Ledge effect in A1 absorption measurements |
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| Affiliation: | 1. Ionospheric Prediction Service, Department of Science & Technology, P.O. Box 702, Darlinghurst, 2010, Australia;2. Department of Physics, University of New South Wales, P.O. Box 1, Kensington, 2033, Australia;1. Department of Neurosurgery, Greenville Health System, Greenville, SC, USA;2. Department of Neurosurgery, Medical University of South Carolina, Charleston, SC, USA;3. Department of Neurosurgery, University at Buffalo, Buffalo, NY, USA;4. Department of Neurosurgery, Icahn School of Medicine at Mount Sinai, New York, NY, USA;5. Cerebrovascular Center, Stony Brook University, Stony Brook, NY, USA;6. Lyerly Neurosurgery, Baptist Medical Center, Jacksonville, FL, USA;7. Department of Radiology, Fort Sanders Regional Medical Center, Knoxville, TN, USA;8. Department of Neurointerventional Radiology, West Virginia University, Morgantown, WV, USA;9. Radiology Imaging Associates/RIA Neurovascular, Swedish Medical Center, Englewood, CO, USA;10. Department of Radiology, Abbott Northwestern Hospital, Minneapolis, MN, USA;11. Department of Surgery, University of Saskatchewan, Saskatoon, SK, Canada;12. Department of Neurosurgery, Semmes Murphey Clinic, Memphis, TN, USA;13. University of Tennessee Health Sciences Center, Memphis, TN, USA;14. Department of Radiology, Erlanger Medical Center, Chatanooga, TN, USA;15. Department of Neurointerventional Services, California Pacific Medical Center, San Francisco, CA, USA;p. Cardiac and Vascular Institute, Miami Vascular Specialist, Miami, FL, USA;q. Department of Neurosurgery, Wake Forest Baptist Medical Center, Winston-Salem, NC, USA;1. Université de Lyon, ENTPE, Laboratoire Génie Civil et Bâtiment (LGCB), 3 rue Maurice Audin, F-69518 Vaulx-en-Velin, France;2. Université de Lyon, Institut National des Sciences Appliquées de Lyon, Laboratoire Vibrations Acoustique (LVA), 25 bis avenue Jean Capelle, F-69621 Villeurbanne, France |
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| Abstract: | The short-term variability in A1 absorption measurements for Camden (34°S, 151°E) is caused by changes in the deviative component of absorption. These changes, in turn, are caused by enhanced electrondensity gradients (referred to here as ‘ledges’) near the reflection level. The ledges perturb the normal E-region electron density profile and introduce a bias (termed the ‘ledge effect’) into the absorption measurements. In the present experiment, the ledge effect was isolated by using the virtual reflection height information to interpret the A1 absorption measurements. During the period of this study (February 1980–January 1981), the ledge effect was observed to have both diurnal and seasonal variations. The effect was most noticeable in the afternoon around the equinoxes, but was essentially absent during the summer months. |
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