I. Science Policy
1. Eight Ways to Get Ready for the March for Science
From sending RSVPs to quickly ordering an event T-shirt to finding out about our premarch gathering, AGU members and their families and friends can take steps now to prepare for the 22 April march.
II. Hydrology, Cryosphere & Earth Surface
1. Stream Network Geometry Correlates with Climate
A "big data" analysis of nearly 1 million river junctions in the contiguous United States shows that branching angles in dendritic drainages vary systematically between humid and arid regions.
III. Hazards & Disasters
1. For Magnetic Reconnection Energy, O—not X—Might Mark the Spot
A new analysis of satellite data could upend conventional wisdom about how solar storms produce their dangerous radiation—not from X-shaped mergers of magnetic field lines but from swirling vortices.
2. “Fingerprinting” Volcanic Tremors May Help Forecast Eruptions
Volcano seismic waves produce distinct tremor patterns, or "fingerprints," shared by different kinds of volcanoes.
IV. Climate Change
1. High Arctic Emissions of a Strong Greenhouse Gas
Isotope data bring scientists one step closer to revealing the microbial processes behind nitrous oxide emission in the tundra.
V. Geophysical Research Letters
1. The Great Cold Spot in Jupiter's upper atmosphere
Past observations and modeling of Jupiter's thermosphere have, due to their limited resolution, suggested that heat generated by the aurora near the poles results in a smooth thermal gradient away from these aurorae, indicating a quiescent and diffuse flow of energy within the subauroral thermosphere. Here we discuss Very Large Telescope-Cryogenic High-Resolution IR Echelle Spectrometer observations that reveal a small-scale localized cooling of ~200 K within the nonauroral thermosphere. Using Infrared Telescope Facility NSFCam images, this feature is revealed to be quasi-stable over at least a 15 year period, fixed in magnetic latitude and longitude. The size and shape of this “Great Cold Spot” vary significantly with time, strongly suggesting that it is produced by an aurorally generated weather system: the first direct evidence of a long-term thermospheric vortex in the solar system. We discuss the implications of this spot, comparing it with short-term temperature and density variations at Earth.
2. Unique, non-Earthlike, meteoritic ion behavior in upper atmosphere of Mars
Interplanetary dust particles have long been expected to produce permanent ionospheric metal ion layers at Mars, as on Earth, but the two environments are so different that uncertainty existed as to whether terrestrial-established understanding would apply to Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission made the first in situ detection of the continuous presence of Na+, Mg+, and Fe+ at Mars and indeed revealed non-Earthlike features/processes. There is no separation of the light Mg+ and the heavy Fe+ with increasing altitude as expected for gravity control. The metal ions are well-mixed with the neutral atmosphere at altitudes where no mixing process is expected. Isolated metal ion layers mimicking Earth's sporadic E layers occur despite the lack of a strong magnetic field as required at Earth. Further, the metal ion distributions are coherent enough to always show atmospheric gravity wave signatures. All features and processes are unique to Mars.
3. A dynamical systems approach to studying midlatitude weather extremes
Extreme weather occurrences carry enormous social and economic costs and routinely garner widespread scientific and media coverage. The ability to predict these events is therefore a topic of crucial importance. Here we propose a novel predictability pathway for extreme events, by building upon recent advances in dynamical systems theory. We show that simple dynamical systems metrics can be used to identify sets of large-scale atmospheric flow patterns with similar spatial structure and temporal evolution on time scales of several days to a week. In regions where these patterns favor extreme weather, they afford a particularly good predictability of the extremes. We specifically test this technique on the atmospheric circulation in the North Atlantic region, where it provides predictability of large-scale wintertime surface temperature extremes in Europe up to 1 week in advance.
4. Local increase of anticyclonic wave activity over northern Eurasia under amplified Arctic warming
In an attempt to resolve the controversy as to whether Arctic sea ice loss leads to more midlatitude extremes, a metric of finite-amplitude wave activity is adopted to quantify the midlatitude wave activity and its change during the period of the drastic Arctic sea ice decline in both ERA Interim reanalysis data and a set of Atmospheric Model Intercomparison Project-type of model experiments. Neither the ensemble mean response to the trend in the SST nor that to the declining trend of Arctic sea ice can replicate the sizable midlatitude-wide increase in the total wave activity (Ae) observed in the reanalysis, leaving its explanation to the atmospheric internal variability. On the other hand, both the diagnostics of the flux of the local anticyclonic wave activity (LAWA) and atmospheric general circulation model experiments lend evidence to a possible linkage between the sea ice loss near the Barents and Kara Seas and the increasing trend of LAWA over the northern part of the central Eurasia and the associated impacts on the frequency of temperature extremes.
5. Pore pressure migration during hydraulic stimulation due to permeability enhancement by low-pressure subcritical fracture slip
Understanding the details of pressure migration during hydraulic stimulation is important for the design of an energy extraction system and reservoir management, as well as for the mitigation of hazardous-induced seismicity. Based on microseismic and regional stress information, we estimated the pore pressure increase required to generate shear slip on an existing fracture during stimulation. Spatiotemporal analysis of pore pressure migration revealed that lower pore pressure migrates farther and faster and that higher pore pressure migrates more slowly. These phenomena can be explained by the relationship between fracture permeability and stress state criticality. Subcritical fractures experience shear slip following smaller increases of pore pressure and promote migration of pore pressure because of their enhanced permeability. The difference in migration rates between lower and higher pore pressures suggests that the optimum wellhead pressure is the one that can stimulate relatively permeable fractures, selectively. Its selection optimizes economic benefits and minimizes seismic risk.
6. Aseismic slip and seismogenic coupling in the Marmara Sea: What can we learn from onland geodesy?
Ever since the Mw7.4 Izmit earthquake in 1999, evaluation of seismic hazard associated with the last unbroken segments of the North Anatolian fault is capital. A strong controversy remains over whether Marmara fault segments are locked or are releasing strain aseismically. Using a Bayesian approach, we propose a preliminary probabilistic interseismic model constrained by published GPS data sets. The posterior mean model show that Ganos and Cinarcik segments are locked while creep is detected in the central portion of Marmara fault. Our analysis, however, reveals that creeping segments are associated with large model uncertainties, which mainly results from the sparsity of current geodetic observations. We then discuss how the GPS network can be improved to attain more reliable assessment of interseismic slip rates. With this purpose, we implement a network optimization procedure to identify the most favorable distribution of stations measuring strain accumulation in the Marmara Sea.
7. Rapid decline in river icings detected in Arctic Alaska: Implications for a changing hydrologic cycle and river ecosystems
Arctic river icings are surface ice accumulations that can be >10 km2 in area and >10 m thick. They commonly impact the hydrology, geomorphology, and ecology of Arctic river environments. Previous examination of icing dynamics in Arctic Alaska found no substantial changes in extent through 2005. However, here we use daily time series of satellite imagery for 2000–2015 to demonstrate that the temporal persistence and minimum summertime extent of large icings in part of Arctic Alaska and Canada have declined rapidly. We identified 122 large ephemeral icings, and 70 are disappearing significantly earlier in the summer, with a mean trend of −1.6 ± 0.9 day−1 for fully ephemeral features. Additionally, 14 of 25 icings that usually persist through the summer have significantly smaller minimum extents (−2.6 ± 1.6% yr−1). These declines are remarkably rapid and suggest that Arctic hydroclimatic systems generating icings, and their associated ecosystems, are changing rapidly.
VI. AGU Blogs
1. O marks the spot for magnetic reconnection
ESA’s Cluster mission is challenging the current view of magnetic reconnection – the breaking and immediate rearrangement of magnetic field lines in the collision of two plasma flows. According to a new study, most of the energy dissipated during a reconnection event is not released at the crossings, or X-lines, between the two plasma flows but rather in swirling vortices, or O-lines, where magnetic field lines bundle up and spiral together. The new finding, which contradicts the accepted consensus, is an important step in the process of understanding the mechanisms that accelerate particles in space plasma.
2. Dr Michael Mann on Science Friday
Science Friday had an excellent interview with Penn State Climatologist Michael Mann today, and you can hear it all here. Dr Mann produced the “hockey stick”, which is destined to become one of the most famous images in the history of science, and it’s caused him plenty of grief. If he’d been wrong, it would not have been so bad! Unfortunately for him, he was right, and that made the …
VII. AGU News
1. NASA’S MAVEN MISSION REVEALS MARS HAS METAL IN ITS ATMOSPHERE
WASHINGTON, DC— Mars has electrically charged metal atoms (ions) high in its atmosphere, according to new results fromNASA’s MAVEN spacecraft. The metal ions can reveal previously invisible activity in the mysterious electrically charged upper atmosphere (ionosphere) of Mars.