AGU期刊一周Research Spotlight (July 14~July 19, 2017)

发布时间:2017-7-19 10:19:33 点击次数:103

I. Climate Change

1. Climate Change Indicators Are Not Enough

Extreme events capture the public’s attention, but gradual climate shifts will more profoundly affect civilization and life on Earth. Scientists must get better at conveying this to the public.

II. Hazards & Disasters

1. Algorithm Discerns Where Tweets Came from to Track Disasters

New pilot system that analyzed more than 35 million flood-related Twitter posts to determine their geographic origin might help first responders locate and react more quickly to calamities.

III. Hydrology, Cryosphere & Earth Surface

1. Build Four New U.S. Polar Icebreakers, Report Urges

All of the ships should be “science ready,” whereas one should be “fully science capable,” according to new recommendations from the National Academies of Sciences, Engineering, and Medicine.

IV. Planetary Sciences

1. Signs of Water in a Moon Rock

NASA Solar System Exploration Research Virtual Institute (SSERVI) Lunar Volatiles Workshop; Laurel, Maryland, 15–17 November 2016

2. How Geomagnetic Storms Light Up the Geocorona

After geomagnetic storms, Earth’s corona abruptly increases in hydrogen density. For the first time, serendipitous observations have allowed researchers to investigate why.

V. Biogeosciences

1. Climate Change Could Make Siberia an Attractive Place to Live

Although anticipated warmer temperatures promise to render the region more comfortable for people, the transformation might turn permafrost areas into inhospitable bogs.

2. New Technique Could Help Scientists Track Nitrous Oxide Sources

A long-term study in Switzerland reveals the promise of a new method to determine isotopic composition of the potent greenhouse gas.

VI. Geophysical Research Letters

1. Ice-dammed lake drainage in west Greenland: Drainage pattern and implications on ice flow and bedrock motion

Ice-dammed lakes drain frequently in Greenland, but the impacts of these events differ between sites. Here we study the quasi-cyclic behavior of the ~40 km2 Lake Tininnilik in west Greenland and its impact on ice flow and crustal deformation. Data reveal rapid drainage of 1.83 ± 0.17 km3 of water in less than 7 days in 2010, leading to a speedup of the damming glacier, and an instantaneous modeled elastic bedrock uplift of 18.6 ± 0.1 mm confirmed by an independent lakeside GPS record. Since ice-dammed lakes are common on Greenland, our results highlight the importance of including other sources of surface loading in addition to ice mass change, when assessing glacial isostatic adjustment or elastic rebound using geodetic data. Moreover, the results illustrates a linkage between subglacial discharge and ice surface velocity, important for assessing ice flux, and thus mass balance, in a future warming climate.

2. Glacierized headwater streams as aquifer recharge corridors, subarctic Alaska

Arctic river discharge has increased in recent decades although sources and mechanisms remain debated. Abundant literature documents permafrost thaw and mountain glacier shrinkage over the past decades. Here we link glacier runoff to aquifer recharge via a losing headwater stream in subarctic Interior Alaska. Field measurements in Jarvis Creek (634 km2), a subbasin of the Tanana and Yukon Rivers, show glacier meltwater runoff as a large component (15–28%) of total annual streamflow despite low glacier cover (3%). About half of annual headwater streamflow is lost to the aquifer (38 to 56%). The estimated long-term change in glacier-derived aquifer recharge exceeds the observed increase in Tanana River base flow. Our findings suggest a linkage between glacier wastage, aquifer recharge along the headwater stream corridor, and lowland winter discharge. Accordingly, glacierized headwater streambeds may serve as major aquifer recharge zones in semiarid climates and therefore contributing to year-round base flow of lowland rivers.

3. Time lag between deformation and seismicity along monogenetic volcanic unrest periods: The case of El Hierro Island (Canary Islands)

Between 2011 and 2014 there were at least seven episodes of magmatic intrusion in El Hierro Island, but only the first one led to a submarine eruption in 2011–2012. In order to study the relationship between GPS deformation and seismicity during these episodes, we compare the temporal evolution of the deformation with the cumulative seismic energy released. In some of the episodes both deformation and seismicity evolve in a very similar way, but in others a time lag appears between them, in which the deformation precedes the seismicity. Furthermore, a linear correlation between decimal logarithm of intruded magma volume and decimal logarithm of total seismic energy released along the different episodes has been observed. Therefore, if a future magmatic intrusion in El Hierro Island follows this behavior with a proper time lag, we could have an a priori estimate on the order of magnitude the seismic energy released would reach.

4. Estimation of the differential stress from the stress rotation angle in low permeable rock

Rotations of the principal stress axes are observed as a result of fluid injection into reservoirs. We use a generic, fully coupled 3-D thermo-hydro-mechanical model to investigate systematically the dependence of this stress rotation on different reservoir properties and injection scenarios. We find that permeability, injection rate, and initial differential stress are the key factors, while other reservoir properties only play a negligible role. In particular, we find that thermal effects do not significantly contribute to stress rotations. For reservoir types with usual differential stress and reservoir treatment the occurrence of significant stress rotations is limited to reservoirs with a permeability of less than approximately 10−12 m2. Higher permeability effectively prevents stress rotations to occur. Thus, according to these general findings, the observed principal stress axes rotation can be used as a proxy of the initial differential stress provided that rock permeability and fluid injection rate are known a priori.

5. Medium-scale gravity wave activity in the bottomside F region in tropical regions

Thermospheric gravity waves (GWs) in the bottomside F region have been proposed to play a key role in the generation of equatorial plasma bubbles (EPBs). However, direct observations of such waves are scarce. This study provides a systematic survey of medium-scale (<620 km) neutral atmosphere perturbations at this critical altitude in the tropics, using 4 years of in situ Gravity Field and Steady-State Ocean Circulation Explorer satellite measurements of thermospheric density and zonal wind. The analysis reveals pronounced features on their global distribution and seasonal variability: (1) A prominent three-peak longitudinal structure exists in all seasons, with stronger perturbations over continents than over oceans. (2) Their seasonal variation consists of a primary semiannual oscillations (SAO) and a secondary annual oscillation (AO). The SAO component maximizes around solstices and minimizes around equinoxes, while the AO component maximizes around June solstice. These GW features resemble those of EPBs in spatial distribution but show opposite trend in climatological variations. This may imply that stronger medium-scale GW activity does not always lead to more EPBs. Possible origins of the bottomside GWs are discussed, among which tropical deep convection appears to be most plausible.

VII. AGU Blogs

1. Weathercasters Views of Climate Change Dramatically Shift

The number of weathercasters who are still sceptical of climate change is rapidly dwindling. I’ve noticed this anecdotally and now there is confirmation in a new paper in BAMS that it indeed the case. I know most of the authors of this paper, and it is worth noting that the survey was among weathercasters which include degreed meteorologists with a science background, and those who may have little in the way …

2. We Have No Idea, by Jorge Cham and Daniel Whiteson

Jorge Cham will likely be known to most of the folks who read this blog as the cartoonist behind the spot-on examination of grad school called Piled Higher and Deeper / PhD Comics. If you’ve read this comic, you’ll know that Cham’s visual style is simple and engaging, and his sense of humor is terrific. In a new book about the unknown territory of physics that we still need to nail down, he teams up with Daniel Whiteson, a physicist. The two of them explore issues like dark matter and gravity in a lighthearted but enthusiastic and informative way.

3. Flow-banded rhyolite from Vulcano, Italy

I collected only a single rock on my summer travels in France and Italy. (Those of you who know me will realize how extraordinary this low number is!)

It’s a flow-banded rhyolite from Vulcano, in the Aeolian Islands north of Sicily a few weeks ago. It contains porphyritic vesicular basalt xenoliths.

I featured a similar sample on Twitter yesterday on the occasion (supposedly) of “International Rock Day”: