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  • 1
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    Active Volcanism on Venus in the Ganiki Chasma Rift Zone (2015)
    Wiley
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    Publication Date: 2015-05-24
    Description: Venus is known to have been volcanically resurfaced in the last third of Solar System history, and to have undergone a significant decrease in volcanic activity a few hundred million years ago [ Ivanov and Head , 2011, 2013]. However, fundamental questions remain: Is Venus still volcanically active today [ Smrekar et al ., 2010; Bondarenko et al ., 2010; Esposito et al ., 1988; Drossart et al ., 2007], and if so, where and in what geological and geodynamic environment [ Basilevsky , 1993]? Here we show evidence from the vex vmc [ Markiewicz et al ., 2007] for transient bright spots that are consistent with the extrusion of lava flows that locally cause significantly elevated surface temperatures. The very strong spatial correlation of the transient bright spots with the extremely young Ganiki Chasma, their similarity to locations of rift-associated volcanism on Earth [ Franke , 2013], provide strong evidence for their volcanic origin and suggests that Venus is currently geodynamically active.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Influence of Extreme Ultraviolet Irradiance Variations on the Precipitating Ion Flux From MAVEN Observations (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract We study the influence of the solar extreme ultraviolet (EUV) flux intensity on the precipitating ion fluxes as seen by the Solar Wind Ion Analyzer, an energy and angular ion spectrometer aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We defined three periods with significantly different EUV flux intensity (1.6 and 3.2 times the lowest EUV intensity) and compare the precipitating ion flux measured by MAVEN/Solar Wind Ion Analyzer during each period. At low energy [30–650] eV, we find that the median (average) precipitating ion flux during the medium and low EUV periods are, respectively, 1.7 (2.1) and 3 (3.5) times more intense than the flux during the high EUV period. At high energy [650–25,000] eV, a similar trend in the intensity of the precipitating ion flux is observed but with an increase by 50% (46%) and 70% (79%), respectively. A larger EUV flux does therefore not seem to favor heavy ion precipitation into Mars's atmosphere, contrary to modeling prediction and overall expectations.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 3
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    The 2018 Martian Global Dust Storm over the South Polar Region studied with MEx/VMC (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract We study the 2018 Martian Global Dust Storm (GDS 2018) over the Southern Polar Region using images obtained by the Visual Monitoring Camera (VMC) on board Mars Express during June and July 2018. Dust penetrated into the polar cap region but never covered the cap completely, and its spatial distribution was nonhomogeneous and rapidly changing. However, we detected long but narrow aerosol curved arcs with a length of ~ 2,000 – 3,000 km traversing part of the cap and crossing the terminator into the night side. Tracking discrete dust clouds allowed measurements of their motions that were towards the terminator with velocities up to 100 ms‐1. The images of the dust projected into the Martian limb show maximum altitudes of ~ 70 km but with large spatial and temporal variations. We discuss these results in the context of the predictions of a numerical model for dust storm scenario.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 4
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    Sensitivity of net thermal flux to the abundance of trace gases in the lower atmosphere of Venus (2016)
    Wiley
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    Publication Date: 2016-08-21
    Description: We calculated the net thermal flux in the atmosphere of Venus from the surface to 100 km altitude. Our atmospheric model was carefully constructed especially for altitudes below the clouds (〈48 km), using recent CO 2 absorption data. It includes updated collision-induced absorptions in the 〈250 cm −1 , 1200–1500 cm −1 , and 2650–3130 cm −1 wavenumber ranges. We studied sensitivity of the net thermal flux below the clouds on the abundances of trace gases that were varied within the range reported by observations. Our results reveal a considerable effect of trace gases on radiative budget. We successfully simulate net thermal flux profiles measured in situ by the Night and North probes of Pioneer Venus using 20–50 ppmv H 2 O, suggesting that the high H 2 O abundance of 200 ppmv derived in the earlier analysis is not required. Our sensitivity study shows that the trace gases SO 2 , H 2 O, and OCS are effective thermal agents, while CO and HCl influences are rather weak. We suggest that the influence of the former three gases should be taken into account to estimate the net radiative energy in the deep atmosphere.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Ionosphere data assimilation capabilities for representing the high-latitude geomagnetic storm event in September 2011 (2014)
    Wiley
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    Publication Date: 2014-12-04
    Description: Severe geomagnetic storms have a strong impact on space communication and satellite navigation systems. Forecasting the appearance of geomagnetically induced disturbances in the ionosphere is one of the urgent goals of the space weather community. The challenge is that the processes governing the distribution of the crucial ionospheric parameters has a rather poor quantitative description and the models, built using the empirical parameterisations, have limited capabilities for operational purposes. On the other hand, data assimilation techniques are becoming more and more popular for nowcasting the state of the large-scale geophysical systems. We present an example of an ionospheric data assimilation system performance assessment during a strong geomagnetic event, which took place on 26 September 2011. The first-principle model has assimilated slant total electron content measurements from a dense network of ground stations, provided by the Norwegian Mapping Authority. The results have shown satisfactory agreement with independent data and demonstrate that the assimilation model is accurate to about 2–4 TEC units, and can be used for operational purposes in high-latitude regions. The operational system performance assessment is the subject of future work.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Dispersive modeling of the 2009 Samoa tsunami (2012)
    Wiley
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    Publication Date: 2012-08-22
    Description: In this study, we investigate the dispersive effects in the 2009 Samoa tsunami through numerical simulations. The wave propagation is first simulated with a weakly nonlinear and dispersive Boussinesq model and a non-dispersive shallow-water-equations model. Comparison of the numerical results between these models indicates that tsunami propagation is significantly affected by the frequency dispersion east of Tonga Trench. Neglecting dispersive effects results in larger wave heights and speeds. The strong frequency dispersion is primarily attributed to the dramatic variation of water surface elevations generated by the earthquake doublet, and enhanced by the uneven bathymetry in Tonga Trench. Tsunami propagation is also simulated with MOST (“Method of Splitting Tsunamis”), which is based on the shallow water equations but uses numerical dispersion to mimic physical frequency dispersion at operational resolutions. A good agreement is observed between MOST and the Boussinesq model, as well as the field measurements in the leading wave. In the shorter trailing waves, agreement becomes poorer due to the mismatch between numerical and physical dispersions.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 7
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    Solar related variations of the cloud top circulation above Aphrodite Terra from VMC/Venus Express wind fields (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Winds derived by a digital tracking technique from UV (365 nm) images captured by the Venus Monitoring Camera onboard the Venus Express spacecraft from 2006 through 2013 were used to study the atmospheric circulation at cloud top level (70±2 km). This data set allows variations of the wind speed with both latitude and longitude to be studied and establishes their correlation with surface topography as well as local time dependence. Both zonal and meridional wind components show some correlation with topography. The minimum zonal wind speed was found at noon above Ovda Regio (10° S, 93° E), the highest region of Aphrodite Terra, one of the largest highlands in the equatorial region. The area of slow zonal wind extends to at least 30° S and shifts in the direction of superrotation in the afternoon and with increasing latitude (poleward). The observed deceleration of cloud top wind was recently attributed to the interaction of the gravity (mountain) waves generated by Aphrodite Terra with the atmospheric circulation. The present study was performed for different local time over the mountainous longitudes. The deceleration pattern in the zonal wind field is mainly conserved within a few hours around noon. Systematic longitude shift is observed in the afternoon in the direction of the evening terminator. Another area of perturbation of both zonal and meridional wind components is observed in the equatorial region around LT=13‐14 h and may be explained by the solar tide.
    Print ISSN: 2169-9097
    Electronic ISSN: 2169-9100
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Deep-sea observations and modeling of the 2004 Sumatra tsunami in Drake Passage (2011)
    Wiley
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    Publication Date: 2011-08-23
    Description: The 2004 Sumatra tsunami was clearly recorded by two UK bottom pressure gauges, DPN and DPS, deployed in Drake Passage between South America and Antarctica. These open-ocean records were examined to estimate characteristics of the tsunami waves and to compare the results of numerical simulations with the observations. Maximum wave heights measured at these gauges were 4.9 cm at DPN and 7.4 cm at DPS; the travel times from the source area were 19 h 46 min and 19 h 39 min respectively, consistent with the times obtained from the nearby coastal tide gauges. The numerical model described well the frequency content, amplitudes and general structure of the observed waves, with only small time shifts probably related to wave dispersion effects. The shifts were 15 min for DPN and 10 min for DPS, with the modeled waves leading the observations in each case. Further inspection of the simulated and observed records revealed that the identified tsunami waves are related to the second (main) train of waves propagating by the energy conserving route along the mid-ocean ridges, while the first train of waves travelling by the fastest route across the ocean remained unrecognizable in the observed DPS and DPN records and undetectable in the records of coastal tide gauges because of their insignificant amplitudes compared to the background variability.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 9
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    Ionosphere state and parameter estimation using the Ensemble Square Root Filter and the global three-dimensional first-principle model (2012)
    Wiley
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    Publication Date: 2012-07-27
    Description: In the present paper we discuss the setup and the results of series of numerical experiments aiming to recover the E→×B→ plasma drift and neutral wind velocities using the Ensemble Square Root Filter together with the ionospheric numerical model. One of the objectives of the current research was assessing the performance of the upper atmosphere state and parameter ensemble estimation technique in the framework of the Observational System Simulation Experiment (OSSE). The other purpose was to improve calculation accuracy for the major driving forces in the ionosphere and to increase modeling reliability in real-data operational cases. In the current paper we describe the setup of the modeling system used to obtain the presented results. In the first section we introduce the background physics-based model used in the simulations and discuss its main assumptions along with E→×B→ drift and the neutral wind velocity calculation algorithms. Further we present the observations simulation system and describe the data used for assimilation and parameter estimation. We also provide a brief description of the Ensemble Square Root Filter and its application in the current study. In the last few sections the results of the numerical experiments are presented and discussed.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Induced Polarization of Rocks Containing Metallic Particles: Evidence of Passivation Effect (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract We studied the impact of electrical isolation (passivation) of metallic particles on induced polarization (IP) parameters. We carried out laboratory experiments with six synthetic models made of sieved sand mixed with metallic particles. The purpose of this experiment was to understand what mechanism (polarization of positive and negative charge carriers within the particles or interfacial polarization) was responsible for the IP effect. Size and location of passivated zones on the particle surfaces varied from model to model. We observed a decrease of the total chargeability and relaxation time values with the increase of passivated surface. Fully passivated metallic particles showed no IP effect. These data suggest the dominant role of the interface phenomena in IP associated with metallic particles.
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    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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