AGU 期刊一周Research Spotlights (Apr 13~Apr 20, 2016)

发布时间:2016-4-21 11:15:19 点击次数:898

I. Atmospheric Sciences

1. Aurorasaurus Puts Thousands More Eyes on the Sky

Citizen scientists share real-time auroral sightings to advance research.

2. Where Does Lightning Come From?

Thunderstorms and Elementary Particle Acceleration (TEPA-2015); Yerevan, Armenia, 5–9 October 2015

3. Icy Clouds May Counter Climate Warming Less Than Expected

A new analysis of cloud composition and behavior suggests that scientists have overestimated the ability of a type of mixed-phase ice-and-water cloud to mitigate climate change effects.

II. Geology & Geophysics

1. The Role of Water in Earth's Tectonic Plumbing Systems

Tidal forces act on well water around the San Andreas Fault, giving researchers a new window into the hydrogeological structure of fault zones.

2. Ecuador Earthquake Kills Hundreds, Injures Thousands

Ecuador's president declared a state of emergency after a large earthquake shook the country.

III. Hazards & Disasters

1. Volcanic Lightning Could Aid Hazard Response During Eruptions

Lightning and ash plume dynamics reflected eruption behavior and signaled the onset of fast-moving rock and gas flows during the 2015 eruption of Chile's Calbuco volcano.

2. Are U.S. States Prepared to Manage Water in a Changing Climate?

An empirical study of water allocation and planning in five states concludes that they lack a statewide strategy to manage the impacts of climate change on water resources.

IV. Biogeosciences

1. Paleofires and Models Illuminate Future Fire Scenarios

Advances in Interdisciplinary Paleofire Research: Data and Model Comparisons for the Past Millennium; Harvard Forest, Petersham, Massachusetts, 27 September to 2 October 2015

2. Villages Must Recalibrate Time to Survive in the Pamir Mountains

Scientists plan projects this year to help a rugged, troubled region of central Asia retune traditional timekeeping methods based on environmental cues in the face of climate change.

V.Hydrology, Cryosphere & Earth Surface

1. Improving the Identification of Extreme Precipitation Trends in the U.S.

By greatly reducing the associated uncertainty, a new model is better able to discern statistically significant trends, offering the potential to improve the seasonal forecasting of rare events.

2. Into the Belly of a Glacier

Ice caving started as a weekend hobby but has now blossomed into a portion of graduate student Kiya Riverman's Ph.D. research.

VI. Education

1. White House Science Fair Celebrates Student Achievements

A suggestion from a 9-year-old science fair participant could lead to a White House committee of kids providing advice about the science that most interests them.

VII. Climate Change

1.Faith and Science Working Together on Climate Change

When science can show that the poorest among us are suffering first and worst from human-induced climate change, religions can motivate people of faith to care and to act.

2. Nitrogen Garners Starring Role in Refined Earth System Model

Scientists create a more realistic representation of plant nitrogen uptake and usage to improve global climate simulations.

VIII.Earth and Space Science

1. Living Together in the Deep Sea

It is difficult to overstate the importance of microbes to animal and plant life. For example, we rely on microbes in our gut to help us process our food, and many plants rely on associations with fungi to help them extract nutrients from the soil. In the deep sea around hydrothermal vents, mutually beneficial associations with microscopic ‘bugs’ make it possible for animals to survive and thrive in this otherwise food limited habitat. In most parts of the deep sea, animals rely on the sparse rain of food that comes from the sunlit waters above. But around hydrothermal vents, many animals have evolved specific relationships with bacteria that use the chemicals in venting fluid to make sugar, providing them with the nutrition the animals need to survive (as mentioned in the previous blog). These bacteria are often actually found inside the animals’ cells. In other words, the animals are essentially farming their own food inside their bodies.

2. Post-wildfire erosion can be major sculptor of forested mountains

Erosion after severe wildfires can be the dominant force shaping forested mountainous landscapes of the U.S. Intermountain West, new research suggests. The study is the first to assess the impact of wildfires on such landscapes by combining several different ways to measure short-term and long-term erosion rates, said Jon Pelletier, a geoscientist at the University of Arizona in Tucson and co-author of the study.

3. Bringing the Seafloor into Focus

The Lau Back-arc Basin is nestled between Tonga and Fiji, and adjacent to the Tonga Trench – where the Pacific Plate is being driven under the Australian Plate.  This process, known as subduction, delivers oceanic crust,sediments and trapped water deep into the earth.

4. The Struggle to Survive

Tubeworms are unusual creatures. They have no eyes (there is no light where they live) and they do not have what we think of as a mouth or stomach. The way they survive is with a mutually beneficial relationship with other creatures. Instead of taking up food with the mouth, little gutless tubeworms house sulfur bacteria in their body. The tubeworms pick up the bacteria from the environment as soon as the tubeworms settle on rocks after dispersing as larvae in the water. Tubeworms provide shelter for the bacteria. They feed their symbionts with inorganic gases so that they can grow like plants on land. In return the symbionts provide food to the tubeworm host so that they grow and reproduce in the absence of a digestive system. Both partners benefit from each other in this mutualistic relationship.

5. Standards dramatically advance streamflow and flood forecasting in the U.S. and elsewhere

This is a story about how water data standards, computational hard work, high-performance computing, serendipity and synergy led to an operational capability for nationwide forecasting of streamflow and flooding at high-resolution, in near-real-time. This has been evolving for several years now, but has gone into hyper-drive in just the last couple years.

6. Common sense and volcano tourism

Volcanology is no stranger to ‘volcano tourism’ ending badly; in the infamous 1993 eruption at Galeras, several local visitors were killed alongside the volcanologists. (Note: Don’t read beyond the abstract of that paper if you’re squeamish – there are no photos of the victims, but the descriptions are graphic.) Even given the precautions that the scientists took, they found themselves in a deadly situation when the dome erupted. Just because the same thing hasn’t happened yet at Santiaguito doesn’t mean that it won’t. Santiaguito has killed people before, in a dome collapse in 1929 that may have killed thousands of people. But that’s out of living memory, and in the last few decades the eruptions at the domes have seemed fairly regular and predictable.

IX. Geophysical Research Letters

1. The honeycomb terrain on the Hellas basin floor, Mars: A case for salt or ice diapirism

We present quantitative plausibility studies of potential formation mechanisms for the “honeycomb” terrain on the northwestern Hellas basin floor. The honeycomb terrain is a unique landscape of ~10.5 x 5 km wide, mostly cell-shaped depressions that are arranged in a regular, dense pattern covering ~36,000 km2. We argue against the honeycombs being (peri-)glacial landforms (till rings, iceberg imprints, thermokarst) or the result of igneous diapirism, as terrestrial analogs do not reproduce their key characteristics. Fossilized impact melt convection cells also appear to be an unsuitable interpretation, as melt solidification should not permit such structures to be retained. We present arguments in favor of salt or ice diapirism as honeycomb formation models. Honeycomb-sized diapirs could be formed by a ~2 km thick salt layer (~72,000 km3 for the entire honeycomb terrain), which might have been derived from the highlands north of Hellas Planitia - an area of abundant chloride-signatures and intense snowfall according to ancient Mars climate models. 

2. Solid-state photochemistry as a formation mechanism for Titan's stratospheric C4N2 ice clouds

We propose that C4N2 ice clouds observed in Titan's springtime polar stratosphere arise due to solid-state photochemistry occurring within extant ice cloud particles of HCN-HC3N mixtures. This formation process resembles the halogen-induced ice particle surface chemistry that leads to condensed nitric acid trihydrate (NAT) particles and ozone depletion in Earth's polar stratosphere. As our analysis of the Cassini Composite Infrared Spectrometer 478 cm−1ice emission feature demonstrates, this solid-state photochemistry mechanism eliminates the need for the relatively high C4N2 saturation vapor pressures required (even though they are not observed) when the ice is produced through the usual procedure of direct condensation from the vapor.

3. Convective Transport and Scavenging of Peroxides by Thunderstorms Observed over the Central U.S. during DC3

One of the objectives of the Deep Convective Clouds and Chemistry (DC3) field experiment was to determine the scavenging of soluble trace gases by thunderstorms. We present an analysis of scavenging of hydrogen peroxide (H2O2) and methyl hydrogen peroxide (CH3OOH) from six DC3 cases that occurred in Oklahoma and northeast Colorado. Estimates of H2O2 scavenging efficiencies are comparable to previous studies ranging from 79-97% with relative uncertainties of 5-25%. CH3OOH scavenging efficiencies ranged from 12-84% with relative uncertainties of 18-558%. The wide range of CH3OOH scavenging efficiencies is surprising, as previous studies suggested that CH3OOH scavenging efficiencies would be <10%. Cloud chemistry model simulations of one DC3 storm produced CH3OOH scavenging efficiencies of 26-61% depending on the ice retention factor of CH3OOH during cloud drop freezing, suggesting ice physics impacts CH3OOH scavenging. 

4. Heat transport in the Hadean mantle: From heat pipes to plates

Plate tectonics is a unique feature of Earth, and it plays a dominant role in transporting Earth's internally generated heat. It also governs the nature, shape, and the motion of the surface of Earth. The initiation of plate tectonics on Earth has been difficult to establish observationally, and modeling of the plate breaking process has not consistently accounted for the nature of the preplate tectonic Earth. We have performed numerical simulations of heat transport in the preplate tectonic Earth to understand the transition to plate tectonic behavior. This period of time is dominated by volcanic heat transport called the heat pipe mode of planetary cooling. These simulations of Earth's mantle include heat transport by melting and melt segregation (volcanism), Newtonian temperature-dependent viscosity, and internal heating. We show that when heat pipes are active, the lithosphere thickens and lithospheric isotherms are kept flat by the solidus. Both of these effects act to suppress plate tectonics. As volcanism wanes, conduction begins to control lithospheric thickness, and large slopes arise at the base of the lithosphere. This produces large lithospheric stress and focuses it on the thinner regions of the lithosphere resulting in plate breaking events.

5. Characteristics of lightning, sprites, and human-induced emissions observed by nadir-viewing cameras on board the International Space Station

The Lightning and Sprites Observation (LSO) experiment was designed to test a new concept of nadir-viewing sprite measurement on board the International Space Station using spectral differentiation methods for lightning and sprite identification. It was composed of two calibrated cameras: one equipped with a narrowband filter at 763 nm to maximize the contrast between sprites and lightning, and the other to monitor lightning. The LSO was operated at night during 15 days from 2001 to 2004 during which 197 lightning flashes, several sprites, hundreds of gas flares, and tens of cities were analyzed. The main strength of this experiment was its high spatial resolution of about 400 m. The structural details of some lightning are thus observed highlighting complex systems. Some features such as the nonlinear increase of the lightning-illuminated cloud top area with the peak radiance and the radial decrease of the lightning flash radiance were quantified. The median area is 129 km2 with median minor and major axes of 12 and 16 km. Two methods of sprite identification are presented and applied to the most intense sprite events observed by LSO. The sprite diameter is 5 km and it is shifted of about 22 km from the center of the parent lightning. A ratio of 1.7% is deduced for lightning flashes between the radiances measured by both cameras. These observations should be useful for the preparation or the analysis of future space missions dedicated to nadir-viewing observations of sprites.

6. Wildfire smoke changes the vertical distribution of zooplankton in an oligotrophic lake by reducing ultraviolet radiation

We used a natural experiment to test whether wildfire smoke induced changes in the vertical distribution of zooplankton in Lake Tahoe by decreasing incident ultraviolet radiation (UV). Fires have a variety of effects on aquatic ecosystems, but these impacts are poorly understood and have rarely been observed directly. UV is an important driver of zooplankton vertical migration, and wildfires may alter it over large spatial scales. We measured UV irradiance and the distribution of zooplankton on two successive days. On one day, smoke haze from a nearby wildfire reduced incident UV radiation by up to 9%, but not irradiance in the visible spectrum. Zooplankton responded by positioning themselves, on average, 4.1 m shallower in the lake. While a limited dataset such as this requires cautious interpretation, our results suggests that smoke from wildfires can change the UV environment and distribution of zooplankton. This process may be important in drought-prone regions with increasingly frequent wildfires, and globally due to widespread biomass burning.