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Geophysical Research Letters

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
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
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
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
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
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
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
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
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
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
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
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
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
D Schmid, R Nakamura, M Volwerk, F Plaschke, Y Narita, W Baumjohann, W Magnes, D Fischer, H U Eichelberger, R B Torbert, C T Russell, R J Strangeway, H K Leinweber, G Le, K R Bromund, B J Anderson, J A Slavin, E L Kepko
We present a statistical study of dipolarization fronts (DFs), using magnetic field data from MMS and Cluster, at radial distances below 12 R E and 20 R E , respectively. Assuming that the DFs have a semicircular cross section and are propelled by the magnetic tension force, we used multispacecraft observations to determine the DF velocities. About three quarters of the DFs propagate earthward and about one quarter tailward. Generally, MMS is in a more dipolar magnetic field region and observes larger-amplitude DFs than Cluster...
June 28, 2016: Geophysical Research Letters
R Nakamura, V A Sergeev, W Baumjohann, F Plaschke, W Magnes, D Fischer, A Varsani, D Schmid, T K M Nakamura, C T Russell, R J Strangeway, H K Leinweber, G Le, K R Bromund, C J Pollock, B L Giles, J C Dorelli, D J Gershman, W Paterson, L A Avanov, S A Fuselier, K Genestreti, J L Burch, R B Torbert, M Chutter, M R Argall, B J Anderson, P-A Lindqvist, G T Marklund, Y V Khotyaintsev, B H Mauk, I J Cohen, D N Baker, A N Jaynes, R E Ergun, H J Singer, J A Slavin, E L Kepko, T E Moore, B Lavraud, V Coffey, Y Saito
We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion...
May 28, 2016: Geophysical Research Letters
J P Eastwood, T D Phan, P A Cassak, D J Gershman, C Haggerty, K Malakit, M A Shay, R Mistry, M Øieroset, C T Russell, J A Slavin, M R Argall, L A Avanov, J L Burch, L J Chen, J C Dorelli, R E Ergun, B L Giles, Y Khotyaintsev, B Lavraud, P A Lindqvist, T E Moore, R Nakamura, W Paterson, C Pollock, R J Strangeway, R B Torbert, S Wang
New Magnetospheric Multiscale (MMS) observations of small-scale (~7 ion inertial length radius) flux transfer events (FTEs) at the dayside magnetopause are reported. The 10 km MMS tetrahedron size enables their structure and properties to be calculated using a variety of multispacecraft techniques, allowing them to be identified as flux ropes, whose flux content is small (~22 kWb). The current density, calculated using plasma and magnetic field measurements independently, is found to be filamentary. Intercomparison of the plasma moments with electric and magnetic field measurements reveals structured non-frozen-in ion behavior...
May 28, 2016: Geophysical Research Letters
T D Pering, A J S McGonigle, M R James, G Tamburello, A Aiuppa, D Delle Donne, M Ripepe
Recent gas flux measurements have shown that Strombolian explosions are often followed by periods of elevated flux, or "gas codas," with durations of order a minute. Here we present UV camera data from 200 events recorded at Stromboli volcano to constrain the nature of these codas for the first time, providing estimates for combined explosion plus coda SO2 masses of ≈18-225 kg. Numerical simulations of gas slug ascent show that substantial proportions of the initial gas mass can be distributed into a train of "daughter bubbles" released from the base of the slug, which we suggest, generate the codas, on bursting at the surface...
May 28, 2016: Geophysical Research Letters
Nicholas J Byrne, Theodore G Shepherd, Tim Woollings, R Alan Plumb
Lagged correlation analysis is often used to infer intraseasonal dynamical effects but is known to be affected by nonstationarity. We highlight a pronounced quasi 2 year peak in the anomalous zonal wind and eddy momentum flux convergence power spectra in the Southern Hemisphere, which is prima facie evidence for nonstationarity. We then investigate the consequences of this nonstationarity for the Southern Annular Mode and for eddy momentum flux convergence. We argue that positive lagged correlations previously attributed to the existence of an eddy feedback are more plausibly attributed to nonstationary interannual variability external to any potential feedback process in the midlatitude troposphere...
April 28, 2016: Geophysical Research Letters
J Dong, X Xiao, G Zhang, M A Menarguez, C Y Choi, Y Qin, P Luo, Y Zhang, B Moore
Paddy rice in monsoon Asia plays an important role in global food security and climate change. Here we documented annual dynamics of paddy rice areas in the northern frontier of Asia, including Northeastern (NE) China, North Korea, South Korea, and Japan, from 2000-2014 through analysis of satellite images. The paddy rice area has increased by 120% (2.5 to 5.5 million ha) in NE China, in comparison to a decrease in South Korea and Japan, and the paddy rice centroid shifted northward from 41.16 °N to 43.70 °N (~310 km) in this period...
April 28, 2016: Geophysical Research Letters
L Shen, L J Mickley, E Gilleland
We develop a statistical model using extreme value theory to estimate the 2000-2050 changes in ozone episodes across the United States. We model the relationships between daily maximum temperature (Tmax) and maximum daily 8-hour average (MDA8) ozone in May-September over 2003-2012 using a Point Process (PP) model. At ~20% of the sites, a marked decrease in the ozone-temperature slope occurs at high temperatures, defined as ozone suppression. The PP model sometimes fails to capture ozone-Tmax relationships, and so we refit the ozone-Tmax slope using logistic regression and a Generalized Pareto Distribution model...
April 28, 2016: Geophysical Research Letters
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