Collaborative Research: CEDAR--Lower Atmospheric Source Regions of Medium-scale Gravity Waves

本项目将研究在Poker Flat和Arecibo两个非相干散射雷达站向上传播的重力波对F区电离层的观测扰动的来源。该研究的一个副产品将是提取时变的F区中性风。研究活动包括利用新技术在两台雷达上进行重力波观测，模拟二次重力波激发及其传播和耗散，以及反向射线追踪研究。大气的F区经常表现出中等尺度的电离层扰动，这些扰动被认为是从低层大气向上传播的重力波，但它们的来源通常是未知的。特别令人感兴趣的是确定次级重力波在产生电离层扰动中的作用。本项目将研究两种类型的二次波产生：冬季高纬度热层山波破碎激发的二次波和中间层重力波破碎激发的二次波。用于识别重力波源的工具之一是反向射线追踪。射线追踪方法所需的基本信息是：1)精确的重力色散关系；2)了解重力波的水平和垂直波长及其周期。最近，在先前的资助下，导出了一个精确的粘性重力波色散关系，该关系考虑了真实的热层耗散，并将其纳入三维射线迹模型。与此同时，关于重力波波长和周期的信息最近在扑克平台和阿雷西博雷达上进行了新的多波束实验。作为该项目的一部分，将在两个雷达上观测与重力波通过有关的电子密度扰动。这些测量结果将成为模型研究的基础，模型研究强调低层大气和热层之间的重力波耦合。具体任务和目标包括：从Poker Flat和Arecibo选定的重力波的密度和速度摄动剖面确定波长和周期；利用粘性重力波频散关系从这些剖面中提取F区中性风和加速度的时间演化；计算了破碎山波激发的二次重力波谱，并通过射线追踪表征了f区重力波的尺度和振幅；在扑克平原的三个案例研究和阿雷西博的一两个案例研究中，确定了热层观测到的重力波的低层大气源；通过比较提取的中性风与阿雷西博沿磁场方向测量的中性风，检验粘性GW色散关系的准确性。

This project will investigate the sources of observed perturbations to the F region ionosphere due to upward propagating gravity waves at two incoherent scatter radar sites, Poker Flat and Arecibo. A by-product of the research will be the extraction of time-varying F region neutral winds. The research activities include making gravity wave observations using a new technique at the two radars, modeling of secondary gravity wave excitation as well as the propagation and dissipation of these gravity waves, and reverse ray tracing studies. The F region of the atmosphere frequently exhibits medium-scale traveling ionospheric disturbances that are thought to be gravity waves propagating upwards from the lower atmosphere, but their sources are generally unknown. Of particular interest is determining the role of secondary gravity waves in producing the ionospheric disturbances. Two types of secondary wave generation will be investigated in this project: those excited by mountain wave breaking in the wintertime thermosphere at high latitudes and those excited by the breaking of gravity waves in the mesosphere. One of the tools used to address the identification of gravity wave sources is reverse ray tracing. The essential information needed for the ray tracing approach is: 1) an accurate gravity dispersion relation, and 2) knowledge of the gravity wave's horizontal and vertical wavelengths and its period. Recently, an accurate viscous gravity wave dispersion relation which accounts for realistic thermospheric dissipation was derived and incorporated into a 3D ray trace model under a previous grant. Meanwhile, information on gravity wave wavelengths and period have recently become available from new multi-beam experiments at the Poker Flat and Arecibo radars. As part of this project, observations of electron density perturbations associated with the passage of gravity waves will be made at the two radars. These measurements will be the basis for the modeling studies, which emphasize gravity wave (GW) coupling between the lower atmosphere and the thermosphere. The specific tasks and objectives include: determining wavelengths and periods from the density and velocity perturbation profiles for selected gravity waves at Poker Flat and Arecibo; extracting the temporal evolution of the neutral winds and accelerations in the F region from these profiles using the viscous gravity wave dispersion relation; calculating the secondary gravity wave spectra excited from breaking mountain waves, and characterizing the scales and amplitudes of the GWs in the F-region via ray tracing; determining the lower-atmospheric sources of the gravity waves observed in the thermosphere for three case studies at Poker Flat and one or two case studies at Arecibo; testing the accuracy of the viscous GW dispersion relation by comparing the extracted neutral winds with the measured neutral winds along the magnetic field at Arecibo.