During the sun's 11 year cycle, the thermosphere and ionosphere of the Earth react considerably to the changing levels of solar activity. It is commonly understood that as the solar activity increases, the ions and neutral particles in the upper levels of the atmosphere become more energized by X-rays from sunspots and flares, and are perturbed by high speed plasma streams, coronal mass ejections (CMEs) and Interplanetary Magnetic Field (IMF) fluctuations that impinge upon the Earth's atmosphere and geomagnetic fields. Consequently, such background perturbations in the thermosphere and ionosphere are expected to affect their densities, compositions and dynamic processes. However, solar minimum conditions have never been sufficiently sampled to predict such processes arising from a more quiescent background.
The Coupled Ion Neutral Dynamics Investigation (CINDI) instruments aboard the Air Force Research Laboratory's Communication/Navigation Outage Forecasting System (C/NOFS) satellite are used to measure parameters in situ at altitudes between 400 and 550 km. These include ion and neutral density, ion velocity, and temperature as functions of location and time. Two efforts stemming from unique opportunities during the recent solar minimum of 2008-2010 are presented: (1) a study of neutral thermospheric particle densities and composition and (2) an approach to mapping, classifying and explaining various types of ionospheric plasma depletion and enhancement plumes resulting from dynamic processes in the ionosphere. Observations made during these extremely quiet space weather conditions provide a number of unusual results, including uncharacteristically low neutral thermospheric particle densities, and helium presence and periodic dominance near 400 km. At the same time in the ionosphere, a significant number of large, well-formed density depletions and enhancements are observed, unveiling seasonal geomagnetic distributions that show new patterns, some of which confirm previous work and others that reveal new behaviors that require additional observations and modeling to promote full understanding.
|Advisor:||Earle, Gregory D.|
|Commitee:||Anderson, Phillip C., Coley, William R., Goeckner, Matthew J., Heelis, Roderick A.|
|School:||The University of Texas at Dallas|
|School Location:||United States -- Texas|
|Source:||DAI-B 73/09(E), Dissertation Abstracts International|
|Subjects:||Aeronomy, Geophysics, Atmospheric sciences, Plasma physics|
|Keywords:||Helium, Ionosphere, Plasma bubbles, Solar minimum, Thermosphere|
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