The investigators will conduct an experimental and theoretical research program to characterize charged dust in the summer polar mesosphere. The characterization of this charged dust and the associated physical processes is a forefront issue in upper atmospheric space science due to the possible intimate relationship with global climate change. Significant progress has been made in the last decade using space-based measurements to characterize this charged dust and correlate the existence of this charged dust with a fascinating ground-based radio signature called Polar Mesospheric Summer Echoes (PMSE). PMSEs result from scattering from electron irregularities which are due to electron charging onto the irregular dust density. Since space-based measurements are still difficult to make accurately, an independent method of characterizing the dust utilizing the ground-based PMSE signatures would be a significant step forward in providing diagnostic capabilities. Recently it has been shown that PMSEs can be modified by heating the source region with a ground-based ionospheric radio wave heating facility. The temporal evolution of the PMSEs during the heating cycle shows tremendous potential for characterizing the dust layer since this temporal evolution has been predicted to be directly related to the physical characteristics of the dust in the PMSE source region. However, current models of the temporal evolution of the irregularities associated with PMSE during the heating cycle are limited and not able to exploit all of the information available with a more accurate description of the irregularity temporal evolution. The study involved here will result in the development of a much more accurate model for the temporal evolution of the electron irregularities believed to produce PMSE during radio wave heating. This study will utilize this more accurate description of the irregularity temporal evolution to provide direct diagnostic information to characterize the dust layer. Experiments will be developed from the predictions of the model calculations. The experiments will concentrate on investigation of modifying High Frequency (HF) PMSE where important new physical processes are predicted to exist which have not been studied by past work which has concentrated on investigating modifying Very High Frequency (VHF) PMSE. Experimental observations will be performed at an ionospheric heating facility in Alaska to corroborate and refine the model and model predictions. This facility is well suited for such an experimental study. Ultimately, the research plan will provide a holistic approach to the development of better diagnostics for characterizing the charged dust layer and also contribute to an understanding of PMSE generation. This study will support human resource development through graduate student training. The effort will also serve to support infrastructure and collaborative work internally within the investigators' institution which is important due to the recent internal initiative to expand upper atmospheric space science research. Finally, the experimental component of the work will be utilized to expose underrepresented undergraduate college and high school students in science and engineering to space science at the investigators' home institution.
