Highlights Collection

A compilation of AGU journal content that has been featured as Research Spotlights, Press Releases, Editors’ Highlights, Editors’ Vox, and GeoSpace blog posts (most recent listed first)

Editors' Highlight, 17 July 2017 in GRL

Two ice core records reconstruct paleoclimate in North Pacific

This paper presents a long-term record of sea salt accumulation in the Denali ice core from Alaska, which is interpreted as a time series of the strength of the wintertime Aleutian Low pressure system. The main conclusions are that the strength of the Aleutian Low has been increasing since the mid-18th century, and the Aleutian Low strength during the instrumental time period is exceptional for the last millennium. The authors hypothesize that a rise in tropical sea surface temperatures may be the cause of this trend. This is an impactful piece of work on recent climate. The remarkable replication in the two new ice cores and complimentary data from Mount Logan is significant and will be of great use to other researchers working on the paleoclimate of the North Pacific sector, as well as at lower latitudes and modeling.

*********
Editors' Highlight, 17 July 2017 in GRL

Insights into the journeys of aerosol particles over the Arctic

Arctic boundary layer clouds play an important role in the surface energy balance. Given the often-pristine conditions, the optical and microphysical properties of these clouds are sensitive to the number concentration of aerosol particles that can act as cloud condensation nuclei (CCN). This study uses a set of large eddy simulations to show that entrainment of aerosol particles from the free troposphere, in part mediated by the clouds themselves, is an important source of CCN to summertime Arctic boundary layer clouds. If true, these clouds are more susceptible to distant sources of aerosol via long-range transport and subsidence than some previous studies have suggested.

*********
Editors' Highlight, 17 July 2017 in GRL

A challenge to the longstanding theory on auroral arc formation

The ionospheric feedback instability (IFI) has been postulated for many years since the seminal paper by Atkinson in 1970. This paper is the first work that applies a simplified height-resolved ionosphere, and it shows a very real problem with previous studies on this instability that all use a flat-sheet, height-integrated ionosphere approximation. This represents a significant development, with important implications for the well-developed and longstanding theory on the auroral arc formation.

*********
Press Release, 17 July 2017 in GRL

Warm winter events in the Arctic are becoming more frequent, lasting longer

Arctic winter warming events – winter days when temperatures peak above minus 10 degrees Celsius – are a normal part of the Arctic climate over the ice-covered Arctic Ocean, but new research finds they are becoming more frequent and lasting longer than they did three decades ago.

A new study analyzing winter air temperatures over the Arctic Ocean from 1893 to 2017 shows that since 1980, an additional six Arctic winter warming events are occurring each winter at the North Pole and these events are lasting about 12 hours longer, on average. In December 2015, scientists recorded a temperature of 2.2 degrees Celsius (36 degrees Fahrenheit) in the Central Arctic, the warmest temperature ever recorded in this region from December through March.

Winter warming events have been observed by scientific excursions in the Arctic as early as the Fram expedition in 1896, when Norwegian explorers froze their ship into the ice in an attempt to reach the North Pole. But the prevalence and length of these events has broken records in recent years…more

*********
Editors' Highlight, 17 July 2017 in Radio Science

New approach to improve prediction of incoming high frequency signal angles

This collaborative investigation presents findings that will improve high frequency (HF) geolocation with potential for major practical impact. The paper demonstrates full HF ionospheric electron density data assimilation using an ensemble of physics-based ionospheric model realizations including travelling ionospheric disturbances. The proposed method provides a significant improvement, specifically in the presence of severe ionospheric gradients caused by travelling ionospheric disturbances, over HF angle-of-arrival prediction using the IRI2012 empirical model or a spherically symmetric ionosphere derived from ionosonde measurements at a point halfway between the transmitter and receiver as employed in the method of single site location. The authors suggest further work on the model through the ingestion of ionosonde data as well as HF delay and Doppler observations, and data from multi-constellation observations of global navigation satellite systems signals.

*********
Editors' Highlight, 17 July 2017 in Radio Science

New insights into the promising millimeter wave band

Using data from multiple-input multiple-output (MIMO) measurements performed in a laboratory, this paper presents an analysis of several fast-fading distributions (Rayleigh, Rice, Nakagami-m, Weibull and a-µ) at the 94 GHz band. Experimental data at this frequency is not easy to obtain so the results are interesting for the research community. The main relevance of the paper is the frequency band; it is a hot topic from the perspective of the use of new frequency bands in millimeter wave.

*********
Editors' Highlight, 17 July 2017 in Radio Science

Effects of the high frequency radio wave propagation along the lines of the Earth’s magnetic field

This paper extends the Hybrid Scintillation Propagation Model (HSPM) to the case of high frequency radio wave propagation in the ionosphere with highly anisotropic irregularities. This case describes well the situation for trans-ionospheric propagation of high frequency radio waves in high latitude regions, especially when the propagation is nearly along the geomagnetic field lines. The results should be of interest to the beacon satellite community.

*********
Press Release, 17 July 2017 in JGR: Planets

New survey highlights gender, racial harassment in astronomy and planetary science

Press Release— 

Women of color working in astronomy and planetary science report more gender and racial harassment than any other gender or racial group in the field, according to a new study revealing widespread harassment in these scientific disciplines.

In a survey of workplace experiences among astronomy and planetary science professionals, about 40 percent of women of color reported feeling unsafe in their workplace because of their gender, while 28 percent feel unsafe due to their race. About 13 percent of the survey’s female respondents reported skipping at least one class, meeting, fieldwork opportunity or other professional event for this reason. Some men of color also skipped events as a result of hearing racist comments at school or work, according to a new study detailing the survey’s results in the Journal of Geophysical Research: Planets, a journal of the American Geophysical Union.  More

*********
Editors' Highlight, 17 July 2017 in JGR: Planets

Radar used to survey enigmatic region of Mars

The Medusae Fossae Formation on Mars is important because it is a voluminous unit that likely contains a well-preserved record of the transition between the eras of fluvial incision, erosion and deposition and the more arid geological processes observed today. Previous research has also indicated that this region contains significant hydrogen – likely as water ice – beneath the surface. The origin of this enigmatic region is an open question with suggestions that the materials are due to accumulations of volcanic ash, atmospheric dust, or the remnants of a former polar ice cap. This study uses radar capable of penetrating beneath the surface to determine how the materials in the Lucas Planum region of the Medusae Fossae region are layered and their properties. The authors find that materials vary with location. At least some areas within Lucas Planum are composed of volcanic ash deposits, while others are less clear, including a region where the radar was unable to sense to a significant depth.

*********
Editors' Highlight, 12 July 2017 in Reviews of Geophysics

Review of methods for understanding interactions between rivers and groundwater

The interaction between surface and sub-surface waters is critical in determining the chemical, physical, and biological properties of both. The distributed and/or below-ground nature of these waters makes them difficult to observe directly at important scale, making remote sensing and modeling approaches key in understanding these coupled systems. This paper provides an excellent and timely review of these methods, with a novel addition of tutorials for readers to help understand and put these methods into practice.

*********
Editors' Highlight, 12 July 2017 in JAMES

Using magnetic field data to infer aspects of ocean circulation

Conductive ocean water, when it moves through Earth’s ambient magnetic field, generates secondary electric field and magnetic fields. The poloidal part of the induced magnetic field can be observed outside the ocean at remote observatories and at satellites. It then follows that the ocean flow can be sensed from magnetic observations. While magnetic fields generated by tides and tsunamis are routinely observed in satellite and ground observatory data, the ocean circulation generated magnetic field has not be observed outside the ocean. This paper does not find these signals either but it does answer a hypothetical question about whether satellite observations of ocean circulation magnetic signals can be used to improve ocean circulation models. The authors find that with a very simple noise structure in the simulated satellite data, the assimilation results up to 7% improvements in ocean flow recovery, with regional enhancements and issues. This study provides important groundwork for uniting geomagnetism and physical oceanography. The idea of using magnetic field data to infer aspects of ocean circulation in a data assimilation context is innovative and potentially very useful, given the dearth of ocean observations and the urgent need to improve our understanding of the impact of climate change on global ocean circulation.

*********
Editors' Highlight, 12 July 2017 in JAMES

Understanding the behavior of modeling in the Terra Incognita regime from a practical view

This paper addresses the practical problem associated with the operational use of nesting for coupling mesoscale and microscale flows with large eddy simulation (LES) modeling during the convection period when parent grids are in the terra incognita (TI) regime. In this situation, it is known that artificially induced cellular or horizontal roll vortices are introduced by PBL closure schemes employed in mesoscale modeling in relatively strong convection. This study provides insights into the properties of LES modeling outcomes using different values of TI parent to LES grid size ratios. This provides a sound and logical basis for the authors’ recommendation and guidance on optimal parent to LES grid nesting ratios when a parent grid is in the TI.

*********
Editors' Highlight, 12 July 2017 in JGR: Biogeosciences

Evaluating the performance of Earth System Model simulated vegetation carbon density

This paper systematically evaluates Earth System Model (ESM) performance in vegetation carbon allocation in root or vegetation. Inconsistencies are present, some suggestions for improved parameterization are presented, and a community-wide need to focus on allocation fraction observations is called out. This represents another important benchmarking analysis of ESMs.

*********
Editors' Highlight, 12 July 2017 in JGR: Planets

Analysis of the sedimentary composition of a Martian dunefield

This paper presents findings from an in-situ analysis of an active dunefield on Mars. The observations advance previous studies at Gusev Crater, which suggested that olivine may get sorted as a mineral more resistant to weathering under the arid, eolian conditions of sediment transport that currently dominate Mars. The authors also develop several alternative hypotheses for sediment processes within active dunes on Mars which can be tested by future work: reduced chemical alteration; removal of alteration rinds at the surface of grains during transport; limited interaction with volcanic gases or aerosols; and physical sorting that removes the smallest and most altered grains.

*********
Press Release, 12 July 2017 in JGR: Planets

Double jeopardy in astronomy and planetary science: Women of color face greater risks of gendered and racial harassment

Women of color working in astronomy and planetary science report more gender and racial harassment than any other gender or racial group in the field, according to a new study revealing widespread harassment in these scientific disciplines.

In a survey of workplace experiences among astronomy and planetary science professionals, about 40 percent of women of color reported feeling unsafe in their workplace because of their gender, while 28 percent feel unsafe due to their race. About 13 percent of the survey’s female respondents reported skipping at least one class, meeting, fieldwork opportunity or other professional event for this reason. Some men of color also skipped events as a result of hearing racist comments at school or work, according to a new study detailing the survey’s results in the Journal of Geophysical Research: Planets, a journal of the American Geophysical Union…more

*********
Editors' Highlight, 12 July 2017 in JGR: Oceans

Biogeochemical sensor performance in the SOCCOM profiling float array

The present-day capability to remotely observe biogeochemical parameters over the water column is a critical issue. This paper describes the performances of a suite of sensors monitoring and observing the biogeochemistry of Southern Ocean, specifically gathering data on oxygen, nitrate, pH, POC and chlorophyll. The authors discuss methods for calibration and the quality control of data, present statistics on the performances of different sensors, and describe the availability and quality of data. This could be a milestone for future studies using BGC Argo and, more generally, for ocean sciences.

*********
Editors' Highlight, 12 July 2017 in JGR: Solid Earth

Nonlinear elasticity placed in the context of frictional models

This paper describes torsional oscillator observations in rock samples under load that have been fractured and mated. A theoretical slider block-type model describes the experimental observations in order to relate the nonlinear response to rate-dependent model, a version of the Dahl model that bears resemblance to rate-state models of friction. Linking fault frictional effects to nonlinear elastic observations has not been done before. It should help the two communities better understand that the effects they observe are fundamentally the same.

*********
Editors' Highlight, 12 July 2017 in JGR: Solid Earth

Toward an understanding of mass transfers across the mantle transition zone

A low-velocity zone atop the 410-km discontinuity (410) could potentially explain the preservation of enriched geochemical reservoirs in the mantle and is of importance for our understanding of mass transfers across the transition zone. The main limitations of seismic studies for characterizing such zones are either a lack of resolution or a lack in coverage. This study allows closing the gap in the latter because it completes the coverage of oceanic regions. However, using underside reflections of S-waves (SS-precursors) for detecting a small decrease of shear-wave impedance atop a low-velocity layer (LVL) on top of the 410 is a major challenge. Indeed, these waves are analyzed at long period so are not impulsive, and this usually prevents from clearly separating the signature of a LVL from sidelobes with large amplitudes. This study proposes three original methods for detecting such LVLs with SS-precursors. The result is important: a LVL would cover 33 to 50 per cent of the Pacific Ocean, which suggests that the mantle transition zone could be significantly hydrated over a large area of the Pacific.

*********
Editors' Highlight, 12 July 2017 in JGR: Space Physics

The Two-Stream Approach: Energizer Bunny of Kinetic Electron Physics

The “two-stream” approach to calculating electron transport along a magnetic field line has been a standard technique since the late 1960s. It works well in the ionospheres of planets with strong internal dipole fields, such as Earth. It’s called a two-stream approach because it reduces electron flight direction from the full 4-pi steradian possibility of motion to just two values, with the B-field direction or against it (i.e., two streams of electrons). The author of this paper is the keeper of one such Earth electron transport two-stream code, the Global Airglow (GLOW) model. This paper presents an update of GLOW, with a few new features, and then uses it to explain an airglow feature of the upper atmosphere. This workhorse code is still going.

*********
Editors' Highlight, 12 July 2017 in JGR: Space Physics

Statistical study of particle acceleration in the core of foreshock transients

Particle energization is a key process in space plasmas. This paper presents a statistical study of ion and electron energization in the core of foreshock transients, showing that the energization of ions and electrons are different. It also shows that the ion and election energization are positively correlated with the solar wind speed.

*********