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AGU Research Spotlight (Jun 01-Jun 07, 2018)

2018-06-08 09:27:08

I. Hydrology, Cryosphere & Earth Surface

1.How Can We Find Out How Much Snow Is in the World?

In Colorado forests, NASA scientists and a multinational team of researchers test the limits of satellite remote sensing for measuring the water content of snow.


II. Hazards & Disasters

1.Huge Spike in Quakes Badly Damages K?lauea Observatory

Meanwhile, some scientists say that the 35-year eruption from the Pu‘u ?‘ō vent has ended and that the flows since 3 May are a new eruption. Others take issue with this view.


III. Climate Change

1.Raising a Tantrum About Climate Change

One year ago today, President Trump vowed to exit the United States from the Paris climate pact. Eos discusses this with climatologist Michael Mann, author of the new book The Tantrum that Saved the World.


IV. Biogeosciences

1.After a Glacier Retreats, Plants Thrive Thanks to Phosphorus

Grasses, small flowers, and mosses colonize glacial till in the Peruvian Andes when researchers apply a phosphorus fertilizer, an ecological surprise with implications for carbon sequestration.


V. Planetary Sciences

1.Peering Through Titan’s Haze to Better Understand Its Surface

Variations in grain size and water ice content detected on Saturn’s largest moon offer evidence of geologically related units that resemble the mountain-to-desert transition on Earth.


2.Solar Flare Caused Increased Oxygen Loss from Mars’s Atmosphere

Measurements by a Mars-orbiting spacecraft indicated heating and chemistry changes in the planet’s atmosphere following an extreme solar eruption last year.


VI. Geophysical Research Letters

1.Full‐Wave Seismic Tomography in the Northeastern United States: New Insights into the Uplift Mechanism of the Adirondack Mountains

Studying the driving force of intracratonic uplifts is important in understanding the deformation mechanism of continental lithosphere and the role of mantle dynamics. The Adirondack Mountains are located at the eastern Laurentian margin in the northeastern United States with a distinct domal uplift. Subsurface structural constraints on its uplift mechanism are limited. Here we construct a high‐resolution velocity model for the crust and mantle lithosphere using full‐wave ambient noise tomography. A distinct low shear velocity anomaly with a diameter of ~70‐100 km is imaged beneath the Moho at the Adirondack Mountains. This anomaly is connected with the large‐scale low‐velocity volume beneath southern New England and eastern New York at greater depths. The observed low‐velocity anomalies may reflect asthenosphere upwelling induced by a combined effect of the Great Meteor hotspot and edge‐driven mantle convection. The buoyancy of upwelling asthenosphere, together with possible thermal expansion, may have uplifted the Adirondack Mountains.


2.Mixing efficiency in the presence of stratification: When is it constant?

The efficiency of the conversion of mechanical to potential energy, often expressed as the flux Richardson number, Rif, is an important determinant of vertical mixing in the ocean. To examine the dependence of Rif on the buoyancy Reynolds number, ReB, we analyze 3 sets of data: microstructure profiler data for which mixing is inferred from rates of dissipation of turbulent kinetic energy (ε) and temperature variance (χ) measured in the open ocean; time series of spectrally fit values ofεand covariance‐derived buoyancy fluxes measured in nearshore internal waves; and time series of spectrally fit values ofεandχmeasured in an energetic estuarine flow. While profiler data is well represented by Rif≈0.2 for 1 < ReB < 1000, the covariance data has much larger values of ReB and, consistent with DNS results, shows that Rif ~ ReB‐0.5. The estuarine data have values of ReB that fall between those of the other two data sets but also shows Rif≈0.2 for ReB < 5000. Overall, these data suggest that Rif is in general not constant, and may be substantially less than 0.2 when ReB is large, although the value at which the transition from constant to ReB‐dependent mixing may depend on additional parameters that are yet to be determined. Nonetheless, for much of the ocean ReB < 100 and so Rif is constant there.


3.Small earthquakes matter in injection‐induced seismicity

A simplistic triggering mechanism, pore pressure increase from injection, has been the focus of injection‐induced seismicity studies for decades. Research into other possible mechanisms, like poroelastic stress changes, is ongoing, but there has been relatively little focus on earthquake interaction. While studies have looked at how moderate magnitude events (M≥3.0) may trigger larger magnitude induced seismicity, research into the cumulative effect of the hundreds to thousands of small magnitude (M≤3.0) events is lacking. Here, we use generic models to compare the possible stress changes from pore pressure increase and from earthquake interactions of small magnitude events. We find that the area of increased pore pressure is much larger than that of positive Coulomb static stress transfer; however, maximum Coulomb static stress change is larger than maximum pore pressure increase. We argue that, yes, small earthquakes do matter, and their interaction may be an important triggering mechanism to consider.


4.Climatic effect of Antarctic meltwater overwhelmed by concurrent Northern hemispheric melt

Records indicate that 14,500 years ago, sea level rose by 12‐22 m in under 340 years. However, the source of the sea level rise remains contentious, partly due to the competing climatic impact of different hemispheric contributions. Antarctic meltwater could indirectly strengthen the Atlantic Meridional Overturning Circulation (AMOC), causing northern warming, whereas Northern Hemisphere ice‐sheet meltwater has the opposite effect. This story has recently become more intriguing, due to increasing evidence for sea level contributions from both hemispheres. Using a coupled climate model with freshwater forcing, we demonstrate that the climatic influence of southern‐sourced meltwater is overridden by northern sources even when the Antarctic flux is double the North American contribution. This is because the Southern Ocean is quickly re‐salinized by Antarctic Circumpolar water. These results imply that the pattern of surface climate changes caused by ice sheet melting cannot be used to fingerprint the hemispheric source of the meltwater.


5.Uranus's northern polar cap in 2014

In October and November 2014, spectra covering the 1.436–1.863‐μm wavelength range from the SINFONI Integral Field Unit Spectrometer on the Very Large Telescope showed the presence of a vast bright North polar cap on Uranus, extending northward from about 40°N and at all longitudes observed. The feature, first detected in August 2014 from Keck telescope images, has a morphology very similar to the southern polar cap that was seen to fade before the 2007 equinox. At strong methane‐absorbing wavelengths (for which only the high troposphere or stratosphere is sampled) the feature is not visible, indicating that it is not a stratospheric phenomenon. We show that the observed northern bright polar cap results mainly from a decrease in the tropospheric methane mixing ratio, rather than from a possible latitudinal variation of the optical properties or abundance of aerosol, implying an increase in polar downwelling near the tropopause level.


6.Solitary waves across supercritical quasi‐perpendicular shocks

We consider intense electrostatic solitary waves (ESW) observed in a supercritical quasi‐perpendicular Earth's bow shock crossing by the Magnetospheric Multiscale Mission. The ESW have spatial scales of a few tens of meters (a few Debye lengths) and propagate oblique to a local quasi‐static magnetic field with velocities from a few tens to a few hundred km/s in the spacecraft frame. Because the ESW spatial scales are comparable to the separation between voltage‐sensitive probes, correction factors are used to compute the ESW electric fields. The ESW have electric fields with amplitudes exceeding 600 mV/m (oriented oblique to the local magnetic field) and negative electrostatic potentials with amplitudes of a few tenths of the electron temperature. The negative electrostatic potentials indicate that the ESW are not electron phase space holes, while interpretation in terms of ions phase space holes is also questionable. Whatever is their nature, we show that due to the oblique electric field orientation the ESW are capable of efficient pitch‐angle scattering and isotropization of thermal electrons. Due to the negative electrostatic potentials the ESW Fermi reflect a significant fraction of the thermal electrons streaming from upstream (downstream) back to upstream (downstream) region, thereby affecting the shock dynamics. The role of the ESW in electron heating is discussed.


VII. AGU Blogs

1.Scientists solve lunar mystery with aid of missing Moon tapes

After eight years spent recovering lost Moon data from the Apollo missions, scientists report in a new study they’ve solved a decades-old mystery of why the Moon’s subsurface warmed slightly during the 1970s. Scientists have wondered about the cause of the warming since soon after the Apollo missions started, when astronauts deployed probes on the Moon to measure the heat coming from its interior. The lost data tapes recovered by the scientists filled in a record gap during the 1970s and helped the researchers pinpoint the source of the warming as the Apollo astronauts themselves.


2.Warm Creek Glaciers,British Columbia Retreat Driven Separation

Warm Creek, (W) Norht Warm Creek (NW) and Bighorn (H) Glaciers in Northwest British Columbia in 1984 and 2017. Red arrows are the 1984 terminus location, yellow arrows the 2017 terminus locations and purple arrows where glaciers have separated.


3.Ocean warming, ‘junk-food’ prey cause of massive seabird die-off, study finds

In the fall of 2014, West Coast residents witnessed a strange, unprecedented ecological event. Tens of thousands of small seabird carcasses washed ashore on beaches from California to British Columbia, in what would become one of the largest bird die-offs ever recorded.


4.Celebrate the ocean and NOAA in June [World Oceans Month]

The month of June is known across the globe as World Oceans Month (although it should be referred to as “Ocean” Month, as there is only one ocean divided into geographic regions). The White House has declared June 2018asNational Ocean Monthin the United States. The United Nations has established an annual celebration on June 8 for World Oceans Day.


5.Hidroituango – an increase in movement rate

In the last few hours, RCN Radio in Colombia has reported an increase in the movement rate in the landslide at the Hidroituango dam site, breaching the alarm threshold of 10 mm per hour. This has triggered evacuation of 45 workers at a part of the dam site. It is unclear as to whether this is merely the landslide showing typical stick-slip type behaviour, or a transition into a new phase of movement. Without a graph of the movement pattern this is impossible to ascertain. Meanwhile, the government is establishing a monitoring centre to collate the data, as recommended by the team from the United Nations and the US Army Corps of Engineers. This is a prudent move.


6.Sol 2070 – 2072: A very, Very, VERY good day on Mars

Every single day that the Curiosity team gets to go into work and operate a one-ton rover on the surface of Mars is a good day. But last Friday was not just your typical good day — it was a very, very, very good day. In my personal opinion, it was probably one of the top five most excellent planning days we’ve had on the mission to date. Early Friday morning we learned that the Feed Extended Sample Transfer (FEST) drop-off of the ‘Duluth’ drill sample to CheMin worked. This means we had enough rock powder in the instrument to measure its mineralogy.



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