LWS TR&T Focus Teams:
Plasma-Neutral Gas Coupling
Team Chair: Geoff Crowley
Target Description: The coupling of ionized plasma to neutral material is a fundamental physical process of importance to many problems in Heliophysics and Astrophysics. It is a key to our understanding of magnetosphere-ionosphere-atmosphree interactions, of the solar chromosphere, and of prominences and spicules embedded in the corona, as well as our understanding of interstellar gas within the solar system, comets in the solar wind, and planetary satellites inside magnetospheres or exposed to the solar wind.
Heliospheric material spans enormous ranges in thermodynamic and magnetic conditions. Regimes of plasma dynamic beta, particle magnetization, and form of conductivity change dramatically between the base of the chromosphere or thermosphere and the corona and magnetosphere, respectively. Mixed plasma conditions occur at interface zones, such as the cool spicules ejected into the solar corona, or ionospheric plasma fountains. Coupling across interfaces is especially strong when a magnetic field linkage threads the transition: mass, momentum, and energy transfer are then highly efficient. Where ions are magnetized, ion-neutral collisions may be the dominant way to convert fast ordered motion into heat. This is a major source of heating for the ionosphere and thermosphere, and possibly for the chromosphere. If significant, this mechanism would place chromospheric UV emission (with its varying influence on the planets) on a firm physical basis. Weakly ionized material may also play a significant role in determining the hydromagnetic state in adjacent regions, such as the corona, as ion-neutral collisions modify the conductivity and magnetic field, and above the aurora, where heating has recently been found to greatly enhance densities. The role of plasma instabilities and irregularities in plasma-neutral coupling is likely to be important, but is not well understood. Plasma-neutral coupling is an area ripe for an inter-disciplinary initiative comparing first principles theory with both solar and ionospheric remote sensing and ionospheric in situ observations, and holds the potential to resolve diverse problems of Heliophysics.
Goals and Measures of Success: The principal goals are (1) establish a cross-disciplinary collaboration between the solar, magnetosphere, and the ionosphere/thermosphere communities to resolve strategically important questions concerning the transition from a weakly ionized dense gas to a fully ionized tenuous plasma with the linkage of the electromagnetic field, (2) enhance our physical understanding of such a system, and (3) encourage chromospheric observations that quantify magnetic and thermal conditions in the chromosphere, in particular, observations with the new generation of spectropolarimetric instruments, and (4) improve numerical modeling of the coupling in both the chromosphere and the ionosphere-thermosphere.
Measures of success include: (1) First-principles self-consistent numerical models of the chromosphere that describe available observations, (2) First-principles self-consistent numerical models that describe realistically the plasma-neutral interaction in the ionosphere-thermosphere, (3) Demonstrated understanding of heating rates produced by ion-neutral relative motions in magnetized regions. (4) Refinement of self-consistent numerical models of energetics in the ionospheric E region that incorporate the full range of ionosphere/thermosphere kinetic and wave effects.
Types of investigations: