This project will conduct a modeling and data analysis effort to assess the extent to which acoustic waves and high frequency gravity waves influence the thermal, chemical, and dynamical states of the upper atmosphere. Specifically, the project will: (1) observe ionospheric perturbations using digital high-frequency Doppler sounders (TIDDBIT) from two North American locations; (2) use a numerical wave propagation model to infer the underlying atmospheric perturbations that cause the observed ionospheric variations and to characterize the energy and momentum flux into the ionosphere; and (3) use group velocity and raytracing models to examine sources of acoustic waves.
This project is focused on a characterization of infrasonic acoustic waves and high-frequency gravity waves in the period range between 1 and 20 minutes based primarily on data from an HF Doppler sounder known as the Traveling Ionospheric Disturbance Detector Built in Texas (TIDDBIT). The system consists of an array of three continuous wave HF radio transmitters and a receiver. When a HF radio wave is reflected from the ionosphere, any movement of the reflection point produces a change in phase path and hence a Doppler shift proportional to the time rate of change of the path. The time difference of the TID signatures at the reflection points from the three spatially separated propagation paths yields information about wave direction, speed and amplitude. The TIDDBIT instrument provides horizontal and vertical wavelength and phase speeds as a function of period down to 1-min. During this project we will use numerical models, ray tracing, and ionospheric data sets at two diverse locations (on in Virginia and the other in Texas) to answer the following science questions pertaining to acoustic and high frequency gravity waves: 1. What are the spectral and propagation characteristics of these acoustic and high frequency TIDs and gravity waves in the bottomside F-region near Wallops Island and San Antonio Texas? 2. What are the Momentum and Energy Fluxes carried by these waves into the F-region ionosphere, and what is their effect on the mean state of the atmosphere? 3. What are the likely sources of the waves, and how did the wave properties vary with the approach of Tropical Storm/Hurricane Noel? This was a collaborative proposal, and ASTRA's co-I role was augmented with additonal contributions from team PI, Mike Hickey, and Co-I Richard Walterscheid. ASTRA's role was to: (a) analyze TIDDBIT data in the acoustic regime; (b) run TIMEGCM model to obtain atmospheric background fields for raytracing; 9c) provide TIDDBIT anayses and TIMEGCM output to project PI and Co-I for input to their models, and for raytracing of acoustic waves. Significant results include: a) 11 conference papers presented b) 6 manuscripts published or in preparation, describing new scientific results c) New findings about the climatology and behaviour of acoustic waves d) Several people at ASTRA, including postdocs, have learned about TIDs, and have been trained to work with the TIDDBIT data and/or the TIMEGCM model during this project. Impacts on other disciplines and Tech Transfer arise from the fact that the TIDDBIT system measures the complete wave characteristics (unlike any other previous system). This means that the TID structure in the ionosphere can be accurately reproduced for the first time. This has implications for DoD applications that utilize reflection of radio waves from the ionosphere, such as direction finding and OTH radars.
