The effects of Bhatnagar‐Gross‐Krook, Brownian, and hard‐sphere ion‐neutral collision models on the incoherent scatter spectrum in the E region

We revisit the theory developed by Hagfors and Brockelman (1971). The purpose of this work is to improve the understanding of variations in the incoherent scatter spectrum in the lower E region of the ionosphere between approximately 85 and 150 km under the assumption of Brownian, Bhatnagar‐Gross‐Krook, and hard‐sphere collisions in the absence of magnetic field influences, for operating frequencies representative of the chain of NSF‐sponsored incoherent scatter radars (ISRs), which range from 50 to 1290 MHz. Also, we extend the computationally limited examples in Hagfors and Brockelman (1971) as well as demonstrate the feasibility of making the E region measurements at the Arecibo Observatory ISR in Puerto Rico (18°N, 67°W). We confirm the theory from Hagfors and Brockelman (1971) and show that the original nondimensionalized examples were representative of spectra at approximately 95, 105, and 150 km. Additionally, our results show that there is more variability in the incoherent scatter spectrum for the aforementioned ion‐neutral collision approximations, especially in the 90–105 km altitude range compared to the results shown by Hagfors and Brockelman (1971). This is most likely due to the greater computational resources currently available and the more up‐to‐date models for atmospheric and ionospheric conditions derived from MSIS‐00 and IRI‐07, respectively. These findings suggest that future work is needed to evaluate the impact, if any, on the ionospheric parameters derived using each of the three ion‐neutral collision approximations.