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

地球电离层是上层大气中含有离子、电子和中性粒子的部分，主要由入射的太阳辐射吸收而形成。这些粒子的运动导致碰撞，离子和中性粒子碰撞的速率的倒数通常被称为离子-中性粒子碰撞频率，这是电离层物理学中广泛使用的参数。这一重要参数在空间天气和国防的关键模型和模拟的开发中起着至关重要的作用。由于这种测量涉及的复杂性，缺乏对这种碰撞频率的直接观测，而且大多数估计都是基于假设。因此，有必要制定方法来确定离子中性频率的实际值。该提案试图使用现有的高频非相干散射雷达（ISR），可以探测电离层上层。还设想开发普及无线电科学主题的教育材料和网站，这将有助于在STEM领域培训下一代，促进劳动力发展。该研究小组由不同的群体组成，其中包括少数民族和早期职业科学家。在电离层高度，离子速度通常近似于各向同性麦克斯韦分布。然而，在中等到强电场的存在下，在弱电离的，磁化的F-区域电离层的离子速度分布从麦克斯韦扭曲。这是离子-中性碰撞和O+和O之间的共振电荷交换（RCE）的结果，这是该区域主要的离子-中性碰撞类型。离子速度分布畸变的结果是离子温度变得各向异性，导致垂直于磁场的离子温度大于平行于磁场的离子温度。为了获得准确的离子温度，迫切需要开发提供准确的O+和O碰撞截面的技术。该提案旨在解决以下科学问题：（i）O+-O REC碰撞截面是什么，（ii）如何使用解析的O+-O截面进行离子温度的雷达测量与假设麦克斯韦离子速度分布的先前测量进行比较，（iii）O+-O RCE碰撞截面和F区域中产生的离子温度各向异性如何通过上升流影响更高的高度？这些科学问题将回答使用蒙特-卡罗模拟计算的离子速度分布的碰撞和等离子体参数范围很广。此外，还将使用来自高纬度先进模块化非相干散射雷达的数据。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.