AGU 期刊一周Research Spotlights (Nov 4~Nov 10, 2016)

发布时间:2016-11-11 9:23:29 点击次数:647

I. Natural Hazards

1. An Early Warning System for Landslide Danger

Advances in satellite imaging, mapping, and rainfall estimations have made it possible to implement a regional real-time assessment of landslide hazard threats across Central America.

II. Geology & Geophysics

1. Former U.S. Science Academy President Ralph Cicerone Dies at 73

Cicerone was a leading authority on atmospheric chemistry and climate change and an outspoken advocate for science during a tumultuous political period.

2. A New Model to Improve Gravity Models

Data from the Gravity Recovery and Climate Experiment (GRACE) mission gets a new and improved look.

3. New NASA Science Head Foresees Progress in Search for Alien Life

Thomas Zurbuchen said other top goals for science and the agency include understanding and protecting life on Earth and probing fundamental aspects of the universe like dark matter and dark energy.

III.Hazards & Disasters

1. Modeling Rainfall Runoff

New framework unifies existing models for better analysis of the flowing water produced by heavy rain events.

IV. Climate Change

1. Challenges of Climate Change Adaptation

Practical and Methodological Challenges of Climate Change Adaptation; Oslo, Norway, 25–26 April 2016

2. Landmark Paris Climate Accord Comes into Force

Still, much work remains to limit emissions and damage from climate change, said top United Nations and World Bank officials, scientists, and leaders of organizations combating the climate threat.

3. Ant Populations Destabilize Under Warming

In forest experiments in which artificial warming mimicked future climate conditions, heat-tolerant ants thrived, leaving other populations unstable.

V. Ocean Sciences

1. Gulf Stream Destabilization Point Is on the Move

Westward migration of the wavelike Gulf Stream pattern could have big effects on ocean mixing and heat transport off the U.S. East Coast.

2. Bringing Biogeochemistry into the Argo Age

Plans are underway to integrate and augment a collection of regional programs to form a global biogeochemical monitoring network.

VI. Geophysical Research Letters

1. The thermodynamic effect of atmospheric mass on early Earth's temperature

Observations suggest that Earth's early atmospheric mass differed from the present day. The effects of a different atmospheric mass on radiative forcing have been investigated in climate models of variable sophistication, but a mechanistic understanding of the thermodynamic component of the effect of atmospheric mass on early climate is missing. Using a 3-D idealized global circulation model (GCM), we systematically examine the thermodynamic effect of atmospheric mass on near-surface temperature. We find that higher atmospheric mass tends to increase the near-surface temperature mostly due to an increase in the heat capacity of the atmosphere, which decreases the net radiative cooling effect in the lower layers of the atmosphere. Additionally, the vertical advection of heat by eddies decreases with increasing atmospheric mass, resulting in further near-surface warming. As both net radiative cooling and vertical eddy heat fluxes are extratropical phenomena, higher atmospheric mass tends to flatten the meridional temperature gradient.

2. The scaling exponent of residual nonwetting phase cluster size distributions in porous media

During an imbibition process in two-phase subsurface flow the imbibing phase can displace the nonwetting phase up to an endpoint at which a residual saturation is reached (which cannot be reduced further by additional wetting phase flow due to the complex pore network of the rock and associated strong capillary forces which trap the nonwetting phase). The residual nonwetting phase is split into many disconnected clusters of different sizes. This size distribution is of key importance, for instance, in the context of hydrocarbon recovery, contaminant transport, or CO2geostorage; and it is well established that this size distribution follows a power law. However, there is significant uncertainty associated with the exact value of the distribution exponent τ, which mathematically describes the size distribution. To reduce this uncertainty and to better constrain τ, we analyzed a representative experimental data set with mathematically rigorous methods, and we demonstrate that τ is substantially smaller (≈1.1) than previously suggested. This raises increasing doubt that simple percolation models can accurately predict subsurface fluid flow behavior; and this has serious consequences for subsurface flow processes: hydrocarbon recovery is easier than predicted, but CO2 geostorage dissolution trapping capacities are significantly reduced and potential remobilization of residual CO2 is more likely than previously believed.

3. Increased light-use efficiency in northern terrestrial ecosystems indicated by CO2and greening observations

Observations show an increasing amplitude in the seasonal cycle of CO2 (ASC) north of 45°N of 56 ± 9.8% over the last 50 years and an increase in vegetation greenness of 7.5–15% in high northern latitudes since the 1980s. However, the causes of these changes remain uncertain. Historical simulations from terrestrial biosphere models in the Multiscale Synthesis and Terrestrial Model Intercomparison Project are compared to the ASC and greenness observations, using the TM3 atmospheric transport model to translate surface fluxes into CO2 concentrations. We find that the modeled change in ASC is too small but the mean greening trend is generally captured. Modeled increases in greenness are primarily driven by warming, whereas ASC changes are primarily driven by increasing CO2. We suggest that increases in ecosystem-scale light use efficiency (LUE) have contributed to the observed ASC increase but are underestimated by current models. We highlight potential mechanisms that could increase modeled LUE.

4. Aquifers switched from confined to semiconfined by earthquakes

Earthquake-induced aquifer parameter changes (e.g., permeability and hydraulic diffusivity) have been documented in many studies. However, changes in the confinement of an aquifer from confined to semiconfined following an earthquake have not been reported. Here we focus on the tidal response of the water level in four wells following the 2008 Wenchuan Mw 7.9 and 2013 Lushan Mw 6.6 earthquakes to show that earthquakes can change confined aquifers to semiconfined aquifers by reopening of preexisting vertical fractures (and later healing). This study has important implications because a switch from confined to semiconfined means a change of vertical hydraulic connection, which may affect the vulnerability of an aquifer, the integrity of underground waste repositories, and the safety of groundwater supplies.

5. Estimate of Rayleigh-to-Love wave ratio in the secondary microseism by a small array at Piñon Flat observatory, California

Using closely located seismographs at Piñon Flat (PFO), California, for 1 year long record (2015), we estimated the Rayleigh-to-Love wave energy ratio in the secondary microseism (0.1–0.35 Hz) in four seasons. Rayleigh wave energy was estimated from a vertical component seismograph. Love wave energy was estimated from rotation seismograms that were derived from a small array at PFO. Derived ratios are 2–2.5, meaning that there is 2–2.5 times more Rayleigh wave energy than Love wave energy at PFO. In our previous study at Wettzell, Germany, this ratio was 0.9–1.0, indicating comparable energy between Rayleigh waves and Love waves. This difference suggests that the Rayleigh-to-Love wave ratios in the secondary microseism may differ greatly from region to region. It also implies that an assumption of the diffuse wavefield is not likely to be valid for this low frequency range as the equipartition of energy should make this ratio much closer.

6. Quantifying cloud base updraft speeds of marine stratocumulus from cloud top radiative cooling

Marine stratocumulus clouds play a significant role in the Earth's radiation budget. The updrafts at cloud base (Wb) govern the supersaturation and therefore the activation of cloud condensation nuclei, which modifies the cloud and precipitation properties. A statistically significant relationship between Wb and cloud top radiative cooling rate (CTRC) is found from the measurements of the Department of Energy's Atmospheric Radiation Measurement Mobile Facility on board a ship sailing between Honolulu and Los Angeles. A similar relation was found on Graciosa Island but with greater scatter and weaker correlation presumably due to the island effect. Based on the relation, we are able to estimate the cloud base updrafts using a simple formula:Wb = −0.44 × CTRC + 22.30 ± 13, where the Wb and CTRC have units of cm/s and W/m2, respectively. This quantification can be utilized in satellite remote sensing and parameterizations of Wb in general circulation models.

7. Saturn's quasiperiodic magnetohydrodynamic waves

Quasiperiodic ~1 h fluctuations have been recently reported by numerous instruments on board the Cassini spacecraft. The interpretation of the sources of these fluctuations has remained elusive to date. Here we provide an explanation for the origin of these fluctuations using magnetometer observations. We find that magnetic field fluctuations at high northern latitudes are Alfvénic, with small amplitudes (~0.4nT), and are concentrated in wave packets similar to those observed in Kleindienst et al. (2009). The wave packets recur periodically at the northern magnetic oscillation period. We use a magnetospheric box model to provide an interpretation of the wave periods. Our model results suggest that the observed magnetic fluctuations are second harmonic Alfvén waves standing between the northern and southern ionospheres in Saturn's outer magnetosphere.

8. Assessing the relative effects of emissions, climate means, and variability on large water supply systems

Some of the greatest societal risks of climate change rise from the potential impacts to water supply. Yet prescribing adaptation policies in the near term is made difficult by the uncertainty in climate projections at relevant spatial scales and the conflating effects of uncertainties in emissions, model error, and internal variability. In this work, a new framework is implemented to explore the vulnerability of reservoir systems in the northeastern U.S. to climate change and attribute vulnerabilities to changes in mean climate, natural variability, or emission scenarios. Analysis of variance is used to explore the contributions of uncertainties to system performance. Diagnosing the relative risks to water supply will help water resource engineers better adapt to uncertain future conditions. The results indicate that uncertainty in water supply system performance can be attributed mostly to uncertainty in internal variability over policy-relevant planning horizons, and thus, adaptation efforts should focus on managing variability.

9. Identification of OSSO as a near-UV absorber in the Venusian atmosphere

The planet Venus exhibits atmospheric absorption in the 320–400 nm wavelength range produced by unknown chemistry. We investigate electronic transitions in molecules that may exist in the atmosphere of Venus. We identify two different S2O2isomers, cis-OSSO and trans-OSSO, which are formed in significant amounts and are removed predominantly by near-UV photolysis. We estimate the rate of photolysis ofcis- and trans-OSSO in the Venusian atmosphere and find that they are good candidates to explain the enigmatic 320–400 nm near-UV absorption. Between 58 and 70 km, the calculated OSSO concentrations are similar to those of sulfur monoxide (SO), generally thought to be the second most abundant sulfur oxide on Venus.

VII.Earth and space science

1. Rare molecule on Venus could shed light on planet’s weather

Scientists’ keen detective work may have solved one of Venus’s oldest secrets: why the planet’s atmosphere absorbs a specific frequency of ultraviolet light. The new findings could help scientists better understand Venus’s thick atmosphere and its heat-trapping clouds, according to the study’s authors.



WASHINGTON, DC — Discover the latest Earth and space science news at the 49th annual AGU Fall Meeting this December, when about 24,000 attendees from around the globe are expected to assemble for the largest worldwide conference in the Earth and space sciences. This year, the meeting runs Monday through Friday, Dec. 12-16, 2016 at the Moscone Center, 747 Howard St., San Francisco, California.