The effect of fluctuating ionospheric electric fields on Es-occurrence at cusp and polar cap latitudes |
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| Institution: | 1. Wuhan Ionospheric Observatory, Wuhan Institute of Physics and Mathematics, Wuhan, P.R. China.;2. Department of Physics, La Trobe University, Bundoora Campus, Victoria 3083, Australia.;3. Polar Research Institute of China, Shanghai, P.R. China.;4. Atmospheric and Space Physics, Australian Antarctic Division, Tasmania 7050, Australia.;1. Lockheed Martin Space Operations, NASA Ames Research Center, P.O. Box 168, Moffett Field, CA 94035, USA;2. NASA, Ames Research Center, Mail Stop 236-5, Moffett Field, CA 94035, USA;3. NASA, Ames Research Center, Mail Stop T20G-2, Moffett Field, CA 94035, USA;1. Institute of Botany, Nat. Acad. Sci. of Ukraine, Kyiv, Ukraine;2. NC State University, USA, Dynamac Corp. KSC, FL, USA;3. Dynamac Corp. KSC, FL, USA;1. NASA Goddard Space Flight Center, Code 800-G, Greenbelt, MD USA 20771;2. SAIC, 2200 Space Park Drive, Suite 200, Houston, TX USA 77058 |
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| Abstract: | Theory predicts that in the high-latitude southern hemisphere, southwest (SW) electric fields will produce convergent ion flow and thereby create thin sporadic E (Es)-layers at node heights > 120 km, whilst northwest (NW) fields will produce downward ion flow and create thicker Es-layers at heights <110 km. To investigate this theory, Digisonde ionograms (giving the Es-occurrence) and drift measurements (giving electric field estimates) at two Antarctic stations were statistically analyzed. As previously found for the polar cap station Casey (81°S magnetic), more of the Es-traces were associated with SW fields than NW fields. However, new results for the cusp station Zhongshan (73°S) show that fewer Es-layers occur there, and NW fields play a slightly more important role than SW fields, similar to the results found at auroral latitudes in the northern hemisphere. To further our understanding of the occurrence distributions, we study the fluctuating properties of the electric fields at the two stations. It is found that the electric fields at Zhongshan fluctuate more than those at Casey. Thus we suggest that the field fluctuation is also an important consideration helping to explain the differences in the Es-occurrence at the two stations. This suggestion is confirmed by our numerical simulations which show that Es-layers are more effectively formed by steady SW fields than by steady NW fields, and less effectively by fluctuating SW fields than by fluctuating NW fields. |
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