AGU 期刊一周Research Spotlights (Dec 15 ~Dec 21, 2016)

发布时间:2016-12-23 9:11:55 点击次数:576

I. Science Policy

1. 2016 Arctic Report Card Highlights Dramatic Changes in Region

The report says that the Arctic is warming twice as fast as the global average.

2California's Governor Promises to Fight for Science

Scientific efforts must ratchet up in the face of rising climate change denial, Governor Brown said to a roomful of scientists.

3. Fearful of Trump, Hundreds in San Francisco Rally for Science

Speakers called on scientists not to remain silent in the face of what they said are threats to the Earth sciences.

II.Atmospheric Sciences

1. Using Isotope Fingerprints to Solve a Methane Mystery

Atmospheric methane levels are rising, and isotopic ratios within the greenhouse gas suggest that the tropics may be to blame.

III. Climate Change

1. Earth's Ground Heat Flux Should Not Be Overlooked

Scientists compare models of how much heat Earth's surface gives off and absorbs from the atmosphere.

2. A Quest to Put Sea Level Rise Data in Your Pocket

A new climate change app uses interactive data maps to engage users and prompt the exploration of questions related to changing sea levels and climate vulnerability.

3. Birds Flock to Areas of Good Weather Across the United States

A survey of birds over several decades shows that many bird species migrate or shrink their habitat to avoid drought and storms.

IV.Hydrology, Cryosphere & Earth Surface

1. Can Data Extracted from Twitter Help Map Flood Hazards?

Tweets, if scrutinized closely, may allow scientists to map hazards in real time, helping to guide emergency response.

V. Natural Hazards

1. A Date Under the Stars? Maybe Not with Aerosol Injection

Injecting aerosols into the atmosphere on purpose could help cool Earth, but new research shows that it could also make the night sky brighter and negatively affect human health.

VI. Geophysical Research Letters

1. Ice flow dynamics forced by water pressure variations in subglacial granular beds

Glaciers and ice streams can move by deforming underlying water-saturated sediments, and the nonlinear mechanics of these materials are often invoked as the main reason for initiation, persistence, and shutdown of fast-flowing ice streams. Existing models have failed to fully explain the internal mechanical processes driving transitions from stability to slip. We performed computational experiments that show how rearrangements of load-bearing force chains within the granular sediments drive the mechanical transitions. Cyclic variations in pore water pressure give rise to rate-dependent creeping motion at stress levels below the point of failure, while disruption of the force chain network induces fast rate-independent flow above it. This finding contrasts previous descriptions of subglacial sediment mechanics, which either assume rate dependence regardless of mechanical state or unconditional stability before the sediment yield point. Our new micromechanical computational approach is capable of reproducing important transitions between these two end-member models and can explain multimodal velocity patterns observed in glaciers, landslides, and slow-moving tremor zones.

2. Where the continent ends

The Earth's continents and islands are bordered by shallow ocean plains that are arguably the most environmentally, economically, and politically important parts of the sea. Yet in spite of this, they remain poorly defined and understood. A quantitative approach is employed here to map and analyze these plains, or shelves. The Earth's ocean bathymetry was used to determine the continent-ocean basin transition at ~1200 m and then parsed with a novel geospatial terrain classification concept/method borrowed from the field of image analysis: the geomorphic phonotype, or geomorphon. The technique is less subjective than visual interpretation and digitization and here illustrates that the ocean coastal plains are deeper, wider, and more steeply sloped than previously recognized. Their variable form is related to tectonics and latitude and ultimately affects function and habitat.

3. The impact of Labrador Sea temperature and salinity variability on density and the subpolar AMOC in a decadal prediction system

Labrador Sea density variability is important for Atlantic Meridional Overturning Circulation (AMOC) dynamics and hence decadal variability in the Atlantic. We investigate whether temperature or salinity dominate top 500 m interannual Labrador Sea density variability in gridded observations, an assimilation of the observations, and a set of multiannual hindcasts. We find that salinity dominates in the observations and assimilation. In the hindcasts salinity remains dominant for the first year but from year three these revert to the same temperature dominance seen in the underlying climate model. This is due to damping of the interannual salinity variability, possibly caused by unrealistically large convection that develops. Crucially, the hindcasts have high correlation skill in temperature/salinity throughout, but no skill in density, dynamic sea level, or the subpolar AMOC due to the incorrect drivers. This highlights the importance of correctly simulating both the sign and magnitude of temperature/salinity variability in a prediction system.

4. Cryogenic flow features on Ceres: Implications for crater-related cryovolcanism

Craters on Ceres, such as Haulani, Kupalo, Ikapati, and Occator show postimpact modification by the deposition of extended plains material with pits, multiple lobate flows, and widely dispersed deposits that form a diffuse veneer on the preexisting surface. Bright material units in these features have a negative spectral slope in the visible range, making it appear bluish with respect to the grey-toned overall surface of Ceres. We calculate the drop height-to-runout length ratio of several flow features and obtain a coefficient of friction of < 0.1: The results imply higher flow efficiency for flow features on Ceres than for similar features on other planetary bodies with similar gravity, suggesting low-viscosity material. The special association of flow features with impact craters could either point to an impact melt origin or to an exogenic triggering of cryovolcanic processes.

5. Inertia-induced accumulation of flotsam in the subtropical gyres

Recent surveys of marine plastic debris density have revealed high levels in the center of the subtropical gyres. Earlier studies have argued that the formation of great garbage patches is due to Ekman convergence in such regions. In this work we report a tendency so far overlooked of drogued and undrogued drifters to accumulate distinctly over the subtropical gyres, with undrogued drifters accumulating in the same areas where plastic debris accumulate. We show that the observed accumulation is too fast for Ekman convergence to explain it. We demonstrate that the accumulation is controlled by finite-size and buoyancy (i.e., inertial) effects on undrogued drifter motion subjected to ocean current and wind drags. We infer that the motion of flotsam in general is constrained by similar effects. This is done by using a newly proposed Maxey-Riley equation which models the submerged (surfaced) drifter portion as a sphere of the fractional volume that is submerged (surfaced).

6. The extraordinarily strong and cold polar vortex in the early northern winter 2015/2016

The Arctic polar vortex in the early winter 2015/2016 was the strongest and coldest of the last 68 years. Using global reanalysis data, satellite observations, and mesospheric radar wind measurements over northern Scandinavia we investigate the characteristics of the early stage polar vortex and relate them to previous winters. We found a correlation between the planetary wave (PW) activity and the strength and temperature of the northern polar vortex in the stratosphere and mesosphere. In November/December 2015, a reduced PW generation in the troposphere and a stronger PW filtering in the troposphere and stratosphere, caused by stronger zonal winds in midlatitudes, resulted in a stronger polar vortex. This effect was strengthened by the equatorward shift of PWs due to the strong zonal wind in polar latitudes resulting in a southward shift of the Eliassen-Palm flux divergence and hence inducing a decreased deceleration of the polar vortex by PWs.

7. Importance of the Gulf of Mexico as a climate driver for U.S. severe thunderstorm activity

Different features of the Gulf of Mexico (GOM), such as the Loop Current and warm-core rings, are found to influence monthly-to-seasonal severe weather occurrence in different regions of the United States (U.S.). The warmer (cooler) the GOM sea surface temperatures, the more (less) hail and tornadoes occur during March–May over the southern U.S. This pattern is reflected physically in boundary layer specific humidity and mixed-layer convective available potential energy, two large-scale atmospheric conditions favorable for severe weather occurrence. This relationship is complicated by interactions between the GOM and El Niño–Southern Oscillation (ENSO) but persists when analyzing ENSO neutral conditions. This suggests that the GOM can influence hail and tornado occurrence and provides another source of regional predictability for seasonal severe weather.



SAN FRANCISCO — Human consumption could deplete groundwater in parts of India, southern Europe and the U.S. in the coming decades, according to new research presented here today.


1. Friday fauxld: The sculptures of José Manuel Castro López

Thanks to my friend Keri Brill, I was alerted to some cool sculpture earlier this morning: the work of José Manuel Castro López. It shows rocks that are sculpted to look as if they were folded, blending the textures of rubber or fabric with the appearance of cobbles and outcrops.

2. How do you track the mass of a tree over time? Watch it move.

Dancing trees may be able to teach scientists about tree health during a drought, according to a new study.

3. New equation describes how Earth cooled from magma into rock

A new mathematical model shows strong evidence that when Earth formed, it cooled from the inside out rather that bottom up. Scientists who presented the research at the 2016 American Geophysical Union Fall Meeting said the new model helps scientists better understand Earth’s early history—how it cooled and became the rocky planet it is today.

4. Some corals and scallops better able to handle ocean acidification, study finds

Some coral and mollusk species are adjusting to acidifying ocean waters better than previously thought, according to new research.

5. Ancient monsoons helped prehistoric humans colonize Tibetan Plateau

Humans first colonized the Tibetan Plateau roughly 10,000 years ago when the climate warmed enough to bring heavy rains, new research finds.

6. Deposits discovered in Monterey Canyon’s mouth may cause marine landslides, study finds

Researchers have discovered a large concentration of sediment deposits at the end of Monterey Canyon, an underwater chasm beneath Monterey Bay, California. The sediment deposits are relatively young and may be more likely to catalyze underwater landslides than other sections of the canyon, according to the researchers who presented their discovery at the 2016 American Geophysical Union Fall Meeting.