Abstract
Abstract. Experimental results from three ionospheric HF pumping experiments in overdense E or F regions are summarized. The experiments were conducted by the use of the EISCAT HF Heating facility located near Tromsø, Norway, allowing HF pumping the ionosphere in a near geomagnetic field-aligned direction. Distinctive features related to auroral activations in the course of the experiments are identified. Typical features observed in all experiments are the following: generation of scattered components in dynamic HF radio scatter Doppler spectra; strong increase of ion temperatures Ti and local ionospheric electric field E0; modification of the auroral arc and local spiral-like formation. However, some effects were observed only when the HF pump wave was reflected from the F2 layer. Among them are the generation of intense field-aligned ion outflows, and a strong increase in the electron temperature Te with altitude. A possible scenario for the substorm triggering due to HF pumping into an auroral ionosphere is discussed. The authors present their interpretation of the data as follows. It is suggested that two populations of charged particles are at play. One of them is the runaway population of electrons and ions from the ionosphere caused by the effects of the powerful HF radio wave. The other is the population of electrons that precipitate from the magnetosphere. It is shown that the hydrodynamical equilibrium was disrupted due to the effects of the HF pumping. We estimate that the parallel electric field can reach values of the order of 30mV/m during substorm triggering.
Highlights
The significance of the general class of problems related to the manmade impact on the near-Earth space environment is evident from the results of well-known scientific programs such as TRIGGER, CRRES, CEDAR, and HAARP
Taking the distinctive features and behavior of the auroral ionosphere into account, one would expect that the interaction between powerful HF radio waves and the auroral near-Earth space plasma can lead to the generation of specific modification effects not encountered at middle latitudes
We suggest that the results obtained provide evidence that HF pumping into nightside auroral ionosphere along the magnetic field-aligned direction produces a modification of the magnetosphere-ionosphere coupling
Summary
The significance of the general class of problems related to the manmade impact on the near-Earth space environment is evident from the results of well-known scientific programs such as TRIGGER, CRRES, CEDAR, and HAARP. Experimental results from multi-instrument observations during Tromsø ionospheric modification experiments (Blagoveshchenskaya et al, 2001), make it evident that HF pumping into a sporadic auroral Es layer in the near field-aligned direction, can lead to a local auroral activation. The successful resolution of the problem concerning the HF pump wave impact on the ionosphere-magnetosphere coupling that could lead to the triggering of auroral activations requires the following: (1) fundamental studies in several fields and sub-fields, including plasma instabilities and nonlinear phenomena, on the one hand, and environmental magnetospheric physics, on the other; (2) the use of multi-instrument observations, new instruments, methods and observational methodology; (3) the performance of HF pumping experiments under specific geophysical conditions; (4) consistant, repeatable effects needed, that is more events showing the same effect. We present our interpretation of the experimental data obtained in the course of HF ionospheric modification experiments in the nightside auroral ionosphere
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