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  • Articles  (37,762)
  • Wiley  (37,762)
  • 2010-2014  (37,762)
  • Physics  (35,707)
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  • Books
  • Articles  (37,762)
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  • 1
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    Implications of a heuristic model of auroral Farley Buneman waves and heating (2013)
    Wiley
    Details
    Publication Date: 2013-09-07
    Description: [1]  The global implications, particularly with respect to altitude dependence, of the heuristic model of Farley Buneman waves put forward initially by Milikh and Dimant (2002) (see also Dimant and Milikh (2003); Milikh and Dimant (2003)) are studied. This model prescribes a relationship between the background convection electric field that excites the waves and the transverse electric fields of the waves that grow in response. It also prescribes the magnetic aspect angle of the waves, which is related to their ability to heat the auroral E region. The prescription is based on the condition of marginal stability. We reformulate the basic model, which is local, and embed it in the SAMI2 ionospheric model, which includes wave and Joule heating, heat transport, cooling, temperature-dependent collisions, and related chemistry. Within the limits of its underlying assumptions, the combined model can be used to predict the phase speeds and magnetic aspect widths of Farley Buneman waves in the auroral zone and the heating they can cause, all as functions of altitude. Model predictions are compared with experimental results, and the efficacy of the model assessed. This modeling exercise highlights the importance of the thickness of the layer in which Farley Buneman waves exist, the strong variations in wave characteristics across the layer, and the consequences this has for coherent scatter radar measurements of the phenomenon.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Record Neutron Monitor Counting Rates from Galactic Cosmic Rays (2013)
    Wiley
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    Publication Date: 2013-09-07
    Description: [1]  Neutron monitors have recorded the flux of high energy Galactic cosmic rays for more than half a century. During the recent prolonged, deep minimum in solar activity many sources indicate that modulated Galactic cosmic rays have attained new space-age highs. However reported neutron monitor rates are ambiguous; some record new highs while others do not. This work examines the record of 15 long-running neutron monitors to evaluate cosmic ray fluxes during the recent extraordinary solar minimum in a long-term context. We show that ground-level neutron rates did reach a historic high during the recent solar minimum, and we present a new analysis of the cosmic ray energy spectrum in the year 2009 versus year 1987. To do this we define a reference as the average of eight high-latitude neutron monitors, four in the northern hemisphere (Apatity, Inuvik, Oulu, Thule) and four in the southern hemisphere (Kerguelen, McMurdo, Sanae, Terre Adelie). Most stations display changes in sensitivity, which we characterize by a simple linear trend. After correcting for the change in sensitivity, a consistent picture emerges. With our correction all stations considered display new highs at the recent solar minimum, approximately 3% above the previous record high. These increases are shown to be consistent with spacecraft observations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Velocity structure beneath the Southern Puna Plateau: Evidence for delamination (2013)
    Wiley
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    Publication Date: 2013-09-08
    Description: The high elevation of the Southern Puna Plateau, the widespread melting of its crust, the gap in intermediate depth seismicity and the recent eruptions of ignimbrite complexes can be explained by delamination of the lithospheric mantle beneath it. To test this hypothesis, an array consisting of 73 broad band and short period seismic stations was deployed in the region for a period of two years starting in 2007. We inverted the data using the two plane wave approach and obtained 1D and 3D Rayleigh wave phase velocities. Our dispersion curve shows that at short periods (〈70 s) the phase velocities are slightly higher than those of the Tibetan plateau and lower than those of the Anatolian plateau. At periods of 100-140 s we observe a low velocity zone that might be remnant hot asthenosphere below a flat slab (7-10 Ma). We estimate the average continental lithosphere thickness for the region to be between 100 and 130 km. Our three dimensional Rayleigh wave phase velocities show a high velocity anomaly at low frequencies (0.007, 0.008 and 0.009 Hz) slightly to the north of Cerro Galan. This would be consistent with the hypothesis of delamination in which a piece of lithosphere has detached and caused upwelling of hot asthenosphere which in turn caused widespread alkaline-collision related volcanism. This interpretation is also corroborated by our shear wave velocity model where a high velocity anomaly beneath the northern edge of Cerro Galan at 130 km depth is interpreted as the delaminated block on top of the subducting Nazca slab.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    EXPLORING THE FAINT YOUNG SUN PROBLEM AND THE POSSIBLE CLIMATES OF THE ARCHEAN EARTH WITH A 3D GCM (2013)
    Wiley
    Details
    Publication Date: 2013-09-08
    Description: [1]  Different solutions have been proposed to solve the ‘faint young Sun problem’, defined by the fact that the Earth was not fully frozen during the Archean despite the fainter Sun. Most previous studies were performed with simple 1D radiative convective models and did not account well for the clouds and ice-albedo feedback or the atmospheric and oceanic transport of energy. We apply a Global Climate Model (GCM) to test the different solutions to the faint young Sun problem. We explore the effect of greenhouse gases (CO 2 and CH 4 ), atmospheric pressure, cloud droplet size, land distribution and Earth's rotation rate. We show that, neglecting organic haze, 100 mbars of CO 2 with 2 mbars of CH 4 at 3.8 Ga and 10 mbars of CO 2 with 2 mbars of CH 4 at 2.5 Ga allow a temperate climate (mean surface temperature between 10 °C and 20 °C). Such amounts of greenhouse gases remain consistent with the geological data. Removing continents produces a warming lower than +4 °C. The effect of rotation rate is even more limited. Larger droplets (radii of 17  µm versus 12  µm ) and a doubling of the atmospheric pressure produce a similar warming of around +7 °C. In our model, ice-free waterbelts can be maintained up to 25° N/S with less than 1 mbar of CO 2 and no methane. An interesting cloud feedback appears above cold oceans, stopping the glaciation. Such a resistance against full glaciation tends to strongly mitigate the faint young Sun problem.
    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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    The self-sputtered contribution to the lunar exosphere (2013)
    Wiley
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    Publication Date: 2013-09-08
    Description: [1]  The lunar exosphere is produced by a combination of processes including thermal desorption, micrometeoroid bombardment, internal gas release, photon-stimulated desorption, and charged-particle sputtering. Here we investigate an additional mechanism not previously considered for the Moon, namely the role that newly-born ions from the exosphere itself play in sputtering additional neutrals from the lunar surface, known as self-sputtering. Our calculations suggest that this process may sputter neutrals into the lunar exosphere at a rate equal to or greater than charged-particle sputtering due to passage through the Earth's plasma sheet when spatially averaged over the lunar dayside, while locally, self-sputtering may equal or exceed solar wind charged particle sputtering and micrometeoroid bombardment. We use known or modeled densities and distributions of exospheric neutrals, laboratory derived values for the photo-ionization rates and neutral sputtering yields, and knowledge of the ambient electromagnetic environment at the Moon to derive estimates of the self-sputtered neutral flux. We present the spatial variation of the self-sputtered neutral flux and discuss the implications thereof.
    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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    3D Martian Ionosphere model: I. The photochemical ionosphere below 180 km (2013)
    Wiley
    Details
    Publication Date: 2013-09-08
    Description: [1]  We describe the Mars ionosphere with unprecedented detail in 3D, as simulated by a Mars General Circulation Model (the LMD-Mars GCM) and compare it with recent measurements. The model includes a number of recent extensions and improvements. Different simulations for a full Martian year have been performed. The electron density at the main ionospheric peak is shown to vary with the Sun-Mars distance and with the solar variability, both in the long term (11-year solar cycle) and on shorter temporal scales (solar rotation). The main electronic peak is shown to be located at the same pressure level during all the Martian year. As a consequence, its altitude varies with latitude, local time and season according to the natural expansions and fluctuations of the neutral atmosphere, in agreement with previous models. The model predicts a nighttime ionosphere due only to photochemistry. The simulated ionosphere close to the evening terminator is in agreement with observations. No effort has been made to explain the patchy ionosphere observed in the deep nightside. We have compared the modeled ionosphere with MGS and MARSIS data. The model reproduces the SZA variability of the electron density and the altitude of the peak, although it underestimates the electron density at the main peak by about 20%. The electron density at the secondary peak is strongly underestimated by the model, probably due to a very crude representation of the X-ray solar flux. This is one of the aspects that needs a revision in future versions of the model.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Suomi-NPP CrIS Radiometric Calibration Uncertainty (2013)
    Wiley
    Details
    Publication Date: 2013-09-08
    Description: [1]  The Cross-track Infrared Sounder (CrIS) is the high spectral resolution spectroradiometer on the Suomi National Polar-Orbiting Partnership (NPP) satellite, providing operational observations of top-of-atmosphere thermal infrared radiance spectra for weather and climate applications. This paper describes the CrIS radiometric calibration uncertainty based on pre-launch and on-orbit efforts to estimate calibration parameter uncertainties, and provides example results of recent post-launch validation efforts to assess the predicted uncertainty. Pre-launch Radiometric Uncertainty (RU) estimates computed for the laboratory test environment are less than ~0.2 K 3-sigma for blackbody scene temperatures above 250 K, with primary uncertainty contributions from the calibration blackbody temperature, calibration blackbody reflected radiance terms and detector nonlinearity. Variability of the pre-launch RU among the longwave band detectors and midwave band detectors is due to different levels of detector nonlinearity. A methodology for on-orbit adjustment of nonlinearity correction parameters to reduce the overall contribution to RU and to reduce FOV-to-FOV variability is described. The resulting on-orbit RU estimates for Earth view spectra are less than 0.2 K 3-sigma in the midwave and shortwave bands, and less than 0.3 K 3-sigma in the longwave band. Post-launch validation efforts to assess the radiometric calibration of CrIS are underway; validation results to date indicate that the on-orbit RU estimates are representative. CrIS radiance products are expected to reach “Validated” status in early 2014.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Assimilation of T-TREC-Retrieved wind data with WRF 3DVAR for the Short-term forecasting of typhoon meranti (2010) near landfall (2013)
    Wiley
    Details
    Publication Date: 2013-09-08
    Description: [1]  An extended Tracking Radar Echo by Correlation (TREC) technique, called T-TREC technique, has been developed recently to retrieve horizontal circulations within tropical cyclones (TCs) from single Doppler radar reflectivity ( Z ) and radial velocity ( V r , when available) data. This study explores, for the first time, the assimilation of T-TREC-retrieved winds for a landfalling typhoon, Meranti (2010), into a convection-resolving model, the WRF (Weather Research and Forecasting). The T-TREC winds or the original V r data from a single coastal Doppler radar are assimilated at the single time using the WRF 3DVAR, at 8, 6, 4 and 2 hours before the landfall of typhoon Meranti. In general, assimilating T-TREC winds results in better structure and intensity analysis of Meranti than directly assimilating V r data. The subsequent forecasts for the track, intensity, structure and precipitation are also better, although the differences becomes smaller as the V r data coverage improves when the typhoon gets closer to the radar. The ability of the T-TREC retrieval in capturing more accurate and complete vortex circulations in the inner-core region of TC is believed to be the primary reason for its superior performance over direct assimilation of V r data; for the latter, the data coverage is much smaller when the TC is far away and the cross-beam wind component is difficult to analyze accurately with 3DVAR method.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Near-term acceleration of hydroclimatic change in the western U.S. (2013)
    Wiley
    Details
    Publication Date: 2013-09-08
    Description: [1]  Given its large population, vigorous and water-intensive agricultural industry, and important ecological resources, the western United States presents a valuable case study for examining potential near-term changes in regional hydroclimate. Using a high-resolution, hierarchical, five-member ensemble modeling experiment that includes a global climate model (CCSM), a regional climate model (RegCM), and a hydrological model (VIC), we find that increases in greenhouse forcing over the next three decades result in an acceleration of decreases in spring snowpack and a transition to a substantially more liquid-dominated water resources regime. These hydroclimatic changes are associated with increases in cold-season days above freezing and decreases in the cold-season snow-to-precipitation ratio. The changes in the temperature and precipitation regime in turn result in shifts toward earlier snowmelt, baseflow, and runoff dates throughout the region, as well as reduced annual and warm-season snowmelt and runoff. The simulated hydrologic response is dominated by changes in temperature, with the ensemble members exhibiting varying trends in cold-season precipitation over the next three decades, but consistent negative trends in cold-season freeze days, cold-season snow-to-precipitation ratio, and April 1 st snow water equivalent. Given the observed impacts of recent trends in snowpack and snowmelt runoff, the projected acceleration of hydroclimatic change in the western U.S. has important implications for the availability of water for agriculture, hydropower and human consumption, as well as for the risk of wildfire, forest die-off, and loss of riparian habitat.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Assessing high-resolution analysis of surface heat fluxes in the gulf stream region (2013)
    Wiley
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    Publication Date: 2013-09-08
    Description: A satellite-based global analysis of high-resolution (0.25o) ocean surface turbulent latent and sensible heat fluxes was developed by the Objectively Analyzed air-sea Fluxes (OAFlux) project. Resolving air-sea flux down to the order to 0.25o is critical for the description of the air-sea interaction on mesoscale scales. In this study, we evaluate the high-resolution product in depicting air-sea exchange in the eddy-rich Gulf Stream region. Two approaches were used for evaluation, one is point-to-point validation based on six moored buoys in the region, and another is basin-scale analysis in terms of wavenumber spectra and probability density functions (PDFs). An intercomparison is also carried out between OAFlux-0.25o, OAFlux-1o, and four atmospheric reanalyses. Results indicate that OAFlux-0.25 o is able to depict sharp oceanic fronts and has the best performance among the six participating products in comparison with buoy measurements. The mean OAFlux-0.25 o differences in latent and sensible heat flux with respect to the buoy are 7.6 Wm -2 (7.7%) with root-mean-square (RMS) difference of 44.9 Wm -2 , and 0.0 Wm -2 with RMS difference of 19.4 Wm -2 , respectively. Large differences are primarily due to mismatch in SST between gridded data and point measurements when strong spatial gradients are presented. The wavenumber spectra and decorrelation length scale analysis indicate OAFlux-0.25 o depicts eddy variability much better than OAFlux-1 o and the four reanalyses; however, its capability in detecting eddies with smaller scale still needs to be improved. Among the four reanalyses, CFSR stands out as the best in comparison with OAFlux-0.25°.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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