Other
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sa61a09g&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SA61A-09
Other
2415 Equatorial Ionosphere, 2467 Plasma Temperature And Density, 2481 Topside Ionosphere, 2494 Instruments And Techniques
Scientific paper
It has been known for quite a while now that the there is a problem with the temperatures deduced from Jicamarca autocorrelation function data. Basically, after performing the least squares fitting with the theory currently in use at all other ISR's, the ion temperature often appears higher than the electron temperature, especially at night, leading to a Te/Ti ratio below one -- obviously a geophysically unrealistic result. The problem becomes more severe the closer the Jicamarca beam points to perpendicular to the magnetic field. In the past most efforts were concentrated with finding a systematic error that would explain the problem, but all such attempts failed in providing an explanation. A different approach was taken by Sulzer and Gonzalez [JGR vol 104 pp 22535-22551, 1999], who realized that the Jicamarca ACF measurements appeared correct, so probably the problem was not caused by a systematic error or instrumental error, but rather by an error in the interpretation of the data through the eyes of the IS theory. Working from that assumption they found that electron Coulomb collisions affect the IS spectrum and as the radar points nearly perpendicular to the magnetic field this effect becomes measurable, and thus must be taken into account in the calculation of the theoretical spectrum. The calculation of this effect, however, is extremely complicated, and so far has only been solved with the help of a very accurate computer simulation. The output of this simulation contains the values of a function (Je) proportional to the electron admittance function (ye). The electron admittance is actually a function of electron temperature, electron density, angle with respect to the magnetic field, and frequency. Thus, in order to use the results from the Coulomb collisions simulations to perform least squares fitting, a library of Je functions must be generated for a reasonable grid in all these parameters. Such a library is now available, and we have incorporated it to an incoherent scattering least squares fitting code. We will give an overview of how these collisions affect the spectrum and will show how the predictions from the theory are necessary in order to obtain realistic ion and electron temperatures over a wide range of geophysical conditions and for various antenna pointing positions.
Aponte Nestor
González Sixto A.
Sulzer Michael P.
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