The investigators will study how waves in the atmosphere transport energy and momentum across large distances and between atmospheric layers. In the mesosphere and lower thermosphere (MLT) region the strongest motions are due to solar tides with periods of a day or fractions thereof and planetary waves with periods that exceed a day. There is a critical need to understand the properties of the tidal and planetary wave activity, the sources and sinks of their energy, and their effects on the atmosphere. Moreover, large perturbations in the lower atmosphere, such as Sudden Stratospheric Warmings (SSWs), the Quasi-Biennial Oscillation (QBO), and the El Nino and Southern Oscillation (ENSO), with their known and potential impacts on weather and climate, are increasingly thought to affect tides and planetary waves. To study the many aspects of wave activity in the atmosphere it is advantageous to appeal to long-term data sets that have sufficient spatial coverage and temporal resolution to resolve the wave modes. The high frequency (HF) radars of the Super Dual Auroral Radar Network (SuperDARN) make routine measurements of mesospheric winds using meteor scatter. In the northern hemisphere the distribution of radars along an arc that measures nearly 180 degrees in longitude facilitates a larger characterization of tide and wave characteristics. The multi-radar measurements extend back to 1993. The TIMED satellite includes the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument which has since 2002 provided in situ measurements of atmospheric properties from which wave activity can be inferred. Comparison of the measurements confirms the coherence of wave activity across the different techniques and leads to an expanded analysis of the wave modes. The research will combine the data sets of SuperDARN and TIMED/SABER and high-latitude Michelson hydroxyl (OH) rotational temperatures to determine a long-term climatology of planetary waves and tidal modes in the MLT region. Specifically the study will determine: 1) the variability of planetary waves and of migrating and non-migrating tides in the middle and high latitudes, and 2) the relationship between long-term activity and drivers in the lower atmosphere such as SSWs, QBO, and ENSO. The perturbations represented by QBO, SSWs, and ENSO have impacts on weather and climate and appear to have consequences for the mesosphere that can be monitored by observations of tides and planetary waves. With the extended data streams that are available for this study, the investigators will be able to characterize the various effects and gain insight into the sources of atmospheric disturbance. This project will help establish the ground-based radar technique in this capacity, i.e., as an 'always-on' monitor of disturbance in the atmosphere. The study involves two university students in research related to this product with the aims of fulfilling their thesis requirements and training them to be experts in the use of satellite and radar data.
Summary findings: Radar and satellite measurements in the upper atmosphere (mesosphere) have been used to track solar cycle (11 years) variations in temperature. We have continued to refine the analysis of mesospheric wind velocity from SuperDARN radar backscatter observations. This has lead to more accurate and reliable results and insight into the sources of variability in the measurement. We have identified non-meteor sources of mesospheric-type backscatter and are developing algorithms to filter them out using Wallops radar data. We are currently analysing in detail more than a solar cycle worth of SuperDARN meteor wind data in which we find significant year to year variability. The preliminary results show that the NASA Thermoshpere Ionosphere Mesosphere Electrodynamics Dynamics (TIMED) Explorer and it's SABER experiment tidal analysis of non-migrating structure reveals long term cooling of the mesosphere during sudden warming of the stratosphere! This undiscovered coupling is crucial to the upwards transfer of energy to the ionized lower layers and possibly to much higher altitudes of Geospace. Figure cation: Top panel: Zonally averaged temperatures from NECP Reanalysis sampled at 36hPa shown as a function of latitude and universal time. Three minor warming and the major "Sudden Stratospheric Warming" (SSW) event centered ofn 27 September. Botto panel: latitude-time cross section of zonal mean zonal winds at 36hPa from NECP Reanalysis showingthe reversal of the wind at the onset of major SSW event.
