LOW-FREQUENCY PLASMA WAVES IN THE OUTER POLAR CUSP: A REVIEW OF OBSERVATIONS FROM PROGNOZ 8, INTERBALL 1, MAGION 4, AND CLUSTER J. BLECKI 1 , R. WRONOWSKI 1 , S. SAVIN 2 , N. CORNILLEAU-WEHRLIN 3 , M. PARROT 4 , Z. NEMECEK 5 , J. SAFRANKOVA 5 , O. SANTOLIK 5 , K. KUDELA 6 and J-A. SAUVAUD 7 1 Space Research Centre PAS, Bartycka 18A, Warsaw, 00716 Poland E-mail: jblecki@cbk.waw.pl; 2 Space Research Institute RAS, Moscow, Russia; 3 CETP/CNRS, Velizy, France; 4 LPCE/CNRS, Orleans, France; 5 Charles University, Prague, Czech Republic; 6 Institute of Experimental Physics of Kosice, SAS, Slovak Republic; 7 CESR/CNRS, Toulouse, France (Received 22 March 2003; Accepted 30 April 2004) Abstract. This paper presents a review of the most interesting observations of low-frequency plasma waves together with plasma particles which were made by the Interball 1, Magion 4 and Prognoz 8 satellites in the outer polar cusp. Accelerated plasma particles, hot electron populations and very strong wave activity, particularly at low frequencies, are observed. A detailed study of the wave spectra together with the distribution function for electrons indicate the correlation between the presence of lower-hybrid waves and the population of the particles with higher energy than in the surrounding space. These experimental facts suggest that strong coupling between waves and particles is responsible for plasma heating. During polar cusp crossings by Interball 1 and Prognoz 8, FFT analysis of the wave form indicates many bursts of ULF emissions in both electric and magnetic components. These waves have highly non- stationary characteristics. To study the dynamics of changes in the spectral characteristics of the waves wavelet analysis has been used. Nonlinear interactions are studied using bispectral methods of analysis. This presentation gives the results of such an analysis for selected cusp crossings at different altitudes. An example of wave activity registered by the STAFF instrument onboard the CLUSTER spacecraft in the polar cusp is also presented. Keywords: bispectral methods, cusp, FFT, plasma waves, wavelet analysis Abbreviations: ISEE – International Sun–Earth Explorers; GSE – Geocentric Solar Ecliptic; GSM – Geocentric Solar Magnetic; HEOS – Highly Eccentric Orbiting Satellite; DMSP – Defense Meterological Satellite Program; ASPI – Analysis of Spectra of Plasma waves and Instabilities; DOC-S – Detektor Ochlazhdaemyj Kremnievyj (Cooled Silicic Detector) Surveys in Geophysics (2005) 26: 177–191 DOI 10.1007/s10712-005-1876-2 Ó Springer 2005