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Sillanpaa I.,Southwest Research Institute | Young D.T.,Southwest Research Institute | Crary F.,Southwest Research Institute | Thomsen M.,Los Alamos National Laboratory | And 6 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

During the Cassini Titan fly by on 2 July 2006 (T15), Titan was surrounded by a magnetospheric plasma flow with density about 0.1 cm-3 as measured by Cassini Plasma Spectrometer (CAPS). A very low fraction of water group ions (O+) was detected in the flow dominated by hydrogen ions. We show that Titan's plasma interaction can be highly sensitive to the small fraction of oxygen ions in the magnetospheric flow. The ion quantities of the magnetospheric flow during the flyby were obtained from numerical moments calculated from the CAPS measurements; the average ambient magnetic field was determined using the Cassini magnetometer data. We simulated the flyby using a global hybrid model; the water group abundance in the flow was varied in three simulation runs. Based on the simulation results, the oxygen content has an especially notable effect on the extent of Titan's induced magnetosphere. A multi-instrument analysis was performed comparing with the simulations, whereby a comprehensive picture of the plasma properties around Titan during this flyby was obtained. Comparisons between the hybrid model simulations and Cassini measurements during the flyby point toward O+ density in the undisturbed magnetospheric flow having been around 0.008 cm-3, which would have accounted for one half of the dynamic pressure of the flow. Copyright 2011 by the American Geophysical Union.


Sittler Jr. E.C.,NASA | Hartle R.E.,NASA | Johnson R.E.,University of Virginia | Cooper J.F.,NASA | And 8 more authors.
Planetary and Space Science | Year: 2010

We present new results of Cassini's T9 flyby with complementary observations from T18. Based on Cassini plasma spectrometer (CAPS) and Cassini magnetometer (MAG), compositional evidence shows the upstream flow for both T9 and T18 appears composed of light ions (H+ and H2+), with external pressures ∼30 times lower than that for the earlier TA flyby where heavy ions dominated the magnetospheric plasma. When describing the plasma heating and sputtering of Titan's atmosphere, T9 and T18 can be considered interactions of low magnetospheric energy input. On the other hand, T5, when heavy ion fluxes are observed to be higher than typical (i.e., TA), represents the limiting case of high magnetospheric energy input to Titan's upper atmosphere. Anisotropy estimates of the upstream flow are 1


Delva M.,Austrian Academy of Sciences | Bertucci C.,Institute for Astronomy and Space Physics | Volwerk M.,Austrian Academy of Sciences | Lundin R.,Swedish Institute of Space Physics | And 2 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

Long-term magnetometer data of Venus Express are analyzed for the occurrence of waves at the proton cyclotron frequency in the spacecraft frame in the upstream region of Venus, for conditions of rising solar activity. The data of two Venus years up to the time of highest sunspot number so far (1 Mar 2011 to 31 May 2012) are studied to reveal the properties of the waves and the interplanetary magnetic field (IMF) conditions under which they are observed. In general, waves generated by newborn protons from exospheric hydrogen are observed under quasi- (anti)parallel conditions of the IMF and the solar wind velocity, as is expected from theoretical models. The present study near solar maximum finds significantly more waves than a previous study for solar minimum, with an asymmetry in the wave occurrence, i.e., mainly under antiparallel conditions. The plasma data from the Analyzer of Space Plasmas and Energetic Atoms instrument aboard Venus Express enable analysis of the background solar wind conditions. The prevalence of waves for IMF in direction toward the Sun is related to the stronger southward tilt of the heliospheric current sheet for the rising phase of Solar Cycle 24, i.e., the "bashful ballerina" is responsible for asymmetric background solar wind conditions. The increase of the number of wave occurrences may be explained by a significant increase in the relative density of planetary protons with respect to the solar wind background. An exceptionally low solar wind proton density is observed during the rising phase of Solar Cycle 24. At the same time, higher EUV increases the ionization in the Venus exosphere, resulting in higher supply of energy from a higher number of newborn protons to the wave. We conclude that in addition to quasi- (anti)parallel conditions of the IMF and the solar wind velocity direction, the higher relative density of Venus exospheric protons with respect to the background solar wind proton density is the key parameter for the higher number of observable proton cyclotron waves near solar maximum. ©2014. American Geophysical Union. All Rights Reserved.


Edberg N.J.T.,Swedish Institute of Space Physics | Andrews D.J.,Swedish Institute of Space Physics | Shebanits O.,Swedish Institute of Space Physics | Agren K.,Swedish Institute of Space Physics | And 11 more authors.
Geophysical Research Letters | Year: 2013

We present Cassini Langmuir probe measurements of the highest electron number densities ever reported from the ionosphere of Titan. The measured density reached 4310 cm-3 during the T85 Titan flyby. This is at least 500 cm-3 higher than ever observed before and at least 50% above the average density for similar solar zenith angles. The peak of the ionospheric density is not reached on this flyby, making the maximum measured density a lower limit. During this flyby, we also report that an impacting coronal mass ejection (CME) leaves Titan in the magnetosheath of Saturn, where it is exposed to shocked solar wind plasma for at least 2 h 45 min. We suggest that the solar wind plasma in the magnetosheath during the CME conditions significantly modifies Titan's ionosphere by an addition of particle impact ionization by precipitating protons. Key Points Titan is located in the magnetosheath of Saturn during the T85 flyby The highest ever ionospheric electron densities at Titan are found during T85 The magnetosheath encounter and the extreme densities are due to a CME impact ©2013. American Geophysical Union. All Rights Reserved.


Romanelli N.,Institute for Astronomy and Space Physics | Bertucci C.,Institute for Astronomy and Space Physics | Gomez D.,Institute for Astronomy and Space Physics | Mazelle C.,French National Center for Scientific Research | Mazelle C.,University Paul Sabatier
Journal of Geophysical Research A: Space Physics | Year: 2015

We use magnetometer data from the Mars Global Surveyor (MGS) spacecraft during portions of the premapping orbits of the mission to study the variability of the Martian-induced magnetotail as a function of the orientation of the interplanetary magnetic field (IMF). The time spent by MGS in the magnetotail lobes during periods with positive solar wind flow-aligned IMF component B∥ IMF suggests that their location as well as the position of the central polarity reversal layer (PRL) are displaced in the direction antiparallel to the IMF cross-flow component B∥ IMF. Analogously, in the cases where B∥ IMF is negative, the lobes are displaced in the direction of B∥ IMF. This behavior is compatible with a previously published analytical model of the IMF draping, where for the first time, the displacement of a complementary reversal layer (denoted as IPRL for inverse polarity reversal layer) is deduced from first principles. ©2015. American Geophysical Union. All Rights Reserved.


Delva M.,Austrian Academy of Sciences | Mazelle C.,French National Center for Scientific Research | Bertucci C.,Institute for Astronomy and Space Physics
Space Science Reviews | Year: 2011

The occurrence of waves generated by pick-up of planetary neutrals by the solar wind around unmagnetized planets is an important indicator for the composition and evolution of planetary atmospheres. For Venus and Mars, long-term observations of the upstream magnetic field are now available and proton cyclotron waves have been reported by several spacecraft. Observations of these left-hand polarized waves at the local proton cyclotron frequency in the spacecraft frame are reviewed for their specific properties, generation mechanisms and consequences for the planetary exosphere. Comparison of the reported observations leads to a similar general wave occurrence at both planets, at comparable locations with respect to the planet. However, the waves at Mars are observed more frequently and for long durations of several hours; the cyclotron wave properties are more pronounced, with larger amplitudes, stronger left-hand polarization and higher coherence than at Venus. The geometrical configuration of the interplanetary magnetic field with respect to the solar wind velocity and the relative density of upstream pick-up protons to the background plasma are important parameters for wave generation. At Venus, where the relative exospheric pick-up ion density is low, wave generation was found to mainly take place under stable and quasi-parallel conditions of the magnetic field and the solar wind velocity. This is in agreement with theory, which predicts fast wave growth from the ion/ion beam instability under quasi-parallel conditions already for low relative pick-up ion density. At Mars, where the relative exospheric pick-up ion density is higher, upstream wave generation may also take place under stable conditions when the solar wind velocity and magnetic field are quasi-perpendicular. At both planets, the altitudes where upstream proton cyclotron waves were observed (8 Venus and 11 Mars radii) are comparable in terms of the bow shock nose distance of the planet, i.e. in terms of the size of the solar wind-planetary atmosphere interaction region. In summary, the upstream proton cyclotron wave observations demonstrate the strong similarity in the interaction of the outer exosphere of these unmagnetized planets with the solar wind upstream of the planetary bow shock. © 2011 Springer Science+Business Media B.V.


Arbo D.G.,Institute for Astronomy and Space Physics | Lemell C.,Vienna University of Technology | Burgdorfer J.,Vienna University of Technology
Journal of Physics: Conference Series | Year: 2015

We analyze the two-dimensional angular momentum-energy distribution of electrons emitted from argon by short laser pulses. We identify characteristic features of both multiphoton and tunneling ionization in the partial-wave distribution for Keldysh parameters close to unity. We observe a remarkable degree of quantum-classical correspondence in the photoinization process which becomes even more pronounced after intensity averaging over the focal volume. We derive an energy-dependent cut-off for the highest angular momentum accessible within the framework of the strong-field approximation, which accurately reproduces the partial wave distributions found from solutions of the time-dependent Schrödinger equation. © 2015 IOP Publishing Ltd.


Romanelli N.,Institute for Astronomy and Space Physics | Modolo R.,LATMOS | Dubinin E.,Max Planck Institute | Berthelier J.-J.,LATMOS | And 10 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2014

Cassini plasma wave and particle observations are combined with magnetometer measurements to study Titan's induced magnetic tail. In this study, we report and analyze the plasma acceleration in Titan's induced magnetotail observed in flybys T17, T19, and T40. Radio and Plasma Wave Science observations show regions of cold plasma with electron densities between 0.1 and a few tens of electrons per cubic centimeter. The Cassini Plasma Spectrometer (CAPS)-ion mass spectrometer (IMS) measurements suggest that ionospheric plasma in this region is composed of ions with masses ranging from 15 to 17 amu and from 28 to 31 amu. From these measurements, we determine the bulk velocity of the plasma and the Alfvén velocity in Titan's tail region. Finally, a Walén test of such measurements suggest that the progressive acceleration of the ionospheric plasma shown by CAPS can be interpreted in terms of magnetic tension forces. Key Points Ionospheric plasma is observed in Titan's wake The plasma acceleration is analyzed through Walen tests This acceleration can be understood in terms of magnetic tension forces ©2014. American Geophysical Union. All Rights Reserved.


Edberg N.J.T.,Swedish Institute of Space Physics | Wahlund J.-E.,Swedish Institute of Space Physics | Agren K.,Swedish Institute of Space Physics | Morooka M.W.,Swedish Institute of Space Physics | And 3 more authors.
Geophysical Research Letters | Year: 2010

We present electron temperature and density measurements of Titan's cold ionospheric plasma from the Langmuir probe instrument on Cassini from 52 flybys. An expression of the density as a function of temperature is presented for altitudes below two Titan radii. The density falls off exponentially with increased temperature as log(n e) = -2.0log(T e) + 0.6 on average around Titan. We show that this relation varies with location around Titan as well as with the solar illumination direction. Significant heating of the electrons appears to take place on the night/wake side of Titan as the density-temperature relation is less steep there. Furthermore, we show that the magnetospheric ram pressure is not balanced by the thermal and magnetic pressure in the topside ionosphere and discuss its implications for plasma escape. The cold ionospheric plasma of Titan extends to higher altitudes in the wake region, indicating the loss of atmosphere down the induced magnetospheric tail. © 2010 by the American Geophysical Union.


Tissera P.B.,Institute for Astronomy and Space Physics
EPJ Web of Conferences | Year: 2012

We studied the chemical properties of Milky-Way mass galaxies. We found common global chemical patterns with particularities which reflect their different assembly histories in a hierarchical scenario. We carried out a comprehensively analysis of the dynamical components (central spheroid, disc, inner and outer haloes) and their chemical properties. © Owned by the authors, published by EDP Sciences, 2012.

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