next up previous contents
Next: Intensity Calibration of Up: Examples of UVCS Previous: Rotation of the

Energy Transport by Suprathermal Electrons

Most theoretical solar wind models assume that the random velocities of the electrons are Maxwellian. However, if there is a significant population of suprathermal electrons, they could play an important role in solar wind acceleration (Olbert 1983). This can be investigated using the combined information provided by the UVCS and the ``in situ" measurements by studying the ionization state of the solar wind. The ionization state of the solar wind is ``frozen in" in a region where the UVCS provides unique and critical plasma diagnostics, 1.3 r 10 (see review by Owocki, 1983). In this region the UVCS can provide the temperature, density and velocity information needed for detailed calculations of the ionization state of the outflowing solar wind plasma, including constraints on the flow velocities of both the electron/proton plasma and the heavy ions. The flow speed of the heavy ions may differ from that of the electron/proton plasma. Studies of the effects of suprathermal electrons on the charge state distribution of elements have demonstrated that the relative populations of various states of ionization are very sensitive to the presence of suprathermal electrons (Owocki and Schudder 1983; Bürgi, 1987). Hence, by comparison of the charge distribution computed for a wind model with the corresponding charge states and relative abundances measured in the solar wind at 1 AU by CELIAS, tight constraints can be placed on the suprathermal electron population. The densities can be inferred out to 30 from C1 measurements carried out by LASCO, inferences of coronal temperatures, and nonthermal velocities can be made inside 3 . UVCS will provide temperatures, electron densities, and velocity widths between 1.3 to 10 As pointed out by Bürgi (1987) an additional empirical constraint is provided by the radial variation of the helum abundance, another parameter which UVCS can measure (see the observation program on Abundance of Elements in the Outer Corona).

Coordinated observations between these three instruments will be carried out in different coronal structures, such as coronal holes, and quiet regions. Using measurements from all three instruments, we can impose tighter constraints on solar wind models.

Energy Transport by Suprathermal Electrons



next up previous contents
Next: Intensity Calibration of Up: Examples of UVCS Previous: Rotation of the



Peter Smith
Fri Jan 17 12:11:15 EST 1997