ABSTRACT

Magnetospheric mass density controls the time response of the magnetosphere to external and internal forcing, and is thus important for understanding and predicting the effects of time dependent phenomena such as sudden impulses and Ultra-Low Frequency (ULF) waves. These dynamic processes can lead to acceleration or loss of radiation belt particles. In this project, spacecraft observations of toroidal Alfven waves will be used to evaluate the magnetospheric mass density and to develop a model to describe both the equatorial and field line distribution of the density as a function of parameters describing the state of the magnetosphere. The main spacecraft observations to be used are magnetic and electric field measurements by GOES, CRRES, Polar, and AMPTE/CCE spacecraft, and velocity moment measurements by LANL geosynchronous satellites. In addition to spacecraft observations of Alfven waves, in-situ electron density (CRRES and Polar), in-situ particle data (LANL geosynchronous satellites), and ground magnetometer data will be used to validate the model and evaluate the average ion mass. State of the art techniques for mass density inversion include adjustable magnetic field models and multi-harmonic frequency input to get the field line dependence of the mass density. Specific questions that will be considered as part of this project are: (1) What is the mass density in the magnetosphere, and how does it depend on L shell, the magnetic local time MLT, the state of the magnetosphere as specified by geomagnetic indices such as Dst, Kp, and the solar wind condition as specified by parameters such as the solar wind velocity and dynamic pressure, and how does the mass density vary during the solar cycle? (2) What is the distribution of mass density along magnetic field lines and what are the physical processes that determine this distribution? Under what conditions is there a peak in local density at the magnetic equator? (3) Is the mass density inferred from the toroidal Alfven waves consistent with the electron density? What is the contribution of heavy ions to the mass density, and how does this contribution depend on the state of the magnetosphere? What physical processes cause the accumulation of heavy ions at the magnetic equator? (4) Are toroidal Alfven frequencies measured on the ground consistent with those in space if the ground location is mapped to the spacecraft location?

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