Theoretical developments on the causes of ionospheric outflow |
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| Institution: | 1. Institute of Soil and Water Conservation, State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, No. 26 Xinong Rd., Yangling 712100, Shaanxi, PR China;2. Institute of Soil and Water Conservation, CAS & MWR, No. 26 Xinong Rd., Yangling 712100, Shaanxi, PR China;1. Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, and School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, China;2. State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy Sciences, Lanzhou, China;3. Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China;4. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany;5. National Center for Environmental Prediction (NCEP), Maryland, USA;6. Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, New York, USA;7. International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China;8. Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, Washington, USA |
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| Abstract: | It is now well known that there is a substantial outflow of ionospheric plasma from the terrestrial ionosphere at high latitudes. The outflow consists of light thermal ions (H+, He+) as well as both light and heavy energized ions (H+, He+, O+, N+, NO+, O2+, N2+). The thermal ion outflows tend to be associated with the classical polar wind, while the energized ions are probably associated with either auroral energization processes or nonclassical polar wind processes. Part of the problem with identifying the exact cause of a given outflow relates to the fact that the ionosphere continuously convects into and out of the various high-latitude regions (sunlight, cusp, polar cap, nocturnal oval) and the time-constant for outflow is comparable to the convection time. Therefore, it is difficult to separate and quantify the possible outflow mechanisms. Some of these mechanisms are as follows. In sunlit regions, the photoelectrons can heat the thermal electrons and the elevated electron temperature acts to increase the polar wind outflow rate. At high altitudes, the escaping photoelectrons can also accelerate the polar wind as they drag the thermal ions with them. In the cusp and auroral oval, the precipitating magnetospheric electrons can heat the thermal electrons in a manner similar to the photoelectrons. Also, energized ions, in the form of beams and conics, can be created in association with field-aligned auroral currents and potential structures. The cusp ion beams and conics that have been convected into the polar cap can destabilize the polar wind when they pass through it at high altitudes, thereby transferring energy to the thermal ions. Additional energization mechanisms in the polar cap include Joule heating, hot magnetospheric electrons and ions, electromagnetic wave turbulence, and centrifugal acceleration.Some of these causes of ionospheric outflow will be briefly reviewed, with the emphasis on the recent simulations of polar wind dynamics in convecting flux tubes of plasma. |
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