AGU期刊一周Research Spotlight
AGU期刊一周Research Spotlight (Feb 8~Feb 14, 2018)
时间:2018年02月13日 22:27来源: 点击数:

I. Climate Change

1. A Novel Approach to a Satellite Mission’s Science Team

NASA’s Plankton, Aerosol, Cloud, Ocean Ecosystem satellite mission, still in planning stages, operates with a framework that could serve as an example for science support of future missions.


2.Medieval Temperature Trends in Africa and Arabia

A synthesis of paleotemperature reconstructions from published case studies suggests warm onshore temperatures persisted across most of Afro-Arabia between 1000 and 1200 CE.


II. Hazards & Disasters

1. California’s Water Savings Dwindle When Drought Fears Subside

Policy changes and media attention affect how much water Californians use, as well as how long these behaviors prevail. Could public awareness shift behaviors toward long-term conservation?


2. More Earthquakes May Be the Result of Fracking Than We Thought

Scientists show small earthquakes caused by fracking near Guy-Greenbrier, Ark., in 2010 that could have been early indicators of high stress levels on larger faults deeper underground.


III. Ocean Sciences

1. Gulf Stream Slowed as Hurricanes Struck

Hurricanes Jose and Maria temporarily decelerated this powerful ocean current’s flow last year, according to data from an ocean glider that rode the stream between Florida and Massachusetts.


IV. Biogeosciences

1. Ocean Wind Satellites Observe an Amazonian Drought

Satellites designed to observe ocean winds can also be used to map both forest structure and water content, allowing researchers to disentangle factors of carbon loss due to drought in the Amazon.


V. Geology & Geophysics

1. Cycles of Mountain Building Formed 2018 Winter Olympics Terrain

The Korean Peninsula’s rich geologic history can be traced on the slopes of the alpine ski course.


2. Acoustic Imaging of Oceanic Mixing in the Gulf of Mexico

Detailed analysis of acoustic reflections suggests that vertical mixing of oceanic water is enhanced at greater depths, thanks to weak stratification and the roughness of the seabed.


VI. Geophysical Research Letters

1. Quantifying Extremely Rapid Flux Enhancements of Radiation Belt Relativistic Electrons Associated With Radial Diffusion

Previous studies have revealed a typical picture that seed electrons are transported inward under the drive of radial diffusion and then accelerated via chorus to relativistic energies. Here we show a potentially different process during the 2–3 October 2013 storm when Van Allen Probes observed extremely rapid (by about 50 times in 2 h) flux enhancements of relativistic (1.8–3.4 MeV) electrons but without distinct chorus at lower L-shells. Meanwhile, Time History of Events and Macroscale Interactions during Substorms satellites simultaneously measured enhanced chorus and fluxes of energetic (~100–300 keV) seed electrons at higher L-shells. Numerical calculations show that chorus can efficiently accelerate seed electrons at L ~ 8.3. Then radial diffusion further increased the phase space density of relativistic electrons throughout the outer radiation belts, with a remarkable agreement with the observation in magnitude and timescale. The current results provide a different physical scenario on the interplay between radial diffusion and local acceleration in outer radiation belt.


2. New High-Pressure Phase of CaCO3 at the Topmost Lower Mantle: Implication for the Deep-Mantle Carbon Transportation

In this study, we have investigated the stability of CaCO3 at high pressures and temperatures using synchrotron X-ray diffraction in laser-heated diamond anvil cells. Our experimental results have shown that CaCO3 in the aragonite structure transforms into CaCO3-VII (P21/c) at 27 GPa and 1,500 K with a negative Clapeyron slope of ?4.3(9) MPa/K. CaCO3-VII is stable between 23 and 38 GPa at 2,300 K and transforms into post-aragonite at 42 GPa and 1,400 K. Furthermore, it reacts with stishovite, an abundant form of SiO2 in subducted oceanic crust, forming CaSiO3-perovskite. The occurrence of CaSiO3-perovskite via the reaction of CaCO3-VII and stishovite provides an explanation for the observation of the high concentrations of CaSiO3-perovskite and some amount of CaCO3 in deep-mantle inclusions. CaCO3-VII is thus an important carbon-bearing phase at the topmost lower mantle and may provide necessary carbon to produce deep-mantle diamonds.


3. The North Atlantic Ocean Is in a State of Reduced Overturning

The Atlantic Meridional Overturning Circulation (AMOC) is responsible for a variable and climatically important northward transport of heat. Using data from an array of instruments that span the Atlantic at 26°N, we show that the AMOC has been in a state of reduced overturning since 2008 as compared to 2004–2008. This change of AMOC state is concurrent with other changes in the North Atlantic such as a northward shift and broadening of the Gulf Stream and altered patterns of heat content and sea surface temperature. These changes resemble the response to a declining AMOC predicted by coupled climate models. Concurrent changes in air-sea fluxes close to the western boundary reveal that the changes in ocean heat transport and sea surface temperature have altered the pattern of ocean-atmosphere heat exchange over the North Atlantic. These results provide strong observational evidence that the AMOC is a major factor in decadal-scale variability of North Atlantic climate.


4. A New Estimate of North American Mountain Snow Accumulation From Regional Climate Model Simulations

Despite the importance of mountain snowpack to understanding the water and energy cycles in North America's montane regions, no reliable mountain snow climatology exists for the entire continent. We present a new estimate of mountain snow water equivalent (SWE) for North America from regional climate model simulations. Climatological peak SWE in North America mountains is 1,006 km3, 2.94 times larger than previous estimates from reanalyses. By combining this mountain SWE value with the best available global product in nonmountain areas, we estimate peak North America SWE of 1,684 km3, 55% greater than previous estimates. In our simulations, the date of maximum SWE varies widely by mountain range, from early March to mid-April. Though mountains comprise 24% of the continent's land area, we estimate that they contain ~60% of North American SWE. This new estimate is a suitable benchmark for continental- and global-scale water and energy budget studies.


5. An Argo-Derived Background Diffusivity Parameterization for Improved Ocean Simulations in the Tropical Pacific

Model biases are substantial in ocean and coupled ocean-atmosphere simulations in the tropical Pacific Ocean, including a too cold tongue and too diffuse thermocline. These biases can be partly attributed to vertical mixing parameterizations in which the background diffusivity depiction has great uncertainties. Here based on the fine-scale parameterization, the Argo data are used to derive the spatially varying background diffusivity, with a magnitude of O(10?6 m2 s?1) in the most area of tropical Pacific. This new scheme is then employed into the version 5.1 of the Modular Ocean Model-based ocean-only and coupled models, resulting in substantial improvements in ocean simulations, including a more realistic cold tongue and equatorial thermocline. The improved simulations can be attributed to the reduced cooling effects induced by weakened equatorial upwelling. Additionally, the subsurface cooling effect is attributed to the reduced heat transfer from the upper layer to the subsurface layer and the convergence of the colder water from off the equator.


6. Linear and Nonlinear Hydrological Cycle Responses to Increasing Sea Surface Temperature

An effective mechanism for determining tropical rainfall patterns in response to sea surface temperature (SST) increases with varying magnitude and horizontal distribution has not been developed thus far in climate change studies. In order to examine changes in precipitation pattern with increasing SST, we conducted a series of atmospheric general circulation model experiments using a 30 year record of observed SST for which either globally uniform SST increases of 1 K, 2 K, and 4 K or El Ni?o/La Ni?a-like patterned SST anomaly has been imposed. Although the global-mean precipitation linearly increases with the SST increase irrespective of its spatial distribution, regional precipitation changes were found to occur nonlinearly depending on the magnitude of the uniform SST increase. Owing to nonlinearity in the atmospheric circulation response, the regional hydrological sensitivity was larger with a smaller increase in SST. The precipitation response to the SST pattern was, however, quasi-linear to the magnitude of the SST change and can be separated from the response to the uniform SST increase. This study thus emphasizes the importance of relative amplitudes of uniform and structured SST increases for future rainfall projection.


VII. AGU Blogs

1. New Hayward Fault earthquake simulations increase fidelity of ground motions

Scientists have used some of the world’s most powerful supercomputers to model ground shaking for a magnitude (M) 7.0 earthquake on the Hayward Fault and show more realistic motions than ever before.


2. Urban heating punches city-shaped holes in fog over India

Scientists have observed discrete holes in widespread fog directly above cities in India, other regions of Asia and Europe. The fog holes increase in size as city populations increase, and the researchers suspect the urban heat island effect is likely to blame for the striking phenomenon.


3. Third Pod from the Sun is back!

Our podcast is back and this time we’re talking about performing science at the edge of glaciers!


4. Juneau: a very large rockslope failure in Alaska in December 2016

KTOO has a very interesting article about a large rockslope failure that occurred at Cowee Creek to the north of Juneau on 30th December 2016.  This rockslope collapse has been investigated by Rick Edwards of the U.S. Forest Service’s Pacific Northwest Research Station after it was detected as a M=3.4 seismic event.  It had a volume of about 540,000 m? according to their analysis, so was a substantial event.  The rockfall descended into a lake at the foot of the slope, displacing 460,000 m? of water.  This forced a 9 m high wave down the valley, cutting a 90 m wide swathe as it went.  The wave was recorded to be almost 2 m high some 13 km downstream.  The wave destroyed 1,500 trees.  KTOO have this image of the site, including the rockfall scar in the background and the path of the displacement wave in the foreground.


5. Predicting failure using ground-based radar and INSAR

A new paper just published in the journal Engineering Geology (Carla et al. 2018) explores the use of ground-based radar and INSAR to predict landslide failure.  The case study is based on events in an unspecified copper mine in November 2016, when an unexpected failure with a volume of 410,000 m? occurred in the excavated and benched walls of the mine.  The landslide was large – about 400 m in length and up to 300 m in width.  Clearly such an event represents a substantial risk to mine operations.  The slope was being monitored with ground-based radar, but the development of the failure was not detected.  This is of course quite disconcerting.



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