light and moderate precipitation for one degree warming in the global temperature. These changes can substantially increase the risk of floods as well as droughts, thus severely affecting the global ecosystems. Atmospheric models used in the reanalysis mode, with the benefit of observed wind and moisture fields, appear to be capable of realistically simulating the change of precipitation intensity with global temperature. In comparison, coupled climate models are capable of simulating the shape of the change in precipitation intensity, but underestimate the magnitude of the change by about one order of magnitude. The most likely reason of the underestimation is that the typical spatial resolution of climate models is too coarse to resolve atmospheric convection.
A window for carbon uptake in the southern subtropical Indian Ocean
Authors: Valsala Vinu , Maksyutov Shamil , Murtugudde Raghu
Published: August 2012

Atmospheric CO2 sinks in the southern Indian Ocean was examined for their seasonal, interannual and interdecadal variability. Two distinct zones of CO2 uptake are identified; located in the 15°S–35°S band is the northern box where CO2 uptake is dominated by the solubility pump, and in the latitudinal range of 35°S–50°S is the southern box where both the solubility and biological pump are equal players. The anthropogenic CO2 inventories appear to be a result of deepening subduction of CO2 and subsequent invasion into the northern domain. The seasonal and interannual variability of CO2 sinks to the north are rather surface trapped, while the deep CO2 variability is found to be coherent with the atmospheric forcing, consistent with decadal wind stress curl anomalies. This is a step towards separating the secular trends of deep ocean CO2 from its natural variability in the analysis region.
Radio‐loud CMEs from the disk center lacking shocks at 1 AU
Authors: Gopalswamy N. , Mäkelä P. , Akiyama S. , Yashiro S. , Xie H. , MacDowall R. J. , Kaiser M. L.
Published: August 2012

A coronal mass ejection (CME) associated with a type II burst and originating close to the center of the solar disk typically results in a shock at Earth in 2–3 days and hence can be used to predict shock arrival at Earth. However, a significant fraction (about 28%) of such CMEs producing type II bursts were not associated with shocks at Earth. We examined a set of 21 type II bursts observed by the Wind/WAVES experiment at decameter‐hectometric (DH) wavelengths that had CME sources very close to the disk center (within a central meridian distance of 30 degrees), but did not have a shock at Earth. We find that the near‐Sun speeds of these CMEs average to ∼644 km/s, only slightly higher than the average speed of CMEs associated with radio‐quiet shocks. However, the fraction of halo CMEs is only ∼30%, compared to 54% for the radio‐quiet shocks and 91% for all radio‐loud shocks. We conclude that the disk‐center radio‐loud CMEs with no shocks at 1 AU are generally of lower energy and they drive shocks only close to the Sun and dissipate before arriving at Earth. There is also evidence for other possible processes that lead to the lack of shock at 1 AU: (i) overtaking CME shocks merge and one observes a single shock at Earth, and (ii) deflection by nearby coronal holes can push the shocks away from the Sun‐Earth line, such that Earth misses these shocks. The probability of observing a shock at 1 AU increases rapidly above 60% when the CME speed exceeds 1000 km/s and when the type II bursts propagate to frequencies below 1 MHz.
Survival of flux transfer event (FTE) flux ropes far along the tail magnetopause
Authors: Eastwood J. P. , Phan T. D. , Fear R. C. , Sibeck D. G. , Angelopoulos V. , Øieroset M. , Shay M. A.
Published: August 2012

During intervals of southward IMF, magnetic reconnection can result in the formation of flux transfer events (FTEs) on the dayside magnetopause which travel along the magnetopause in the anti‐sunward direction. Of particular interest is their fate and the role they play transporting solar wind plasma into the magnetosphere. We present the discovery of FTEs far along the distant tail magnetopause (x = −67 Earth radii) using data from ARTEMIS on the dusk flank magnetopause under southward/duskward IMF conditions. The identification of several events is further supported by excellent fits to a force‐free flux rope model. The axis of each structure is principally north‐south, i.e., perpendicular to the Sun‐Earth line. Simultaneous observations by THEMIS on the dayside magnetopause indicate that FTEs are being produced there, although perhaps 2–4 times smaller in size. The convection time from the dayside magnetopause to ARTEMIS is 30 min, and the FTEs have a flux content comparable to those typically observed on the dayside magnetopause, indicating that these features are in quasi‐equilibrium as they are convected downtail. By considering the relative orientations of the FTEs observed by THEMIS and ARTEMIS, the magnetic field geometry is consistent with the FTEs being produced on the dayside magnetopause along an extended X‐line in the presence of IMF By and bending as they are convected to the flanks.
Charge moment change and lightning‐driven electric fields associated with negative sprites and halos
Authors: Li Jingbo , Cummer Steven , Lu Gaopeng , Zigoneanu Lucian
Published: August 2012

Sprites are structured high altitude optical emissions produced by lightning‐driven electric fields. Both strong positive and negative cloud to ground flashes (CGs) are capable of initiating sprites. However, reported sprites are almost exclusively produced by +CGs. The very limited number of negative polarity sprites makes it difficult to reveal their morphologies and mechanisms. Since 2008, we have operated low light cameras at 5 locations in the United States to detect lightning‐driven transient luminous events (TLEs). At Duke University, two pairs of magnetic sensors simultaneously record lightning‐radiated magnetic fields. During 4 years of observations, the low light cameras collectively captured 1651 sprite events. Among them, 6 were produced by −CG lightning, which was confirmed by both the National Lightning Detection Network (NLDN) and magnetic field measurements. All of these negative sprites show similar features in their morphology, lightning source current, and lightning‐driven ambient electric fields. They all initiate within a few ms from their parent lightning discharges and always are accompanied by sprite halos. Compared to positive sprites, the downward streamers in negative sprites terminate at higher altitudes, about 55–60 km. The extracted source current of their parent lightning discharges is very impulsive and produces at least 450 C km charge moment change in 0.5 ms or less. Unlike most +CG strokes, essentially no continuing current follows these −CGs. Thus the uniformity of negative sprite morphology appears to reflect the uniformity of the characteristics of high charge transfer negative strokes. Numerical simulation shows these impulsive source currents produce very high (>2 Ek, where Ek is the local air breakdown field) but short‐lived electric fields at halo altitudes between 70 km and 90 km. At streamer termination altitudes, the inferred background electric field is 0.2–0.3 Ek, which is close to but below the critical field (0.4 Ek) for negative streamer propagation. The simulations also show that the timescale of the lightning source current has a significant impact on the high altitude electric fields and thus the sprite initiation and morphology. With the same amount of charge transfer, a more impulsive current source produces a higher electric field of shorter duration at halo and sprite altitudes. The short timescales may explain why a larger threshold of total charge moment change is required to initiate negative sprites than short‐delayed positive sprites, whose parent lightning source current is usually less impulsive.
Evolution of equatorial irregularities under varying electrodynamical conditions: A multitechnique case study from Indian longitude zone
Authors: Hajra R. , Chakraborty S. K. , Mazumdar S. , Alex S.
Published: August 2012

A comprehensive multitechnique study on the postsunset evolutions of equatorial ionization anomaly (EIA) and equatorial plasma density irregularities in the context of the varying electrodynamical conditions under normal equatorial electrojet (EEJ), complete and partial counter electrojet (CEJ) events is presented from the Indian longitude zone. The study involves analysis of scintillation data at VHF (250 MHz) and GPS L1 (1575.42 MHz) frequency, ionosonde data, magnetometer data along with global ionospheric maps (GIMs) of total electron content (TEC) for the vernal equinoctial months (March–April) of 2011. The investigation reveals inefficiency of the noontime peak EEJ to dictate the day‐to‐day variability of postsunset irregularity phenomena. Intensification of EEJ after ∼1530 IST (Indian standard time) on normal EEJ days and significantly enhanced residual fields presumably due to CEJ event after ∼1700 IST on complete and partial CEJ days are found to be associated with the resurgence of EIA and evolution of postsunset irregularities. The results are discussed in terms of superposition effects of electric fields arising from E‐ and F‐ region dynamos.
Very‐low‐frequency saucers observed on DEMETER
Authors: James H. G. , Parrot M. , Berthelier J.‐J.
Published: August 2012

Observations of very‐low‐frequency saucers by the electric field instrument (Instrument Champ Electrique, ICE) aboard the DEMETER spacecraft have added new evidence about the nature of the highly localized source of this radiation. DEMETER orbited sun‐synchronously at altitudes around 660 km, significantly below those at which earlier spacecraft detected saucers. Also, DEMETER data establish the existence of saucer sources in the dayside ionosphere. Frequency‐time slopes of saucers in DEMETER spectrograms have been analyzed with two‐dimensional ray tracing. To produce such slopes requires long vertical separations between the source and the spacecraft, in some cases much greater than the height of the spacecraft above ground. It is concluded that the sources lie above the satellite and radiate downward. Bidirectional radiation patterns and the broadband quasielectrostatic whistler mode energy spectrum are consistent with the published results of simulations of nonlinear two‐stream instabilities.
Upwelling filaments off Cap Blanc: Interaction of the NW African upwelling current and the Cape Verde frontal zone eddy field?
Authors: Meunier T. , Barton E. D. , Barreiro B. , Torres R.
Published: August 2012

The hydrographical and dynamical properties of the upwelling filaments forming off Cap Blanc (Mauritania) are investigated using remotely sensed and in situ data collected in April/May 2009 during the strongest upwelling season. The area is situated at the southern edge of the NW African upwelling system, where the Cape Verde Frontal Zone (CVFZ) separates warmer, saltier North Atlantic Central Water (NACW) and cooler, fresher South Atlantic Central Water (SACW). Sea surface temperature images indicated the presence of an upwelling filament extending >280 km offshore, rooted over the Cap Blanc promontory and entrained around a warm‐core anticyclonic eddy. After this filament started to decay, a new cold filament developed at the approximate same location. High resolution Moving Vessel Profiler (MVP) and Acoustic Doppler Current Profiler (ADCP) surveys of these mesoscale structures revealed that both filaments were carrying South Atlantic Central Water (SACW) offshore through an intense jet‐like flow. Similarity of the relative vorticity structure across the filament with that of the tangent eddy suggested that the latter was responsible for the offshore current. Tracking of this eddy in altimetric data demonstrated that it originated from the CVFZ, as implied by its hydrographic structure. Altimetric data also revealed that another anticyclonic structure centered over the Cap Blanc promontory was responsible for the northwestward advection of SACW into the base of the filament. The results support the idea that some upwelling filaments can be produced by the interaction of an external eddy field, including topographic eddies, with the upwelled water.
Variability of Indonesian throughflow within Makassar Strait, 2004–2009
Authors: Susanto R. Dwi , Ffield Amy , Gordon Arnold L. , Adi T. Rameyo
Published: August 2012

In contrast to earlier measurements, January 2004 through May 2009 Makassar Strait velocities within the main Pacific inflow pathway of the Indonesian throughflow (ITF) are larger with a clear signal of the Asian‐Australian monsoon overriding the relatively weak 2006/2007 El Niño and 2007/2008 La Niña. The Makassar flow is thermocline intensified with maximum along‐channel velocity of −0.8 m/s near 120 m during the southeast monsoon, July to September, decreasing to −0.6 m/s from October to December, during the transition to the northwest monsoon. The temperature variability is highly correlated to ENSO, and the salinity variability reveals low‐salinity surface water inputs to the ITF, possibly from the Java and Sulu seas. Empirical Orthogonal Function (EOF) analysis of the velocity profile reveals that the first mode (45%) is dominated by the intrusions of Kelvin waves from the south, the second mode (30%) reflects ENSO modulation, and the third mode (17%) is associated with regional monsoon winds. The strength of the northward intrusions of Kelvin waves plays an important role in the total transport. The 2004–2009 average seasonal transport varied from −15.5 Sv (Sv = 106 m3/s) during the northwest monsoon (January to March) to −9.6 Sv during the monsoon transition (October to December). The annual mean transport is southward at 13.3 ± 3.6 Sv, with small year‐to‐year range from 12.5 to 14.0 Sv, substantially higher than measurements from 1997 when El Niño suppressed the transport (9.2 Sv).
Is the deep Indian Ocean MOC sustained by breaking internal waves?
Authors: Huussen T. N. , Naveira‐Garabato A. C. , Bryden H. L. , McDonagh E. L.
Published: August 2012

The Indian Ocean hosts a vigorous basin‐scale overturning that constitutes one of the major deep upwelling branches of the global meridional overturning circulation (MOC). The extent to which the deep Indian Ocean MOC is sustained by breaking internal waves is assessed by quantifying and comparing the energetics of the overturning and those of the regional internal wave field. A range of published inverse estimates of the circulation across 32°S is used to assess the basin average buoyancy fluxes. The turbulent dissipation needed to sustain the MOC ranges between 0.17 ± 0.04 and 1.19 ± 0.17 TW, which is consistent with the estimated 0.35−0.26+1.04 TW dissipated by breaking internal waves, as inferred from observed fine structure. Both estimates of turbulent dissipation are consistent with the total energy input into the regional internal wave field (0.21−0.05+0.08TW) based on published estimates of energy conversion from winds, tides and geostrophic bottom flows. However, a discrepancy arises when comparing the energetics at different density levels. At mid‐ocean density levels (∼1000–3000 m) the dissipation of internal wave energy is found to be significantly smaller (factor 5–10) than the dissipation needed to sustain inverse estimates of the MOC. The uncertainty related to undersampling of internal wave breaking hot spots was analyzed and found to be small, which suggests that mixing processes other than wave breaking due to weak wave‐wave interactions, may be significant in the deep Indian Ocean.
Assessment of future flood hazard in Europe using a large ensemble of bias‐corrected regional climate simulations
Authors: Rojas R. , Feyen L. , Bianchi A. , Dosio A.
Published: August 2012

We assess future flood hazard in view of climate change at pan‐European scale using a large ensemble of climate projections. The ensemble consists of simulations from 12 climate experiments conducted within the ENSEMBLES project, forced by the SRES A1B emission scenario for the period 1961–2100. Prior to driving the hydrological model LISFLOOD, climate simulations are corrected for bias in precipitation and temperature using a Quantile Mapping (QM) method. For time slices of 30 years, a Gumbel distribution is fitted by the maximum likelihood method through the simulated annual maximum discharges. Changes in extreme river flows, here exemplified by the 100‐year discharge (Q100), are then analyzed with respect to a control period (1961–1990). We assess the uncertainty arising from using alternative climate experiments to force LISFLOOD and from the fitting of extreme value distributions. Results show large discrepancies in the magnitude of change in Q100among the hydrological simulations for different climate experiments, with some regions even showing an opposite signal of change. Due to the low signal‐to‐noise ratio in some areas the projected changes showed not all to be statistically significant. Despite this, western Europe, the British Isles and northern Italy show a robust increase in future flood hazard, mainly due to a pronounced increase in extreme rainfall. A decrease inQ100, on the other hand, is projected in eastern Germany, Poland, southern Sweden and, to a lesser extent, the Baltic countries. In these areas, the signal is dominated by the strong reduction in snowmelt induced floods, which offsets the increase in average and extreme precipitation.
A study of X‐ray emissions from thunderstorms with emphasis on subsequent strokes in natural lightning
Authors: Mallick S. , Rakov V. A. , Dwyer J. R.
Published: August 2012

X‐ray emissions associated with leaders of natural cloud‐to‐ground lightning are examined. For 23 (8 first and 15 subsequent) strokes within 2 km of the Lightning Observatory in Gainesville, the occurrence of detectable X‐rays was 88% and 47% for the first and subsequent strokes, respectively. Some subsequent‐stroke leaders, retracing previously formed, low‐density channels, are more prolific producers of detectable X‐rays than their corresponding first‐stroke leaders, developing in the virgin air. The energy of some photons was in the MeV range (in one case possibly in excess of 5 MeV); that is, in the gamma‐ray range. There was a significant difference between first and subsequent leaders in terms of the distribution of estimated X‐ray source heights. For first leaders, the maximum source height did not exceed 800 m, whereas for subsequent leaders the source height distribution appeared to extend to about 3.6 km. Not all leaders within a flash produced detectable X‐rays. For the same leader near ground, some steps were accompanied by detectable X‐ray emissions, while others were not. One possible explanation is that electric field enhancements (>30 MV/m or so for the case of normal air density), needed for the cold runaway breakdown, are very brief and highly localized, so that in many cases a sufficiently energetic electron from the tail of the bulk distribution may be unavailable to start the runaway process. This implies that the cold runaway breakdown is not a necessary feature of lightning leaders, even if the required fields do occur.
Regional‐scale phenology modeling based on meteorological records and remote sensing observations
Authors: Yang Xi , Mustard John F. , Tang Jianwu , Xu Hong
Published: August 2012

Changes of vegetation phenology in response to climate change in the temperate forests have been well documented recently and have important implications on the regional and global carbon and water cycles. Predicting the impact of changing phenology on terrestrial ecosystems requires an accurate phenology model. Although species‐level phenology models have been tested using a small number of vegetation species, they are rarely examined at the regional level. In this study, we used remotely sensed phenology and meteorological data to parameterize the species‐level phenology models. We used a remotely sensed vegetation index (Two‐band Enhanced Vegetation Index, EVI2) derived from the Moderate Resolution Spectroradiometer (MODIS) 8‐day reflectance product from 2000 to 2010 of New England, United States to calculate remotely sensed vegetation phenology (start/end of season, or SOS/EOS). The SOS/EOS and the daily mean air temperature data from weather stations were used to parameterize three budburst models and one senescence model. We compared the relative strengths of the models to predict vegetation phenology and selected the best model to reconstruct the “landscape phenology” in New England from year 1960 to 2010. Of the three budburst models tested, the spring warming model showed the best performance with an averaged Root Mean Square Deviation (RMSD) of 4.59 days. The Akaike Information Criterion supported the spring warming model in all the weather stations. For senescence modeling, the Delpierre model was better than a null model (the averaged phenology of each weather station, averaged model efficiency = 0.33) and has a RMSD of 8.05 days. A retrospective analysis using the spring warming model suggests a statistically significant advance of SOS in New England from 1960 to 2010 averaged as 0.143 days per year (p = 0.015). EOS calculated using the Delpierre model and growing season length showed no statistically significant advance or delay between 1960 and 2010 in this region. These results suggest the applicability of species‐level phenology models at the regional level (and potentially terrestrial biosphere models) and the feasibility of using these models in reconstructing and predicting vegetation phenology.
The influence of reservoirs, climate, land use and hydrologic conditions on loads and chemical quality of dissolved organic carbon in the Colorado River
Authors: Miller Matthew P.
Published: August 2012

Longitudinal patterns in dissolved organic carbon (DOC) loads and chemical quality were identified in the Colorado River from the headwaters in the Rocky Mountains to the United States–Mexico border from 1994 to 2011. Watershed‐ and reach‐scale climate, land use, river discharge and hydrologic modification conditions that contribute to patterns in DOC were also identified. Principal components analysis (PCA) identified site‐specific precipitation and reach‐scale discharge as being correlated with sites in the upper basin, where there were increases in DOC load from the upstream to downstream direction. In the lower basin, where DOC load decreased from upstream to downstream, sites were correlated with site‐specific temperature and reach‐scale population, urban land use and hydrologic modification. In the reaches containing Lakes Powell and Mead, the two largest reservoirs in the United States, DOC quantity decreased, terrestrially derived aromatic DOC was degraded and/or autochthonous less aromatic DOC was produced. Taken together, these results suggest that longitudinal patterns in the relatively unregulated upper basin are influenced by watershed inputs of water and DOC, whereas DOC patterns in the lower basin are reflective of a balance between watershed contribution of water and DOC to the river and loss of water and DOC due to hydrologic modification and/or biogeochemical processes. These findings suggest that alteration of constituent fluxes in rivers that are highly regulated may overshadow watershed processes that would control fluxes in comparable unregulated rivers. Further, these results provide a foundation for detailed assessments of factors controlling the transport and chemical quality of DOC in the Colorado River.
The evolutionary success of sex
Authors: Colegrave Nick
Published: August 2012

Sexual reproduction remains a major puzzle for biologists. How did it evolve and why have so many species maintained it, despite its extensive costs? Recent research is shedding light on the answers to some of these questions.