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Geophysical Research Letters

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https://www.readbyqxmd.com/read/28503005/electron-acceleration-during-streamer-collisions-in-air
#1
Christoph Köhn, Olivier Chanrion, Torsten Neubert
High-voltage laboratory experiments show that discharges in air, generated over a gap of one meter with maximal voltage of 1 MV, may produce X-rays with photon energies up to 1 MeV. It has been suggested that the photons are bremsstrahlung from electrons accelerated by the impulsive, enhanced field during collisions of negative and a positive streamers. To explore this process, we have conducted the first self-consistent particle simulations of streamer encounters. Our simulation model is a 2-D, cylindrically symmetric, particle-in-cell code tracing the electron dynamics and solving the space charge fields, with a Monte Carlo scheme accounting for collisions and ionization...
March 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28503004/factors-controlling-the-evaporation-of-secondary-organic-aerosol-from-%C3%AE-pinene-ozonolysis
#2
Taina Yli-Juuti, Aki Pajunoja, Olli-Pekka Tikkanen, Angela Buchholz, Celia Faiola, Olli Väisänen, Liqing Hao, Eetu Kari, Otso Peräkylä, Olga Garmash, Manabu Shiraiwa, Mikael Ehn, Kari Lehtinen, Annele Virtanen
Secondary organic aerosols (SOA) forms a major fraction of organic aerosols in the atmosphere. Knowledge of SOA properties that affect their dynamics in the atmosphere is needed for improving climate models. By combining experimental and modeling techniques, we investigated the factors controlling SOA evaporation under different humidity conditions. Our experiments support the conclusion of particle phase diffusivity limiting the evaporation under dry conditions. Viscosity of particles at dry conditions was estimated to increase several orders of magnitude during evaporation, up to 10(9) Pa s...
March 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28405053/observed-strengthening-of-interbasin-exchange-via-the-indonesian-seas-due-to-rainfall-intensification
#3
Shijian Hu, Janet Sprintall
A proxy of the Indonesian Throughflow (ITF) transport, developed using in situ hydrographic measurements along with assimilations, shows a significant strengthening trend during the past decade. This trend is due to a freshening and subsequent increase in the halosteric component of the ITF transport associated with enhanced rainfall over the Maritime Continent over the same period. The strengthening of the ITF transport leads to a significant change in heat and freshwater exchange between the Pacific and Indian Oceans and contributes to the warming and freshening of the eastern Indian Ocean...
February 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28344367/cross-saharan-transport-of-water-vapor-via-recycled-cold-pool-outflows-from-moist-convection
#4
Tomasz M Trzeciak, Luis Garcia-Carreras, John H Marsham
Very sparse data have previously limited observational studies of meteorological processes in the Sahara. We present an observed case of convectively driven water vapor transport crossing the Sahara over 2.5 days in June 2012, from the Sahel in the south to the Atlas in the north. A daily cycle is observed, with deep convection in the evening generating moist cold pools that fed the next day's convection; the convection then generated new cold pools, providing a vertical recycling of moisture. Trajectories driven by analyses were able to capture the direction of the transport but not its full extent, particularly at night when cold pools are most active, and analyses missed much of the water content of cold pools...
February 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28356606/stratospheric-variability-contributed-to-and-sustained-the-recent-hiatus-in-eurasian-winter-warming
#5
Chaim I Garfinkel, Seok-Woo Son, Kanghyun Song, Valentina Aquila, Luke D Oman
The recent hiatus in global-mean surface temperature warming was characterized by a Eurasian winter cooling trend, and the cause(s) for this cooling is unclear. Here we show that the observed hiatus in Eurasian warming was associated with a recent trend toward weakened stratospheric polar vortices. Specifically, by calculating the change in Eurasian surface air temperature associated with a given vortex weakening, we demonstrate that the recent trend toward weakened polar vortices reduced the anticipated Eurasian warming due to increasing greenhouse gas concentrations...
January 16, 2017: Geophysical Research Letters
https://www.readbyqxmd.com/read/28239205/a-study-of-the-dissociative-recombination-of-cao-with-electrons-implications-for-ca-chemistry-in-the-upper-atmosphere
#6
D L Bones, M Gerding, J Höffner, Juan Carlos Gómez Martín, J M C Plane
The dissociative recombination of CaO(+) ions with electrons has been studied in a flowing afterglow reactor. CaO(+) was generated by the pulsed laser ablation of a Ca target, followed by entrainment in an Ar(+) ion/electron plasma. A kinetic model describing the gas-phase chemistry and diffusion to the reactor walls was fitted to the experimental data, yielding a rate coefficient of (3.0 ± 1.0) × 10(-7) cm(3) molecule(-1) s(-1) at 295 K. This result has two atmospheric implications. First, the surprising observation that the Ca(+)/Fe(+) ratio is ~8 times larger than Ca/Fe between 90 and 100 km in the atmosphere can now be explained quantitatively by the known ion-molecule chemistry of these two metals...
December 28, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28275286/sources-of-cosmic-dust-in-the-earth-s-atmosphere
#7
J D Carrillo-Sánchez, D Nesvorný, P Pokorný, D Janches, J M C Plane
There are four known sources of dust in the inner solar system: Jupiter Family comets, asteroids, Halley Type comets, and Oort Cloud comets. Here we combine the mass, velocity, and radiant distributions of these cosmic dust populations from an astronomical model with a chemical ablation model to estimate the injection rates of Na and Fe into the Earth's upper atmosphere, as well as the flux of cosmic spherules to the surface. Comparing these parameters to lidar observations of the vertical Na and Fe fluxes above 87...
December 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28190903/potential-negative-consequences-of-geoengineering-on-crop-production-a-study-of-indian-groundnut
#8
Huiyi Yang, Steven Dobbie, Julian Ramirez-Villegas, Kuishuang Feng, Andrew J Challinor, Bing Chen, Yao Gao, Lindsay Lee, Yan Yin, Laixiang Sun, James Watson, Ann-Kristin Koehler, Tingting Fan, Sat Ghosh
Geoengineering has been proposed to stabilize global temperature, but its impacts on crop production and stability are not fully understood. A few case studies suggest that certain crops are likely to benefit from solar dimming geoengineering, yet we show that geoengineering is projected to have detrimental effects for groundnut. Using an ensemble of crop-climate model simulations, we illustrate that groundnut yields in India undergo a statistically significant decrease of up to 20% as a result of solar dimming geoengineering relative to RCP4...
November 28, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28190902/constraining-the-kinematics-of-metropolitan-los-angeles-faults-with-a-slip-partitioning-model
#9
S Daout, S Barbot, G Peltzer, M-P Doin, Z Liu, R Jolivet
Due to the limited resolution at depth of geodetic and other geophysical data, the geometry and the loading rate of the ramp-décollement faults below the metropolitan Los Angeles are poorly understood. Here we complement these data by assuming conservation of motion across the Big Bend of the San Andreas Fault. Using a Bayesian approach, we constrain the geometry of the ramp-décollement system from the Mojave block to Los Angeles and propose a partitioning of the convergence with 25.5 ± 0.5 mm/yr and 3...
November 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28239204/closing-the-sea-level-budget-on-a-regional-scale-trends-and-variability-on-the-northwestern-european-continental-shelf
#10
Thomas Frederikse, Riccardo Riva, Marcel Kleinherenbrink, Yoshihide Wada, Michiel van den Broeke, Ben Marzeion
Long-term trends and decadal variability of sea level in the North Sea and along the Norwegian coast have been studied over the period 1958-2014. We model the spatially nonuniform sea level and solid earth response to large-scale ice melt and terrestrial water storage changes. GPS observations, corrected for the solid earth deformation, are used to estimate vertical land motion. We find a clear correlation between sea level in the North Sea and along the Norwegian coast and open ocean steric variability in the Bay of Biscay and west of Portugal, which is consistent with the presence of wind-driven coastally trapped waves...
October 28, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/27917011/an-unprecedented-coastwide-toxic-algal-bloom-linked-to-anomalous-ocean-conditions
#11
Ryan M McCabe, Barbara M Hickey, Raphael M Kudela, Kathi A Lefebvre, Nicolaus G Adams, Brian D Bill, Frances M D Gulland, Richard E Thomson, William P Cochlan, Vera L Trainer
A coastwide bloom of the toxigenic diatom Pseudo-nitzschia in spring 2015 resulted in the largest recorded outbreak of the neurotoxin, domoic acid, along the North American west coast. Elevated toxins were measured in numerous stranded marine mammals and resulted in geographically extensive and prolonged closures of razor clam, rock crab, and Dungeness crab fisheries. We demonstrate that this outbreak was initiated by anomalously warm ocean conditions. Pseudo-nitzschia australis thrived north of its typical range in the warm, nutrient-poor water that spanned the northeast Pacific in early 2015...
October 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/27917010/fragmented-patterns-of-flood-change-across-the-united-states
#12
S A Archfield, R M Hirsch, A Viglione, G Blöschl
Trends in the peak magnitude, frequency, duration, and volume of frequent floods (floods occurring at an average of two events per year relative to a base period) across the United States show large changes; however, few trends are found to be statistically significant. The multidimensional behavior of flood change across the United States can be described by four distinct groups, with streamgages experiencing (1) minimal change, (2) increasing frequency, (3) decreasing frequency, or (4) increases in all flood properties...
October 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/27867237/facets-of-arctic-energy-accumulation-based-on-observations-and-reanalyses-2000-2015
#13
Michael Mayer, Leopold Haimberger, Marianne Pietschnig, Andrea Storto
Various observation- and reanalysis-based estimates of sea ice mass and ocean heat content trends imply that the energy imbalance of the Arctic climate system was similar [1.0 (0.9,1.2) Wm(-2)] to the global ocean average during the 2000-2015 period. Most of this extra heat warmed the ocean, and a comparatively small fraction went into sea ice melt. Poleward energy transports and radiation contributed to this energy increase at varying strengths. On a seasonal scale, stronger radiative energy input during summer associated with the ice-albedo feedback enhances seasonal oceanic heat uptake and sea ice melt...
October 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/27840459/identifying-errors-in-dust-models-from-data-assimilation
#14
R J Pope, J H Marsham, P Knippertz, M E Brooks, A J Roberts
Airborne mineral dust is an important component of the Earth system and is increasingly predicted prognostically in weather and climate models. The recent development of data assimilation for remotely sensed aerosol optical depths (AODs) into models offers a new opportunity to better understand the characteristics and sources of model error. Here we examine assimilation increments from Moderate Resolution Imaging Spectroradiometer AODs over northern Africa in the Met Office global forecast model. The model underpredicts (overpredicts) dust in light (strong) winds, consistent with (submesoscale) mesoscale processes lifting dust in reality but being missed by the model...
September 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/27773954/abrupt-b%C3%A3-lling-warming-and-ice-saddle-collapse-contributions-to-the-meltwater-pulse-1a-rapid-sea-level-rise
#15
Lauren J Gregoire, Bette Otto-Bliesner, Paul J Valdes, Ruza Ivanovic
Elucidating the source(s) of Meltwater Pulse 1a, the largest rapid sea level rise caused by ice melt (14-18 m in less than 340 years, 14,600 years ago), is important for understanding mechanisms of rapid ice melt and the links with abrupt climate change. Here we quantify how much and by what mechanisms the North American ice sheet could have contributed to Meltwater Pulse 1a, by driving an ice sheet model with two transient climate simulations of the last 21,000 years. Ice sheet perturbed physics ensembles were run to account for model uncertainties, constraining ice extent and volume with reconstructions of 21,000 years ago to present...
September 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28408771/was-venus-the-first-habitable-world-of-our-solar-system
#16
M J Way, Anthony D Del Genio, Nancy Y Kiang, Linda E Sohl, David H Grinspoon, Igor Aleinov, Maxwell Kelley, Thomas Clune
Present-day Venus is an inhospitable place with surface temperatures approaching 750K and an atmosphere 90 times as thick as Earth's. Billions of years ago the picture may have been very different. We have created a suite of 3-D climate simulations using topographic data from the Magellan mission, solar spectral irradiance estimates for 2.9 and 0.715 Gya, present-day Venus orbital parameters, an ocean volume consistent with current theory, and an atmospheric composition estimated for early Venus. Using these parameters we find that such a world could have had moderate temperatures if Venus had a rotation period slower than ~16 Earth days, despite an incident solar flux 46-70% higher than Earth receives...
August 28, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/27867236/direct-observation-of-the-thermal-demagnetization-of-magnetic-vortex-structures-in-nonideal-magnetite-recorders
#17
Trevor P Almeida, Adrian R Muxworthy, András Kovács, Wyn Williams, Leslei Nagy, Pádraig Ó Conbhuí, Cathrine Frandsen, Radchagrit Supakulopas, Rafal E Dunin-Borkowski
The thermal demagnetization of pseudo-single-domain (PSD) magnetite (Fe3O4) particles, which govern the magnetic signal in many igneous rocks, is examined using off-axis electron holography. Visualization of a vortex structure held by an individual Fe3O4 particle (~250 nm in diameter) during in situ heating is achieved through the construction and examination of magnetic-induction maps. Stepwise demagnetization of the remanence-induced Fe3O4 particle upon heating to above the Curie temperature, performed in a similar fashion to bulk thermal demagnetization measurements, revealed that its vortex state remains stable under heating close to its unblocking temperature and is recovered upon cooling with the same or reversed vorticity...
August 28, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/27773953/small-global-effect-on-terrestrial-net-primary-production-due-to-increased-fossil-fuel-aerosol-emissions-from-east-asia-since-the-turn-of-the-century
#18
M O'Sullivan, A Rap, C L Reddington, D V Spracklen, M Gloor, W Buermann
The global terrestrial carbon sink has increased since the start of this century at a time of growing carbon emissions from fossil fuel burning. Here we test the hypothesis that increases in atmospheric aerosols from fossil fuel burning enhanced the diffuse light fraction and the efficiency of plant carbon uptake. Using a combination of models, we estimate that at global scale changes in light regimes from fossil fuel aerosol emissions had only a small negative effect on the increase in terrestrial net primary production over the period 1998-2010...
August 16, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/27773952/spatially-resolved-so2-flux-emissions-from-mt-etna
#19
R D'Aleo, M Bitetto, D Delle Donne, G Tamburello, A Battaglia, M Coltelli, D Patanè, M Prestifilippo, M Sciotto, A Aiuppa
We report on a systematic record of SO2 flux emissions from individual vents of Etna volcano (Sicily), which we obtained using a permanent UV camera network. Observations were carried out in summer 2014, a period encompassing two eruptive episodes of the New South East Crater (NSEC) and a fissure-fed eruption in the upper Valle del Bove. We demonstrate that our vent-resolved SO2 flux time series allow capturing shifts in activity from one vent to another and contribute to our understanding of Etna's shallow plumbing system structure...
July 28, 2016: Geophysical Research Letters
https://www.readbyqxmd.com/read/28503003/characterization-of-moderate-ash-and-gas-explosions-at-santiaguito-volcano-guatemala-from-infrasound-waveform-inversion-and-thermal-infrared-measurements
#20
S De Angelis, O D Lamb, A Lamur, A J Hornby, F W von Aulock, G Chigna, Y Lavallée, A Rietbrock
The rapid discharge of gas and rock fragments during volcanic eruptions generates acoustic infrasound. Here we present results from the inversion of infrasound signals associated with small and moderate gas-and-ash explosions at Santiaguito volcano, Guatemala, to retrieve the time history of mass eruption rate at the vent. Acoustic waveform inversion is complemented by analyses of thermal infrared imagery to constrain the volume and rise dynamics of the eruption plume. Finally, we combine results from the two methods in order to assess the bulk density of the erupted mixture, constrain the timing of the transition from a momentum-driven jet to a buoyant plume, and to evaluate the relative volume fractions of ash and gas during the initial thrust phase...
June 28, 2016: Geophysical Research Letters
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