Vibrational and rotational cooling of electrons by molecular hydrogen

The cooling of electrons by vibrational and rotational excitation of molecular hydrogen plays an important role in the thermal balance of electrons in atmospheres containing significant amounts of H₂. Calculations of vibrational and rotational cooling rates of electrons by H₂ are described. Results are presented for a wide range of electron and neutral temperatures. Analytical formulae for some of the cooling rates are also provided.     

Crossing Boundaries in a Collaborative Modeling Workspace

There is substantial literature on the importance of bridging across disciplinary and science–management boundaries. One of the ways commonly suggested to cross boundaries is for participants from both sides of the boundary to jointly produce information (i.e., knowledge co-production). But simply providing tools or bringing people together in the same room is not sufficient. Here we present a case study documenting the mechanisms by which managers and scientists collaborated to incorporate climate change projections into Colorado’s State Wildlife Action Plan. A critical component of the project was the use of a collaborative modeling and visualization workspace: the U.S. Geological Survey’s Resource for Advanced Modeling (RAM). Using video analysis and pre/post surveys from this case study, we examine how the RAM facilitated cognitive and social processes that co-produced a more salient and credible end product. This case provides practical suggestions to scientists and practitioners who want to implement actionable science.     

Nitric oxide gamma band emission rate factor

Molecular fluorescence emission rate factors for the strong bands of the nitric oxide gamma system have been calculated using recent branching ratios and different temperatures. For the 1-0 gamma band the effects of self-absorption by NO have been taken into account, and effective emission rate factors were calculated for a range of NO column densities at several different temperatures. For column densities near 10¹⁶ cm^?2 self-absorption corrections to the emission rate factor can be significant. The emission rate factor for the 1-0 gamma band is 7.19 or 7.68 × 10^?6 photons molecule^?1 sec^?1 depending upon the use of experimental or theoretical branching ratios.     

The absorption of energetic electrons by molecular hydrogen gas

The processes by which energetic electrons lose energy in a weakly ionized gas of molecular hydrogen are analysed and calculations are carried out taking into account the discrete nature of the excitation processes. The excitation, ionization and heating efficiencies are computed for electrons with energies up to 100 eV absorbed in a gas with fractional ionizations up to 10^?2 and the mean energy per neutral hydrogen atom pair is calculated.     

Disappearing ionospheres on the nightside of Venus

Instruments on the Pioneer Venus Orbiter have detected a substantial ionosphere on the nightside of Venus during most orbits. However, during some orbits the nightside ionosphere seems to have almost disappeared, existing only as irregular patches of low-density plasma. The solar wind dynamic pressure on these occasions is greater than average. We have correlated data from several instruments (Langmuir probe, ion mass spectrometer, retarding potential analyzer, magnetometer, and plasma analyzer) for a number of orbits during which the nightside ionosphere had disappeared. The magnetic field tends to be coherent, horizontal, and larger than usual, and the electron and ion temperatures are much larger than they usually are on the nightside. We suggest mechanisms which might explain the reasons for the disappearance of the ionosphere when the solar wind dynamic pressure is large.     

Comparisons of Cassini flybys of the Titan magnetospheric interaction with an MHD model: Evidence for organized behavior at high altitudes

Recent papers suggest the significant variability of conditions in Saturn’s magnetosphere at the orbit of Titan. Because of this variability, it was expected that models would generally have a difficult time regularly comparing to data from the Titan flybys. However, we find that in contrast to this expectation, it appears that there is underlying organization of the interaction features roughly above ～1800 km (1.7 Rt) altitude by the average external field due to Saturn’s dipole moment. In this study, we analyze Cassini’s plasma and magnetic field data collected at 9 Titan encounters during which the external field is close to the ideal southward direction and compare these observations to the results from a 2-fluid (1 ion, 1 electron) 7-species MHD model simulations obtained under noon SLT conditions. Our comparative analysis shows that under noon SLT conditions the Titan plasma interaction can be viewed in two layers: an outer layer between 6400 and 1800 km where interaction features observed in the magnetic field are in basic agreement with a purely southward external field interaction and an inner layer below 1800 km where the magnetic field measurements show strong variations and deviate from the model predictions. Thus the basic features inferred from the Voyager 1 flyby seem to be generally present above ～1800 km in spite of the ongoing external variations from SLT excursions, time variability and magnetospheric current systems as long as a significant southward external field component is present. At around ～1800 km kinetic effects (such as mass loading and heavy ion pickup) and below 1800 km ionospheric effects (such as drag of ionospheric plasma due to coupling with neutral winds and/or magnetic memory of Titan’s ionosphere) complicate what is observed.     

Coupled ion and neutral rotating model of Titan's upper atmosphere

A one-dimensional composition model of Titan's upper atmosphere is constructed, coupling 36 neutral species and 47 ions. Energy inputs from the Sun and from Saturn's magnetosphere and updated temperature and eddy coefficient parameters are taken into account. A rotating technique at constant latitude and varying local-time is proposed to account for the diurnal variation of solar inputs. The contributions of photodissocation, neutral chemistry, ion-neutral chemistry, and electron recombination to neutral production are presented as a function of altitude and local time. Local time-dependent mixing ratio and density profiles are presented in the context of the TA and T₅ Cassini data and are compared in detail to previous models. An independent and simplified ion and neutral scheme (19-species) is also proposed for future 3D-purposes. The model results demonstrate that a complete understanding of the chemistry of Titan's upper atmosphere requires an understanding of the coupled ion and neutral chemistry. In particular, the ionospheric chemistry makes significant contributions to production rates of several important neutral species.     

Airglow from the inner comas of comets

The intensities of radiation from the inner comas of comets which are composed primarily of water and carbon monoxide have been calculated. Only “airglow” emissions initiated by the absorption of extreme ultraviolet radiation have been considered. The photoionizations of H₂O, CO, CO₂, and N₂ are the most important emission sources, although photoelectron excitation is also considered. Among the emission features for which intensities were calculated are H₂O⁺ ($\text{A}\text{?}{}^2\text{A}{}_{\mathrm{1?}}\text{X}\text{?}{}^2\text{B}{}_1$), CO⁺ (first negative), CO (fourth positive), CO (Cameron), CO₂⁺ ($\text{B}\text{?}{}^2\text{?}{}_{\mathrm{u}}\text{?}\text{X}\text{?}{}^2\text{II}{}_{\mathrm{g}}$), N₂ (Vegard-Kaplan), N₂⁺ (first negative), and OI (1304 Å). In the inner coma (collision region) these airglow mechanisms are shown to be possible competitors with the usually assumed resonance scattering and flourescence excitation mechanisms which are appropriate for the outer coma and tail.     

Titan's corona: The contribution of exothermic chemistry

The contribution of exothermic ion and neutral chemistry to Titan's corona is studied. The production rates for fast neutrals N₂, CH₄, H, H₂, ³CH₂, CH₃, C₂H₄, C₂H₅, C₂H₆, N(⁴S), NH, and HCN are determined using a coupled ion and neutral model of Titan's upper atmosphere. After production, the formation of the suprathermal particles is modeled using a two-stream simulation, as they travel simultaneously through a thermal mixture of N₂, CH₄, and H₂. The resulting suprathermal fluxes, hot density profiles, and energy distributions are compared to the N₂ and CH₄ INMS exospheric data presented in [De La Haye, V., Waite Jr., J.H., Johnson, R.E., Yelle, R.V., Cravens, T.E., Luhmann, J.G., Kasprzak, W.T., Gell, D.A., Magee, B., Leblanc, F., Michael, M., Jurac, S., Robertson, I.P., 2007. J. Geophys. Res., doi:10.1029/2006JA012222, in press], and are found insufficient for producing the suprathermal populations measured. Global losses of nitrogen atoms and carbon atoms in all forms due to exothermic chemistry are estimated to be and .     

Solar wind charge exchange and local hot bubble X‐ray emission with the DXL sounding rocket experiment

The Diffuse X‐ray emission from the Local Galaxy (DXL) sounding rocket is a NASA approved mission with a scheduled first launch in December 2012. Its goal is to identify and separate the X‐ray emission of the solar wind charge exchange (SWCX) from that of the local hot bubble (LHB) to improve our understanding of both. To separate the SWCX contribution from the LHB, DXL will use the SWCX signature due to the helium focusing cone at l = 185°, b = –18°. DXL uses large area proportional counters, with an area of 1000 cm² and grasp of about 10 cm² sr both in the 1/4 and 3/4 keV bands. Thanks to the large grasp, DXL will achieve in a 5‐minute flight what cannot be achieved by current and future X‐ray satellites (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)