Current AGU Journal Covers

Current covers of AGU Journals.  For older covers, see the archives of each journal.  High resolution images are available in the issue information PDF of each issue.

Hydrothermal nontronite formation associated with microbes from low-temperature diffuse hydrothermal vents at the South Mid-Atlantic Ridge in JGR: Biogeosciences

Ta et al. reported the formation of hydrothermal nontronite associated with microbes from low-temperature diffuse
hydrothermal vents at the South Mid-Atlantic Ridge. NanoSIMS imaging reveals the bacteria cells (red) are surrounded by nontron
ite (green). The
formation of nontronite may begin with the adsorption of cationic iron in the hydrothermal fluid to anionic cellular surfaces.
Biologically induced
mineralization might be widely responsible for the formation of nontronit
e in modern low-temperature hydrothermal environments.

Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto: Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU in JGR: Space Physics

Image from instruments on SDO, STEREO, and SOHO of the CME that launched from the Sun on 14 October 2014. The CME was observed fromthe Sun all the way to New Horizons at 32 AU, en route to Pluto.

 

Evolution of submarine eruptive activity during the 2011–2012 El Hierro event as documented by hydroacoustic images and remotely operated vehicle observations in G-Cubed

 Image shows ROV images of the hornitos at the summit of the Tagoro volcano: (a) Location on the images on the multibeam bathymetry from the 28 June 2012. (b) Deepest hornito formed by 4–5 m tall pyramid-like of agglutinated lava blocks intermixed with yellow hydrothermal deposits (115 m water depth). (c) Detail of degassing vents (yellow orifices) along the flanks of the chimney interpreted as active hydrothermal vents (118 m water depth). (d) Top of the shallowest “hornito” (89 m water depth) showing abundance of red flocculates covering the lava deposits. (e) Detail of the flank of a hornito showing white bacterial mats. (f ) Detail the tapestry of red to orange amorphous Fe-oxyhydroxide flocculates covering the overall summit of the Tagoro volcanic edifice.

Fidelity of the Sr/Ca proxy in recording ocean temperature in the western Atlantic coral Siderastrea siderea in G-Cubed

In Kufner et al. [DOI: 10.1002/2016GC006640], image shows an example of one of the 39 Siderastrea siderea colonies included in this study (a) attached

to a calcication monitoring block with a temperature logger (black, on left) on the Fowey Rocks reef crest, and (b) slabbed in half showing Alizarin Red-S stain
lines (pink) marking 29 April 2011 (lower line) and 9 May 2012 (upper line). The upper surface of the slab marks the collection date of 16 May 2013. Scale bar
on left of Figure 1b is a cm ruler with mm markings. (c) Inset box from Figure 1b with annual cycle of Sr/Ca in two replicate drill-paths (blue and green lines)
between the stain lines. Y axis is reversed so that Sr/Ca values (mmol mol
–1
) indicating warmer values are up. X axis is time (decimal years).

Horizontal propagation of large-amplitude mountain waves into the polar night jet in JGR: Atmospheres

In Ehard et al. [DOI: 10.1002/2016JD025621], horizontal wind speed (m s−1, color coded) along 170°E on 31 July 2014 at 1200 UTC. The black dashed vertical line denotes the position of Lauder, New Zealand.

Advances in understanding river-groundwater interactions in Reviews of Geophysics

The figure illustrates river water and groundwater interactions at the reach scale (left) and the hyporheic scale (right). These interactions are at the core of a wide
range of major contemporary challenges, including the provision of high-quality drinking water in sufficient quantities, the loss of biodiversity in river ecosystems, or
the management of environmental flow regimes. Brunner et al. [10.1002/2017RG000556] review state of the art approaches in characterizing and modeling river and
groundwater interactions, including remote sensing to characterize the streambed, emerging methods to measure exchange fluxes between rivers and groundwater, and
developments in several disciplines relevant to the river-groundwater interface. These novel approaches show great potential to tackle the most critical water resources
challenges at the watershed scale.

Photon Pressure Force on Space Debris TOPEX/Poseidon Measured by Satellite Laser Ranging in Earth and Space Science

The orientation circles in the orbital coordinate system calculated for 132 amplitudes A measured during the 3 day period (26–29 October 2015). The intersection of the circles indicates the satellite spin axis orientation (az
imuth = 18.7°, elevation = −7.8°);
the position of the orbital perigee is at azimuth = 0°, elevation = 0°.

A PV-approach for dense water formation along fronts: Application to the Northwestern Mediterranean in JGR: Oceans

Giordani et al. [DOI: 10.1002/2016JC012019], intense surface buoyancy losses (–400 W/m2, colour) occurred under the path of Mistral and Tramontane winds (black arrows, N/m2) in the Gulf of Lion (GL) during the ASICS-MED experiment (February 2013). These buoyancy fluxes and positive Ekman pumping (cyan positive, green negative wind-stress curl used as proxy of the Ekman pumping,  N/m3 x 10 5; interval 0.2 x 10–5 N/m3 x 1.105) are key atmospheric conditions for dense water formation (DWF) and preconditioning in the GL. DWF also occurs along the Catalan coast i.e. along the northern branch of the Liguro-Provençal Current where strong horizontal density gradients are present (see brown lines of surface density). DWF results from the coupling between the surface wind stress (black arrows) and lateral buoyancy gradients because this coupling leads to efficient destratification and PV-destruction in frontal regions. As consequence DWF cannot be reduced as a buoyancy flux problem.

Observational properties of dayside throat aurora and implications on the possible generation mechanisms in JGR: Space Physics

Observational properties of a newly discovered auroral form near local noon, called throat aurora, revealing combined contributions from inside and outside of the magnetosphere on the generation. The image gives a schematic summarizing the physical process leading to the formation of throat aurora.

Modeling tabular icebergs submerged in the ocean in JAMES

 Schematic showing how tabular icebergs are constructed using Lagrangian elements. (a) Hierarchy of ice elements’ physical structure: (i) Previous iceberg models represent icebergs using non-interacting point-particle elements; (ii) In the new framework ice elements are given finite extent so that they are able to interact with the ocean across multiple grid cells, and can interact with other elements; (iii) These finite extent elements can be joined together by numerical bonds (magenta lines) to form larger structures such as tabular icebergs. (b) Areal photograph of a tabular iceberg with elements superimposed over it to illustrate how the Lagrangian elements can be used to model tabular icebergs. In this schematic, the ice elements (purple dots) are initialized in a staggered lattice covering the surface area of the iceberg. For purposes of mass aggregation, the ice elements are assumed to have hexagonal shape (red hexagons). For purposes of element interactions, the ice elements are assumed to be circular (black circles). Elements are initially bonded to adjacent elements using numerical bonds (magenta lines). These numerical bonds form equilateral triangles which give the shape rigidity. An ocean grid has been included (dashed cyan lines). The background photo is an areal photograph of iceberg PIIB (Area5 42 km2) taken in Baffin Bay in 2012. A red ship can be identified on the bottom of the photo for scale.

An Optimally Stable and Accurate Second-Order SSP Runge-Kutta IMEX Scheme for Atmospheric Applications in JAMES

 Rokhzad et al studied optimization of dissipation and dispersion errors for two-frequency system of equations using IMEX Runge-Kutta schemes. They found A-stability property to be more useful than L-stability property, more specifically for stiff limits, since A-stability allows to increase the range of stability (first row) and decrease the phase errors (second and third rows), which are related to larger stable time step size and more accurate solutions respectively.

Modeling Seismic Cycles of Great Megathrust Earthquakes Across the Scales With Focus at Postseismic Phase in G-Cubed

Image shows (a)–(f ) Snapshots of the spatial distributions of viscosity (background colors) and velocities (vectors) for the different stages of the seismic cycle from 1 h (a) to century (f ) of the typical earthquake (Mw 9.3)generated by the high-
resolution version of the reference nonlinear transient model. Note different scales of the velocity vectors. The red triangle at the surface indicates the position of the virtual GPS station located about 300 km landward from the trench.

Building the Pamir-Tibetan Plateau—Crustal stacking, extensional collapse, and lateral extrusion in the Central Pamir: 1. Geometry and kinematics in Tectonics

In Rutte et al., image shows (a–d) Panoramic views of the Muskol dome. Distortion increases toward the image edges. Figures 4a and 4b are along section A in Figure 8. Thrusts and north vergent, recumbent, isoclinal folds in Figure 4d are in left part of Figure 4c. (e–h) Fault scarps in colluvial and alluvial deposits and range front normal faults along the active Sarez-Karakul graben system.

Relationship between the direction of diurnal rainfall migration and the ambient wind over the Southern Sumatra Island in Earth and Space Science

In Yanase et al., image shows time-longitude cross sections of the composite surface rain rate from TRMM 2A25 for (a) December, January, and February; (b) March, April, and May; (c) June, July, and August; and (d) September, October, and November

Northern Hemisphere winter warming and summer monsoon reduction after volcanic eruptions over the last millennium in JGR: Atmospheres

Sea level pressure anomalies with respect to the 5 years preceding each eruption (hPa) for the

first winter (DJF) after the 10 largest tropical eruptions spanning 850–1850 (Table 1) for (a) CEA-forced PMIP runs, (b) GRA-forced PMIP runs, (c) CEA-
forced GISS-E2-R runs, (d) 2×GRA-forced GISS-E2-R runs, (e) all-forcing CESM-LME runs, and (f) volcano-only CESM-LME runs. Hatching displays areas
below 95% significance using a two-tailed t test. Contours represent 2 hPa intervals below −2 hPa and above 2 hPa.

Decoupling of coral skeletal δ13C and solar irradiance over the past millennium caused by the oceanic Suess effect in Paleoceanography

In Deng et al., satellite image of Hainan Island and the northern SCS. Yellow stars indicate sampling locations.

Tidal flow separation at protruding beach nourishments in JGR: Oceans

Radermach et al. [DOI: 10.1002/2016JC011942] observed tidal ow separation o the Sand Motor, a mega-scale beach nourishment at the Dutch

coastline. Field measurements and model simulations show that the presence and characteristics of the generated eddies (visible in the suspended matter
concentration in the left picture) depend on a combination of the shape of the coastline perturbation, tidal excursion length and bottom friction. As a result
the eddy intensities at these coastal protection works vary with the spring-neap tidal cycle and their large-scale morphological evolution.

Increased water yield due to the hemlock woolly adelgid infestation in New England in GRL

Two eddy-covariance flux towers at the Harvard Forest in New England where the hemlock woolly adelgid (Adelges tsugae) infestation has resulted in eastern hemlock (Tsuga canadensis) mortality (photo by David A. Orwig).

Relative linkages of stream water quality and environmental health with the land use and hydrologic drivers in the coastal-urban watersheds of southeast Florida in GeoHealth

The estimated linkages of stream water quality with the land use and hydrologic drivers identify the management targets and priorities to achieve healthy coastal-urban stream ecosystems.