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  • 1
    Digitale Medien
    Digitale Medien
    A photodiode array detection system: Design concept and implementation (1982)
    Springer
    Chromatographia 15 (1982), S. 419-425 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Linear photodiode array ; Specitral exquisition ; High speed microprocessors ; UV/Vis detection ; HPLC
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Use of a linear photodiode array as the elemental detector for an HPLC UV/Visible detector can provide both quantitative and semi-qualitative information for the analytical chemist. This paper discusses the primary needs of the analyst, the goals to be achieved in hardware and software, and possible applications for such a detection system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02261601
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  • 2
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    Longitudinal variations in the F region ionosphere and the topside ionosphere-plasmasphere: Observations and model simulations (2011)
    Wiley
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    Publikationsdatum: 2011-12-07
    Beschreibung: Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) observations of the total electron content (TEC) above and below 800 km are used to study the local time and seasonal variation of longitude structures in both the F region ionosphere as well as the topside ionosphere and plasmasphere. The COSMIC observations reveal the presence of distinct longitude variations in the topside ionosphere-plasmasphere TEC, and these further exhibit a seasonal and local time dependence. The predominant feature observed at all local times in the topside ionosphere-plasmasphere TEC is a substantial maximum (minimum) during Northern Hemisphere winter (summer) around 300°–360° geographic longitude. Around equinox, at a fixed local time, a wave 4 variation in longitude prevails in the daytime F region TEC as well as the topside ionosphere-plasmasphere TEC. The wave 4 variation in longitude persists into the nighttime in the F region; however, the nighttime topside ionosphere-plasmasphere TEC exhibits two maxima in longitude. The COSMIC observations clearly reveal the presence of substantial longitude variations in the F region and topside ionosphere-plasmasphere, and to elucidate the source of the longitude variations, results are presented based on the coupling between the Global Ionosphere Plasmasphere model and the Thermosphere Ionosphere Electrodynamics General Circulation Model. The model simulations demonstrate that the orientation of the geomagnetic field plays a fundamental role in generating significant longitude variations in the topside ionosphere-plasmasphere but does not considerably influence longitude variations in the F region ionosphere. The model results further confirm that nonmigrating tides are the primary mechanism for generating longitude variations in the F region ionosphere. The coupled model additionally demonstrates that nonmigrating tides are also of considerable importance for the generation of longitude variations in the topside ionosphere-plasmasphere TEC.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 3
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    Sources of low-latitude ionospheric E × B drifts and their variability (2012)
    Wiley
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    Publikationsdatum: 2012-06-14
    Beschreibung: The complete mechanism of how upward propagating tropospheric tides connect to the upper atmosphere is not yet fully understood. One proposed mechanism is via ionospheric wind dynamo. However, other sources can potentially alter the vertical E × B drift: gravity and plasma pressure gradient driven current, the geomagnetic main field, and longitudinal variation in the conductivities. In this study we examine the contribution to the vertical drift from these sources, and compare them. We use March equinox results from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model. We found that the gravity and plasma pressure gradient driven current and the longitudinal variation of the conductivities excluding the variation due to the geomagnetic main field do not change the longitudinal variation of the vertical drift significantly. Modifying the geomagnetic main field will change the vertical drift at 5–6 LT, 18–19 LT and 23–24 LT at almost all longitudes. In general the influence of the geomagnetic main field on the vertical drift is larger, with respect to the maximum difference, at 18–19 LT and 23–24 LT, equal at 5–6 LT, and smaller at 14–15 LT than the influence due to nonmigrating tidal components in the neutral winds. Examination of the contribution from E- and F-region neutral winds to the vertical drift shows that their importance depends on the local time and the solar activity. This implies that the vertical drift has to be analyzed at specific local times to examine the relation between the wave number in the vertical drift and in the neutral winds.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 4
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    A photodiode array detection system: Design concept and implementation (1982)
    Springer
    Details
    Publikationsdatum: 1982-07-01
    Print ISSN: 0009-5893
    Digitale ISSN: 1612-1112
    Thema: Chemie und Pharmazie
    Publiziert von Springer
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  • 5
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    Ionospheric and thermospheric variations associated with prompt penetration electric fields (2012)
    Wiley
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    Publikationsdatum: 2012-08-10
    Beschreibung: This paper presents a comprehensive modeling investigation of ionospheric and thermospheric variations during a prompt penetration electric field (PPEF) event that took place on 9 November 2004, using the Thermosphere-Ionosphere-Mesosphere Electrodynamic General Circulation Model (TIMEGCM). The simulation results reveal complex latitudinal and longitudinal/local-time variations in vertical ion drift in the middle- and low-latitude regions owing to the competing influences of electric fields and neutral winds. It is found that electric fields are the dominant driver of vertical ion drift at the magnetic equator; at midlatitudes, however, vertical ion drift driven by disturbance meridional winds exceeds that driven by electric fields. The temporal evolution of the UT-latitude electron density profile from the simulation depicts clearly a super-fountain effect caused by the PPEF, including the initial slow-rise of the equatorial F-layer peak height, the split of the F-layer peak density, and the subsequent downward diffusion of the density peaks along magnetic field lines. Correspondingly, low-latitude total electron content (TEC) becomes bifurcated around the magnetic equator. The O/N2 column density ratio, on the other hand, shows very little variations during this PPEF event, excluding composition change as a potential mechanism for the TEC variations. By using realistic, time-dependent, high-latitude electric potential and auroral precipitation patterns to drive the TIMEGCM, the model is able to successfully reproduce the large vertical ion drift of ∼120 m/s over the Jicamarca incoherent radar (IS) in Peru, which is the largest daytime ion drift ever recorded by the radar. The simulation results are validated with several key observations from IS radars, ground GPS-TEC network, and the TIMED-GUVI O/N2 column density ratio. The model-data intercomparison also reveals some deficiencies in the TIMEGCM, particularly the limitations imposed by its upper boundary height as well as the prescribed O+ flux.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 6
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    Examining the magnetic signal due to gravity and plasma pressure gradient current with the TIE-GCM (2017)
    Wiley
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    Publikationsdatum: 2017-11-21
    Beschreibung: Accurate magnetic field measurements at ground and Low-Earth Orbit (LEO) are crucial to describe Earth's magnetic field. One of the challenges with processing LEO magnetic field measurements to study Earthâ's magnetic field is that the satellite flies in regions of highly varying ionospheric currents which needs to be characterized accurately. The present study focuses on ionospheric current systems due to gravity and plasma pressure gradient forcing, and aims to provide guidance on the estimation of their magnetic effect at LEO altitudes with the help of numerical modeling. We assess the diamagnetic approximation which estimates the magnetic signal of the plasma pressure gradient current. The simulations indicate that the diamagnetic effect should not be removed from LEO magnetic observations without considering the gravity current effect, as this will lead to an error larger than the magnetic signal of these currents. We introduce and evaluate a method to capture the magnetic effect of the gravity driven current. The diamagnetic and gravity current approximations ignore the magnetic effect from currents set up by the induced electric field. The combined gravity and plasma pressure gradient magnetic effect tends to cancel above the F-region peak, however between approximately 300 km and the peak it exhibits a significant height and latitudinal variation with magnitudes up to 8nT. During solar minimum the combined magnetic signal is less than 1nT above 300 km. In addition to the solar cycle dependence, the magnetic signal strength varies with longitude (approximately by 50%) and season (up to 80%) at solar maximum.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 7
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    An application of principal component analysis to the interpretation of ionospheric current systems (2017)
    Wiley
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    Publikationsdatum: 2017-05-13
    Beschreibung: Ionospheric currents are driven by several different physical processes and exhibit complex spatial and temporal structure. Magnetic field measurements of ionospheric sources are often spatially sparse, causing significant challenges in visualizing current flow at a specific time. Standard methods of fitting equivalent current models to magnetic observations, such as line currents, spherical harmonic analysis, spherical cap harmonic analysis, and spherical elementary current systems (SECS), are often unable to capture the full spatial complexity of the currents, or require a large number of parameters which cannot be fully determined by the available data coverage. These methods rely on a set of generic basis functions which contain limited information about the geometries of the various ionospheric sources. In this study, we develop new basis functions for fitting ground and satellite measurements, which are derived from physics-based ionospheric modeling combined with principal component analysis (PCA). The physics-based modeling provides realistic current flow patterns for all of the primary ionospheric sources, including their daily and seasonal variability. The PCA technique extracts the most relevant spatial geometries of the currents from the model run into a small set of equivalent current modes. We fit these modes to magnetic measurements of the Swarm satellite mission at low and mid-latitudes and compare the resulting model with independent measurements and with the SECS approach. We find that our PCA method accurately reproduces features of the equatorial electrojet and Sq current systems with only 10 modes, and can predict ionospheric fields far from the data region.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 8
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    A Comparison of Model-Based Ionospheric and Ocean Tidal Magnetic Signals With Observatory Data (2018)
    American Geophysical Union
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    Publikationsdatum: 2018-06-25
    Beschreibung: Observed tidal geomagnetic field variations are due to a combination of electric currents in the ionosphere, ocean, and their induced counterparts. Using these variations to constrain subsurface electrical conductivity in oceanic regions is a promising frontier; however, properly separating the ionospheric and oceanic tidal contributions of the magnetic field is critical for this. We compare semidiurnal lunar tidal magnetic signals (i.e., the signals due to the M2 tidal mode) estimated from 64 global observatories to physics-based forward models of the ionospheric M2 magnetic field and the oceanic M2 magnetic field. At ground level, predicted ionospheric M2 amplitudes are strongest in the horizontal components, whereas the predicted oceanic amplitudes are strongest in the vertical direction. There is good agreement between the predicted and estimated M2 phases for the Y component; however, the F and X components experience deviations that may be indicative of unmodeled ionospheric processes or unmodeled coastal effects. Overall, we find that the agreement between the physics-based model predictions and the observations is very encouraging for electromagnetic sensing applications, especially since the predicted ionospheric vertical component is very weak. ©2018. American Geophysical Union. All Rights Reserved.
    Print ISSN: 0094-8276
    Digitale ISSN: 1944-8007
    Thema: Geologie und Paläontologie , Physik
    Publiziert von American Geophysical Union
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  • 9
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    Dependence of Lunar Tide of the Equatorial Electrojet on the Wintertime Polar Vortex, Solar Flux, and QBO (2018)
    American Geophysical Union
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    Publikationsdatum: 2018-05-07
    Beschreibung: The lower atmospheric forcing effects on the ionosphere are particularly evident during extreme meteorological events known as sudden stratospheric warmings (SSWs). During SSWs, the polar stratosphere and ionosphere, two distant atmospheric regions, are coupled through the SSW-induced modulation of atmospheric migrating and nonmigrating tides. The changes in the migrating semidiurnal solar and lunar tides are the major source of ionospheric variabilities during SSWs. In this study, we use 55 years of ground-magnetometer observations to investigate the composite characteristics of the lunar tide of the equatorial electrojet (EEJ) during SSWs. These long-term observations allow us to capture the EEJ lunar tidal response to the SSWs in a statistical sense. Further, we examine the influence of solar flux conditions and the phases of quasi-biennial oscillation (QBO) on the lunar tide and find that the QBO phases and solar flux conditions modulate the EEJ lunar tidal response during SSWs in a similar way as they modulate the wintertime Arctic polar vortex. This work provides first evidence of modulation of the EEJ lunar tide due to QBO. ©2018. American Geophysical Union. All Rights Reserved.
    Print ISSN: 0094-8276
    Digitale ISSN: 1944-8007
    Thema: Geologie und Paläontologie , Physik
    Publiziert von American Geophysical Union
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  • 10
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    Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents (2016)
    Springer
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    Publikationsdatum: 2016-09-14
    Print ISSN: 0038-6308
    Digitale ISSN: 1572-9672
    Thema: Physik
    Publiziert von Springer
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