Plain Language Summaries Collection

Plain Language Summaries are published alongside a paper’s scientific abstract, and are a great way to communicate your work to a broader audience. Submitting a Plain Language Summary is now an option across all AGU Journals. We showcase some good examples here. Find out more about how to write a good Plain Language Summary.

 

Impacts of intensive livestock production on human health in densely populated regions by Lidwien A. M. Smit, et al in GeoHealth

In several regions worldwide, in particular in the Western world and Asia, large-scale livestock farms are located in densely populated areas. The presence of large numbers of farm animals raises questions about health risks for neighboring residents who are not farmers themselves. Large-scale livestock farms expanded rapidly in the last few decades, but their potential impact on neighboring residents’ health has hardly been accompanied by any research. In our commentary, we argue that the current situation in densely populated livestock farming areas could be regarded as a “natural experiment”, with residents being exposed to potentially harmful bacteria, viruses, and air pollutants. We discuss studies in people living near farms, with examples of infectious diseases that can be transmitted from animals to humans, and transmission of bacteria that are resistant to antibiotics. It is less well known that people living close to livestock farms are also exposed to air pollutants that may affect the airways, such as fine dust and ammonia. Recent studies have shown that air pollution from livestock farms is associated with a worsening in lung function.

Tracking CMEs using data from the Solar Stormwatch project; observing deflections and other properties by Shannon R. Jones, et al in Space Weather

Coronal mass ejections are the main driver of hazardous space weather. The Solar Stormwatch citizen science project asked members of the public to find and measure coronal mass ejections (CMEs) in images of the Sun’s atmosphere taken by NASA’s twin STEREO spacecraft. In particular, participants tracked CMEs through the fields of view of three imagers that monitor different regions of the Sun’s atmosphere: an extreme ultraviolet camera, EUVI, and two Coronagraphs, COR1 and COR2. In this work we process the measurements of the citizen scientists to produce a catalogue of 41 CMEs, including details of the CME source location, size, and speed. The resulting catalogue is the first that self-consistently tracks CMEs through each of the EUVI, COR1, and COR2 imagers. We demonstrate that CMEs tend to accelerate, increase in width, and deflect toward the heliospheric current sheet as they propagate through the combined EUVI, COR1, and COR2 fields of view.

Magnetospheric ion influence at the dayside magnetopause by S. A. Fuselier, et al in JGR: Space Physics

Magnetic reconnection is the interconnection of magnetic fields that results in energy release. At the Earth’s boundary with the solar wind, the magnetopause, reconnection occurs between the solar wind magnetic field and the Earth’s magnetic field. Magnetic reconnection can be affected by the presence of high densities of cold ions that originate from the Earth’s high latitude ionosphere. However, this study shows that under normal conditions in near-Earth space, the ion densities are too low to have a significant effect on the reconnection process.

Bacteria-induced mixing in natural waters by T. Sommer, et al in GRL

Small aquatic organisms (size < ≈1 cm) do not efficiently mix water by swimming, because they are too small and swim too slowly to create whirls that lead to mixing. In bioconvection, however, small organisms (that are denser than water and, on average, swim upwards) can mix water. When such organisms accumulate locally in a layer, the density of the water increases. This layer of heavier water on top of lighter water sinks and mixes with the surrounding water. Continuous upward swimming provides the energy to maintain the water motion. Bioconvective mixing has been observed for a wide range of species, but so far only in the laboratory. We report the first observation of bioconvection in a natural water body and show that the only 10-μm-long bacterium Chromatium okenii causes mixing in the Alpine Lake Cadagno (Switzerland). The observed mixed layer is 0.3- to 2-m-thick and located at around 12-m-depth. We suggest that bioconvection may influence the composition of organisms in natural waters and affect large-scale phenomena like algal blooms.

Linear response of field-aligned currents to the interplanetary electric field by D. R. Weimer, et al in JGR: Space Physics

In the ionosphere at high latitudes there are electric fields that are involved with the currents that form the aurora. It is known that the voltage and auroral currents respond to the electric field in the solar wind, which is the product of the solar wind’s velocity and an embedded magnetic field. In the past it has been found that as the solar wind’s electric field increases, the voltage steadily increases linearly, at first, then levels off. This response is known as electric potential saturation. A number of different theories have been proposed to explain these phenomena. To help solve the puzzle of why the potentials saturate, it is necessary to know more about how the currents respond as well, but measurements of the currents are more difficult than the electric fields. This paper reports results of a study that determined how the currents change as the driving in the solar wind increases, using measurements of magnetic fields taken on five different satellites over several years. It was found that unlike the electric potentials, the currents do not saturate. This result was not expected.

A parsimonious modular approach to building a mechanistic belowground carbon and nitrogen model by Rose Z. Abramoff, et al in JGR: Biogeosciences

Soil stores a lot of carbon, carbon that could otherwise be in the atmosphere. We understand that the microorganisms that grow in the soil, like bacteria and fungi, affect how much carbon resides in the soil and how much is released to the atmosphere as CO2 and some cases methane (CH4). The difficult, however, is how best to describe the activity of soil microbes in mathematical models. This is important because mathematical models are used to make predictions about the future, like climate change. The research we’ve conducted helps us build better models. We used well established descriptions of water, temperature temperature effects on soil microbes to predict how fast carbon and nitrogen cycles in the soil. Our modeling approach is unique because it is simple and based on well defined physical and biological properties. Our hope is that this model will be analyzed by other research groups and perhaps one day be implemented in the large, complex models that are used to simulate the earth’s climate.

Causes and importance of new particle formation in the present-day and preindustrial atmospheres by Hamish Gordon, et al in JGR: Atmospheres

New particle formation in the atmosphere is the process by which gas molecules collide and stick together to form atmospheric aerosol particles. Aerosols act as seeds for cloud droplets, so the concentration of aerosols in the atmosphere affects the properties of clouds. It is important to understand how aerosols affect clouds because they reflect a lot of incoming solar radiation away from Earth’s surface, so changes in cloud properties can affect the climate. Before the Industrial Revolution, aerosol concentrations were significantly lower than they are today. In this article, we show using global model simulations that new particle formation was a more important mechanism for aerosol production than it is now. We also study the importance of gases emitted by vegetation, and of atmospheric ions made by radon gas or cosmic rays, in preindustrial aerosol formation. We find that the contribution of ions and vegetation to new particle formation was also greater in the preindustrial period than it is today. However, the effect on particle formation of variations in ion concentration due to changes in the intensity of cosmic rays reaching Earth was small.

Composition of the low seismic velocity E′ layer at the top of Earth's core by John Brodholt, et al in GRL

The Earth’s outer core is mostly made of liquid iron at extremely high temperatures (up to ~6000 K) together with a small amount of other elements such as oxygen or silicon. The high temperatures generate vigorous convection and so the core is generally considered to be well mixed. Nevertheless, evidence from seismology as far back as the 1980s show that there is a layer at the top of the Earth’s core of a hundred kilometers or so thick. We call this the E′ layer. There are a number of ideas of what this layer is made of and how it formed, but the data on the properties of iron and its light elements has not been available to test these ideas. In this paper we use recent ab initio data to rule out many ideas for its formation. We also show that the properties of the E′ layer can be explained as (a) reaction between the liquid iron core and the rocky mantle above it, (b) the incomplete mixing of an early Earth core with a late impactor, or (c) the residue from crystallisation of a very Fe-rich phase at the top of the core.

An HF and Lower VHF Spectrum Assessment System Exploiting Instantaneously Wideband Capture by Rod I. Barnes, et al in Radio Science

This work describes a receiver and recording system used to accurately and robustly measure the amount and nature of the radio-frequency energy existing at a radio site. The measurement system is instantaneously wideband which means it characterizes the entire spectrum between 2 and 45 MegaHertz simultaneously. Previous receiver systems that attempt instantaneously wideband HF capture have had difficulty robustly characterizing the weakest and the strongest signals simultaneously, due to imitations in the capability of critical receiver hardware components. This paper describes some novel techniques that permit the instantaneously wideband operation but achieve robust characterization of the full spectrum.The instantaneous capture has advantages over traditional swept methods, by allowing rapid repeated characterization of the environment. This also enables novel applications such as the recording of new radio signatures of the ionosphere, such as ‘flashagrams’ that are produced from the propagation of lightning strikes through the ionosphere and in to the receiver.

The stratigraphy and history of Mars' northern lowlands through mineralogy of impact craters: A comprehensive survey by Lu Pan, et al in JGR: Planets

The northern lowlands of Mars (encompassing 1/3 of the planet’s surface area) could have hosted a global ocean in the past. The lowlands are comprised of several topographic depressions (“basins”) filled with sediments, which mask the nature of the underlying crust. Impact craters excavate up to several kilometers into the subsurface of the lowlands and expose the hidden record of its geologic history. Our comprehensive survey of the subsurface mineralogy excavated by these impact craters reveals widespread volcanic and hydrated silicate minerals. We did not find widespread carbonate, chloride, or sulfate salts, which would have suggested a long-lived global ocean. However, our observations do suggest that impact craters have excavated a crust made of 1 – 2 km of volcanic material, which is on top of a water-altered basement containing hydrated silicate minerals. We have also discovered local variations in the different basins with evidence for new volcanic sources and for hydrated minerals in ancient crust near the north polar cap.

Fire severity alters the distribution of pyrogenic carbon stocks across ecosystem pools in a Californian mixed-conifer forest by Bernardo Maestrini, et al in JGR: Biogeosciences

Charcoal (i.e. pyrogenic carbon) is an important form of carbon present in forest soil subject to fire events that is characterized by a high resistance to decomposition, and thus may remain in soil for hundreds of years before it is transformed into carbon dioxide (an important green house gas). However charcoal production is so far not considered when assessing the impact of forest fires on green house gas production. It is possible that due to this neglection the impact of forest fires on the carbon cycle is currently overestimated. Here we quantified charcoal production during forest fires in a forest that fires of different severity. We found that fire severity does not alter the amount of charcoal created whereas it influences the distribution in the forest compartments (forest floor vs trees). Our results have important implications for the residence time of charcoal in the terrestrial ecosystems, because charcoal is expected to stay longer in standing trees and coarse woody debris compared to the forest floor, where it is susceptible to rapid losses through erosion.

Uplift, Rupture, and Rollback of the Farallon Slab reflected in Volcanic Perturbations along the Yellowstone Adakite Hotspot Track by Victor E. Camp, et al in JGR: Solid Earth

Yellowstone National Park is underlain by a rising plume of hot rock from the Earth’s deep mantle that has provided the melt source for three super-eruptions over the last 2 million years. This hotspot, or mantle plume, appears to be a long-lived feature that resided offshore beneath the oceanic Farallon plate before being overridden by the westward moving North American plate about 42 million years ago (mya). Between 42 and 17 mya the Yellowstone plume was shielded beneath the subducting Farallon slab, with little surface expression on the overriding North American plate. After 17 mya the plume reemerged to produce a great outpouring of basaltic lava known as the Columbia River flood basalts of eastern Oregon and southeastern Washington. New and compiled chemical and age data suggests that the Farallon slab was uplifted and dislocated by the thermally buoyant Yellowstone mantle plume between 30 and 20 mya, with oceanic crust of the Farallon slab melting to generate unusual rocks called adakite. Eventual destruction of the Farallon slab beneath eastern Oregon was associated with a long-lived period of thermal erosion tearing of the slabe from 30-17 mya, followed by the foundering and sinking of slab segments from 16-10 mya.

Diffusive Loss of Argon in Response to Melt Vein Formation in Polygenetic Impact Melt Breccias by Cameron M. Mercer and Kip V. Hodges in JGR: Planets

Many planets, moons, and asteroids in the solar system have experienced extensive impact bombardment throughout their histories. With each impact, new rocks can be assembled that incorporate fragments of older rocks and freshly melted rock produced by the energy of impact. The molten portions eventually cool, and the combination of older and younger materials, which we call an impact melt breccia (IMB), becomes a time capsule with a record of the impacts that the IMB has endured. Radioactive elements trapped in the minerals of the breccia act as clocks called geochronometers, which we can potentially use to unravel the timing of the impacts. We model how much these geochronometers are heated in older rock fragments when new impact melts form and cool and assess how much the geochronometers of older materials can be disturbed. We found that geochronometers are not heavily affected in breccias that incorporate thin, millimeter-scale melt bodies, especially if the new melt bodies also contain older rock fragments. Therefore, IMBs that contain multiple generations of rocks and now-solidified impact melts can accurately record the timing of each of the impacts that affected it.

Modeling tabular icebergs submerged in the ocean by A. A. Stern, et al in JAMES

Large tabular icebergs break away from ice shelves around Antarctica, and drift into the ocean. As the icebergs move, they melt, which injects freshwater into the ocean. This freshwater can promote sea-ice growth, affect deep-water formation and alter ocean temperatures and salinities. In this way icebergs play an important part in the climate system, and need to be modeled accurately. However, the current generation of iceberg models is unable to model large tabular icebergs. In this paper, we develop a new model which can simulate the movement of large tabular icebergs drifting in the ocean. Most previous iceberg models treat iceberg as point particles which do not occupy any physical space. In our model, we represent iceberg using element which do occupy physical space, and can interact with the ocean and other elements more realistically. We then create large tabular icebergs by bonding together many smaller elements to form large structures. This allows us to simulate the movement of larger tabular icebergs in the ocean. An advantage of this approach is that by breaking the bonds between elements, we can simulate an iceberg calving away from an ice shelf, or an iceberg breaking into two or more parts.

Methodology for time-domain estimation of storm-time geoelectric fields using the 3D magnetotelluric response tensors by Anna Kelbert, et al in Space Weather

Magnetic storms can pose significant risks to critical technology infrastructure such as the electric power grids. Real-time estimation of geoelectric fields can give the grid operators an opportunity for prompt intervention that would mitigate the long-term consequences. We develop and validate a method to efficiently and accurately (to within 85–90%) “nowcast” storm time geoelectric fields in close to real time in places where both geomagnetic field data are collected or estimated, and a magnetotelluric impedance has been previously measured. This method can be applied in all regions where magnetotelluric data have been collected, including in the United States, where USArray magnetotelluric data survey is ongoing and by 2018 will cover about two thirds of the country. In this work, we focus on the algorithm development only.

Slowdown of global surface air temperature increase and acceleration of ice melting by André Berger, et al in Earth's Future

Although the last decade is the warmest decade in the instrumental record and COcontinues to rise, global surface air temperature has not increased as much as before over the last 10–15 years, leading to the so-called hiatus or slowdown of the global warming. This is a key event which has still not received any definitive explanation, although many possible causes have already been adduced. Here we take into account the almost simultaneous phenomena which arose at the beginning of the 21st century: acceleration in the disappearance of the summer arctic sea ice, increase of the rate of ice sheets and glacier melting and of seal-level rise, and the appearance of a decrease of the warming trend of the atmosphere. Our calculations based on three climate records show that the energy left in the atmosphere by the slowdown of the global warming is pretty similar to the energy requested to melt the ice over the same period. While the heat content of the atmosphere alone shows a leveling off after 2002, no such behavior is observed when the heat of ice melting is added, suggesting a redistribution of heat within the atmosphere–cryosphere system.

Advancing Atmospheric River Forecasts into Subseasonal-to-Seasonal Timescales by Cory F. Baggett, et al in GRL

Along the west coast of North America, intense rain storms that produce extreme and impactful weather occasionally happen. These rain storms are called “atmospheric rivers.” Atmospheric rivers cause considerable mayhem – delivering flooding rains when they occur and desiccating droughts during their absence. Because their impacts are so extreme, it would be beneficial to have as much forewarning as possible about when and where they will occur. Unfortunately, modern-day weather models are unable to forecast atmospheric rivers beyond two weeks in advance. However, we find that the potential exists to improve forecasts of atmospheric rivers by using knowledge of the current weather in the tropics. The weather in the tropics foretells many weeks in advance when and where atmospheric rivers will impact the west coast of North America. Our findings offer an opportunity to improve weather forecasts and thereby provide more forewarning for atmospheric rivers and their extreme impacts.

Tropical Pacific climate variability over the last 6000 years as recorded in Bainbridge Crater Lake, Galapagos by Diane M. Thompson, et al in Paleoceanography

Sediments accumulating at the bottom of Bainbridge Crater Lake have provided a record of Galapagos climate and the frequency of El Niño events over the past ~6000 years. Motivated by the importance of this lake for our understanding of climate in the tropical Pacific Ocean, we have been monitoring the link between climate, lake conditions and the physical and chemical properties of the lake sediments since 2009. Based on this long-term monitoring, we find that the Bainbridge sediment record preserves both El Niño and La Niña events. This makes Bainbridge a particularly valuable archive of past climate, as most sediment-based records typically preserve only one or the other key phase of tropical Pacific climate.

Assessing variability in the size and strength of the North Atlantic subpolar gyre by Nicholas P. Foukal, et al in JGR: Oceans

For over a decade there has been a discrepancy in the observed variability of the size and strength of the subpolar gyre: satellite estimates based on the height of the sea-surface were interpreted as showing a rapid decline in the gyre since the early 1990s, while direct measurements from ships and moorings showed the gyre to be quite stable over the same time period. In this work, we reconcile these two measurement techniques by subtracting the long-term sea level rise from the satellite altimetry. Changes to ocean circulation require changes to the slope of the sea-surface, so sea-surface height variability that is present across the gyre can obscure variability in the ocean circulation. Our new measures of the size and strength of the gyre indicate a weakening, but at about 1/4 the rate of previous estimates, and a stable gyre size over the study period. Both of these are consistent with the direct measurements. In addition, we find that the eastern boundary of the gyre does not have large coherent excursions to the east and west, and we find that it most likely does not control the temperature and salinity the eastern subpolar region as has been previously theorized.

Modeling observations of solar coronal mass ejections with heliospheric imagers verified with the Heliophysics System Observatory by C. Möstl, et al in Space Weather

Solar storms are formed by incredibly powerful explosions on the Sun, and travel as clouds of plasma threaded by magnetic fields through the solar system. Depending on their propagation direction, they may impact planets such as Earth, where they elicit colorful aurorae or, in very seldom cases, can lead to power failures with potentially tremendous economical and societal effects, thus posing a serious natural hazard.In this work, we have shown how well the solar storm impact can be forecasted when using a special type of instrument that can actually image the solar storms as they propagate towards the planets and even as they sweep over them. Our analysis includes two thirds of a solar cycle with 8 years of data, and spacecraft at Mercury, Venus, Earth and in the solar wind to check on the correctness of our predictions. We could forecast the arrival time within +/- 16 hours, and for 1 correct impact there are 2 to 3 false alarms. This forms a new baseline for the science of space weather prediction. Clearly the modeling should be further improved to be used on a daily basis for a space weather mission to the Sun-Earth L5 point.