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Geophysical Research Letters

G R Gladstone, M H Versteeg, T K Greathouse, V Hue, M W Davis, J-C Gérard, D C Grodent, B Bonfond, J D Nichols, R J Wilson, G B Hospodarsky, S J Bolton, S M Levin, J E P Connerney, A Adriani, W S Kurth, B H Mauk, P Valek, D J McComas, G S Orton, F Bagenal
Juno ultraviolet spectrograph (UVS) observations of Jupiter's aurora obtained during approach are presented. Prior to the bow shock crossing on 24 June 2016, the Juno approach provided a rare opportunity to correlate local solar wind conditions with Jovian auroral emissions. Some of Jupiter's auroral emissions are expected to be controlled or modified by local solar wind conditions. Here we compare synoptic Juno-UVS observations of Jupiter's auroral emissions, acquired during 3-29 June 2016, with in situ solar wind observations, and related Jupiter observations from Earth...
August 16, 2017: Geophysical Research Letters
Sander Goossens, Terence J Sabaka, Antonio Genova, Erwan Mazarico, Joseph B Nicholas, Gregory A Neumann
Knowledge of the average density of the crust of a planet is important in determining its interior structure. The combination of high-resolution gravity and topography data has yielded a low density for the Moon's crust, yet for other terrestrial planets the resolution of the gravity field models has hampered reasonable estimates. By using well-chosen constraints derived from topography during gravity field model determination using satellite tracking data, we show that we can robustly and independently determine the average bulk crustal density directly from the tracking data, using the admittance between topography and imperfect gravity...
August 16, 2017: Geophysical Research Letters
H G Sizemore, T Platz, N Schorghofer, T H Prettyman, M C De Sanctis, D A Crown, N Schmedemann, A Neesemann, T Kneissl, S Marchi, P M Schenk, M T Bland, B E Schmidt, K H G Hughson, F Tosi, F Zambon, S C Mest, R A Yingst, D A Williams, C T Russell, C A Raymond
Prior to the arrival of the Dawn spacecraft at Ceres, the dwarf planet was anticipated to be ice-rich. Searches for morphological features related to ice have been ongoing during Dawn's mission at Ceres. Here we report the identification of pitted terrains associated with fresh Cerean impact craters. The Cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on Mars (where ice is implicated in pit development) and Vesta (where the presence of ice is debated)...
July 16, 2017: Geophysical Research Letters
James L Davis, Nadya T Vinogradova
The tide-gauge record from the North American East Coast reveals significant accelerations in sea level starting in the late twentieth century. The estimated post-1990 accelerations range from near zero to ∼0.3 mm yr(-2). We find that the observed sea level acceleration is well modeled using several processes: mass change in Greenland and Antarctica as measured by the Gravity Recovery and Climate Experiment satellites; ocean dynamic and steric variability provided by the GECCO2 ocean synthesis; and the inverted barometer effect...
May 28, 2017: Geophysical Research Letters
N Rastak, A Pajunoja, J C Acosta Navarro, J Ma, M Song, D G Partridge, A Kirkevåg, Y Leong, W W Hu, N F Taylor, A Lambe, K Cerully, A Bougiatioti, P Liu, R Krejci, T Petäjä, C Percival, P Davidovits, D R Worsnop, A M L Ekman, A Nenes, S Martin, J L Jimenez, D R Collins, D O Topping, A K Bertram, A Zuend, A Virtanen, I Riipinen
A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary organic aerosol (SOA). Isoprene (IP) and monoterpenes (MT) are the most important precursors of SOA originating from forests. The climate impacts from OA are currently estimated through parameterizations of water uptake that drastically simplify the complexity of OA. We combine laboratory experiments, thermodynamic modeling, field observations, and climate modeling to (1) explain the molecular mechanisms behind RH-dependent SOA water-uptake with solubility and phase separation; (2) show that laboratory data on IP- and MT-SOA hygroscopicity are representative of ambient data with corresponding OA source profiles; and (3) demonstrate the sensitivity of the modeled aerosol climate effect to assumed OA water affinity...
May 28, 2017: Geophysical Research Letters
G Le, P J Chi, R J Strangeway, C T Russell, J A Slavin, K Takahashi, H J Singer, B J Anderson, K Bromund, D Fischer, E L Kepko, W Magnes, R Nakamura, F Plaschke, R B Torbert
We report global observations of high-m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m ~ 100)...
April 28, 2017: Geophysical Research Letters
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
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
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
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
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
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
Nancy L Chabot, Carolyn M Ernst, David A Paige, Hari Nair, Brett W Denevi, David T Blewett, Scott L Murchie, Ariel N Deutsch, James W Head, Sean C Solomon
Images obtained during MESSENGER's low-altitude campaign in the final year of the mission provide the highest-spatial-resolution views of Mercury's polar deposits. Images for distinct areas of permanent shadow within 35 north polar craters were successfully captured during the campaign. All of these regions of permanent shadow were found to have low-reflectance surfaces with well-defined boundaries. Additionally, brightness variations across the deposits correlate with variations in the biannual maximum surface temperature across the permanently shadowed regions, supporting the conclusion that multiple volatile organic compounds are contained in Mercury's polar deposits, in addition to water ice...
September 28, 2016: Geophysical Research Letters
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