PROJECTS

Mary Hudson, P. I.

The Dartmouth-Berkeley-Minnesota theory team has identified a number of mesoscale phenomena to be investigated as part of the GGS program. A broad range of techniques are implemented including ideal and reduced MHD, two fluid, hybrid, particle-in-cell and test particle simulations. Detailed comparison of simulations results with GGS satellite and ground based data will be undertaken.

William Lotko, P. I.

The main visual cues for magnetospheric dynamics are provided by the aurora, and its observed forms pose fundamental questions on the interaction between the magnetosphere and ionosphere: What causes auroral intensifications, dynamics, and multiplicity? Why do individual discrete arcs span a thousand kilometers in longitudeyet only one kilometer in latitude? What determines their locations? Where do auroral arcs map to in the magnetosphere, and what are their magnetospheric signatures? Why is auroral particle acceleration confined largely to low altitudes? And there are many more.

NASA: Magnetic Storm Effects on Particle Energization in the Magnetosphere

Mary Hudson, P. I.

Our goal is to study the effects of hydromagnetic waves on the relaxation of the storm time ring current. We have modified the ring current Lorentz trajectory code used by Li et al. (JGR, 98, 215, 1993) to handle relativistic guiding center trajectories for study of the rapid formation of new radiation belts associated with the March 24, 1991 storm sudden commencement. This model has been highly successful at explaining the observed acceleration of electrons (Li et al., GRL, 20, 2423, 1993) and protons (Hudson et al., GRL, 22, 291, 1995) by tens of MeV in less than a drift period.

Mary Hudson, P. I.

Richard Denton, Co-I., Victor Marchenko, Co-I.

We are studying 1) inner magnetospheric cavity modes, 2) general properties of field line resonance modes, and 3) excitation of internally-driven field line resonance modes by energetic ring current particles. Key questions to be examined are: what is the cavity mode structure in the inner magnetosphere and the frequencies one should expect to see in ground and satellite magnetometer data, and what is the efficiency of energy transport from the outer magnetosphere; what controls the field line resonant mode radial structure; and what causes the nonlinear saturation of the drift-bounce resonant mode, and what is the self-consistent effect of the mode on ion motion. The primary objective is to gain a quantitative understanding of magnetospheric hydrodynamic modes and their coupling to external perturbations and internal sources of free energy such as the ring current. The hybrid MHD-gyrokinetic code has been fully developed.

Richard Denton, P. I.

We are studying electromagnetic ion cyclotron and mirror waves in the magnetosheath and magnetosphere. The goal is to firmly identify these waves and to understand their stability, and spectral and polarization properties. We developed a bounded anisotropy model which models the macroscopic effect of cyclotron wave scattering on ion temperature evolution.

Ground Based Measurements of Auroral Radio Emissions

Ground based measurements of auroral radio emissions by Dartmouth College have been taking place since 1992 when our first radio receiver was placed in Circle Hot Springs, Alaska. In addition to the original equipment we now have have similar radio receivers in Kangerlussuaq (Søndre Strømfjord), Greenland, at the south pole station, many others in Antartica, and a chain of five sites in northern Canada (see map).

• Auroral Emission Observations -- James LaBelle and Simon Shepherd
  An overview of auroral emissions which have been observed by Dartmouth.

  Auroral Roar Fine Structure; Part I -- James LaBelle and Richard Brittain

  An initial look at the fine structure detail of auroral roar.

  Medium Frequency (MF) Bursts -- James LaBelle and Simon Shepherd

  A broadband, bursty emission recently discovered by Dartmouth Researchers.

  Auroral Roar Fine Structure; Part II -- Simon Shepherd and James LaBelle

  A more comprehensive look at the fine structure detail of auroral roar.

  Polarization of Auroral Radio Emissions -- Simon Shepherd and James LaBelle

  A look at the polarization of emissions of various emissions.

In situ Measurements of Ionospheric Irregularities

Dartmouth is involved in many rocket campaigns.

NASA: High-Altitude Spread-F -- James LaBelle and Jörg-Micha Jahn

Equatorial spread-F (ESF) is a dramatic nighttime plasma instability phenomenon typical for Earth's equatorial ionosphere. It produces structures at scales from more than 1000 km to less than 10 cm. The altitude ranges covered by spead-F can at times exceed 1000 km. In October 1994 a NASA/Dartmouth sounding rocket was launched from Brazil to carry a payload into high-altitude spread-F conditions. Data from this flight provide the first in situ measurements within spread-F above 600 km altitude. Collisional effects in this region are negligible, much in contrast to lower altitudes where we have to look at the problem in a collisional context. Based on the rocket measurements our research tries to provide an understanding of high-altitude spread-F, particular in comparison to the wealth of results gained at lower altitudes.