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  • Articles  (144)
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  • 1
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    Scientific objectives and capabilities of the Coronal Solar Magnetism Observatory (2016)
    Wiley
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    Publication Date: 2016-07-08
    Description: Magnetic influences increase in importance in the solar atmosphere from the photosphere out into the corona, yet our ability to routinely measure magnetic fields in the outer solar atmosphere is lacking. We describe the scientific objectives and capabilities of the COronal Solar Magnetism Observatory (COSMO), a proposed synoptic facility designed to measure magnetic fields and plasma properties in the large-scale solar atmosphere. COSMO comprises a suite of three instruments chosen to enable the study of the solar atmosphere as a coupled system: 1) a coronagraph with a 1.5-m aperture to measure the magnetic field, temperature, density and dynamics of the corona; 2) an instrument for diagnostics of chromospheric and prominence magnetic fields and plasma properties; and 3) a white-light K-coronagraph to measure the density structure and dynamics of the corona and coronal mass ejections. COSMO will provide a unique combination of magnetic field, density, temperature and velocity observations in the corona and chromosphere that have the potential to transform our understanding of fundamental physical processes in the solar atmosphere and their role in the origins of solar variability and space weather.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Global‐Scale Observations of the Equatorial Ionization Anomaly (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The National Aeronautics and Space Administration Global‐scale Observations of the Limb and Disk ultraviolet spectrograph has been imaging the equatorial ionization anomaly (EIA), regions of the ionosphere with enhanced electron density north and south of the magnetic equator, since October 2018. The initial 3 months of observations was during solar minimum conditions, and they included observations in December solstice of unanticipated variability and depleted regions. Depletions are seen on most nights, in contrast to expectations from previous space‐based observations. The variety of scales and morphologies also pose challenges to understanding of the EIA. Abrupt changes in the EIA location, which could be related to in situ measurements of large‐scale depletion regions, are observed on some nights. Such synoptic‐scale disruptions have not been previously identified.
    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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  • 3
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    Isostaticity and elasticity of colloidal gels [Applied Physical Sciences] (2012)
    National Academy of Sciences
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    Publication Date: 2012-10-03
    Description: We report a simple correlation between microstructure and strain-dependent elasticity in colloidal gels by visualizing the evolution of cluster structure in high strain-rate flows. We control the initial gel microstructure by inducing different levels of isotropic depletion attraction between particles suspended in refractive index matched solvents. Contrary to previous ideas...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 4
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    An Investigation Comparing Ground-Based Techniques that Quantify Auroral Electron Flux and Conductance (2015)
    Wiley
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    Publication Date: 2015-09-29
    Description: We present three case studies that examine optical and radar methods for specifying precipitating auroral flux parameters and conductances. Three events were chosen corresponding to moderate non-substorm auroral activity with 557.7 nm intensities greater than 1 kR. A technique that directly fits the electron number density from a forward electron transport model to alternating code incoherent scatter radar data is presented. A method for determining characteristic energy using neutral temperature observations is compared against estimates from the incoherent scatter radar. These techniques are focused on line-of-sight observations that are aligned with the local geomagnetic field. Good agreement is found between the optical and incoherent scatter radar methods for estimates of the average energy, energy flux, and conductances. The Pedersen conductance predicted by Robinson et al. [1987] is in very good agreement with estimates calculated from the incoherent scatter radar observations. However, we present an updated form of the relation by Robinson et al. [1987], Σ H / Σ P =0.57〈 E 〉 0 . 5 3 , which was found to be more consistent with the incoherent scatter radar observations. These results are limited to similar auroral configurations as in these case studies. Case studies are presented that quantify auroral electron flux parameters and conductance estimates which can be used to specify the magnitude of energy dissipated within the ionosphere resulting from magnetospheric driving.
    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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    Solar EUV and XUV energy input to thermosphere on solar rotation time scales derived from photoelectron observations (2012)
    Wiley
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    Publication Date: 2012-05-18
    Description: Solar radiation below ∼100 nm produces photoelectrons, a substantial portion of the F region ionization, most of the E region ionization, and drives chemical reactions in the thermosphere. Unquantified uncertainties in thermospheric models exist because of uncertainties in solar irradiance models used to fill spectral and temporal gaps in solar irradiance observations. We investigate uncertainties in solar energy input to the thermosphere on solar rotation time scales using photoelectron observations from the FAST satellite. We compare observed and modeled photoelectron energy spectra using two photoelectron production codes driven by five different solar irradiance models. We observe about 1.7% of the ionizing solar irradiance power in the escaping photoelectron flux. Most of the code/model pairs used reproduce the average escaping photoelectron flux over a 109-day interval in late 2006. The code/model pairs we used do not completely reproduce the observed spectral and solar rotation variations in photoelectron power density. For the interval examined, 30% of the variability in photoelectron power density with equivalent wavelengths between 18 and 45 nm was not captured in the code/model pairs. For equivalent wavelengths below ∼16 nm, most of the variability was missed. This result implies that thermospheric model runs based on the solar irradiance models we tested systematically underestimate the energy input from ionizing radiation on solar rotation time scales.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 6
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    The summer evening anomaly and conjugate effects (2011)
    Wiley
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    Publication Date: 2011-01-22
    Description: The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) GPS occultation data have been analyzed in this study to provide a better understanding of the Weddell Sea Anomaly (WSA) and to place it in the wider context of a general phenomenon that occurs near dusk in summer, which we are calling the summer evening anomaly to better capture its global nature. The terminator and the magnetically conjugate points for the terminator in the other hemisphere have been plotted on top of global maps of COSMIC NmF2 and hmF2 for 2 months either side of the December and June solstices for 2006–2008. These plots show that there are distinct enhancements of NmF2 and increases in hmF2 as soon as the conjugate footprint of the field line on the winter terminator is seen at middle latitudes in the summer hemisphere. This effect is most pronounced where the WSA is formed, but it also occurs across the South Pacific Ocean in the southern summer and across much of the North Atlantic Ocean, Siberia, and Kamchatka during the northern summer. An hmF2 increase occurs between the two terminators even at locations where there is no increase in NmF2. A similar, but reversed, effect occurs in hmF2 near dawn. This behavior appears to be most consistent with upward and poleward ion drifts in the evening, but neutral wind and downward precipitation may make important contributions to this effect.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 7
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    The Long‐Term Trends of Nocturnal Mesopause Temperature and Altitude Revealed by Na Lidar Observations Between 1990 and 2018 at Midlatitude (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract The mesopause, a boundary between mesosphere and thermosphere with the coldest atmospheric temperature, is formed mainly by the combining effects of radiative cooling of CO2, and the vertical adiabatic flow in the upper atmosphere. A continuous multidecade (1990‐2018) nocturnal temperature data base of an advanced Na lidar, obtained at Fort Collins, CO (41°N, 105°W), and at Logan, UT (42°N, 112°W), provides an unprecedented opportunity to study the long‐term variations of this important atmospheric boundary. In this study, we categorize the lidar‐observed mesopause into two categories: the “high mesopause” (HM) above 97 km during nonsummer months, mainly formed through the radiative cooling, and the “low mesopause” (LM) below 92 km during nonwinter months, generated mostly by the adiabatic cooling. These lidar observations reveal a cooling trend of more than 2 K/decade in absolute mesopause temperature since 1990, along with a decreasing trend in mesopause height: The HM is moving downward at a speed of ~ 450 ± 90 m/decade, while the LM has a slower downward trend of ~ 130 ± 160 m/decade. However, since 2000, while the height trend (‐ 470 ± 160 m/decade for the HM and 150 ± 290 m/decade for the LM) is consistent, the temperature trend becomes statistically insignificant (‐ 0.2 ± 0.7 K/decade and ‐1 ± 0.9 K/decade for the HM and the LM, respectively). A long‐term study by Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) also indicated the similar mesopause changes, mostly caused by stratosphere‐lower mesosphere cooling and contraction.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Heating of the Sunlit Polar Cap Ionosphere by Reflected Photoelectrons (2014)
    Wiley
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    Publication Date: 2014-10-02
    Description: Photoelectrons escape from the ionosphere on sunlit polar cap field lines. In order for those field lines to carry zero current without significant heavy ion outflow or cold electron inflow, field-aligned potential drops must form to reflect a portion of the escaping photoelectron population back to the ionosphere. Using a 1-D ionosphere-polar wind model and measurements from the Resolute Bay Incoherent Scatter Radar (RISR-N), this paper shows that these reflected photoelectrons are a significant source of heat for the sunlit polar cap ionosphere. The model includes a kinetic suprathermal electron transport solver, and it allows energy input from the upper boundary in three different ways: thermal conduction, soft precipitation, and potentials that reflect photoelectrons. The simulations confirm that reflection potentials of several 10s of eV are required to prevent cold electron inflow and demonstrate that the flux tube integrated change in electron heating rate (FTICEHR) associated with reflected photoelectrons can reach 10 9 eVcm − 2 s − 1 . Soft precipitation can produce FTICEHR of comparable magnitudes, but this extra heating is divided among more electrons as a result of electron impact ionization. Simulations with no reflected photoelectrons and with downward field-aligned currents (FAC) primarily carried by the escaping photoelectrons have electron temperatures which are ~ 250 − 500 K lower than the RISR-N measurements in the 300-600 km region; however, simulations with reflected photoelectrons, zero FAC, and no other form of heat flux through the upper boundary can satisfactorily reproduce the RISR-N data.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 9
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    On the Solar Cycle Variation of the Winter Anomaly (2014)
    Wiley
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    Publication Date: 2014-05-24
    Description: Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), Ionosonde and Global Ultraviolet Imager (GUVI) data have been used to investigate the solar cycle changes in the winter anomaly (the winter anomaly is defined as the enhancement of the F 2 peak electron density in the winter hemisphere over that in the summer hemisphere) in the last solar cycle. There is no winter anomaly in solar minimum, and an enhancement of about 50 % in winter over summer ones on the same day of the year at solar maximum. This solar cycle variation in the winter anomaly is primarily due to greater winter to summer differences of [O]/[N 2 ] in solar maximum than in solar minimum, with a secondary contribution from the effects of temperature on the recombination coefficient between O + and the molecular neutral gas. The greater winter increases in electron density in the northern hemisphere than in the southern hemisphere appear to be related to the greater annual variation of [O]/[N 2 ] in the north than in the south.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    Observations of the north polar region of Mars from the Mars orbiter laser altimeter (1998)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1998-12-16
    Description: Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zuber, M T -- Smith, D E -- Solomon, S C -- Abshire, J B -- Afzal, R S -- Aharonson, O -- Fishbaugh, K -- Ford, P G -- Frey, H V -- Garvin, J B -- Head, J W -- Ivanov, A B -- Johnson, C L -- Muhleman, D O -- Neumann, G A -- Pettengill, G H -- Phillips, R J -- Sun, X -- Zwally, H J -- Banerdt, W B -- Duxbury, T C -- New York, N.Y. -- Science. 1998 Dec 11;282(5396):2053-60.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. zuber@tharsis.gsfc.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9851922" target="_blank"〉PubMed〈/a〉
    Keywords: *Carbon Dioxide ; Extraterrestrial Environment ; *Ice ; *Mars ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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