AGU 期刊一周Research Spotlights (May 20~May 26, 2016)

发布时间:2016-5-27 11:34:08 点击次数:865

I. Atmospheric Sciences

1. Four Perspectives on Order From Chaos

What makes thunderstorms clump, even to the point of singularity, over uniform oceans? Three recent papers inJAMES address this question, and a new Commentary ties them together.


II. Ocean Sciences

1. Streamlining Rapid Tsunami Forecasting

With enough sensors, traditional forecasting methods could be replaced by models continuously updated with real-time wave data.

2. Advisory Panel Calls for Large Increase for Ocean Exploration

The recently established Ocean Exploration Advisory Board also urged the National Oceanic and Atmospheric Administration to increase its role in federal coordination of exploration.

3. Satellite Radar to Observe Earth’s Changing Surface

NASA-ISRO SAR Mission Science and Applications Workshops; Ahmedabad, India, 19–20 November 2015


III. Climate Change

1. Toward a Reassessment of Daily Temperature Range Trends

To reduce the uncertainty associated with this important climate change index, recent studies have developed a new diurnal temperature range data set and compared the results to previous estimates.


IV. Planetary Sciences

1. Pluto's Interactions with the Solar Wind Are Unique

Space physicists say that Pluto's atmosphere interacts with the solar wind in a never-before-seen hybrid way, one that's both comet-like and planet-like.

2. Did Solar Flares Cook Up Life on Earth?

Scientists have found that "super" solar flares could have warmed the ancient planet and jump-started life.

3. Mysterious Heavy Ion Beams Above Mars Explained

NASA's latest mission to Mars has uncovered the origins of fast-moving streams of particles high above the planet, flowing against the solar wind.

4. Tsunamis Splashed Ancient Mars

Massive meteorites likely slammed into a Martian ocean billions of years ago, unleashing tsunami waves up to 120 meters tall, a close study of a region of the Red Planet's terrain has found.

5. Comet with Stunted Tail Hints at How Solar System Formed

Finding out whether just a few or many of this newfound type of rocky object roam deep space should help scientists sort among contrasting scenarios of the solar system's infancy.


V.Earth and Space Science

1. Van Allen Probes reveal long-term behavior of Earth’s ring current

New findings based on a year’s worth of observations from NASA’s Van Allen Probes have revealed that the ring current — an electrical current carried by energetic ions that encircles our planet — behaves in a much different way than previously understood.

2. Data science for collaboration and community-building

Many of us are interested in social networking sites like Facebook. In addition to cat videos and food pictures, it’s a great way to keep up to date and engage with friends. Recently, it’s even become a way to share and engage in science. Yet, there’s another, sometimes overlooked, aspect of social networks that can contribute to better science—analysis of the underlying network itself.

3. History of Greenland snowfall hidden in ancient leaf waxes

The history of Greenland’s snowfall is chronicled in an unlikely place: the remains of aquatic plants that died long ago, collecting at the bottom of lakes in horizontal layers that document the passing years. Using this ancient record, scientists are attempting to reconstruct how Arctic precipitation fluctuated over the past several millennia, potentially influencing the size of the Greenland Ice Sheet as the Earth warmed and cooled.

4. Watch underwater canyons take shape in real time

Submarine canyons are major underwater routes for transporting rapidly-moving water that is heavy with sediment from the continental shelf to the deep ocean. Here, a group of researchers uses a sandbox experiment to simulate how a fast, sediment-laden current carves these canyons out of the continental slope. They recorded the entire experiment with time-lapse video, shown here.

5. Scientific Data Manager: A career deserving of better recognition

Within the scientific data lifecycle, from data acquisition, to publication and preservation, the data manager (also known as a data steward) plays an increasingly important and often unappreciated role. This role is growing in importance due to the rapid growth in the volume of data—unlike the funds to manage it—the need for interoperability of these data, the new regulations regarding open access and long-term preservation. Data managers are driven by the dictum and aspiration that well documented, citable and preserved data is an investment in science, one that is critical to future discoveries.

6. Fatal landslides in 2016 so far

As the rainy season starts to loom in the global landslide hotspots of South and South-East Asia, this is a good time to review the global pattern of fatal landslides in 2016 to date.  This is data that I have been collecting since 2002 – I wrote it up in a paper (Petley 2016) a few years ago – see the blog posts of the time – and Melanie and I are currently working on an update (watch this space).

7. The GFDRR Think Hazard! tool

Yesterday the new GFDRR ThinkHazard tool was launched.  This is a new web based system for developing countries that allows a basic assessment of hazard across a range of perils on a geographical basis.  The GFDRR description is as follows:

The Global Facility for Disaster Reduction and Recovery (GFDRR) has created a new online tool for the development community, which enables non-experts to consider natural hazard information in project design. ThinkHazard! has been developed by GFDRR’s Innovation Lab, in collaboration with BRGM (the French geological survey), Camptocamp, and Deltares. Many other organizations and individuals have contributed data sets and expert input into information provided in the tool.

ThinkHazard! is a simple and quick, yet robust, analytical tool that enables a development specialist to determine for a given project location, the potential likelihood of eight natural hazards, and what actions they should take to make their project resilient. The tool analyzes hazard under current climate but also provides guidance from IPCC on how climate change may affect hazard frequency and intensity into the future.


 VI. Geophysical Research Letters

1. Lithospheric shear velocity structure of South Island, New Zealand, from amphibious Rayleigh wave tomograph

We present a crust and mantle 3-D shear velocity model extending well offshore of New Zealand's South Island, imaging the lithosphere beneath the South Island as well as the Campbell and Challenger Plateaus. Our model is constructed via linearized inversion of both teleseismic (18–70 s period) and ambient noise-based (8–25 s period) Rayleigh wave dispersion measurements. We augment an array of 4 land-based and 29 ocean bottom instruments deployed off the South Island's east and west coasts in 2009–2010 by the Marine Observations of Anisotropy Near Aotearoa experiment with 28 land-based seismometers from New Zealand's permanent GeoNet array. Major features of our shear wave velocity (Vs) model include a low-velocity (Vs < 4.4 km/s) body extending from near surface to greater than 75 km depth beneath the Banks and Otago Peninsulas and high-velocity (Vs~4.7 km/s) mantle anomalies underlying the Southern Alps and off the northwest coast of the South Island. Using the 4.5 km/s contour as a proxy for the lithosphere-asthenosphere boundary, our model suggests that the lithospheric thickness of Challenger Plateau and central South Island is substantially greater than that of the inner Campbell Plateau. The high-velocity anomaly we resolve at subcrustal depths (>50 km) beneath the central South Island exhibits strong spatial correlation with upper mantle earthquake hypocenters beneath the Alpine Fault. The ~400 km long low-velocity zone we image beneath eastern South Island and the inner Bounty Trough underlies Cenozoic volcanics and the locations of mantle-derived helium measurements, consistent with asthenospheric upwelling in the region.

2. An assessment of the ICE6G_C(VM5a) glacial isostatic adjustment model

The recent release of the next-generation global ice history model, ICE6G_C(VM5a), is likely to be of interest to a wide range of disciplines including oceanography (sea level studies), space gravity (mass balance studies), glaciology, and, of course, geodynamics (Earth rheology studies). In this paper we make an assessment of some aspects of the ICE6G_C(VM5a) model and show that the published present-day radial uplift rates are too high along the eastern side of the Antarctic Peninsula (by ~8.6 mm/yr) and beneath the Ross Ice Shelf (by ~5 mm/yr). Furthermore, the published spherical harmonic coefficients—which are meant to represent the dimensionless present-day changes due to glacial isostatic adjustment (GIA)—contain excessive power for degree ≥90, do not agree with physical expectations and do not represent accurately the ICE6G_C(VM5a) model. We show that the excessive power in the high-degree terms produces erroneous uplift rates when the empirical relationship of Purcell et al. (2011) is applied, but when correct Stokes coefficients are used, the empirical relationship produces excellent agreement with the fully rigorous computation of the radial velocity field, subject to the caveats first noted by Purcell et al. (2011). Using the Australian National University (ANU) groups CALSEA software package, we recompute the present-day GIA signal for the ice thickness history and Earth rheology used by Peltier et al. (2015) and provide dimensionless Stokes coefficients that can be used to correct satellite altimetry observations for GIA over oceans and by the space gravity community to separate GIA and present-day mass balance change signals. We denote the new data sets as ICE6G_ANU.

3. Characterization of Saturn's bow shock: Magnetic field observations of quasi-perpendicular shocks

Collisionless shocks vary drastically from terrestrial to astrophysical regimes resulting in radically different characteristics. This poses two complexities. First, separating the influences of these parameters on physical mechanisms such as energy dissipation. Second, correlating observations of shock waves over a wide range of each parameter, enough to span across different regimes. Investigating the latter has been restricted since the majority of studies on shocks at exotic regimes (such as supernova remnants) have been achieved either remotely or via simulations, but rarely by means of in situ observations. Here we present the parameter space of MA bow shock crossings from 2004 to 2014 as observed by the Cassini spacecraft. We find that Saturn's bow shock exhibits characteristics akin to both terrestrial and astrophysical regimes (MA of order 100), which is principally controlled by the upstream magnetic field strength. Moreover, we determined the θBn of each crossing to show that Saturn's (dayside) bow shock is predominantly quasi-perpendicular by virtue of the Parker spiral at 10 AU. Our results suggest a strong dependence on MA in controlling the onset of physical mechanisms in collisionless shocks, particularly nontime stationarity and variability. We anticipate that our comprehensive assessment will yield deeper insight into high MA collisionless shocks and provide a broader scope for understanding the structures and mechanisms of collisionless shocks.

4. Quantifying structural states of soft mudrocks

In this paper, a cm model is proposed to quantify structural states of soft mudrocks, which are dependent on clay fractions and porosities. Physical properties of natural and reconstituted soft mudrock samples are used to derive two parameters in the cm model. With the cm model, a simplified homogenization approach is proposed to estimate geomechanical properties and fabric orientation distributions of soft mudrocks based on the mixture theory. Soft mudrocks are treated as a mixture of nonclay minerals and clay-water composites. Nonclay minerals have a high stiffness and serve as a structural framework of mudrocks when they have a high volume fraction. Clay-water composites occupy the void space among nonclay minerals and serve as an in-fill matrix. With the increase of volume fraction of clay-water composites, there is a transition in the structural state from the state of framework supported to the state of matrix supported. The decreases in shear strength and pore size as well as increases in compressibility and anisotropy in fabric are quantitatively related to such transition. The new homogenization approach based on the proposed cm model yields better performance evaluation than common effective medium modeling approaches because the interactions among nonclay minerals and clay-water composites are considered. With wireline logging data, the cm model is applied to quantify the structural states of Colorado shale formations at different depths in the Cold Lake area, Alberta, Canada. Key geomechancial parameters are estimated based on the proposed homogenization approach and the critical intervals with low strength shale formations are identified.

5. Three-dimensional surface deformation derived from airborne interferometric UAVSAR: Application to the Slumgullion Landslide

In order to provide surface geodetic measurements with “landslide-wide” spatial coverage, we develop and validate a method for the characterization of 3-D surface deformation using the unique capabilities of the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) airborne repeat-pass radar interferometry system. We apply our method at the well-studied Slumgullion Landslide, which is 3.9 km long and moves persistently at rates up to ~2 cm/day. A comparison with concurrent GPS measurements validates this method and shows that it provides reliable and accurate 3-D surface deformation measurements. The UAVSAR-derived vector velocity field measurements accurately capture the sharp boundaries defining previously identified kinematic units and geomorphic domains within the landslide. We acquired data across the landslide during spring and summer and identify that the landslide moves more slowly during summer except at its head, presumably in response to spatiotemporal variations in snowmelt infiltration. In order to constrain the mechanics controlling landslide motion from surface velocity measurements, we present an inversion framework for the extraction of slide thickness and basal geometry from dense 3-D surface velocity fields. We find that the average depth of the Slumgullion Landslide is 7.5 m, several meters less than previous depth estimates. We show that by considering a viscoplastic rheology, we can derive tighter theoretical bounds on the rheological parameter relating mean horizontal flow rate to surface velocity. Using inclinometer data for slow-moving, clay-rich landslides across the globe, we find a consistent value for the rheological parameter of 0.85 ± 0.08.

6. The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam on board Curiosity

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. From ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations reveals that the mean K2O abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.


VII. AUG Newsroom

1. SCIENTISTS DISCOVER METHANE-PRODUCING MICROBES IN CALIFORNIA ROCKS

WASHINGTON, DC — Deep in vents on the ocean floor, methane-producing microbes feed off chemical reactions between water and rock. Now evidence of this process has been found on land in a freshwater spring in California.

2. WILL MORE SNOW OVER ANTARCTICA OFFSET RISING SEAS? DON’T COUNT ON IT

WASHINGTON, DC — Many factors related to warming will conspire to raise the planet’s oceans over coming decades — thermal expansion of the world’s oceans, melting of snow and ice worldwide, and the collapse of massive ice sheets.

3. EUROPA'S OCEAN MAY HAVE AN EARTHLIKE CHEMICAL BALANCE

WASHINGTON, DC — The ocean of Jupiter’s moon Europa could have the necessary balance of chemical energy for life, even if the moon lacks volcanic hydrothermal activity, finds a new study.