• Issue
    Volume 44, Issue 13
    6471-7094
    16 July 2017

Issue Information

Free Access

Issue Information

  • Pages: 6471-6475
  • First Published: 25 July 2017

Research Letters

Space Sciences

Open Access

Juno/JEDI observations of 0.01 to >10 MeV energetic ions in the Jovian auroral regions: Anticipating a source for polar X-ray emission

  • Pages: 6476-6482
  • First Published: 26 May 2017
Key Points

  • JEDI observed heavy ions to energies >10 MeV precipitating over the northern and southern auroral regions
  • The heavy ion intensity is too low to produce the polar X-rays
  • JEDI observed a strong transient signature of heavy ions with mass between those of sulfur and oxygen

Free Access

VLF waves from ground-based transmitters observed by the Van Allen Probes: Statistical model and effects on plasmaspheric electrons

  • Pages: 6483-6491
  • First Published: 23 June 2017
Key Points

  • Statistical model of VLF (10-60 kHz) waves from ground-based transmitters in the plasmasphere using the Van Allen Probes
  • Average VLF wave power varies with L, MLT, local season, and geomagnetic activity
  • VLF waves from transmitters play a key role in energetic electron loss at low L

Free Access

Explaining the rolling-pin distribution of suprathermal electrons behind dipolarization fronts

  • Pages: 6492-6499
  • First Published: 21 June 2017
Key Points

  • The rolling pin distribution of suprathermal electrons is studied
  • It is a consequence of global-Fermi and local-betatron acceleration
  • It can only be formed at energies higher than 26 keV

Free Access

On the nonstationarity of collisionless shocks and its impact on deriving the cross-shock potential

  • Pages: 6500-6507
  • First Published: 14 June 2017
Key Points

  • Concept of the adaptive deHoffmann-Teller frame, appropriate to derive the cross-shock potential of nonstationary collisionless shocks
  • Illustration by a moderately high Mach number low-beta simulation of a quasi-perpendicular shock where nonstationarity dominates
  • Electron phase space structures' contribution to magnetic field fluctuations and shock nonstationarity appears to be significant

Open Access

Direction-finding measurements of Jovian low-frequency radio components by Juno near Perijove 1

  • Pages: 6508-6516
  • First Published: 26 June 2017
Key Points

  • We perform direction-finding analysis for Jupiter's low-frequency radio emissions
  • Northern bKOM radio sources are located along high-latitude auroral magnetic field lines
  • Four smooth components provide a proxy of the electron density profiles in Jovian inner magnetosphere

Free Access

MMS observations of oblique small-scale magnetopause flux ropes near the ion diffusion region during weak guide-field reconnection

  • Pages: 6517-6524
  • First Published: 27 June 2017
Key Points

  • A series of five small-scale magnetopause flux ropes was observed near ion diffusion region during reconnection with a small guide field
  • The axes of the flux ropes form a large angle to the guide-field direction and are tilted toward the direction of the reconnecting field
  • Our findings are similar to those obtained from a 3-D kinetic simulation of turbulent simulation

Free Access

Dual E × B flow responses in the dayside ionosphere to a sudden IMF By rotation

  • Pages: 6525-6533
  • First Published: 27 June 2017
Key Points

  • A sudden IMF By rotation produces an immediate dawnward E × B flow in the polar cap with no initial change of duskward E × B auroral zone flow
  • The initial 11 min transition period is followed by a 6–8 min dayside E × B reconfiguration from duskward to dawnward auroral zone flow
  • Auroral zone E × B flow magnitudes correlate with magnetosheath plasma density with no discernible time delay

Free Access
Highlight

The stabilizing effect of collision-induced velocity shear on the ionospheric feedback instability in Earth's magnetosphere

  • Pages: 6534-6542
  • First Published: 11 July 2017
Key Points

  • The ionospheric feedback instability is stabilized due to the strong vertical shear of horizontal ion flow in the E layer
  • The shear distorts initially field-aligned shape of an ionospheric density perturbation causing the perturbation to decay rather than grow
  • Rapid decay of ion-neutral collision frequency with altitude in the Earth's is not captured by available theories of feedback instability

Planets

Free Access

The effect of ilmenite viscosity on the dynamics and evolution of an overturned lunar cumulate mantle

  • Pages: 6543-6552
  • First Published: 14 June 2017
Key Points

  • We apply the latest experimental result of ilmenite to the lunar mantle dynamics
  • The weak ilmenite rheology leads to a viscosity reduction of ilmenite-bearing cumulates
  • A 1 order magnitude of viscosity reduction in the cumulate mantle causes the upwelling dynamics to a dramatic change

Free Access

The 3-D geological model around Chang'E-3 landing site based on lunar penetrating radar Channel 1 data

  • Pages: 6553-6561
  • First Published: 05 July 2017
Key Points

  • A 3-D geological model with lava flow directions near the Chang'E-3 landing site is presented
  • The homogeneity of Imbrian paleoregolith supports a lunar quiescence period
  • Imaged subsurface structures are similar to those found at Apollo landing sites

Open Access

Shock metamorphism of clay minerals on Mars by meteor impact

  • Pages: 6562-6569
  • First Published: 20 June 2017
Key Points

  • Five clay minerals known to exist on Mars were experimentally shocked from 10 to 40 GPa and products were analyzed with infrared spectroscopy
  • At 10 GPa, chlorite exhibits impact-induced oxidation of Fe, and at 20–30 GPa, kaolinite exhibits signs of structural disorder
  • Laboratory results are applied to infrared remote sensing of clays on Mars

Open Access

Pitted terrains on (1) Ceres and implications for shallow subsurface volatile distribution

  • Pages: 6570-6578
  • First Published: 27 June 2017
Key Points

  • Fresh complex craters on Ceres host distinctive pitted terrains that are morphologically similar to pitted materials on Mars and Vesta
  • Pitted terrains on Ceres likely form via the rapid volatilization of molecular H2O entrained in impact materials
  • Pitted terrains may be common morphological markers of volatile-rich near-surface material in the asteroid belt

Free Access

Large-scale fluid-deposited mineralization in Margaritifer Terra, Mars

  • Pages: 6579-6588
  • First Published: 05 July 2017
Key Points

  • Structurally controlled mineral precipitation is reported at crater floor fractures in Margaritifer Terra, Mars
  • Deposits are most consistent with a sedimentary genesis through subsurface cementation and subaerial hot spring precipitation
  • Ridges have biosignature-preservation potential, and this potential may also apply to similar ridges at the NE Syrtis Mars 2020 landing site

Solid Earth

Open Access

The shallow magma chamber of Stromboli Volcano (Italy)

  • Pages: 6589-6596
  • First Published: 08 May 2017
Key Points

  • First tomographic images of Stromboli's volcanic structures by using active and passive seismic sources
  • Revealed the region beneath Stromboli where magma cumulated at shallow depth and its preferential pathway feeding the present activity
  • The 3-D velocity structure can provide the groundwork for future modelling aimed to enhance the forecast of hazardous volcanic activity

Free Access
Highlight

Two regions of seafloor deformation generated the tsunami for the 13 November 2016, Kaikoura, New Zealand earthquake

  • Pages: 6597-6606
  • First Published: 12 June 2017
Key Points

  • The 2016 Kaikoura earthquake produced tsunami signals that indicate sizeable seafloor deformation in addition to onshore surface ruptures
  • Iterative modeling of teleseismic P and SH waves and regional tide and wave gauge recordings indicates two regions of seafloor deformation
  • Tsunami excitation involved oblique thrusting on the southern Hikurangi megathrust and offshore extension of transpressional faults

Free Access

Ground deformation before the 2015 eruptions of Cotopaxi volcano detected by InSAR

  • Pages: 6607-6615
  • First Published: 09 June 2017
Key Points

  • InSAR supported by CGPS measurements confirm precursory inflation prior to the 2015 eruptions at Cotopaxi volcano
  • Deformation is attributed to an opening sheet intrusion beneath the SW flank that contributed to internal edifice growth
  • Preexisting structures may guide ascending magma under the volcano's SW flank, explaining the noncentrality of the observed deformation

Free Access

Transient slab flattening beneath Colombia

  • Pages: 6616-6623
  • First Published: 14 June 2017
Key Points

  • The flat slab beneath Colombia originally extended much farther south than it does today
  • Volcanic ages suggest that flattening began at ~9 Ma, with full arc cessation by ~6 Ma
  • Modern arc in the south was reestablished after 4 Ma during slab tearing and resteepening

Free Access

Reduced convergence within the Tibetan Plateau by 26 Ma?

  • Pages: 6624-6632
  • First Published: 14 June 2017
Key Points

  • Southern Tibet was around the similar latitude in the early Miocene as it is today
  • N-S convergence at 900–1100 km was concentrated within the interval 55–26 Ma
  • N-S intra-Asia convergence was reduced at ~26 Ma

Free Access

Reawakening of large earthquakes in south central Chile: The 2016 Mw 7.6 Chiloé event

  • Pages: 6633-6640
  • First Published: 19 June 2017
Key Points

  • The 2016 Chiloe earthquake is a sign of the seismic reactivation of the south central Chile megathrust after the Mw 9.5 earthquake of 1960
  • South central Chile has been affected by postseismic viscoelastic relaxation and superinterseismic locking after the 2010 Maule earthquake
  • The Chiloe earthquake broke an ~15 km radius area at ~30 km depth, near the bottom of the seismogenic zone

Free Access

Trench motion-controlled slab morphology and stress variations: Implications for the isolated 2015 Bonin Islands deep earthquake

  • Pages: 6641-6650
  • First Published: 19 June 2017
Key Points

  • Variation in trench retreat velocity controls the observed slab morphology in Izu-Bonin subduction zone
  • The 30 May 2015 Bonin Islands earthquake may be explained as the result of Pacific slab buckling due to slow trench retreat
  • Subducted slab is inherently heterogeneous due to nonlinear viscosity, contributing to the occurrences of isolated deep earthquakes

Free Access

Crustal structure across the eastern North American margin from ambient noise tomography

  • Pages: 6651-6657
  • First Published: 19 June 2017
Key Points

  • We use ambient noise tomography at both onland and offshore stations to examine crustal structure across the eastern North American margin
  • We observe three structural portions of the passive ENAM: continental crust, transitional crust, and oceanic crust
  • The East Coast magnetic anomaly demarks the boundary between continental and oceanic crustal material

Free Access

Solute mixing regulates heterogeneity of mineral precipitation in porous media

  • Pages: 6658-6666
  • First Published: 20 June 2017
Key Points

  • The mode of solute mixing strongly governs the rate and pattern of mineral precipitation and promotes anisotropic permeability evolution
  • Mineral deposition decreases the median pore size and increases the skewness of the pore size distribution while preserving its unimodality
  • Similar evolution of pore clogging patterns under two mixing modes shows the strong role of local pore geometry and supersaturation state

Free Access

The recrystallized grain size piezometer for quartz: An EBSD-based calibration

  • Pages: 6667-6674
  • First Published: 21 June 2017
Key Points

  • We introduce a routine for separating relict and recrystallized grains based on characterizing intragranular lattice distortion
  • Grain size data from EBSD and light optical microscopy are compared to explore the effect of resolution on grain size measurements
  • We define two EBSD-based recrystallized grain size paleopiezometers for quartz

Free Access

Influences on the location of repeating earthquakes determined from a and b value imaging

  • Pages: 6675-6682
  • First Published: 21 June 2017
Key Points

  • We explore where earthquakes tend to recur using frequency-magnitude distribution
  • Repeating earthquakes occur within areas with high a values ~3 and high b values ~1
  • The productivity of microearthquakes is the key factor controlling the location of repeating earthquakes

Free Access

Tectonic tremor and LFEs on a reverse fault in Taiwan

  • Pages: 6683-6691
  • First Published: 16 June 2017
Key Points

  • Method to find new low-frequency earthquake (LFE) templates
  • Triggered and ambient tremor share a common source
  • LFEs and therefore tremor locate on the deep extension of the Chaochou-Lishan Fault

Free Access

Propagation and arrest of dikes under topography: Models applied to the 2014 Bardarbunga (Iceland) rifting event

  • Pages: 6692-6701
  • First Published: 20 June 2017
Key Points

  • Recent diking events along rift zones showed that dikes can propagate laterally for tens of kilometers arresting before reliefs
  • Analogue models show that topographic lateral pressure gradient and crustal rigidity layering assist lateral propagation
  • Numerical models show that the stress field induced by topography leads to dike arrest

Free Access

A hot midmantle anomaly in the area of the Indian Ocean Geoid Low

  • Pages: 6702-6711
  • First Published: 27 June 2017
Key Points

  • PP and SS precursors are used to investigate the topography of mantle transition zone discontinuities beneath the Indian Ocean Geoid Low
  • A hot midmantle anomaly is found beneath the center of the geoid low and a cold anomaly below the transition zone farther south
  • Superposition of the effects of a hot midmantle anomaly and a cold lower mantle anomaly cause the large Indian Ocean Geoid Low

Free Access

Seismic characteristics of supershear and sub-Rayleigh earthquakes: Implication from simple cases

  • Pages: 6712-6717
  • First Published: 28 June 2017
Key Points

  • The common conclusion that supershear earthquake transmits farther distance than subshear one is confirmed by numerical simulations
  • Shaking of subshear earthquake is more intensive than that of supershear one at short distance to the fault plane
  • The supershear earthquake has relatively quiet aftershock potential based on Coulomb failure stress analysis

Open Access

The fracture energy of ruptures driven by flash heating

  • Pages: 6718-6725
  • First Published: 05 July 2017
Key Points

  • We compute the fracture energy associated with flash heating in an updated model accounting for bulk thermal effects
  • Flash heating explains laboratory friction data obtained under imposed slip rate conditions
  • The fracture energy for flash heating during earthquakes is small compared to thermal pressurization and off-fault energy dissipation

Free Access

Global rates of mantle serpentinization and H2 production at oceanic transform faults in 3-D geodynamic models

  • Pages: 6726-6734
  • First Published: 05 July 2017
Key Points

  • 3-D simulations predict intense mantle serpentinization and H2 production at oceanic transform faults
  • Rates of serpentinization and H2 production increase with fault length and are maximum at intermediate slip rates
  • Mid-ocean ridges and oceanic transform faults produce similar amounts of H2 by mantle serpentinization reactions

Free Access

Mantle flow through a tear in the Nazca slab inferred from shear wave splitting

  • Pages: 6735-6742
  • First Published: 05 July 2017
Key Points

  • Splitting at ESP and SIEMBRA stations is dominantly Nazca plate-motion parallel, regardless of how much mantle wedge material is sampled
  • Plate-motion-parallel subslab anisotropy is only seen below the flat slab, with trench-parallel anisotropy to both the north and south
  • Mantle material flows through the tear in the subducting Nazca slab connecting dynamics in the subslab mantle and mantle wedge.

Free Access

Three-dimensional density structure of La Soufrière de Guadeloupe lava dome from simultaneous muon radiographies and gravity data

  • Pages: 6743-6751
  • First Published: 10 July 2017
Key Points

  • We simultaneously image the La Soufrière de Guadeloupe lava dome with three muon telescopes aiming at the volcano from different locations
  • We jointly invert the multitelescope muon data with gravity data to retrieve the three-dimensional density distribution in the dome
  • We find a low-density, mechanically weak region where the hydrothermal system is most active, suggestive of an edifice collapse hazard

Free Access

From velocity and attenuation tomography to rock physical modeling: Inferences on fluid-driven earthquake processes at the Irpinia fault system in southern Italy

  • Pages: 6752-6760
  • First Published: 24 April 2017
Key Points

  • Three-dimensional attenuation images and rock properties of the crustal volume embedding the fault system associated with the destructive Ms 6.9, 1980 Irpinia earthquake
  • Evidence for a fractured and fluid-saturated medium, with the presence of brine-CO2 and CH4-CO2
  • Pore pressure increase is the dominant mechanisms triggering and controlling the microseismicity

Free Access

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

  • Pages: 6761-6770
  • First Published: 08 May 2017
Key Points

  • Injection-induced stress tensor rotations can be used to estimate the differential stress
  • Controlling factors for stress rotation are permeability, initial differential stress, and injection rate
  • Thermal effects have no significant influence on stress rotations

Free Access

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

  • Pages: 6771-6777
  • First Published: 05 July 2017
Key Points

  • Seven volcanic episodes of unrest took place at El Hierro Island between 2011 and 2014
  • In some of the episodes of unrest, a time lag is observed between the acceleration phases of deformation and seismicity
  • Logarithm of both intruded volume and seismic energy released corresponding to all the episodes of unrest shows a linear correlation

Open Access

Geodetic model of the 2016 Central Italy earthquake sequence inferred from InSAR and GPS data

  • Pages: 6778-6787
  • First Published: 06 July 2017
Key Points

  • Coseismic ground deformation of the 2016 Central Italy earthquake sequence measured with InSAR and GPS data
  • At least four main normal fault segments played an active role in the sequence
  • Antithetic faults and/or preexisting compressional structures may have been reactivated during the sequence with extensional kinematics

Commentaries

Solid Earth

Free Access

Reconciling the deformational dichotomy of the 2016 Mw 7.8 Kaikoura New Zealand earthquake

  • Pages: 6788-6791
  • First Published: 12 June 2017
Key Points

  • Complex Kaikoura earthquake ruptured subduction interface and produced large surface offsets on crustal strike-slip faults
  • Bai et al. (2017) demonstrate that tsunami observations imply coseismic slip occurred on the shallow megathrust
  • Combining multiple geophysical observations helps constrain nature of earthquake rupture process

Free Access

Stress in recrystallized quartz by electron backscatter diffraction mapping

  • Pages: 6792-6794
  • First Published: 21 June 2017
Key Points

  • Cross et al. present a quartz piezometer calibrated by EBSD
  • Recrystallized grains are distinguished from old grains by the cumulative misorientation
  • EBSD calibrated piezometer for quartz reproduces within error previous piezometer in optical microscopy with the same samples and conditions

Research Letters

Hydrology and Land Surface Studies

Free Access

Constrained variability of modeled T:ET ratio across biomes

  • Pages: 6795-6803
  • First Published: 19 June 2017
Key Points

  • Mechanistic modeling constrains T:ET ratio across biomes to 70 ± 9%
  • T:ET ratio across biomes does not depend on precipitation, wetness index, and leaf area index
  • Evaporation from ground and from interception have compensatory effects

Open Access

Multi vegetation model evaluation of the Green Sahara climate regime

  • Pages: 6804-6813
  • First Published: 12 June 2017
Key Points

  • First systematic dynamic vegetation model evaluation of the Green Sahara climate regime such as the mid-Holocene and Last Interglacial
  • Three different dynamic vegetation models show a range of rainfall required to green the Sahara, largely caused by intermodel differences in moisture stress formulations
  • All models require that mid-Holocene rainfall likely exceeded that inferred from pollen assemblages, averaging 500–800 mm over 20°–25°N

Free Access

Attribution of surface temperature anomalies induced by land use and land cover changes

  • Pages: 6814-6822
  • First Published: 27 June 2017
Key Points

  • A widely used method for attributing surface temperature changes assumes that the Bowen ratio is independent of aerodynamic resistance
  • The independence assumption leads to an overestimation of the impact of aerodynamic resistance
  • A new method that does not invoke the assumption of independence between the Bowen ratio and aerodynamic resistance is proposed

Free Access

Assimilating satellite-based canopy height within an ecosystem model to estimate aboveground forest biomass

  • Pages: 6823-6832
  • First Published: 05 July 2017
Key Points

  • The global ORCHIDEE ecosystem model is suitable for assimilating remotely sensed forest structure data to estimates AGB in tropical forests
  • The FOTO-Pleiades products used for the assimilation system bear too large systematic errors to retrieve the fine-scale structure of AGB
  • Most of the systematic errors related to ORCHIDEE-CAN could be reduced by improving the allometric equations

Free Access

Partitioning evapotranspiration using long-term carbon dioxide and water vapor fluxes

  • Pages: 6833-6840
  • First Published: 27 June 2017
Key Points

  • A new method is developed to partition ET using multiyear carbon and water flux measurements
  • The method is applied to semiarid sites and shows that E peaks at the start of rainy season and declines as the growing season progresses
  • Magnitudes and trends in E and T/ET are consistent with field observations and known effects from surface and climate controls

Free Access

Water stress detection in the Amazon using radar

  • Pages: 6841-6849
  • First Published: 06 July 2017
Key Points

  • Simultaneous ground measurements of tree water status and RapidScat backscatter
  • Diurnal variation in backscatter differs during wet and dry seasons
  • Radar backscatter is sensitive to tree water stress in Amazon

Free Access

A multiscalar Palmer drought severity index

  • Pages: 6850-6858
  • First Published: 06 July 2017
Key Points

  • A new method that could extend the time scale of PDSI into a wide range was proposed
  • The newly generated multiscalar PDSI presents a more stable behavior in the aspect of frequency distribution than the original version
  • The multiscalar PDSI is capable of capturing the onset, termination, and other evolution processes of droughts at different time scales

The Cryosphere

Free Access

Impacts of El Niño and La Niña on interannual snow accumulation in the Andes: Results from a high-resolution 31 year reanalysis

  • Pages: 6859-6867
  • First Published: 16 June 2017
Key Points

  • Using data assimilation, retrospective high-resolution SWE estimates were generated over the extratropical Andean region
  • SWE over the Andes shows significant temporal variability and a marked contrast between western and eastern watersheds
  • El Niño plays a significant positive role in deep snow accumulations; however, the effects of La Niña in SWE are not as clear

Free Access
Highlight

Unprecedented springtime retreat of Antarctic sea ice in 2016

  • Pages: 6868-6875
  • First Published: 20 June 2017
Key Points

  • During austral spring 2016 total Antarctic sea ice extent decreased at a record rate that was 18% faster than previously observed
  • The most anomalous sea ice retreat took place during November and in the Weddell and Ross Sea sectors
  • Record surface pressure anomalies occurred during spring, with the most negative November Southern Annular Mode index since 1968

Open Access
Highlight

Glacierized headwater streams as aquifer recharge corridors, subarctic Alaska

  • Pages: 6876-6885
  • First Published: 06 July 2017
Key Points

  • Glacier meltwater discharge represents >15% of total annual streamflow in a subarctic headwater with 3% glacier coverage
  • Headwater streams lose 38 to 56% of annual streamflow to recharge of lowland aquifers
  • Glacier-derived aquifer recharge via headwater streambeds may explain long-term increases in lowland river base flow

Oceans

Open Access

Near-glacier surveying of a subglacial discharge plume: Implications for plume parameterizations

  • Pages: 6886-6894
  • First Published: 15 June 2017
Key Points

  • 3-D structure and transport of a subglacial discharge plume from novel near-glacier surveying
  • Observed plume is inconsistent with axisymmetric plume theory commonly used to model submarine melt and near-glacier circulation
  • Observations point toward a wider plume that drives higher entrainment and more submarine melting

Free Access

El Niño–Southern Oscillation-time scale covariation of sea surface salinity and freshwater flux in the western tropical and northern subtropical Pacific

  • Pages: 6895-6903
  • First Published: 19 June 2017
Key Points

  • We investigated covariation of SSS and freshwater flux in western tropical Pacific and the subsequent behavior in the subtropical region
  • Positive SSS anomalies are induced by freshwater flux reduction east of the Philippines in El Niño and advected to the KE region
  • Negative SSS anomalies are induced by freshwater flux enhancement east of the Philippines in La Niña but are annihilated by evaporation

Free Access

Niche construction by non-diazotrophs for N2 fixers in the eastern tropical North Atlantic Ocean

  • Pages: 6904-6913
  • First Published: 21 June 2017
Key Points

  • Non-diazotrophic cyanobacteria create an environment of excess phosphate for their diazotrophic phylum group members
  • Iron inputs determine the magnitude of nitrogen fixing rates
  • Our findings are a step forward in understanding the biological controls on N2 fixation

Open Access

Indonesian Throughflow drove Australian climate from humid Pliocene to arid Pleistocene

  • Pages: 6914-6925
  • First Published: 22 June 2017
Key Points

  • Northwestern shelf sediments record major shifts in Australian climate at 5.5, 3.3, and 2.4 Ma
  • We interpret NGR-derived proxies as changes in terrestrial climate from annually to seasonally wet
  • Neogene Australian climate is defined by the progressive restriction of ITF by the Maritime Continent

Free Access

On the shape of sea level anomaly signal on periphery of mesoscale ocean eddies

  • Pages: 6926-6932
  • First Published: 26 June 2017
Key Points

  • Alternating rings appear on sea level anomaly eddy composites
  • Nonrandom spatial eddy polarity distribution may cause this signal
  • Interaction between eddies is a possible mechanism for organizing eddies of different polarities

Free Access
Highlight

Particulate concentration and seasonal dynamics in the mesopelagic ocean based on the backscattering coefficient measured with Biogeochemical-Argo floats

  • Pages: 6933-6939
  • First Published: 26 June 2017
Key Points

  • bbp (700) values at 900-950 m are nearly constant in most areas of the oceans
  • Seasonality is observed at high latitudes, and higher values are observed in association with significant O2 minimum zones
  • Values are consistent with measurements of suspended particulate concentrations performed in the 70s

Climate

Free Access

Contribution of urbanization to the increase of extreme heat events in an urban agglomeration in east China

  • Pages: 6940-6950
  • First Published: 06 June 2017
Key Points

  • The observational stations in Yangze River Delta are dynamically classified into urban and rural types to evaluate urbanization effects
  • Urbanization contributes to more than one third of the increase of hot days, warm night, and heat wave intensity
  • Urban stations show more notable shifts to the right in the probability distribution of extreme temperature indices

Free Access

Physical controls of Southern Ocean deep-convection variability in CMIP5 models and the Kiel Climate Model

  • Pages: 6951-6958
  • First Published: 16 June 2017
Key Points

  • Variability of open-ocean deep convection varies widely among climate models with implications reaching beyond the Southern Ocean
  • Stratification influences the timescale of deep-convection variability in these models
  • Sea ice volume affects the models' predominant regime: convective or nonconvective

Free Access

The role of the Southern Hemisphere semiannual oscillation in the development of a precursor to central and eastern Pacific Southern Oscillation warm events

  • Pages: 6959-6965
  • First Published: 20 June 2017
Key Points

  • Variations in the Southern Hemisphere semiannual oscillation can affect El Niño development
  • A large-amplitude semiannual oscillation can contribute to the development of a strong eastern Pacific El Niño event
  • A small-amplitude semiannual oscillation can contribute to the development of a relatively weak central Pacific El Niño event

Free Access
Highlight

Competing effects of surface albedo and orographic elevated heating on regional climate

  • Pages: 6966-6973
  • First Published: 16 June 2017
Key Points

  • Land surface albedo in nonpolar regions generally increases with surface height
  • The brighter albedo of high surfaces induces cooling that compensates for orographic elevated heating
  • Surfaces with the albedo and elevation of modern peninsular India would enter a local runaway greenhouse regime without ventilation by large-scale winds

Open Access
Highlight

Increasing frequency and duration of Arctic winter warming events

  • Pages: 6974-6983
  • First Published: 10 July 2017
Key Points

  • Arctic winter warming events are a normal part of the Arctic winter climate. Observations of these events date back to the Fram expedition
  • North Pole region typically experiences 10 distinct warming events per winter, compared with 5 in the Pacific Central Arctic
  • Positive trends in the number and duration of Arctic winter warming events (1980–2016), with strongest trends for North Pole domain

Free Access

Reduced ENSO variability at the LGM revealed by an isotope-enabled Earth system model

  • Pages: 6984-6992
  • First Published: 20 June 2017
Key Points

  • Isotope-enabled CESM simulations suggest that ENSO variability at the LGM is most likely weaker than that of the preindustrial
  • Total variance from some IFA reconstructions may only reflect changes in the annual cycle instead of ENSO variability
  • Habitat depth of subsurface foraminifera and their vertical migration can complicate interpretations of subsurface IFA reconstructions

Free Access
Highlight

Long-term Caspian Sea level change

  • Pages: 6993-7001
  • First Published: 21 June 2017
Key Points

  • PER flux-reconstructed Caspian Sea level change agrees remarkably well with tide gauge and satellite measurements
  • Increased evaporation rates over the Caspian Sea play a dominant role in reversing the Caspian Sea level trends during the past 37 years
  • The current Caspian Sea level decline is expected to continue into the foreseeable future, under global warming scenarios

Free Access

Effects of climate oscillations on wildland fire potential in the continental United States

  • Pages: 7002-7010
  • First Published: 27 June 2017
Key Points

  • Cyclostationary empirical orthogonal functions are used to analyze the effects of climate oscillations on wildland fire potential
  • The modulated annual cycle is primarily associated with variations in wildland fire potential in the western U.S. and Florida
  • Effects of El Niño and La Niña are widespread, with the largest changes relative to the mean occurring in the northwest and southeast

Free Access

Regional warming of hot extremes accelerated by surface energy fluxes

  • Pages: 7011-7019
  • First Published: 11 July 2017
Key Points

  • Climate model simulations show distinct hot spots, robust across most CMIP5 models, where daily hot extremes warm faster than mean temperatures
  • Changes in surface energy fluxes, consistent with drying soils, accelerate warming on the day hot extremes occur
  • The spatial patterns of accelerated warming of hot extremes in the CMIP5 models are inconsistent with observations, except over Europe

Atmospheric Science

Open Access

Hourly storm characteristics along the U.S. West Coast: Role of atmospheric rivers in extreme precipitation

  • Pages: 7020-7028
  • First Published: 21 June 2017
Key Points

  • On average, storms in the U.S. West Coast (USWC) and southeast U.S. (SEUS) have the largest precipitation totals in the conterminous U.S.
  • Precipitation totals are more strongly correlated with storm duration in the USWC and with storm maximum intensity in the SEUS
  • The most extreme USWC storms are most often the most persistent atmospheric rivers rather than high-intensity ones

Free Access

Upward negative leaders in positive triggered lightning: Stepping and branching in the initial stage

  • Pages: 7029-7035
  • First Published: 22 June 2017
Key Points

  • First fine observation of upward negative leaders in rare positive rocket-triggered lightning
  • Charge transferred in each step of the upward negative leader was nearly an order of magnitude greater than the upward positive leader
  • Initial extension of the main leader channel was influenced by neighboring branches and even paused

Free Access
Highlight

WINDII airglow observations of wave superposition and the possible association with historical “bright nights”

  • Pages: 7036-7043
  • First Published: 06 June 2017
Key Points

  • Historical accounts of naked-eye “bright nights” have been reported for centuries
  • Candidate airglow bright night events have been identified in the WINDII satellite data set
  • It is found that these are the result of the infrequent superposition of zonal waves of zonal wave numbers 1–4

Free Access

New AIM/CIPS global observations of gravity waves near 50–55 km

  • Pages: 7044-7052
  • First Published: 26 June 2017
Key Points

  • New gravity wave data set from the Aeronomy of Ice in the Mesosphere Cloud Imaging and Particle Size satellite instrument
  • Near-global coverage at 50–55 km altitude for waves with horizontal wavelength from 15 to 600 km and vertical wavelength longer than 15 km
  • New data fill key spatial and temporal gaps in current record and are particularly relevant to vertical propagation of gravity waves

Free Access
Highlight

The free troposphere as a potential source of arctic boundary layer aerosol particles

  • Pages: 7053-7060
  • First Published: 05 July 2017
Key Points

  • High aerosol concentrations were sometimes observed to be in contact with the boundary layer top in the summertime Arctic during ASCOS
  • Free tropospheric aerosol can be transported to the boundary layer by direct entrainment or by cloud-mediated activation and regeneration
  • Aerosol properties measured at the surface may not be a good indicator of aerosol properties in the cloud layer

Free Access

Large biogenic contribution to boundary layer O3-CO regression slope in summer

  • Pages: 7061-7068
  • First Published: 20 June 2017
Key Points

  • Observations show a robust O3-CO regression in the boundary layer in daytime over the eastern U.S. in summer
  • Oxidation of biogenic isoprene makes a significant contribution to the observed boundary layer O3-CO regression slope
  • The consistent enhancement of O3 relative to CO in the boundary layer provides a useful constraint on model photochemistry and emissions

Free Access

Sulfate production by reactive bromine: Implications for the global sulfur and reactive bromine budgets

  • Pages: 7069-7078
  • First Published: 27 June 2017
Key Points

  • Inclusion of HOBr + S(IV) reactions in the model reduces global tropospheric Bry burden by 50%
  • Large fraction of sulfate is produced via HOBr oxidation in the presence of clouds and high HOBr abundance over low-latitude oceans
  • In-cloud sulfate production via HOBr oxidation does not necessarily result in less gas-phase SO2 oxidation

Open Access

Long-term (2005–2014) trends in formaldehyde (HCHO) columns across North America as seen by the OMI satellite instrument: Evidence of changing emissions of volatile organic compounds

  • Pages: 7079-7086
  • First Published: 20 June 2017
Key Points

  • We detect significant HCHO trends over North America from space
  • We see evidence of changing emissions of VOCs from space, in particular from oil/gas operations
  • The impact of declining NOx emissions on HCHO columns is greatest in the southeastern U.S.

Free Access

Connections matter: Updraft merging in organized tropical deep convection

  • Pages: 7087-7094
  • First Published: 28 June 2017
Key Points

  • Cloudy updraft parcels that merge detrain 1.5 km higher on average than those that do not merge
  • Despite similar initial buoyancy, merged parcels are more buoyant than nonmerged during ascent
  • Merging, cloud base area, and initial vertical velocity are independently related to detrainment height