Inferring D Region Parameters Using Improved Incoherent Scatter Radar Techniques at Arecibo

Abstract

With the increased sensitivity and bandwidth, Arecibo 430 MHz incoherent scatter radar was run on 23 July 2006 using two radar modes with a focus on measuring D region parameters. One mode measured the ion line spectra over D region altitudes; the other mode was used as a new way to calibrate the electron densities in the D region and also to correct the ion line spectra. The ion line primarily provided a power profile connecting the D region to altitudes where the plasma line is useful. The plasma line provided the absolute electron density, used in the lower altitudes for calibration, and at F region altitudes for determining the baseline level in the D region spectra due to the folding-in of F region scattered power. It is found that the electron line contribution is about 1–3 times the ion line between 60–75 km altitude ranges. Electron concentration was found to be in the range of a few hundred to 5000 cm⁻³ in the 65–90 km altitude range. The new technique agrees well with the previous measurements. The D region spectral widths were used to calculate the ratio of negative ion to electron concentration (λ). Between 0900 and 1100 LT, a 4 km thick layer of negative ions was observed with λ ∼ 1.6 ± 0.3 around 73–77 km. In the altitude range of 81–91 km, we inferred temperatures ∼ 195–215 K using ion-neutral collision frequencies determined from the spectral widths.