ISSN 0016-7932, Geomagnetism and Aeronomy, 2011, Vol. 51, No. 8, pp. 1109–1120. © Pleiades Publishing, Ltd., 2011. Original Russian Text © N.F. Blagoveshchenskaya, T.D. Borisova, M.T. Rietveld, T.K. Yeoman, D.M. Wright, M. Rother, H. Lühr, E.V. Mishin, C. Roth, 2011, published in Solnechno-Zemnaya Fizika, 2011, Vol. 18, pp. 16–26. 1109 INTRODUCTION The impact of powerful HF radiowaves on the ion- ospheric plasma leads to the development of a wide range of phenomena (Gurevich, 2007), the main one of which is the development of parametric (striction and thermal) instabilities within the plasma near the reflection level of powerful ordinary polarized (O-mode) HF radiowaves, triggering the generation of intense plasma oscillations, electron temperature increases, excitation of artificial small-scale iono- spheric irregularities (ASIs) (l ⊥ < 30 m), stimulated electromagnetic emissions (SEEs) of the ionosphere, and acceleration of background plasma electrons to superthermal speeds, which, in turn, leads to artificial optical emissions from the disturbed ionospheric region and to artificial plasma ionization. It should be noted that the use of powerful HF waves to modify the high-latitude ionosphere, where there are naturally intense horizontal currents (electrojet), longitudinal currents, natural irregularities of different scales, pre- cipitating particle fluxes, plasma instabilities, etc., leads to the generation of new phenomena, principally impossible at midlatitudes (Blagoveshchenskaya, 2001). In late 2008, the Arctic and Antarctic Research Institute (AARI) and European Incoherent Scatter Scientific Association (EISCAT) signed an agreement allowing AARI specialists to conduct experiments using the EISCAT facilities, which have no Russian analogs in both technical characteristics and geo- graphic position (HF heating complex EISAT/ Heat- ing (Tromsø, Norway) and the system of high-latitude radars of incoherent scatter (IS) of radiowaves in North Scandinavia and at Spitsbergen Archipelago). Considering that Russia has no analogous high-effi- ciency technical facilities at high latitudes and will hardly have them in the foreseeable future, studies with the use of the EISCAT facilities are of prior importance. Experiments have been regular since March 2009, and three measurement cycles have been performed recently in the deep solar activity minimum epoch: on March 5–12, 2009; October 29–November 6, 2009; and March 2–8, 2010. Results of Russian Experiments Dealing with the Impact of Powerful HF Radiowaves on the High-Latitude Ionosphere Using the EISCAT Facilities N. F. Blagoveshchenskaya a , T. D. Borisova a , M. T. Rietveld b , T. K. Yeoman c , D. M. Wright c , M. Rother d , H. Lühr d , E. V. Mishin e , and C. Roth f a Arctic and Antarctic Research Institute, St. Petersburg b EISCAT Scientific Association, Ramfjordmoen, Norway c University of Leicester, Leicester, UK d GeoForschungsZentrum, Potsdam, Germany e Air Force Research Laboratory, Hanscom, Massachusetts, United States f AER Inc., Lexington, Massachusetts, United States Received October 15, 2010 Abstract—We present the results of complex experiments dealing with the impact of powerful HF radiowaves on the high-latitude ionosphere using the European Incoherent Scatter Scientific Association (EISCAT) facilities. During the ionospheric F-region heating by powerful extraordinary (X-mode) polarized HF radio- waves under the conditions of heating near the critical f H frequency f H ≈ f x F2 of the extraordinary wave of the F2-layer, we were first to detect the excitation of intense artificial small-scale ionospheric irregularities (ASIs), accompanied by electron temperature increases by approximately 50%. The results of coordinated satellite and ground-based observations of the powerful HF radiowave impact on the high-latitude iono- sphere are considered. During ionospheric F-region heating by powerful HF radiowaves of ordinary polariza- tion (O-mode) during evening hours, the phenomenon of ion outflow accompanied by electron temperature increases and thermal plasma expansion was revealed. Concurrent DMSP-F15 satellite measurements at a height of about 850 km indicate an O + ion density increase. The CHAMP satellite observations identified ULF emissions at the modulation frequency (3 Hz) of the powerful HF radiowave, generated during modu- lated emissions of the powerful HF radiowave of O-polarization and accompanied by a substantial increase in the electron temperature and ASI generation. DOI: 10.1134/S0016793211080160