Ionospheric HF pump wave triggering of local auroral activation
Results from ionospheric HF pumping experiments in the nightside auroral E region above Tromsø, Norway, are reported. We found intriguing evidence that a modification of the ionosphere-magnetosphere coupling, due to the effects of powerful HF waves beamed into an auroral sporadic E layer, can lead t...
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| Format: | Text |
| Language: | English |
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1999
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.261.7808 http://arxiv.org/pdf/physics/9906057v2.pdf |
| Summary: | Results from ionospheric HF pumping experiments in the nightside auroral E region above Tromsø, Norway, are reported. We found intriguing evidence that a modification of the ionosphere-magnetosphere coupling, due to the effects of powerful HF waves beamed into an auroral sporadic E layer, can lead to a local intensification of the auroral activity. Summarizing multi-instrument groundbased observations, one can distinguish the following peculiarities related to this auroral activation: modification of the auroral arc and its break-up above Tromsø; local changes of the horizontal currents in the vicinity of Tromsø; increase of the electron temperature and ion velocities at altitudes above the HF pump reflection level; distinctive features in dynamic HF radio scatter Doppler spectra; pump-induced electron precipitation; substorm activation exactly above Tromsø. The mechanisms of the modification of the ionosphere-magnetosphere coupling through the excitation of the turbulent boundary layer between the base of the ionosphere ( ∼ 100 km) and the level of sharp increase of the Alfvén velocity ( ∼> 1000 km), and the formation of a local magnetospheric current system are discussed. The results suggest that a possible triggering of local auroral activation requires specific geophysical conditions. |
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