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  • Articles  (425)
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  • Journal of Geophysical Research JGR - Space Physics  (167)
  • Crystal Growth & Design  (47)
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  • Geosciences  (425)
  • 11
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    Topside Correction of IRI by global modeling of ionospheric scale height using COSMIC radio occultation data (2016)
    Wiley
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    Publication Date: 2016-05-27
    Description: The ionosphere scale height is one of the most significant ionospheric parameters, which contains information about the ion and electron temperatures and dynamics in upper ionosphere. In this paper, an empirical orthogonal function (EOF) analysis method is applied to process all the ionospheric radio occultations of GPS/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) from the year 2007 to 2011 to reconstruct a global ionospheric scale height model. This monthly medium model has spatial resolution of 5° in geomagnetic latitude (-87.5° ~ 87.5°), and temporal resolution of 2 hours in local time. EOF analysis preserves the characteristics of scale height quite well in the geomagnetic latitudinal, anural, seasonal and diurnal variations. In comparison with COSMIC measurements of the year of 2012, the reconstructed model indicates a reasonable accuracy. In order to improve the topside model of International Reference Ionosphere (IRI), we attempted to adopt the scale height model in the Bent topside model by applying a scale factor q as an additional constraint. With the factor q functioning in the exponent profile of topside ionosphere, the IRI scale height should be forced equal to the precise COSMIC measurements. In this way, the IRI topside profile can be improved to get closer to the realistic density profiles. Internal quality check of this approach is carried out by comparing COSMIC realistic measurements and IRI with or without correction respectively. In general, the initial IRI model overestimates the topside electron density to some extent, and with the correction introduced by COSMIC scale height model, the deviation of vertical total electron content (VTEC) between them is reduced. Furthermore, independent validation with Global Ionospheric Maps (GIM) VTEC implies a reasonable improvement in the IRI VTEC with the topside model correction.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 12
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    Multi-model comparison of the ionosphere variability during the 2009 sudden stratosphere warming (2016)
    Wiley
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    Publication Date: 2016-07-19
    Description: A comparison of different model simulations of the ionosphere variability during the 2009 sudden stratosphere warming (SSW) is presented. The focus is on the equatorial and low latitude ionosphere simulated by the Ground-to-topside model of the Atmosphere and Ionosphere for Aeronomy (GAIA), Whole Atmosphere Model plus Global Ionosphere Plasmasphere (WAM+GIP), and Whole Atmosphere Community Climate Model eXtended version plus Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (WACCMX+TIMEGCM). The simulations are compared with observations of the equatorial vertical plasma drift in the American and Indian longitude sectors, zonal mean F-region peak density (NmF2) from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites, and ground based Global Positioning System (GPS) total electron content (TEC) at 75 ∘ W. The model simulations all reproduce the observed morning enhancement and afternoon decrease in the vertical plasma drift, as well as the progression of the anomalies towards later local times over the course of several days. However, notable discrepancies among the simulations are seen in terms of the magnitude of the drift perturbations, and rate of the local time shift. Comparison of the electron densities further reveals that although many of the broad features of the ionosphere variability are captured by the simulations, there are significant differences among the different model simulations, as well as between the simulations and observations. Additional simulations are performed where the neutral atmospheres from four different whole atmosphere models (GAIA, HAMMONIA (Hamburg Model of the Neutral and Ionized Atmosphere), WAM, and WACCMX) provide the lower atmospheric forcing in the TIME-GCM. These simulations demonstrate that different neutral atmospheres, in particular differences in the solar migrating semidiurnal tide, are partly responsible for the differences in the simulated ionosphere variability in GAIA, WAM+GIP, and WACCMX+TIMEGCM.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 13
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    Temporal evolutions of the solar wind conditions at 1 AU prior to the near-Earth X-lines in the tail: Superposed epoch analysis (2016)
    Wiley
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    Publication Date: 2016-07-20
    Description: Utilizing conjunction observations of the Geotail and ACE satellites from 1998 to 2005, we investigated the temporal evolutions of the solar wind conditions prior to the formation of X-lines in the near-Earth magnetotail. We first show the statistical properties of Bz, By, density, and velocity of the solar wind related to the 374 tail X-line events. A superposed epoch analysis is performed to study the temporal evolutions of the solar wind conditions 5 hours prior to the tail X-lines. The solar wind conditions for tail X-lines during southward IMF (SW-IMF) and northward IMF (NW-IMF) are analyzed. The main results are as follows: 1) For events classified as SW-IMF, near-Earth X-line observations in the magnetosphere are preceded by ~2 hour intervals of southward IMF; 2) For events classified a NW-IMF, the northward IMF orientation preceding near-Earth X-line observations lasts ~ 40 minutes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 14
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    Observations of the Migrating 12-hour and 6-hour Tides from the RAIDS/NIRS Instrument (2016)
    Wiley
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    Publication Date: 2016-04-08
    Description: In this paper we analyze temperature data from the Near Infra-Red Spectrometer (NIRS) instrument on Remote Atmospheric and Ionospheric Detection System (RAIDS) experiment on the International Space Station (ISS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on NASA's Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite during June and July 2010 to investigate structures of the migrating 12-hour and 6-hour tides in the upper mesosphere and lower thermosphere over a broad range of middle and low latitudes. Temperature measurements from the NIRS and SABER instruments allow us to examine the tides from the stratosphere to the lower thermosphere. We find that the amplitude of the migrating 6-hour tide grows from ~5 K near 100 km altitude to ~30 K near 130 km. The amplitudes of the tide at altitudes accessible by NIRS are much larger than those previously reported at lower altitudes from the Aura Microwave Limb Sounder and the SABER instruments. The amplitude of the 12-hr tide in the NIRS data shows two peaks in the lower thermosphere between 30° S and 50° N latitudes with a maximum around 60 K occurring in the winter hemisphere and a second maximum around 40 K occurring in the summer hemisphere near 30°. The structure of the TDW3 tide is also investigated in the NIRS data and shows increasing amplitude with altitude over a broad range of latitudes, roughly between 50° N and 30° S. Altitudinal variations seen in the 6-, 8-, and 12-hr amplitudes suggest an evolving mix of various Hough modes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 15
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    Formation of Alfvénic resonance layers in magnetic reconnection (2016)
    Wiley
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    Publication Date: 2016-04-09
    Description: n the framework of two-dimensional incompressible MHD, we investigate the formation of Alfvénic resonance layers with different super-Alfvénic shear flows. It is found that Alfvénic resonance layers are formed in the inflow region for the cases with the shear flow thickness larger than the current sheet thickness. The Alfvénic layers exist at where the flow velocity equals the local Alfvén speed and slowly drift away from the current sheet region as a magnetic island develops. The ratio ( D ) between the separation of the Alfvénic resonance layers and the current sheet thickness plays a crucial role on magnetic reconnection. It is found that D~3 is a critical value, which is about the saturated size of a magnetic island in magnetic reconnection without super-Alfvénic shear flow. For D〈3 the super-Alfvénic shear flow shows mainly a suppressing effect on magnetic reconnection and the peaked reconnection rate drops below the rate without a super-Alfvénic shear flow. When D〉3, the boosting effect of KHI surpasses the suppressing effect by Alfvénic resonance and the peaked reconnection rate is larger than that without a super-Alfvénic shear flow. For D~5, the super-Alfvénic shear flow gives rise to a strongest boosting effect on magnetic reconnection. Possible applications are briefly discussed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 16
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    Recognition of S···Cl Chalcogen Bonding in Metal-Bound Alkylthiocyanates (2016)
    American Chemical Society (ACS)
    Details
    Publication Date: 2016-04-07
    Description: Crystal Growth & Design DOI: 10.1021/acs.cgd.6b00346
    Print ISSN: 1528-7483
    Electronic ISSN: 1528-7505
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by American Chemical Society (ACS)
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  • 17
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    Effect of Aspartic Acid and Glycine on Calcite Growth (2016)
    American Chemical Society (ACS)
    Details
    Publication Date: 2016-08-25
    Description: Crystal Growth & Design DOI: 10.1021/acs.cgd.5b01635
    Print ISSN: 1528-7483
    Electronic ISSN: 1528-7505
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by American Chemical Society (ACS)
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  • 18
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    Investigating Reaction Conditions To Control the Self-Assembly of Cobalt-Seamed Nanocapsules (2016)
    American Chemical Society (ACS)
    Details
    Publication Date: 2016-06-03
    Description: Crystal Growth & Design DOI: 10.1021/acs.cgd.6b00306
    Print ISSN: 1528-7483
    Electronic ISSN: 1528-7505
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by American Chemical Society (ACS)
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  • 19
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    Bursty bulk flows at different magnetospheric activity levels: Dependence on IMF conditions (2016)
    Wiley
    Details
    Publication Date: 2016-09-11
    Description: Based on concurrent observations of the ACE and Geotail satellites from 1998 to 2005, we statistically analyzed and compared the earthward bursty bulk flows (BBFs) with local positive Bz under different interplanetary magnetic field (IMF) conditions. Four different magnetospheric activity levels (MALs), including quiet times and substorm growth/expansion/recovery phases are considered. The properties of the BBFs, including their ion temperature (T), Vx component, X component of the energy flux density (Qx), and the solar wind dawn-dusk electric field Ey (observed at ~1 AU) are analyzed. Main observations include that: 1) BBF tends to have less penetration distance for northward IMF (NW-IMF) than for southward IMF (SW-IMF). Inward of 15 R E the BBFs for SW-IMF are dominant. Few BBFs for NW-IMF occur within 15 R E ; 2) the occurrence probability of the BBFs at each MAL depend highly on the orientations of the IMF. During quiet times, the BBFs for NW-IMF are dominant. Reversely, during the growth and expansion phases of a substorm, the BBFs for SW-IMF are dominant; 3) the strengths of the BBF have significant evolution with substorm development. For SW-IMF condition, the strengths of the BBFs are the lowest for quiet times. The strength of the BBFs tends to increase during the growth phase, and reaches to the strongest value during the expansion phase, then, decays during the recovery phase. For NW-IMF condition, the strengths of the BBFs evolve with the substorm development in a similar way as for SW-IMF condition; 4) For SW-IMF, the solar wind Ey evolves with the substorm development in a similar way to the strength of the BBFs. However, no clear evolution is found for NW-IMF; 5) The strengths of the BBF Qx and solar wind Ey are closely related. Both tend to be stronger for growth phase than for quite time, reach the strongest for expansion phase, then decay for recovery phase. It appears that to trigger a substorm, the strength of the BBFs should achieve energy thresholds with values different for NW-IMF and SW-IMF.
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    Topics: Geosciences , Physics
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  • 20
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    Statistical properties of substorm auroral onset beads/rays (2016)
    Wiley
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    Publication Date: 2016-09-04
    Description: Auroral substorms are often associated with optical ray or bead structures during initial brightening (substorm auroral onset waves). Occurrence probabilities and properties of substorm onset waves have been characterized using 112 substorm events identified in THEMIS all-sky imager data, and compared to Rice Convection Model-Equilibrium (RCM-E) and kinetic instability properties. All substorm onsets were found to be associated with optical waves, and thus optical waves are a common feature of substorm onset. Eastward-propagating wave events are more frequent than westward-propagating wave events, and tend to occur during lower-latitude substorms (stronger solar wind driving). The wave propagation directions are organized by orientation of initial brightening arcs. We also identified notable differences in wave propagation speed, wavelength (wavenumber), period and duration between westward and eastward propagating waves. In contrast, the wave growth rate does not depend on the propagation direction or substorm strength but is inversely proportional to the wave duration. This suggests that the waves evolve to poleward expansion at a certain intensity threshold, and that the wave properties do not directly relate to substorm strengths. However, waves are still important for mediating the transition between the substorm growth phase and poleward expansion. The relation to arc orientation can be explained by magnetotail structures in the RCM-E, indicating that substorm onset location relative to the pressure peak determines the wave propagation direction. The measured wave properties agree well with kinetic ballooning interchange instability, while cross-field current instability and electromagnetic ion cyclotron instability give much larger propagation speed and smaller wave period.
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    Topics: Geosciences , Physics
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