Physics – Plasma Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsa12a0664s&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SA12A-0664
Physics
Plasma Physics
6929 Ionospheric Physics (2409), 7800 Space Plasma Physics
Scientific paper
The measurement of temperatures in the various atmospheric regions is essential for meeting the goals of the CEDAR program. The ion and electron temperatures in the F region and topside ionosphere over the Jicamarca Radio Observatory, one of the world's most powerful incoherent scatter radars, have been under question for almost forty years because carefully-made statistically significant measurements show that the apparent electron temperatures are often less than than the apparent ion temperatures. This violates the physics of the region: energy flows from the electrons to the ions during the day, and equilibrium exists at night. Although measurements at Jicamarca have certain possible biases, no one has ever shown that the problem was due difficulties with interpreting the data. The problem resulted from the omission of the effects of electron-ion and electron-electron Coulomb collisions in the equation for the incoherent scatter spectrum. A numerical solution gives spectra such that comparisons with data imply equal ion and electron temperatures when expected. The new spectra have interesting and unexpected consequences. The collisonal effect is far greater that simple collisonal models such as Langevin's equation or the BGK approximation imply when observations are made looking vertically, or nearly so, with the Jicamarca radar. It has been necessary to include both types of collisions with high accuracy in a numerical model since the resulting effect is dependent upon the interaction between the two and is unlike either alone. A great simplifying principle of incoherent scatter (IS) theory is that in many situations the spectrum is a simple combination of the spectra of the individual species of the plasma which would apply in the absence of the electrostatic interaction. Assuming this, then we need consider only the collisional effect on electrons freely streaming along the magnetic field. Furthermore the gyration radius is small compared to the radar wavelength, and the field enters only as a trigonometric factor which slows the progress of the electrons along the radar line of sight. Numerical simulations show the following results:
The rapid decrease of the collisional coefficients with increasing electron speed plays a very important role in the resulting IS spectral shape. Electron-ion collisions, affecting only the directions and not the speeds of the electrons, would alter only the central part of the IS spectrum because of result 1. Electron-electron collisions, affecting both the speeds and directions of the electrons, significantly modify the spectrum of result 2. even though their collisional coefficients are relatively small.
Aponte Nestor
Gonzalez Salustio
Sulzer Michael P.
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