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Khodachenko M.L.,Austrian Academy of Sciences | Alexeev I.,Moscow State University | Belenkaya E.,Moscow State University | Lammer H.,Austrian Academy of Sciences | And 5 more authors.
Astrophysical Journal | Year: 2012

Weak intrinsic magnetic dipole moments of tidally locked close-in giant exoplanets ("hot Jupiters") have been shown in previous studies to be unable to provide an efficient magnetospheric protection for their expanding upper atmospheres against the stellar plasma flow, which should lead to significant non-thermal atmosphere mass loss. The present work provides a more complete view of the magnetosphere structure of "hot Jupiters," based on a paraboloid magnetospheric model (PMM). Besides the intrinsic planetary magnetic dipole, the PMM considers among the main magnetic field sources also the electric current system of the magnetotail, magnetopause currents, and the ring current of a magnetodisk. Due to the outflow of ionized particles from the hydrodynamically expanding upper atmosphere, "hot Jupiters" may have extended magnetodisks. The magnetic field produced by magnetodisk ring currents dominates above the contribution of an intrinsic magnetic dipole of a "hot Jupiter" and finally determines the size and shape of the whole magnetosphere. A slower-than-the-dipole-type decrease of the magnetic field with the distance forms the essential specifics of magnetodisk-dominated magnetospheres of "hot Jupiters." This results in their 40%-70% larger scales compared to those traditionally estimated by only the planetary dipole taken into account. Therefore, the formation of magnetodisks has to be included in the studies of the stellar wind plasma interaction with close-in exoplanets, as well as magnetospheric protection for planetary atmospheres against non-thermal escape due to erosion by the stellar plasma flow. Source

Delport B.,University of KwaZulu - Natal | Collier A.B.,University of KwaZulu - Natal | Lichtenberger J.,Etvs University | Rodger C.J.,University of Otago | And 3 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

On 4 August 2010 a moderate geomagnetic storm occurred with minimum Dst of-65 nT and maximum Kp of 7-. Shortly after the onset of this storm, VLF chorus was observed at Marion Island (L = 2.6). Over time the spectral structure of the chorus transformed into a hiss band spanning the same frequency range. The observation of overlapping chorus and hiss suggests that Marion Island was close to the plasmapause at the time of this event, and provides ground-based observational confirmation of the generation mechanism of plasmaspheric hiss from chorus waves outside of the plasmasphere. Chorus observations at Marion Island were not common during this period of the solar cycle and so this event was investigated in detail. The geomagnetic conditions are discussed and geosynchronous particle data and broadband data from two other stations are presented. Empirical models are employed to predict the location of the plasmapause, and its location is inferred from a knee whistler recorded at Dunedin, New Zealand. These show that Marion Island is in the vicinity of the plasmapause during the event. The event is also compared to chorus observed at similar L after the Halloween storms of 2003. The rarity of the chorus observation is quantified using DEMETER VLF data. The DEMETER data, along with the various ground based VLF measurements, allows us to infer temporal and spatial variations in the chorus source region. © 2012. American Geophysical Union. All Rights Reserved. Source

Clilverd M.A.,Natural Environment Research Council | Rodger C.J.,University of Otago | Gamble R.J.,University of Otago | Ulich T.,University of Oulu | And 7 more authors.
Journal of Geophysical Research: Space Physics | Year: 2010

AARDDVARK data from a radio wave receiver in Sodankyl, Finland have been used to monitor transmissions across the auroral oval and just into the polar cap from the very low frequency communications transmitter, call sign NAA (24.0 kHz, 44°N, 67°W, L = 2.9), in Maine, USA, since 2004. The transmissions are influenced by outer radiation belt (L = 3-7) energetic electron precipitation. In this study, we have been able to show that the observed transmission amplitude variations can be used to determine routinely the flux of energetic electrons entering the upper atmosphere along the total path and between 30 and 90 km. Our analysis of the NAA observations shows that electron precipitation fluxes can vary by 3 orders of magnitude during geomagnetic storms. Typically when averaging over L = 3-7 we find that the >100 keV POES "trapped" fluxes peak at about 106 el. cm-2 s-1 sr-1 during geomagnetic storms, with the DEMETER >100 keV drift loss cone showing peak fluxes of 105 el. cm -2 s-1 sr-1, and both the POES >100 keV "loss" fluxes and the NAA ground-based >100 keV precipitation fluxes showing peaks of ∼104 el. cm-2 s-1 sr-1. During a geomagnetic storm in July 2005, there were systematic MLT variations in the fluxes observed: electron precipitation flux in the midnight sector (22-06 MLT) exceeded the fluxes from the morning side (0330-1130 MLT) and also from the afternoon sector (1130-1930 MLT). The analysis of NAA amplitude variability has the potential of providing a detailed, near real-time, picture of energetic electron precipitation fluxes from the outer radiation belts. Copyright 2010 by the American Geophysical Union. Source

Krafft C.,Ecole Polytechnique - Palaiseau | Krafft C.,University Paris - Sud | Volokitin A.S.,Space Research Institute | Krasnoselskikh V.V.,Laboratoire Of Physique Et Chimie Of Lenvironnement Et Of Lespace
Astrophysical Journal | Year: 2015

Langmuir turbulence excited by electron flows in solar wind plasmas is studied on the basis of numerical simulations. In particular, nonlinear wave decay processes involving ion-sound (IS) waves are considered in order to understand their dependence on external long-wavelength plasma density fluctuations. In the presence of inhomogeneities, it is shown that the decay processes are localized in space and, due to the differences between the group velocities of Langmuir and IS waves, their duration is limited so that a full nonlinear saturation cannot be achieved. The reflection and the scattering of Langmuir wave packets on the ambient and randomly varying density fluctuations lead to crucial effects impacting the development of the IS wave spectrum. Notably, beatings between forward propagating Langmuir waves and reflected ones result in the parametric generation of waves of noticeable amplitudes and in the amplification of IS waves. These processes, repeated at different space locations, form a series of cascades of wave energy transfer, similar to those studied in the frame of weak turbulence theory. The dynamics of such a cascading mechanism and its influence on the acceleration of the most energetic part of the electron beam are studied. Finally, the role of the decay processes in the shaping of the profiles of the Langmuir wave packets is discussed, and the waveforms calculated are compared with those observed recently on board the spacecraft Solar TErrestrial RElations Observatory and WIND. © 2015. The American Astronomical Society. All rights reserved.. Source

Dimmock A.P.,University of Sheffield | Balikhin M.A.,University of Sheffield | Krasnoselskikh V.V.,Laboratoire Of Physique Et Chimie Of Lenvironnement Et Of Lespace | Walker S.N.,University of Sheffield | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

The cross-shock electrostatic potential at the front of collision-less shocks plays a key role in the distribution of energy at the shock front. Multipoint measurements such as those provided by the Cluster II mission provide an ideal framework for the study of the cross-shock potential because of their ability to distinguish between temporal and spacial variations at the shock front. We present a statistical study of the cross-shock potential calculated for around 50 crossings of the terrestrial bow shock. The statistical dependency of the normalized (with resect to upstream ion kinetic energy) cross-shock potential (K) on the upstream Alfvén Mach number is in good agreement with analytical results that predict decrease of k with increasing Mach number. Copyright 2012 by the American Geophysical Union. Source

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