Highlights Collection

Recent highlights across AGU Journals

AGU Blog Post, 28 March 2017 in JGR: Space Physics

Relativistic electrons uncovered with NASA’s Van Allen Probes

Earth’s radiation belts, two doughnut-shaped regions of charged particles encircling our planet, were discovered over fifty years ago, but their behavior is still not completely understood. Now, new observations from NASA’s Van Allen Probes mission shows that the fastest, most energetic electrons in the inner radiation belt are not present as much of the time as previously thought. The results, presented in a new study in the Journal of Geophysical Research: Space Physics, a journal of the American Geophysical Union, show there typically isn’t as much radiation in the inner belt as previously assumed – good news for spacecraft flying in the region…

*********
AGU Blog Post, 28 March 2017 in JGR: Solid Earth

Historic earthquakes discovered along San Andreas Fault

A new U.S. Geological Survey study offers a view into the past behavior of large earthquakes along the southern San Andreas Fault.

In the study, USGS geologist Kate Scharer and her team excavated trenches across the fault near Frazier Mountain in northeastern Ventura County. This section of the San Andreas previously had no long paleoearthquake record. The researchers found evidence of 10 ground-rupturing earthquakes on this section of the fault between 800 A.D. and the last rupture in 1857.

*********
Press Release, 28 March 2017 in Earth's Future

Increase in extreme sea levels could endanger European coastal communities

Massive coastal flooding in northern Europe that now occurs once every century could happen every year if greenhouse gas emissions continue to rise, according to a new study.

New projections considering changes in sea level rise, tides, waves and storm surge over the 21st century find global warming could cause extreme sea levels to increase significantly along Europe’s coasts by 2100. Extreme sea levels are the maximum levels of the sea that occur during a major storm and produce massive flooding.

*********
Editors' Highlight, 28 March 2017 in JGR: Planets

Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean

This paper investigates lobate deposits in Arabia Terra, Mars, speculated to be tsunami deposits associated with the existence of a former ocean. The authors compared the geomorphologic characteristics of the Martian deposits with terrestrial tsunami models, scaled to Mars, for three potential sea levels. The paleo-tsunami phenomena documented in this study (along with a complementary study by Rodriguez et al. (2016) in Nature: Scientific Reports) provide new, compelling evidence for the past existence of an immense water body, “Oceanus Borealis,” that existed over time scales of at least a few million years on the surface of early Mars. The ocean hypothesis, long controversial in the Mars science community, has immense implications for understanding the volatile inventory of Mars, its hydrologic and climatic evolution, and the potential for the origin of survival of life.

*********
Editors' Highlight, 28 March 2017 in JGR: Planets

Onset of solid-state mantle convection and mixing during magma ocean solidification

Planets that experience an earlier period where most or all of the outer rock layers are molten, termed a magma ocean, have the course of the rest of their history set by this singular event.  A consequence of a magma ocean is a layered structure of rock prone to an overturn that imposes a stabilizing density gradient that can act against mantle convection—a process that is important for how the Earth and many other planetary bodies cool.  Maurice et al. investigate mixing and convection in the solidified part of the planet during and just after the complete crystallization of the magma ocean.  The authors find that if a magma ocean persists longer than approximately 1 million years, then solid state convection beneath solidifying magma ocean will efficiently erase much of the compositional layering left behind by the crystallization process.

*********
Editors' Highlight, 28 March 2017 in Reviews of Geophysics

Seismic properties and anisotropy of the continental crust: Predictions based on mineral texture and rock microstructure

This review paper discusses the elastic properties of the continental crust providing a summary of the single crystal elastic properties of crustal minerals, and in what tectonic situation these minerals are expected to be important. This study helps better understand the role of intrinsic mineral properties (e.g., composition) and extrinsic bulk properties (e.g., fractures) have on seismic signals and hence how seismic data are interpreted.

*********
Editors' Highlight, 28 March 2017 in JAMES

Evaluating the tradeoffs between ensemble size and ensemble resolution in an ensemble-variational data assimilation system

This paper examines a fundamental question in the modern era of ensemble weather forecasting: what is a better use of additional computer resources, increasing the spatial resolution of the forecast model or increasing the ensemble size? Although both changes improve forecast performance in the National Centers for Environmental Prediction operational forecast and data assimilation system, increasing model resolution leads to slightly but significantly more improvement. Much of the benefit of increasing resolution comes from reducing small-scale errors, and eliminating the need for a single deterministic very-high-resolution control forecast, replacing it with an ensemble average.

*********
Editors' Highlight, 28 March 2017 in WRR

Peaks Over Threshold (POT): A methodology for automatic threshold estimation using goodness-of-fit p-value

This paper proposes a new methodology than can be used to automatically select the threshold for Peaks Over Threshold (POT) analysis. The method utilizes p-values of the Anderson-Darling Goodness of Fit test together with estimation of parameters using L-moments method. This takes into account the estimation uncertainty of the threshold as well as of the high return period quantiles. This method could be helpful to hydrological analysts studying flood distributions.

*********
Editors' Highlight, 28 March 2017 in WRR

Modeling complex flow structures and drag around a submerged plant of varied posture

­­Most work on modeling the influence of vegetation on river flow has considered natural plants to be morphologically simple but they actually have complex morphology. This paper describes a combined flume and numerical model experiment to examine flow structure and drag around a submerged plant. Given the importance of vegetation in river corridor management, the numerical scheme developed by the authors has potential application for understanding how natural vegetation partitions discharge between changes in velocity and depth, and how this impacts the conveyance.

*********
Editors' Highlight, 28 March 2017 in JGR: Atmospheres

The Role of Monsoon-like Zonally Asymmetric Heating in Interhemispheric Transport

Through numerical experiments using a simplified global model, this study illustrates the distinct roles in inter-hemispheric transport played by heating associated with two dominant phenomena in the Earth System: the zonally symmetric Hadley circulation and the zonally asymmetric monsoon. It demonstrates that realistic inter-hemispheric transport can be reproduced only when heating of both is included.

*********
Editors' Highlight, 28 March 2017 in JGR: Atmospheres

Ship observations and numerical simulation of the marine atmospheric boundary layer over the spring oceanic front in the northwestern South China Sea

Sharp gradients in sea surface temperature are known as SST fronts. They exist in many locations across the world’s oceans. Understanding of how SST fronts affect the atmosphere remains rudimental. In this study, numerical model simulations over an SST front in the South China Sea were first validated by ship-born observations and then used to diagnose physical processes that transport influences of the SST front through the boundary layer. The findings show that surface wind from the warm to cold sides of the front slows down through an adjustment in the surface pressure gradient, which exhibits a baroclinic structure that affects the wind profile in the boundary layer.

*********
Editors' Highlight, 28 March 2017 in JGR: Oceans

Observations of waves and currents during barrier island inundation

This paper describes field observations of overwash and inundation caused by storms across a barrier island in The Netherlands. Using a comprehensive set of data on water levels, waves, winds and currents the authors found different forcing and dissipation mechanisms from each side of the island. Their analysis also showed the influence of gradients between the oceanic and basin water levels. A better understanding of wave/current transformations from offshore to barrier environments is important for predicting storm impacts on barrier islands.

*********
Editors' Highlight, 28 March 2017 in JGR: Space Physics

A mechanism of mid-latitude noontime foE long-term variations inferred from European observations

The study of long-term trends and in long-term variations in thermospheric and ionospheric parameters are currently very popular, and conclusions of these studies differ substantially. The authors of this paper demonstrate that the main source of long-term variations of ionospheric parameters in critical frequencies of E layer is long-term variations in solar activity.

*********
Editors' Highlight, 28 March 2017 in JGR: Space Physics

Survey of Voyager Plasma Science Ions at Jupiter: I Analysis Method

In our field, so much emphasis is put on the spectacular and ground-breaking, and not the fundamental work of producing high quality measurements with documentation and access to the wider community. The authors of this paper found an old data set from the Planetary Data System (NASA’s repository for planetary mission observations), updated old MIT codes written in the 1970s, and made it accessible online for the current generation of researchers. They also carried out a statistical survey of the reprocessed data. This type of work opens doors to the spectacular and ground-breaking, but is rarely recognized for its significance.

*********
Editors' Highlight, 28 March 2017 in GRL

Ambient observations of dimers from terpene oxidation in the gas-phase: implications for new particle formation and growth

This study represents an extension of laboratory work on highly oxygenated molecule (HOM) formation with field measurements from boreal forest areas in Finland across two spring seasons. The authors present new data on the occurrence of so-called dimers in both gas phase and particle phase in the boreal environment, showing the power of fast online detection methods. This work contributes to a better understanding of atmospheric processes affecting particle formation in the boreal forest environment.

*********
Editors' Highlight, 28 March 2017 in GRL

Diurnal atmosphere-ocean signals in Earth's rotation rate and a possible modulation through ENSO

This paper takes a mixed torque/angular momentum approach to study the effect of the S1 atmosphere/ocean tide on length-of-day. The authors show that the amplitude and phase of the S1 tide is modulated with the modulation being related to the ENSO phenomena. The results are surprising. For many years it was well accepted that torques were quantities less stable and precise than atmospheric angular momentum, which is a kind of integration; seeing the opposite is quite impressive as it indicates that the model precision has really made some progress. These results point the way to better modeling the effects of the S1 tide on length-of-day measurements and are an important contribution to the geodetic literature on this subject.

*********
Editors' Highlight, 28 March 2017 in GRL

The projected demise of Barnes Ice Cap: Evidence of an unusually warm 21st century Arctic

Paleo evidence suggests that earlier deglaciations of the Barnes Ice Cap rarely approached the current ice-cap dimensions. This study suggests that the ice cap is likely to disappear in the near future despite summer insolation near minimum levels. This provides strong evidence that the current level of greenhouse gas forcing is exceptional, and may result in an Arctic climate not seen since the Pliocene.

*********
Editors' Highlight, 24 March 2017 in JGR: Oceans

Downstream evolution of the Kuroshio's Time Varying Transport and Velocity Structure

This study of the Kuroshio ocean current looks at its changing characteristics as it flows between Luzon and Taiwan. It is based on in-situ data sets from two companion field programs that measured the current’s strength and velocity structure. The results reveal that the current’s evolution is influenced by factors such as downstream thickening, bathymetric ridges, and eddies from the ocean interior. Given contemporary discussions about the role of Western boundary currents in global observing systems, this is a great example of how boundary observations tie together basin-wide circulation.

*********
Editors' Highlight, 24 March 2017 in JGR: Oceans

Under-ice water fCO2, sea-air CO2 fluxes and effect of storm events and an under-ice phytoplankton bloom on during the winter-spring transition in the high Arctic Ocean

This paper presents a winter-to-spring dataset of under-ice water fCO2 in an area of the high Arctic Ocean. The authors seek to understand the exchange of CO2 between the ocean and the atmosphere, and how this dynamic varies in relation to sea ice cover decrease in the area. These findings are important since the Arctic Ocean is one of the most affected areas by global warming.

*********
Editors' Highlight, 24 March 2017 in JGR: Solid Earth

Geometry and evolution of a fault-controlled Quaternary basin by means of TDEM and single-station ambient vibration surveys: the example of the 2009 L’Aquila earthquake area

This paper presents the results of seismic geophysical surveys in the area of central Italy where the 2009 L’Aquila earthquake caused considerable damage. The data provide new insight into the 3D shape of the basin and has uncovered some potential new faults whose activity should be considered in any hazard assessments. It also provides an example of the potential of inexpensive geophysical methods.

*********