CEDAR: Evaluating Ion Temperature Anisotropy in the Weakly Collisional F-region Ionosphere

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The Earth’s ionosphere is the part of the upper atmosphere that has ions, electrons, and neutrals, and is mainly formed by the absorption of the incident solar radiation. The motion of these particles results in collisions and the inverse of the rate at which ions and neutrals collide is often referred to as ion-neutral collision frequency, a widely used parameter in ionospheric physics. This important parameter plays a crucial role in the development of models and simulations critical to space weather and national defense. The direct observations of this collision frequency are lacking due to complexities involved in such measurements, and most of the estimations are based on assumptions. Thus, there is a need to develop methodologies to determine realistic values of ion-neutral frequency. The proposal seeks to use existing high frequency incoherent scatter radars (ISRs) that can probe the upper ionosphere. Development of educational materials and websites for popularizing radio science topics is also envisioned, which will contribute to the training of the next generation in STEM aeras facilitating workforce development. The research team consists of diverse groups with representation from minorities and early-career scientists.At ionospheric altitudes, ion velocity is usually approximated by an isotropic Maxwellian distribution. However, in the presence of moderate to strong electric fields the ion velocity distribution in the weakly-ionized, magnetized F-region ionosphere distorts from a Maxwellian. This is the result of ion-neutral collisions and Resonant Charge Exchange (RCE) between O+ and O, which is the dominant ion-neutral collision type in this region. A consequence of the distortion of the ion velocity distribution is that the ion temperature becomes anisotropic, leading to larger ion temperatures perpendicular to the magnetic field than parallel. To obtain accurate ion temperatures, there is a strong need to develop techniques that provide accurate O+ and O collision cross section. The proposal seeks to address following science questions: (i) what is the O+-O REC collision cross-section, (ii) How do radar measurements of ion temperatures using the resolved O+-O cross-section compare to prior measurements that assume Maxwellian ion velocity distributions, (iii) How does the O+-O RCE collision cross-section and resulting ion temperature anisotropy in the F-region impact higher altitudes through upflows? These science questions will be answered using a Monte-Carlo simulation to compute the ion velocity distributions for a wide range of collisional and plasma parameters. Additionally, data from high-latitude advanced modular incoherent scatter radars will be used.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.