AGU期刊一周Research Spotlight (Aug 2~Aug 9, 2017)

发布时间:2017-8-11 13:56:44 点击次数:95

I.Climate Change

1. What Caused the Ongoing Flooding on Lake Ontario?

The floodwaters have also affected residents downstream along the Saint Lawrence River. Although politicians quickly blamed regulations, scientists say it was a perfect storm of natural factors.

II. Hazards & Disasters

1. Offshore Wind Turbines Can’t Yet Withstand Category 5 Hurricanes

A new study suggests that more robust turbine design is needed to weather high winds.

2. Caught on Camera: Volcanic Bombs in Flight

A recent paper in Reviews of Geophysics revealed new insights into the flight patterns of solid and molten debris flung out of volcanos during explosive eruptions.

3. Indonesian Cave Reveals Nearly 5,000 Years of Tsunamis

Researchers explore a coastal cave containing layers of sand deposited by 11 prehistoric tsunamis and demonstrate that the time period between massive waves is highly variable.

4. A Test Bed for Coastal and Ocean Modeling

An ocean modeling program is improving our ability to predict circulation along the U.S. West Coast, dead zones and other coastal ecosystem responses, and storm surges in island environments.

5. A Promising New Tool for Forecasting Volcanic Hazards

A new model that simulates the behavior of surging ash clouds may help scientists to better predict the hazards associated with the deadliest type of volcanic flows.

III. Hydrology, Cryosphere & Earth Surface

1. Artificial Snow Could Make Alpine Glacier Grow Again

A retired professor devises a plan and evaluates the cost of saving one town’s signature glacier from climate change.

IV.Planetary Sciences

1. Blending Satellite Data to Monitor Agricultural Water Use

A new technique that merges data gathered by multiple satellites can be used to monitor agricultural water use and improve water quality assessments around the globe.

2. A New Model for River Meanders

A river’s twists and turns are shaped by its past flood events.

V. Global Change

1. The Future Hangs in the (Carbon) Balance

A new study suggests that Canada’s boreal forests could absorb more carbon than they release as climate change progresses.

VI.Geophysical Research Letters

1. Hiatus-like decades in the absence of equatorial Pacific cooling and accelerated global ocean heat uptake

A surface cooling pattern in the equatorial Pacific associated with a negative phase of the Interdecadal Pacific Oscillation is the leading hypothesis to explain the smaller rate of global warming during 1998–2012, with these cooler than normal conditions thought to have accelerated the oceanic heat uptake. Here using a 30-member ensemble simulation of a global Earth system model, we show that in 10% of all simulated decades with a global cooling trend, the eastern equatorial Pacific actually warms. This implies that there is a 1 in 10 chance that decadal hiatus periods may occur without the equatorial Pacific being the dominant pacemaker. In addition, the global ocean heat uptake tends to slow down during hiatus decades implying a fundamentally different global climate feedback factor on decadal time scales than on centennial time scales and calling for caution inferring climate sensitivity from decadal-scale variability.

2. Southern Ocean mesocyclones and polar lows from manually tracked satellite mosaics

A new reference data set of mesocyclone activity over the Southern Ocean has been developed from the manual analysis of high-resolution infrared satellite mosaics for winter 2004. Of the total 1735 mesocyclones which were identified and analyzed, about three quarters were classified as being “polar lows” (i.e., intense systems; see Rasmussen and Turner, 2003). The data set includes mesocyclone track, size, associated cloud vortex type, and background synoptic conditions. Maxima in track density were observed over the Bellingshausen Sea and around East Antarctica and are highly correlated with cyclogenesis regions. A comparison against QuikSCAT and reanalyses wind characteristics shows that the reanalyses, while capturing mesocyclone events, tend to considerably underestimate their wind speed (by up to 10 m s−1). This mesocyclone data set is available as a reference for further analysis of mesocyclones and for the evaluation and development of cyclone-tracking algorithms.

3. Snow accumulation variability on a West Antarctic ice stream observed with GPS reflectometry, 2007–2017

Land ice loss from Antarctica is a significant and accelerating contribution to global sea level rise; however, Antarctic mass balance estimates are complicated by insufficient knowledge of surface mass balance processes such as snow accumulation. Snow accumulation is challenging to observe on a continental scale and in situ data are sparse, so we largely rely on estimates from atmospheric models. Here we employ a novel technique, GPS interferometric reflectometry (GPS-IR), to measure upper (<2 m) firn column thickness changes across a 23-station GPS array in West Antarctica. We compare the results with antenna heights measured in situ to establish the method's daily uncertainty (0.06 m) and with output from two atmospheric reanalysis products to categorize spatial and temporal variability of net snow accumulation. GPS-IR is an effective technique for monitoring surface mass balance processes that can be applied to both historic GPS data sets and future experiments to provide critical in situ observations of processes driving surface height evolution.

4. Medium-scale traveling ionospheric disturbances triggered by Super Typhoon Nepartak (2016)

Two remarkable typhoon-induced traveling ionospheric disturbances (TIDs) with concentric and northwest-southeast (NW-SE) alignments, respectively, associated with concentric gravity waves (CGWs) and ionosphere instabilities possibly seeded by CGWs, were observed in total electron content (TEC) derived from ground-based Global Navigation Satellite System networks in Taiwan and Japan when the Category 5 Super Typhoon Nepartak approached Taiwan on 7 July 2016. The concentric TIDs (CTIDs) first appear with horizontal phase velocities of ~161–200 m/s, horizontal wavelengths of ~160–270 km, and periods of ~15–22 min during 08:00–11:20 UT. Following the CTIDs, the NW-SE aligned nighttime medium-scale TIDs (MSTIDs) are formed on the west edge of the CTIDs over the Taiwan Strait during 11:30–14:00 UT. It is suggested that the MSTIDs are produced by the electrodynamical coupling of Perkins instability and CGW-induced polarization electric fields. This study proposes connections of typhoon-induced CTIDs and subsequently occurring MSTIDs in the low-latitude ionosphere.

5. Quantifying black carbon deposition over the Greenland ice sheet from forest fires in Canada

Black carbon (BC) concentrations observed in 22 snowpits sampled in the northwest sector of the Greenland ice sheet in April 2014 have allowed us to identify a strong and widespread BC aerosol deposition event, which was dated to have accumulated in the pits from two snow storms between 27 July and 2 August 2013. This event comprises a significant portion (57% on average across all pits) of total BC deposition over 10 months (July 2013 to April 2014). Here we link this deposition event to forest fires burning in Canada during summer 2013 using modeling and remote sensing tools. Aerosols were detected by both the Cloud-Aerosol Lidar with Orthogonal Polarization (on board CALIPSO) and Moderate Resolution Imaging Spectroradiometer (Aqua) instruments during transport between Canada and Greenland. We use high-resolution regional chemical transport modeling (WRF-Chem) combined with high-resolution fire emissions (FINNv1.5) to study aerosol emissions, transport, and deposition during this event. The model captures the timing of the BC deposition event and shows that fires in Canada were the main source of deposited BC. However, the model underpredicts BC deposition compared to measurements at all sites by a factor of 2–100. Underprediction of modeled BC deposition originates from uncertainties in fire emissions and model treatment of wet removal of aerosols. Improvements in model descriptions of precipitation scavenging and emissions from wildfires are needed to correctly predict deposition, which is critical for determining the climate impacts of aerosols that originate from fires.

6. A decadal tropical Pacific condition unfavorable to central Pacific El Niño

The frequency of central Pacific (CP) El Niño events displays strong decadal variability but the associated dynamics are unclear. The Interdecadal Pacific Oscillation (IPO) and the tropical Pacific decadal variability (TPDV) are two dominant modes of tropical Pacific decadal variability that can interact with high-frequency activities. Using a 500 year control integration from the Geophysical Fluid Dynamics Laboratory Earth System Model, we find that the difference in mean state between the low-frequency and high-frequency CP El Niño periods is similar to the decadal background condition concurrently contributed by a negative IPO and a positive TPDV. This decadal state features strengthened trade winds west of the International Date Line and anomalous cool sea surface temperatures across the central tropical Pacific. As such, positive zonal advection feedback is difficult to be generated over the central to western tropical Pacific during the CP El Niño developing season, resulting in the low CP El Niño frequency.

VII. AGU Blogs

1. 70-year record shows long-term trend in atmospheric river activity along U.S. West Coast

A new study has identified the climate variation patterns which exert the most influence on atmospheric river activity along the West Coast. One of these patterns is the long-term increasing trend associated with Pacific Ocean warming likely due to human activity.

2. New study details earthquake, flood risk for Eastern European, Central Asian countries

How will future disasters affect countries in Eastern Europe and Central Asia?

Researchers aiming to answer this question used projected changes in population and Gross Domestic Product (GDP) for 33 countries, along with climate, flood and earthquake risk models, to estimate how each country is affected by flooding and earthquakes now and in the future. In addition, the earthquake model was used to estimate fatalities and capital losses from a strong quake.

3. Updates from the Karrat Fjord landslide in Greenland

Updates from the Karrat Fjord landslide in Greenland

In the aftermath of the tsunamigenic landslide in Greenland, which is now widely known as the Karrat Fjord landslide, a number of groups have been working on an analysis of the event. The NSF Rapid Team led by Hermann Fritz have some amazing 3D models online and accessible via a Vimeo page.  This video provides a nice summary of their analysis.




WASHINGTON, DC — The 2017 North American wildfire season has begun. Several American Geophysical Union scientists are available to comment on the science of wildfires and their possible impacts throughout the season, including the connections between climate and wildfires, historical wildfire activity, and wildfire impacts on forest ecosystems.