P. Guio

ESR mapping of polar‐cap patches in the dark cusp

We present the first ever measurement of the full thermal plasma properties, of an ionospheric patch in full darkness in the noon region where patches are believed to form. Further these data present the first experimental evidence for the Lockwood and Carlson class of mechanisms for forming patches by plasma injection. These data were possible only because of a new measurement capability we had to develop. We introduce the capability here because it crosses the high-speed threshold that now allows study of a broader class of mesoscale plasma flow-transients, which are thought to occur over time scales near 2 minutes vice 8-10 minutes. Cumulatively such transients may significantly drive global convection. We demonstrate both the validity of and need for our new measurement capability, by presenting a transient flow reversal sweeping across a 500 by 1000 km area, with initial reversal in 4 minutes, and recovery within 6 minutes.

Zakharov simulations of Langmuir turbulence: Effects on the ion-acoustic waves in incoherent scattering

This paper presents a numerical study of the effect of Langmuir turbulence on incoherent scatter spectra. The Langmuir turbulence is driven by low energy beams of electrons in the Earth’s upper ionosphere above 300km. The nonlinear coupling between Langmuir waves and ion-acoustic waves is governed by the Zakharov system of equations. The model is enhanced with stochastic forcing in order to estimate by how much over the thermal level the spectrum seen by an incoherent scatter radar will be enhanced. This also allows us to directly compare the modeled spectra to the observed spectra collected by the incoherent scattering technique, as well as to statistically investigate the signature of the modeled spectra through an exploratory data analysis. Results for different beam energies are presented, covering the regimes of weak as well as strong turbulence. The incoherent scatter spectra signature is discussed in light of these regimes. It is shown that incoherent scatter radar observations of enhanced ion-acou...

Influence of hot plasma pressure on the global structure of Saturn's magnetodisk

Using a model of force balance in Saturns disk-like magnetosphere, we show that variations in hot plasma pressure can change the magnetic field configuration. This effect changes (i) the location of the magnetopause, even at fixed solar wind dynamic pressure, and (ii) the magnetic mapping between ionosphere and disk. The model uses equatorial observations as a boundary condition-we test its predictions over a wide latitude range by comparison with a Cassini high-inclination orbit of magnetic field and hot plasma pressure data. We find reasonable agreement over time scales larger than the period of Saturn kilometric radiation (also known as the camshaft period).

Response of the Jovian thermosphere to a transient ‘pulse’ in solar wind pressure

Abstract The importance of the Jovian thermosphere with regard to magnetosphere–ionosphere coupling is often neglected in magnetospheric physics. We present the first study to investigate the response of the Jovian thermosphere to transient variations in solar wind dynamic pressure, using an azimuthally symmetric global circulation model coupled to a simple magnetosphere and fixed auroral conductivity model. In our simulations, the Jovian magnetosphere encounters a solar wind shock or rarefaction region and is subsequently compressed or expanded. We present the ensuing response of the coupling currents, thermospheric flows, heating and cooling terms, and the aurora to these transient events. Transient compressions cause the reversal, with respect to steady state, of magnetosphere–ionosphere coupling currents and momentum transfer between the thermosphere and magnetosphere. They also cause at least a factor of two increase in the Joule heating rate. Ion drag significantly changes the kinetic energy of the thermospheric neutrals depending on whether the magnetosphere is compressed or expanded. Local temperature variations appear between ~ − 45 and 175 K for the compression scenario and ~ − 20 and 50 K for the expansion case. Extended regions of equatorward flow develop in the wake of compression events – we discuss the implications of this behaviour for global energy transport. Both compressions and expansions lead to a ~ 2000 TW increase in the total power dissipated or deposited in the thermosphere. In terms of auroral processes, transient compressions increase main oval UV emission by a factor of ~ 4.5 whilst transient expansions increase this main emission by a more modest 37%. Both types of transient event cause shifts in the position of the main oval, of up to 1° latitude.Previously, we have presented the first study to investigate the response of the Jovian thermosphere to transient variations in solar wind dynamic pressure, using a coupled, azimuthally symmetric global circulation model coupled with a simple magnetosphere model. This work (Yates et al., 2013, submitted) described the response of thermospheric flows, momentum sources, and the magnetosphere-ionosphere coupling currents to transient compressions and expansions in the magnetosphere. The present study describes the response of thermospheric heating, cooling and the auroral emissions to the aforementioned transient events. We find that transient compressions and expansions, on time scales<= 3 hours, cause at least a factor of two increase in Joule heating per unit volume. Ion drag significantly changes the kinetic energy of the thermospheric neutrals depending on whether the magnetosphere is compressed or expanded. These processes lead to local temperature variations>= 25 K and a ~2000 TW increase in the total power dissipated in the thermosphere. In terms of auroral processes, transient compressions increase main oval UV emission by a factor of ~4.5 whilst transient expansions increase this main emission by a more modest 37%. Both types of transient event cause shifts in the position of the main oval, of up to 1 deg latitude.

Internally driven large-scale changes in the size of Saturn's magnetosphere

Abstract Saturns magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the systems dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10–15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively “plasma‐loaded” or “plasma‐depleted” states, defined in terms of the internal suprathermal plasma pressure.

Influence of upstream solar wind on thermospheric flows at Jupiter

The coupling of Jupiters magnetosphere and ionosphere plays a vital role in creating its auroral emissions. The strength of these emissions is dependent on the difference in speed of the rotational flows within Jupiters high-latitude thermosphere and the planets magnetodisc. Using an azimuthally symmetric global circulation model, we have simulated how upstream solar wind conditions affect the energy and direction of atmospheric flows. In order to simulate the effect of a varying dynamic pressure in the upstream solar wind, we calculated three magnetic field profiles representing compressed, averaged and expanded ‘middle’ magnetospheres. These profiles were then used to solve for the angular velocity of plasma in the magnetosphere. This angular velocity determines the strength of currents flowing between the ionosphere and magnetosphere. We examine the influence of variability in this current system upon the global winds and energy inputs within the Jovian thermosphere. We find that the power dissipated by Joule heating and ion drag increases by ∼190%∼190% and ∼185%∼185% from our compressed to expanded model respectively. We investigated the effect of exterior boundary conditions on our models and found that by reducing the radial current at the outer edge of the magnetodisc, we also limit the thermospheres ability to transmit angular momentum to this region.

Water in the near-infrared spectrum of comet 8P/Tuttle

A B S T R A C T High-resolution spectra of comet 8P/Tuttle were obtained in the frequency range 3449.0– 3462.2 cm −1 on 2008 January 3 UT using CGS4 with echelle grating on United Kingdom Infrared Telescope. In addition to observing solar pumped fluorescent lines of H 2O, the long integration time (152 min on target) enabled eight weaker H 2O features to be assigned, most of which had not previously been identified in cometary spectra. These transitions, which are from higher energy upper states, are similar in character to the so-called SH lines recorded in the post Deep Impact spectrum of comet Tempel 1. We have identified certain characteristics that these lines have in common, and which in addition to helping to define this new class of cometary line give some clues to the physical processes involved in their production. Finally, we derive an H 2O rotational temperature of 62 ± 5 K and a water production rate of (1.4 ± 0.3) × 10 28 molecules s −1 .

Phase space structures generated by an absorbing obstacle in a streaming plasma

The dynamic behavior of an ion flow around an obstacle in a collisionless plasma is investigated. The obstacle consists here of an absorbing cylinder, and a 2 dimensional electrostatic particle-in-cell simulation is used to study the flow characteristics. The formation of irregular filamented density depletions, oblique to the flow, is observed. The dynamics of these structures depend on the physical parameters of the plasma. The structures form at the edges of the wake behind the obstacle, in a region with a strong velocity shear, and are found to be associated with phase-space vortices, observed specially in the velocity direction perpendicular to the flow. The results can be of interest in the interpretation of structures in space plasmas as observed by instrumented space crafts.

Asymmetries observed in Saturn's magnetopause geometry

Abstract For over 10 years, the Cassini spacecraft has patrolled Saturns magnetosphere and observed its magnetopause boundary over a wide range of prevailing solar wind and interior plasma conditions. We now have data that enable us to resolve a significant dawn‐dusk asymmetry and find that the magnetosphere extends farther from the planet on the dawnside of the planet by 7 ± 1%. In addition, an opposing dawn‐dusk asymmetry in the suprathermal plasma pressure adjacent to the magnetopause has been observed. This probably acts to reduce the size asymmetry and may explain the discrepancy between the degree of asymmetry found here and a similar asymmetry found by Kivelson and Jia (2014) using MHD simulations. Finally, these observations sample a wide range of season, allowing the “intrinsic” polar flattening (14 ± 1%) caused by the magnetodisc to be separated from the seasonally induced north‐south asymmetry in the magnetopause shape found theoretically (5 ± 1% when the planets magnetic dipole is tilted away from the Sun by 10–17°).

Electric field variability and classifications of Titan's magnetoplasma environment

Abstract. The atmosphere of Saturns largest moon Titan is driven by photochemistry, charged particle precipitation from Saturns upstream magnetosphere, and presumably by the diffusion of the magnetospheric field into the outer ionosphere, amongst other processes. Ion pickup, controlled by the upstream convection electric field, plays a role in the loss of this atmosphere. The interaction of Titan with Saturns magnetosphere results in the formation of a flow-induced magnetosphere. The upstream magnetoplasma environment of Titan is a complex and highly variable system and significant quasi-periodic modulations of the plasma in this region of Saturns magnetosphere have been reported. In this paper we quantitatively investigate the effect of these quasi-periodic modulations on the convection electric field at Titan. We show that the electric field can be significantly perturbed away from the nominal radial orientation inferred from Voyager 1 observations, and demonstrate that upstream categorisation schemes must be used with care when undertaking quantitative studies of Titans magnetospheric interaction, particularly where assumptions regarding the orientation of the convection electric field are made.