bluuebunny/crossref_metadata_2025 huggingface dataset:
Water Masers Toward Star-Forming Regions in the Bolocam Galactic Plane Survey
Authors: Dunham Miranda K. ,   The BGPS Team
Published: July 2012

We present preliminary results of a search for 22 GHz water masers toward 1400 star-forming regions seen in the Bolocam Galactic Plane Survey (BGPS) using the Green Bank Telescope (GBT). The BGPS is a blind survey of the Northern Galactic plane in 1.1 mm thermal dust emission that has cataloged star-forming regions at all evolutionary stages. Further information is required to determine the stage of each BGPS source. Since water masers are produced by outflows from low and high-mass star forming regions, their presence is a key component of determining whether the BGPS sources are forming stars and which evolutionary stage they are in. We present preliminary detection statistics, basic properties of the water masers, and correlations with physical properties determined from the 1.1 mm emission and ammonia observations obtained concurrently with the water masers on the GBT.
Simultaneous observations of SiO and H2O masers toward known stellar SiO and/or H2O maser sources
Authors: Kim Jaeheon , Cho Se-Hyung , Kim Sang Joon
Published: July 2012

We present the results of simultaneous observations of SiO v = 1, 2, 29SiO v = 0, J = 1−0 and H2O 616-523 maser lines toward 318 known stellar SiO and/or H2O maser sources using the Yonsei 21-m radio telescope of the Korean VLBI Network. Toward 166 known SiO and H2O maser sources, both SiO and H2O maser emissions were detected from 112 sources giving a detection rate of 67.5 %. On the other hand, toward 152 known H2O-only maser sources, both SiO and H2O maser emissions were detected from 62 sources, giving a detection rate of 40.8 %. Characteristics of all observed sources in the IRAS two-color diagram is investigated including their evolutionary sequence and mutual relations between SiO and H2O maser properties.
Cosmology and the Hubble Constant: On the Megamaser Cosmology Project (MCP)
Authors: Henkel C. , Braatz J. A. , Reid M. J. , Condon J. J. , Lo K. Y. , Impellizzeri C. M. Violette , Kuo C. Y.
Published: July 2012

The Hubble constant H0 describes not only the expansion of local space at redshift z ~ 0, but is also a fundamental parameter determining the evolution of the universe. Recent measurements of H0 anchored on Cepheid observations have reached a precision of several percent. However, this problem is so important that confirmation from several methods is needed to better constrain H0 and, with it, dark energy and the curvature of space. A particularly direct method involves the determination of distances to local galaxies far enough to be part of the Hubble flow through water vapor (H2O) masers orbiting nuclear supermassive black holes. The goal of this article is to describe the relevance of H0 with respect to fundamental cosmological questions and to summarize recent progress of the ‘Megamaser Cosmology Project’ (MCP) related to the Hubble constant.
AGN and Megamasers
Authors: Tarchi Andrea
Published: July 2012

Luminous extragalactic masers are traditionally referred to as the ‘megamasers’. Those produced by water molecules are associated with accretion disks, radio jets, or outflows in the nuclear regions of active galactic nuclei (AGN). The majority of OH maser sources are instead driven by intense star formation in ultra-luminous infrared galaxies, although in a few cases the OH maser emission traces rotating (toroidal or disk) structures around the nuclear engines of AGN. Thus, detailed maser studies provide a fundamental contribution to our knowledge of the main nuclear components of AGN, constitute unique tools to measure geometric distances of host galaxies, and have a great impact on probing the, so far, paradigmatic Unified Model of AGN.
Maser Astrometry: from Galactic Structure to Local Group Cosmology
Authors: Reid Mark J.
Published: July 2012

This review summarizes current advances in astrometry of masers as they pertain to large-scale Galactic structure and dynamics and Local Group cosmology. Parallaxes and proper motions have now been measured for more than 60 massive star forming regions using the Japanese VERA array, the EVN and the VLBA. These results provide “gold standard” distances and 3-dimensional velocities for sources across the Milky Way, revealing its spiral structure. Modeling these data tightly constrains the fundamental parameters of the Milky Way: R0and Θ0. Proper motions of Local Group galaxies have been measured, improving our understanding of the history and fate of the Group.
3D velocity fields from methanol and water masers in an intermediate-mass protostar
Authors: Goddi C. , Moscadelli L. , Sanna A.
Published: July 2012

We report multi-epoch VLBI observations of molecular masers towards the high-mass star forming region AFGL 5142, leading to the determination of the 3D velocity field of circumstellar molecular gas at radii <0.″23 (or 400 AU) from the protostar MM–1. Our observations of CH3OH maser emission enabled, for the first time, a direct measurement of infall of a molecular envelope on to an intermediate-mass protostar (radius of 300 AU, velocity of 5 km s−1, and infall rate of 6 × 10−4n8M⊙ yr−1, where n8 is the ambient volume density in units of 108 cm−3). In addition, our measurements of H2O maser (and radio continuum) emission revealed a collimated bipolar molecular outflow (and ionized jet) from MM–1. The evidence of simultaneous accretion and outflow at small spatial scales, makes AFGL 5142 an extremely compelling target for high-angular resolution studies of high-mass star formation.
The bar effect in the galactic gas motions traced by 6.7 GHz methanol maser sources with VERA
Authors: Matsumoto Naoko , Honma Mareki ,   VERA project members
Published: July 2012

To establish the existence of the galactic bar, ten methanol maser sources around the starting points of the spiral arms were observed with VERA (VLBI Exploration of radio astrometry) using the phase-referencing technique at 6.7 GHz band. For six out of ten sources, absolute proper motions were obtained with better than 3σ accuracy. Using VLBI 3-D data of eight sources, including our five sources, we compared the observed data with three galactic models and found that the model including the bar effect is better to explain the 3-D data, than a flat circular rotation model. A non-flat circular rotation model is also consistent with the VLBI data. Based on a dynamical model with a bar, we estimate an inclination angle of the bar around 35°, which is consistent with previous studies.
Distance and Size of the Red Hypergiant NML Cyg
Authors: Zhang B. , Reid M. J. , Menten K. M. , Zheng X. W. , Brunthaler A.
Published: July 2012

We present astrometric results of phase-referencing VLBI observations of 22 GHz H2O maser and 43 GHz SiO maser emission towards the red hypergiant NML Cyg using VLBA. We obtained an annual parallax of 0.62 ± 0.04 mas, corresponding to a distance of 1.61+0.13−0.11 kpc. With a VLA observation in its largest (A) configuration at 43 GHz, we barely resolve the radio photosphere of NML Cyg, and find a uniform-disk diameter of 44 ± 16 mas.
Class I Methanol Masers in the Galactic Center
Authors: Sjouwerman Loránt O. , Pihlström Ylva M.
Published: July 2012

We report on 36 and 44 GHz Class I methanol (CH3OH) maser emission in the Sagittarius A (Sgr A) region with the Expanded Very Large Array (EVLA). At least three different maser transitions tracing shocked regions in the cm-wave radio regime can be found in Sgr A. 44 GHz masers correlate with the positions and velocities of 36 GHz CH3OH masers, but the methanol masers correlate less with 1720 MHz OH masers. Our results agree with theoretical predictions that the densities and temperatures conducive for 1720 MHz OH masers may also produce 36 and 44 GHz CH3OH maser emission. However, many 44 GHz masers do not overlap with 36 GHz methanol masers, suggesting that 44 GHz masers also arise in regions too hot and too dense for 36 GHz masers to form. This agrees with the non-detection of 1720 MHz OH masers in the same area, which are thought to be excited under cooler or denser conditions. We speculate that the geometry of the bright 36 GHz masers in Sgr A East outlines the location of a SNR shock front.
Maser observations with new instruments
Authors: Wootten Alwyn
Published: July 2012

The Atacama Large Millimeter/submillimeter Array (ALMA)‡, and the Jansky Very Large Array (JVLA) have recently begun probing the Universe. Both provide the largest collecting area available at locations on a high dry site, endowing them with unparalleled potential for sensitive spectral line observations. Over the next few years, these telescopes will be joined by other telescopes to provide advances in maser science, including NOEMA and the LMT. Other instruments of note for maser science which may commence construction include the North American Array, the CCAT, and an enlarged worldwide VLB network outfitted to operate into the millimeter wavelength regime.
OH maser observations using the Russian interferometric network “Quasar” in preparation for scientific observations with the space mission RadioAstron.
Authors: Litovchenko I. D. , Alakoz A. V. , Kostenko V. I. , Lihachev S. F. , Finkelstein A. M. , Ipatov A. V.
Published: July 2012

We present results of a VLBI experiment at a wavelength of 18 cm, which simulates the ground-space interferometer with space link to RadioAstron. An array of five antennas was used, four of them are located in the Russian Federation, plus the the 32-m radio telescope in Medicine (Italy). The 22-m radio telescope in Pushchino (Moscow Region) acted in place of the space arm. It has an effective area of 100 square meters. The three other Russian 32-m antennas are operated by the Institute of Applied Astronomy RAS; they are located at Badary, Svetloe and Zelenchukskaya (interferometer network “Quasar”). The maximum base-line, Badary-Svetloe, was about 4402 km, providing an angular resolution of about 0.009 arc seconds at a wavelength of 18 cm. The duration of the experiment was 10 hours on 02/03 February 2011. The program of observations included quasars 3C273, 3C279, 3C286 and the maser source - W3(OH). W3(OH) was observed only by the Russian telescopes and was investigated at the frequency of the 1665 MHz main line. The data were recorded on the MK5 recorder (32-m radio telescopes) and the RDR system (RadioAstron Digital Recorder) in Pushchino. The low SEFD (system equivalence of flux density) of Pushchino emulated the RadioAstron antenna. Correlation was performed with the universal software correlator of the AstroSpace Center of Lebedev Physical Institute. The correlator output format is compatible with that used by the AIPS package, which was used for data analysis. After analyzing the correlated data we obtained relative coordinates of the maser components. The main results are tabulated and presented in the figures. The data quality is sufficient for astrophysical analysis and comparison with previous observations of maser source W3(OH) on VLBI networks EVN and VLBA.
IAU (Maser) Symposium 287 Summary
Authors: Menten Karl M.
Published: July 2012

Almost exactly twenty years ago, the first of a series of conferences dedicated to cosmic masers took place in Arlington, Virginia in the USA (March 9–11, 1992). Two more followed, each on a different continent, in Mangaratiba, near Rio de Janeiro, Brasil (March 5–10, 2001) and in Alice Springs, Australia (March 12–16, 2007). As at all others, a large part of the international maser community convened from January 29 to February 3, 2012 in splendid Stellenbosch, South Africa, to discuss the state of the art of the field.
The importance of the terrestrial weathering feedback for multimillennial coral reef habitat recovery
Authors: Meissner Katrin J. , McNeil Ben I. , Eby Michael , Wiebe Edward C.
Published: July 2012

Modern‐day coral reefs have well defined environmental envelopes for light, sea surface temperature (SST) and seawater aragonite saturation state (Ωarag). We examine the changes in global coral reef habitat on multimillennial timescales with regard to SST and Ωaragusing a climate model including a three‐dimensional ocean general circulation model, a fully coupled carbon cycle, and six different parameterizations for continental weathering (the UVic Earth System Climate Model). The model is forced with emission scenarios ranging from 1,000 Pg C to 5,000 Pg C total emissions. We find that the long‐term climate change response is independent of the rate at which CO2 is emitted over the next few centuries. On millennial timescales, the weathering feedback introduces a significant uncertainty even for low emission scenarios. Weathering parameterizations based on atmospheric CO2 only display a different transient response than weathering parameterizations that are dependent on temperature. Although environmental conditions for SST and Ωaragstay globally hostile for coral reefs for millennia for our high emission scenarios, some weathering parameterizations induce a near‐complete recovery of coral reef habitat to current conditions after 10,000 years, while others result in a collapse of coral reef habitat throughout our simulations. We find that the multimillennial response in sea surface temperature (SST) substantially lags the aragonite saturation recovery in all configurations. This implies that if corals can naturally adapt over millennia by selecting thermally tolerant species to match warmer ocean temperatures, prospects for long‐term recovery of coral reefs are better since Ωarag recovers more quickly than SST.
Geophysical controls on C band polarimetric backscatter from melt pond covered Arctic first‐year sea ice: Assessment using high‐resolution scatterometry
Authors: Scharien R. K. , Yackel J. J. , Barber D. G. , Asplin M. , Gupta M. , Isleifson D.
Published: July 2012

Geophysical controls on C band polarimetric backscatter from the discrete surface cover types which comprise advanced melt first‐year sea ice (FYI): snow covered ice, bare ice, and melt pond; are assessed using polarimetric radar scatterometry from test sites representing high Arctic and marginal ice zones in the Canadian Arctic. Surface characterization data is used to evaluate the interaction of polarized radiation with each feature, and dominant scattering mechanisms are assessed in a regional context. High‐resolution time series (diurnal) scatterometry and coincident atmospheric boundary layer profile data are used to explain linkages between ice‐atmosphere interactions and polarimetric backscatter in a marginal ice zone. The co‐polarization ratio for FYI melt ponds is shown to be distinct from snow covered ice or bare ice during early and peak phases of advanced melt, making it a candidate parameter for the unambiguous detection of pond formation and the inversion of melt pond fraction. The ratio displays an increasing trend with radar incidence angle in a manner consistent with Bragg surface scattering theory, though it is not predictable by a Bragg model. Cross‐polarization backscatter intensity shows potential for discriminating the onset and duration of freeze events in a marginal ice zone, due to dominant backscatter from the snow cover adjacent to melt ponds. Preliminary results here outline the potential of covariance matrix derived polarimetric measurements for the inversion of advanced melt sea ice geophysical parameters, and provide a basis for the investigation of distributed targets in late season spaceborne polarimetric SAR scenes.
Interpretation of cloud structure anomalies over the tropical Pacific during the 1997/98 El Niño
Authors: Sun Moguo , Cess Robert D. , Doelling Dave R.
Published: July 2012

Cloud structure changes and their associated radiative property changes over the tropical Pacific Ocean during the strong 1997/98 El Niño are studied using a merged satellite data set from the Clouds and the Earth's Radiant Energy System (CERES) project. This one‐degree by one‐degree gridded data set provides monthly mean values of radiative fluxes at the top of the atmosphere in addition to cloud fraction, cloud top altitude and cloud optical depth for the first eight months of 1998. This time period includes much of the 1997/98 El Niño, which reached peak intensity in March 1998 and essentially subsided by August 1998. The west‐to‐east shift of the center of convection that occurred during the El Niño resulted in cloud fraction, cloud top altitude and cloud optical depth increasing in the eastern equatorial Pacific while decreasing in the western tropical Pacific. For both regions all three cloud parameters are strongly correlated with each other and contribute to the strong linear relationship between longwave (LW) and shortwave (SW) cloud‐radiative forcings (CRFs). This strong El Niño serves as a suitable test case for climate models. Results using the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM) 4.0 show many of the observed changes in 500 hPa vertical velocity, cloud‐radiative forcing, cloud top altitude and cloud fraction within the tropical Pacific during the El Niño event, but fail to capture the observed relationship between radiation anomalies and cloud optical depth anomalies.
Computation of clear‐air radar backscatter from numerical simulations of turbulence: 3. Off‐zenith measurements and biases throughout the lifecycle of a Kelvin‐Helmholtz instability
Authors: Fritts David C. , Wan Kam , Franke Patricia M. , Lund Tom
Published: July 2012

Previous papers by Franke et al. (2011) and Fritts et al. (2011) described the computation of radar backscatter power and vertical velocities from numerical simulations of turbulence arising due to Kelvin‐Helmholtz (KH) shear instability. Comparisons of backscatter power and inferred velocities with the distributions of turbulence and the true velocities revealed biases in the identification of active or intense turbulence and in the inferred Doppler spectrum and vertical velocities throughout the flow evolution. This paper extends these analyses to off‐zenith viewing angles typical of multiple‐beam MF, HF, and VHF radars. These reveal similar biases in the identification of turbulence occurrence, Doppler spectra, and inferred radial velocities, with additional sensitivity to the off‐zenith angle relative to the mean shear across the turbulence layer. Radial velocities are typically underestimated during turbulence generation and breakdown of the KH billows, except where turbulence refractive index gradients are strong. Doppler spectra are biased toward regions retaining strong refractive index gradients, implying strong aspect sensitivity at later stages in the evolution. Persistent tilted structures at late stages of the evolution contribute to radial velocity measurement biases that also are functions of off‐zenith angle and time.
Constraining recent lead pollution sources in the North Pacific using ice core stable lead isotopes
Authors: Gross B. H. , Kreutz K. J. , Osterberg E. C. , McConnell J. R. , Handley M. , Wake C. P. , Yalcin K.
Published: July 2012

Trends and sources of lead (Pb) aerosol pollution in the North Pacific rim of North America from 1850 to 2001 are investigated using a high‐resolution (subannual to annual) ice core record recovered from Eclipse Icefield (3017 masl; St. Elias Mountains, Canada). Beginning in the early 1940s, increasing Pb concentration at Eclipse Icefield occurs coevally with anthropogenic Pb deposition in central Greenland, suggesting that North American Pb pollution may have been in part or wholly responsible in both regions. Isotopic ratios (208Pb/207Pb and 206Pb/207Pb) from 1970 to 2001 confirm that a portion of the Pb deposited at Eclipse Icefield is anthropogenic, and that it represents a variable mixture of East Asian (Chinese and Japanese) emissions transported eastward across the Pacific Ocean and a North American component resulting from transient meridional atmospheric flow. Based on comparison with source material Pb isotope ratios, Chinese and North American coal combustion have likely been the primary sources of Eclipse Icefield Pb over the 1970–2001 time period. The Eclipse Icefield Pb isotope composition also implies that the North Pacific mid‐troposphere is not directly impacted by transpolar atmospheric flow from Europe. Annually averaged Pb concentrations in the Eclipse Icefield ice core record show no long‐term trend during 1970–2001; however, increasing208Pb/207Pb and decreasing 206Pb/207Pb ratios reflect the progressive East Asian industrialization and increase in Asian pollutant outflow. The post‐1970 decrease in North American Pb emissions is likely necessary to explain the Eclipse Icefield Pb concentration time series. When compared with low (lichen) and high (Mt. Logan ice core) elevation Pb data, the Eclipse ice core record suggests a gradual increase in pollutant deposition and stronger trans‐Pacific Asian contribution with rising elevation in the mountains of the North Pacific rim.
Spatially varying fractional flow in radial CO2‐brine displacement
Authors: Mijic Ana , LaForce Tara C.
Published: July 2012

In analytical modeling of two‐phase flow problems in porous media, the saturation profile for a fixed time can be obtained by using the method of characteristics (MOC). One of the basic assumptions in the application of the MOC is that the fractional flow is a function of saturation only. However, when gas is injected, it is often flowing under nonlinear flow conditions and inertial losses are significant in the near‐well region. Therefore, in a radial displacement non‐Darcy flow applies at the injection well, but as the saturation front gets further away, its velocity will decrease and the fractional flow curve will vary with the distance along the streamline. This paper presents the extension of the Buckley‐Leverett analytical solution when the injected gas phase flow is governed by the two‐phase extension to the Forchheimer equation and the fractional flow function depends both on the saturation and radial distance from the well. The behavior of a gas‐liquid system under non‐Darcy flow conditions is shown for carbon dioxide injection into saline aquifers. Finally, this analytical solution is tested against the corresponding finite difference numerical model and the limitations of the approach are discussed.
Groundwater recharge from overbank floods
Authors: Doble Rebecca C. , Crosbie Russell S. , Smerdon Brian D. , Peeters Luk , Cook Freeman J.
Published: July 2012

Overbank flood recharge is increasingly acknowledged as important for estimations of aquifer sustainable yield. The physics of this process in areas with shallow groundwater, however, is not well understood and typically is not included in river or groundwater models. Modeling of the overbank flood recharge process was undertaken using a fully coupled, surface‐subsurface flow model to compare the volume of infiltration through a floodplain with varying surface sediment, aquifer, and flood parameters. The infiltration volume was found to increase with the conductance of the clogging layer (represented by a thin veneer of sediments across the floodplain and river bed), flood wave height, peak duration, and aquifer transmissivity and to decrease with increasing water table gradient (positive toward the river). The influence of the flood wave and aquifer hydraulic parameters was more pronounced in systems with sand or loam clogging layers. Irregularities in floodplain elevation had a large effect on infiltration volume. A dimensionless analysis of the flood recharge process identified the factors that limited flood infiltration for each of the modeled scenarios: the clogging layer conductance, unsaturated aquifer storage, or aquifer transmissivity. A dimensionless numberF* was used to predict the limiting factor in floodplain systems. An analytical equation was developed to estimate the infiltration volume for catchments where full numerical modeling is not warranted or applicable. Results from the analytical equation compared favorably with recharge modeled using a more complex numerical model.
Multiscale spatial recorrelation of RCM precipitation to produce unbiased climate change scenarios over large areas and small
Authors: Bárdossy András , Pegram Geoffrey
Published: July 2012

Previously, Bárdossy and Pegram (2011) achieved downscaling of regional climate model (RCM) rainfall, dependent on circulation patterns (CPs), over 172 areas of the Rhine basin at the 25 km scale. Uneasy about the spatial statistics of the downscaled RCM rainfall, we calculated the spatial cross‐correlation coefficients (CCCs) of daily rainfalls of the same set. We found that the CCCs of the RCM precipitations were significantly lower than those of the observations. CP‐based downscaling led to an increase of the CCCs which still remained below the observed CCCs. This underestimation of spatial correlation, hence observed clustering, has potentially deleterious consequences for flood calculations over large areas based on RCM outputs, even after full CP‐based bias elimination at the 25 km scale. In this paper we therefore describe two novel recorrelation methods designed to correct the CCCs of the RCM estimates back to those of the observed set before undertaking the final quantile‐quantile transform. We use two methods of recorrelation: matrix methods and sequential regression. They both produced similar results and were successful in that they captured the observed CCCs almost exactly, coping with problems presented by the high proportion of dry days. In spite of the complete success of the recorrelation techniques (when comparing spatial correlations before and after treatment) the methodology does not solve the reconstitution problem fully: (1) extreme daily rainfall totals on large areas are not recaptured completely and (2) clustering behavior, as computed by entropy on nonoverlapping triple sites, confirms that the two‐dimensional covariance dependence measure, although very effective, does not capture all of the clustering observed in natural rainfall.
Systematic mapping of the Spanish continental margin
Authors: Acosta Juan , Muñoz Araceli , Uchupi Elazar
Published: July 2012

For economic, environmental, recreational, military, and political reasons it is critical for coastal states to have up‐to‐date information on their marine margins. Spain began to acquire such data 17 years ago. From 1995 to the present, the Spanish Oceanographic Institute (IEO), a research organization of the state, has carried out a systematic geological and geophysical study of the Spanish margins. Among these projects are (1) the hydrographic and oceanographic study of the Spanish Exclusive Economic Zone (EEZ) that was implemented by the Navy Hydrographic Institute (IHM); (2) the Espace Project, a study of the Spanish continental shelf; and (3) the Capesme Project, which created fisheries maps of the Mediterranean Sea. The latter two projects were carried out in collaboration with the Secretariat General of the Sea (SGM).
First tribal college or university to offer hydrology degree program
Authors: Dalbotten Diana
Published: July 2012

American Indian tribes and tribal confederations exert sovereignty over about 27% of freshwater resources in the United States. Yet only about 20–30 Native American students receive bachelor's degrees in the geosciences each year, and few of those degrees are in the field of hydrology. To help increase the ranks of Native American hydrologists, the Salish Kootenai College (SKC) in Pablo, Mont., now has associate and bachelor of science degree programs in hydrology, the first hydrology and geoscience degree programs offered by any of the Tribal Colleges and Universities in North America. SKC received approval to offer the degree programs from the Northwest Commission on Colleges and Universities in 2010.
AGU journals continue to rank highly in Impact Factors
Authors: Sears Jon , Warner Mary
Published: July 2012

AGU journals continue to rank highly in the 2011 Journal Citation Reports (JCR), which was released by Thomson Reuters on 28 June. The impact factor of several AGU journals increased significantly, continuing their trend over the previous 5 years, while others remained consistent with the previous year's ranking. Paleoceanography is an outstanding performer in both the Paleontology and Oceanography categories. Since 1995, Paleoceanography has been the top‐ranked journal in the Paleontology category (of 49 titles in 2011), with an Impact Factor of 3.357. In the Oceanography group (59 journals total), Paleoceanography ranks third in Impact Factor. Reviews of Geophysics, with an Impact Factor of 12.364 (an increase of 2.826 from the prior year's score of 9.538), ranks second in Geochemistry and Geophysics out of a total of 77 journals in this cohort. Water Resources Research comes in at second place in the Limnology group, with 19 titles, and third place in the Water Resources group, which has a cohort of 78 titles.
Wind may have driven avalanches on Martian dunes
Authors: Balcerak Ernie
Published: July 2012

In the sand dunes in the north polar sand sea of Mars, sand avalanches that appear as wedge‐shaped alcoves can be seen above fan‐shaped deposits. The avalanches, which are typically several meters across, are currently actively forming, with new alcoves showing up in recent images taken in consecutive Mars years. Some scientists have proposed that these sand avalanches occur when frozen carbon dioxide (CO2) sublimates, triggering the downslope flow (mass wasting) of sand grains and rock that had been lying on top of the CO2 frost. However, Horgan and Bell now suggest that these alcoves may actually have been formed by wind‐driven movement of sand, not by CO2 sublimation.
New images of complex structures underneath the Tibetan Plateau
Authors: Kumar Mohi
Published: July 2012

The Tibetan Plateau contains some of the highest mountains in the world and was formed by the collision between the Indian and Eurasian plates beginning around 55 million years ago. Curious about how such elevated terrains form, Yue et al. used data collected from a seismic experiment conducted between 2007 and 2009 to image the complex three‐dimensional geometry of the crust and upper mantle in northeastern Tibet. The scientists' results detected the interaction between components of thrust and subduction, shed light on the conditions surrounding crustal loading, and located mantle discontinuities and small‐scale mantle convection. Despite the thick crust of the plateau, which can reach depths of 65–75 kilometers, the authors were able to capture for the first time major vertical offsets (ranging from 10 to 20 kilometers) in the Mohorovičić discontinuity, the boundary between the crust and the mantle underlying the region. These offsets, along with the presence of other structures, bear testament to the intricate evolution of the Tibetan Plateau; the authors posit different scenarios on the history of this evolution, including the presence of buried remnant slabs of possible oceanic origin that continue to sink and create mantle eddies. (Journal of Geophysical Research‐Solid Earth, doi:10.1029/2011JB008545, 2012)
Commercial ocean liners could be equipped to track tsunamis
Authors: Schultz Colin
Published: July 2012

Though observational networks exist to provide warning of an impending tsunami, Foster et al. propose a way to improve observational ability at a relatively low cost compared to ramping up the use of existing techniques. Triggered by shallow subaquatic earthquakes or eruption of an ocean floor volcano, tsunamis are nearly imperceptible waves in the open ocean but can grow to extreme heights near the shore. Currently the existence of a tsunami is initially determined by analyzing the wave‐generating event itself, where earthquakes or eruptions fitting a specific depth and strength profile are considered tsunami generating. After a tsunami‐generating event is detected, a sparse network of seafloor‐mounted sensors tracks the propagating waves.
Entire thermal infrared spectrum observed for first time
Authors: Schultz Colin
Published: July 2012

The driving mechanism of the greenhouse effect and the underpinning of modern anthropogenic warming is the absorption, emission, and transmission of infrared radiation by atmospheric gases. The heat‐trapping ability of a gas depends on its chemical composition, and each type of gas absorbs infrared radiation of different energies. The amount of infrared radiation that escapes into space depends on the net effect of the myriad gases in the atmosphere, with water vapor being the primary gaseous absorber of infrared radiation. Water vapor absorbs a wide range of infrared radiation, masking the effects of other gases. In fact, in many spectral regions (or infrared radiation energy bands), water vapor is so strongly absorbing that it makes testing the accuracy of infrared radiation absorption parameterizations used in general circulation models difficult.
No evidence of polar warming during penultimate interglacial
Authors: Bhattacharya Atreyee
Published: July 2012

The Atlantic Meridional Overturning Circulation (AMOC), driven by temperature and salinity gradients, is an important component of the climate system; it transfers an enormous amount of heat via ocean currents and atmospheric circulation to high northern latitudes and hence has bearing on climate in the region. Freshening of the surface ocean could weaken AMOC. But during warm interglacial periods the effect of a fresh surface ocean on AMOC may be muted. In fact, climate models predict that heat transfer from the North Atlantic to the Arctic may increase over the 21st century. A series of interconnected processes in the North Atlantic, known as polar amplification, could cause the Arctic to warm up faster compared to the rest of the world. It could even lead to ice‐free conditions in the Arctic.
Landscape‐level controls on dissolved carbon flux from diverse catchments of the circumboreal
Authors: Tank Suzanne E. , Frey Karen E. , Striegl Robert G. , Raymond Peter A. , Holmes Robert M. , McClelland James W. , Peterson Bruce J.
Published: July 2012

While much of the dissolved organic carbon (DOC) within rivers is destined for mineralization to CO2, a substantial fraction of riverine bicarbonate (HCO3−) flux represents a CO2 sink, as a result of weathering processes that sequester CO2 as HCO3−. We explored landscape‐level controls on DOC and HCO3− flux in subcatchments of the boreal, with a specific focus on the effect of permafrost on riverine dissolved C flux. To do this, we undertook a multivariate analysis that partitioned the variance attributable to known, key regulators of dissolved C flux (runoff, lithology, and vegetation) prior to examining the effect of permafrost, using riverine biogeochemistry data from a suite of subcatchments drawn from the Mackenzie, Yukon, East, and West Siberian regions of the circumboreal. Across the diverse catchments that we study, controls on HCO3−flux were near‐universal: runoff and an increased carbonate rock contribution to weathering (assessed as riverwater Ca:Na) increased HCO3− yields, while increasing permafrost extent was associated with decreases in HCO3−. In contrast, permafrost had contrasting and region‐specific effects on DOC yield, even after the variation caused by other key drivers of its flux had been accounted for. We used ionic ratios and SO4 yields to calculate the potential range of CO2sequestered via weathering across these boreal subcatchments, and show that decreasing permafrost extent is associated with increases in weathering‐mediated CO2 fixation across broad spatial scales, an effect that could counterbalance some of the organic C mineralization that is predicted with declining permafrost.
Recycling versus export of bioavailable dissolved organic matter in the coastal ocean and efficiency of the continental shelf pump
Authors: Lønborg Christian , Álvarez‐Salgado Xosé Antón
Published: July 2012

At least 15% of the 2 Pg y−1 of dissolved organic carbon (DOC) that accumulates in the surface layer of the open ocean has been exported from the ocean margins. The C: N: P stoichiometry of the production and microbial degradation of dissolved organic matter (DOM) in the coastal ocean conditions the quality of the exported substrates. In this work, DOC, dissolved organic nitrogen (DON) and phosphorus (DOP) bioavailability measurements from published bottle incubation experiments have been compiled and reanalyzed to examine the role of bioavailable DOM (BDOM) in the coastal ocean. DOM bioavailability decreased significantly (p< 0.001) in the sequence DOP > DON > DOC, with bioavailable DOC (BDOC) representing 22 ± 12% (mean ± SD) of the total DOC, bioavailable DON (BDON) 35 ± 13% of the total DON and bioavailable DOP (BDOP) 70 ± 18% of the total DOP. This suggests that the role of DOM on the recycled and export production of the coastal ocean is more relevant for the P than for the N and for the N than for the C biogeochemical cycles. First‐order microbial degradation rate constants (κ) of BDOM (normalized to 15°C) increased significantly (p < 0.05) in the same sequence, with κC being 0.066 ± 0.065 day−1, κN 0.111 ± 0.096 and κP 0.154 ± 0.137 day−1. Significant (p < 0.001) power relationships were found among κC, κN and κP (R2 = 0.84–0.87). The C: N: P molar ratio of the DOM that resists microbial degradation was extremely depleted in N and P, 2835 (±3383): 159 (±187): 1, compared with the BDOM fraction, 197 (±111): 25 (±16): 1. The flushing time (τ) of the coastal ocean in relation to the turnover time of BDOM (1/κ), i.e., τ · κ, dictates the fate ―degradation versus accumulation― of the large scale export of BDOM, which could fuel parts of the oceanic new production and influence the N/P limitation of the open ocean.
Birth of an ocean in the Red Sea: Initial pangs
Authors: Ligi Marco , Bonatti Enrico , Bortoluzzi Giovanni , Cipriani Anna , Cocchi Luca , Caratori Tontini Fabio , Carminati Eugenio , Ottolini Luisa , Schettino Antonio
Published: July 2012

We obtained areal variations of crustal thickness, magnetic intensity, and degree of melting of the sub‐axial upwelling mantle at Thetis and Nereus Deeps, the two northernmost axial segments of initial oceanic crustal accretion in the Red Sea, where Arabia is separating from Africa. The initial emplacement of oceanic crust occurred at South Thetis and Central Nereus roughly ∼2.2 and ∼2 Ma, respectively, and is taking place today in the northern Thetis and southern Nereus tips. Basaltic glasses major and trace element composition suggests a rift‐to‐drift transition marked by magmatic activity with typical MORB signature, with no contamination by continental lithosphere, but with slight differences in mantle source composition and/or potential temperature between Thetis and Nereus. Eruption rate, spreading rate, magnetic intensity, crustal thickness and degree of mantle melting were highest at both Thetis and Nereus in the very initial phases of oceanic crust accretion, immediately after continental breakup, probably due to fast mantle upwelling enhanced by an initially strong horizontal thermal gradient. This is consistent with a rift model where the lower continental lithosphere has been replaced by upwelling asthenosphere before continental rupturing, implying depth‐dependent extension due to decoupling between the upper and lower lithosphere with mantle‐lithosphere‐necking breakup before crustal‐necking breakup. Independent along‐axis centers of upwelling form at the rifting stage just before oceanic crust accretion, with buoyancy‐driven convection within a hot, low viscosity asthenosphere. Each initial axial cell taps a different asthenospheric source and serves as nucleus for axial propagation of oceanic accretion, resulting in linear segments of spreading.
Determining the mixing of oil and sea water using polarimetric synthetic aperture radar
Authors: Minchew Brent
Published: July 2012

Knowledge of the characteristics of spilled oil in the ocean is important for cleanup operations, predictions of the impact on wildlife, and studies of the nature of the ocean surface and currents. Herein I discuss a method for evaluating the characteristics of oil in a marine environment using synthetic aperture radar (SAR) and present a new, simple classification, called the oil/water mixing index (Mdex), to quickly assess the results. I link the Mdex results to the Bonn Agreement for Oil Appearance Codes (BAOAC) for aerial observers and demonstrate the Mdex on Uninhabited Aerial Vehicle SAR (UAVSAR) data collected June 23, 2010 over the former site of the Deepwater Horizon (DWH) drilling rig. The Mdex map shows a more heterogeneous oil swath than do radar backscatter images and features within the oil are consistent with features present in previously published, near‐coincident optical imagery. The Mdex results indicate that most of the oil near the DWH was mixed with sea water to a minimum depth of a few millimeters, though some areas containing relatively thin films are observed.
Geodetic constraints on afterslip characteristics following the March 9, 2011, Sanriku‐oki earthquake, Japan
Authors: Ohta Yusaku , Hino Ryota , Inazu Daisuke , Ohzono Mako , Ito Yoshihiro , Mishina Masaaki , Iinuma Takeshi , Nakajima Junichi , Osada Yukihito , Suzuki Kensuke , Fujimoto Hiromi , Tachibana Kenji , Demachi Tomotsugu , Miura Satoshi
Published: July 2012

A magnitude 7.3 foreshock occurred at the subducting Pacific plate interface on March 9, 2011, 51 h before the magnitude 9.0 Tohoku earthquake off the Pacific coast of Japan. We propose a coseismic and postseismic afterslip model of the magnitude 7.3 event based on a global positioning system network and ocean bottom pressure gauge sites. The estimated coseismic slip and afterslip areas show complementary spatial distributions; the afterslip distribution is located up‐dip of the coseismic slip for the foreshock and northward of hypocenter of the Tohoku earthquake. The slip amount for the afterslip is roughly consistent with that determined by repeating earthquake analysis carried out in a previous study. The estimated moment release for the afterslip reached magnitude 6.8, even within a short time period of 51h. A volumetric strainmeter time series also suggests that this event advanced with a rapid decay time constant compared with other typical large earthquakes.
Damage in step‐overs may enable large cascading earthquakes
Authors: Finzi Y. , Langer S.
Published: July 2012

Seismic hazard analysis relies on the ability to predict whether an earthquake will terminate at a fault tip or propagate onto adjacent faults, cascading into a larger, more devastating event. While ruptures are expected to arrest at fault discontinuities larger than 4–5 km, scientists are often puzzled by much larger rupture jumps. Here we show that material properties between faults significantly affect the ability to arrest propagating ruptures. Earthquake simulations accounting for fault step‐over zones weakened by accumulated damage provide new insights into rupture propagation. Revealing that lowered rigidity and material interfaces promote rupture propagation, our models show for the first time that step‐overs as wide as 10 km may not constitute effective earthquake barriers. Our results call for re‐evaluation of seismic hazard analyses that predict rupture length and earthquake magnitude based on historic records and fault segmentation models.
Secular temperature trends for the southern Rocky Mountains over the last five centuries
Authors: Berkelhammer M. , Stott L. D.
Published: July 2012

Pre‐instrumental surface temperature variability in the Southwestern United States has traditionally been reconstructed using variations in the annual ring widths of high altitude trees that live near a growth‐limiting isotherm. A number of studies have suggested that the response of some trees to temperature variations is non‐stationary, warranting the development of alternative approaches towards reconstructing past regional temperature variability. Here we present a five‐century temperature reconstruction for a high‐altitude site in the Rocky Mountains derived from the oxygen isotopic composition of cellulose (δ18Oc) from Bristlecone Pine trees. The record is independent of the co‐located growth‐based reconstruction while providing the same temporal resolution and absolute age constraints. The empirical correlation betweenδ18Ocand instrumental temperatures is used to produce a temperature transfer function. A forward‐model for cellulose isotope variations, driven by meteorological data and output from an isotope‐enabled General Circulation Model, is used to evaluate the processes that propagate the temperature signal to the proxy. The cellulose record documents persistent multidecadal variations inδ18Octhat are attributable to temperature shifts on the order of 1°C but no sustained monotonic rise in temperature or a step‐like increase since the late 19th century. The isotope‐based temperature history is consistent with both regional wood density‐based temperature estimates and some sparse early instrumental records.
Recent unrest of Changbaishan volcano, northeast China: A precursor of a future eruption?
Authors: Xu Jiandong , Liu Guoming , Wu Jianping , Ming Yuehong , Wang Qingliang , Cui Duxin , Shangguan Zhiguan , Pan Bo , Lin Xudong , Liu Junqing
Published: July 2012

Over 12 years of continuous monitoring of Changbaishan volcano in the border region of China and North Korea by means of volcanic seismicity, ground deformation, and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006. In this so‐called “active period,” the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background “inactive periods.” The active period was also accompanied by ground inflation, high values of CO2, He, H2, and high ratios of N2/O2and3He/4He in volcanic gases released from three hot springs near the caldera rim. The monitoring evidence implies pressurization of the magma chamber, possibly caused by incremental magma recharge. The ground deformation data from both GPS and precise leveling are modeled to suggest the corresponding deformation source is at 2–60 km depth beneath the volcano's summit, where earthquake swarms were detected in 2002 and 2003. Our findings suggest that the magma chamber beneath Changbaishan volcano has awakened and resumed activity after remaining dormant since AD 1903. There is an urgent need to keep close watch on this active and very hazardous volcano in northeast China.
Sea spray spume droplet production in high wind speeds
Authors: Veron F. , Hopkins C. , Harrison E. L. , Mueller J. A.
Published: July 2012

Sea spray droplets are known to enhance the fluxes of momentum, heat, and mass at the air‐sea interface. Evaluating these fluxes depends in part on the so‐called “spray generation function”, the size distribution of droplets generated. At high wind speeds, spray is empirically observed to be plentiful near the ocean surface, however, the generation function has remained elusive both theoretically and experimentally. We report on a photographic laboratory experiment designed to directly quantify spume droplets observed at high wind speeds. The resulting sea spray concentration functions for spume droplets (diameter > 140μm) are reported for three high wind speed conditions (31.3, 41.2, and 47.1 ms−1). Our data suggest that large supra‐millimeter droplets are more prevalent than previously thought. We also observed a previously unreported spray generation mechanism whereby liquid sheets form at the crests of breaking waves and generate, upon breakup, a significant number of small spume drops.