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

该项目将调查在两个非相干散射雷达站Poker Flat和阿雷西博上传播的重力波对F区电离层的观测扰动的来源。这项研究的一个副产品将是提取时变的F区中性风。研究活动包括在两个雷达上使用一种新技术进行重力波观测，对二次重力波激发以及这些重力波的传播和耗散进行模拟，以及反向射线跟踪研究。大气层的F区经常出现中等尺度的电离层行进扰动，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。本项目将研究两种次生波的产生：高纬冬季热层山波破裂激发的次生波产生和中间层重力波破裂激发的次生波产生。用于识别重力波源的工具之一是反向射线追踪法。射线追踪法所需要的基本信息是：1)准确的重力频散关系，2)知道重力波的水平和垂直波长及其周期。最近，一个精确的粘性重力波色散关系被推导出来，它解释了真实的热层耗散，并在先前的资助下被纳入到一个三维射线追踪模式中。与此同时，最近从扑克平台和阿雷西博雷达的新的多波束实验中获得了关于重力波波长和周期的信息。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。这些测量将是模拟研究的基础，模拟研究强调低层大气和热层之间的重力波(GW)耦合。具体任务和目标包括：从普克平原和阿雷西博选定重力波的密度和速度扰动廓线确定波长和周期；利用粘性重力波色散关系从这些剖面提取F区中性风和加速度的时间演变；计算山波破裂激发的二次重力波谱，并通过射线追踪表征F区重力波的尺度和幅度；确定在热层观测到的重力波的低层大气来源，包括在普克平原的三个案例和在阿雷西博的一个或两个案例；通过将提取的中性风与沿阿雷西博磁场测量的中性风进行比较，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.