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  • 1
    Online Resource
    Online Resource
    First simulation results of Titan's atmosphere dynamics with a global 3-D non-hydrostatic circulation model
    Copernicus GmbH ; 2006
    In:  Annales Geophysicae Vol. 24, No. 8 ( 2006-09-13), p. 2115-2129
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 24, No. 8 ( 2006-09-13), p. 2115-2129
    Abstract: Abstract. We present the first results of a 3-D General Circulation Model of Titan's atmosphere which differs from traditional models in that the hydrostatic equation is not used and all three components of the neutral gas velocity are obtained from the numerical solution of the Navier-Stokes equation. The current version of our GCM is, however, a simplified version, as it uses a predescribed temperature field in the model region thereby avoiding the complex simulation of radiative transfer based on the energy equation. We present the first simulation results and compare them to the results of existing GCMs and direct wind observations. The wind speeds obtained from our GCM correspond well with data obtained during the Huygens probe descent through Titan's atmosphere. We interpret the most unexpected feature of these data which consist of the presence of a non-monotonicity of the altitude profile of the zonal wind speed between 60 and 75 km.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-24-2115-2006
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2006
    detail.hit.zdb_id: 1458425-6
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  • 2
    Online Resource
    Online Resource
    Temperature variations in Titan's upper atmosphere: Impact on Cassini/Huygens
    Copernicus GmbH ; 2005
    In:  Annales Geophysicae Vol. 23, No. 4 ( 2005-06-03), p. 1183-1189
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 23, No. 4 ( 2005-06-03), p. 1183-1189
    Abstract: Abstract. Temperature variations of Titan's upper atmosphere due to the plasma interaction of the satellite with Saturn's magnetosphere and Titan's high altitude monomer haze particles can imply an offset of up to ±30K from currently estimated model profiles. We incorporated these temperature uncertainties as an offset into the recently published Vervack et al. (2004) (Icarus, Vol. 170, 91-112) engineering model and derive extreme case (i.e. minimum and maximum profiles) temperature, pressure, and density profiles. We simulated the Huygens probe hypersonic entry trajectory and obtain, as expected, deviations of the probe trajectory for the extreme atmosphere models compared to the simulation based on the nominal one. These deviations are very similar to the ones obtained with the standard Yelle et al. (1997) (ESA SP-1177) profiles. We could confirm that the difference in aerodynamic drag is of an order of magnitude that can be measured by the probe science accelerometer. They represent an important means for the reconstruction of Titan's upper atmospheric properties. Furthermore, we simulated a Cassini low Titan flyby trajectory. No major trajectory deviations were found. The atmospheric torques due to aerodynamic drag, however, are twice as high for our high temperature profile as the ones obtained with the Yelle maximum profile and more than 5 times higher than the worst case estimations from the Cassini project. We propose to use the Cassini atmospheric torque measurements during its low flybys to derive the atmospheric drag and to reconstruct Titan's upper atmosphere density, pressure, and temperature. The results could then be compared to the reconstructed profiles obtained from Huygens probe measurements. This would help to validate the probe measurements and decrease the error bars.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-23-1183-2005
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2005
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  • 3
    Online Resource
    Online Resource
    Visibility of Type III burst source location as inferred from stereoscopic space observations
    Copernicus GmbH ; 2014
    In:  Advances in Radio Science Vol. 12 ( 2014-11-10), p. 167-170
    Details
    In: Advances in Radio Science, Copernicus GmbH, Vol. 12 ( 2014-11-10), p. 167-170
    Abstract: Abstract. We study solar Type III radio bursts simultaneously observed by RPWS/Cassini, URAP/Ulysses and WAVES/Wind experiments. The observations allows us to cover a large frequency bandwidth from 16 MHz down to a few kHz. We consider the onset time of each burst, and estimate the corresponding intensity level. Also we measure the Langmuir frequency as observed on the dynamic spectra recorded by the Ulysses spacecraft. The distances of Wind, Ulysses and Cassini spacecraft, with regard to the Sun, were in the order of 1 AU, 2.4 AU and 4.5 AU, respectively. The spacecraft trajectories were localized in the ecliptic plane in the case of Wind and Cassini, and for Ulysses in the southern hemisphere (i.e. heliocentric latitude higher than −50°). Despite the different locations, the spectral patterns of the selected solar bursts are found to be similar between 10 MHz and 2 MHz but unalike at lower frequency. We discuss the variation of the intensity level as recorded by the three spacecraft. We show that the reception system of each experiment affected the way the Type III burst intensity is measured. Also we attempt to estimate the electron beam along the interplanetary magnetic field where the trajectory is an Archimedean spiral. This leads us to infer on the visibility of the source location with regard to the spacecraft position.
    Type of Medium: Online Resource
    ISSN: 1684-9973
    URL: Article
    DOI: 10.5194/ars-12-167-2014
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2014
    detail.hit.zdb_id: 2135129-6
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  • 4
    Online Resource
    Online Resource
    Linear prediction studies for the solar wind and Saturn kilometric radiation
    Copernicus GmbH ; 2006
    In:  Annales Geophysicae Vol. 24, No. 11 ( 2006-11-22), p. 3139-3150
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 24, No. 11 ( 2006-11-22), p. 3139-3150
    Abstract: Abstract. The external control of Saturn kilometric radiation (SKR) by the solar wind has been investigated in the frame of the Linear Prediction Theory (LPT). The LPT establishes a linear filter function on the basis of correlations between input signals, i.e. time profiles for solar wind parameters, and output signals, i.e. time profiles for SKR intensity. Three different experiments onboard the Cassini spacecraft (RPWS, MAG and CAPS) yield appropriate data sets for compiling the various input and output signals. The time period investigated ranges from DOY 202 to 326, 2004 and is only limited due to limited availability of CAPS plasma data for the solar wind. During this time Cassini was positioned mainly on the morning side on its orbit around Saturn at low southern latitudes. Four basic solar wind quantities have been found to exert a clear influence on the SKR intensity profile. These quantities are: the solar wind bulk velocity, the solar wind ram pressure, the magnetic field strength of the interplanetary magnetic field (IMF) and the y-component of the IMF. All four inputs exhibit nearly the same level of efficiency for the linear prediction indicating that all four inputs are possible drivers for triggering SKR. Furthermore, they act at completely different lag times ranging from ~13 h for the ram pressure to ~52 h for the bulk velocity. The lag time for the magnetic field strength is usually beyond ~40 h and the lag time for the y-component of the magnetic field is located around 30 h. Considering that all four solar wind quantities are interrelated in a corotating interaction region, only the influence of the ram pressure seems to be of reasonable relevance. An increase in ram pressure causes a substantial compression of Saturn's magnetosphere leading to tail collapse, injection of hot plasma from the tail into the outer magnetosphere and finally to an intensification of auroral dynamics and SKR emission. So, after the onset of magnetospheric compression at least ~1.2 rotations of the planet elapse until intensified SKR emission is visible in a Cassini-RPWS dynamic spectrum.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-24-3139-2006
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2006
    detail.hit.zdb_id: 1458425-6
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  • 5
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    Online Resource
    Planetary radio astronomy: Earth, giant planets, and beyond
    Copernicus GmbH ; 2014
    In:  Advances in Radio Science Vol. 12 ( 2014-11-10), p. 211-220
    Details
    In: Advances in Radio Science, Copernicus GmbH, Vol. 12 ( 2014-11-10), p. 211-220
    Abstract: Abstract. The magnetospheric phenomenon of non-thermal radio emission is known since the serendipitous discovery of Jupiter as radio planet in 1955, opening the new field of "Planetary Radio Astronomy". Continuous ground-based observations and, in particular, space-borne measurements have meanwhile produced a comprehensive picture of a fascinating research area. Space missions as the Voyagers to the Giant Planets, specifically Voyager 2 further to Uranus and Neptune, Galileo orbiting Jupiter, and now Cassini in orbit around Saturn since July 2004, provide a huge amount of radio data, well embedded in other experiments monitoring space plasmas and magnetic fields. The present paper as a condensation of a presentation at the Kleinheubacher Tagung 2013 in honour of the 100th anniversary of Prof. Karl Rawer, provides an introduction into the generation mechanism of non-thermal planetary radio waves and highlights some new features of planetary radio emission detected in the recent past. As one of the most sophisticated spacecraft, Cassini, now in space for more than 16 years and still in excellent health, enabled for the first time a seasonal overview of the magnetospheric variations and their implications for the generation of radio emission. Presently most puzzling is the seasonally variable rotational modulation of Saturn kilometric radio emission (SKR) as seen by Cassini, compared with early Voyager observations. The cyclotron maser instability is the fundamental mechanism under which generation and sufficient amplification of non-thermal radio emission is most likely. Considering these physical processes, further theoretical investigations have been started to investigate the conditions and possibilities of non-thermal radio emission from exoplanets, from potential radio planets in extrasolar systems.
    Type of Medium: Online Resource
    ISSN: 1684-9973
    URL: Article
    DOI: 10.5194/ars-12-211-2014
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2014
    detail.hit.zdb_id: 2135129-6
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  • 6
    Online Resource
    Online Resource
    High-frequency performance of electric field sensors aboard the RESONANCE satellite
    Copernicus GmbH ; 2015
    In:  Geoscientific Instrumentation, Methods and Data Systems Vol. 4, No. 1 ( 2015-05-04), p. 81-88
    Details
    In: Geoscientific Instrumentation, Methods and Data Systems, Copernicus GmbH, Vol. 4, No. 1 ( 2015-05-04), p. 81-88
    Abstract: Abstract. We present the high-frequency properties of the eight electric field sensors as proposed to be launched on the spacecraft "RESONANCE" in the near future. Due to the close proximity of the conducting spacecraft body, the sensors (antennas) have complex receiving features and need to be well understood for an optimal mission and spacecraft design. An optimal configuration and precise understanding of the sensor and antenna characteristics is also vital for the proper performance of spaceborne scientific instrumentation and the corresponding data analysis. The provided results are particularly interesting with regard to the planned mutual impedance experiment for measuring plasma parameters. Our computational results describe the extreme dependency of the sensor system with regard to wave incident direction and frequency, and provides the full description of the sensor system as a multi-port scatterer. In particular, goniopolarimetry techniques like polarization analysis and direction finding depend crucially on the presented antenna characteristics.
    Type of Medium: Online Resource
    ISSN: 2193-0864
    URL: Article
    DOI: 10.5194/gi-4-81-2015
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2015
    detail.hit.zdb_id: 2690575-9
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