ON THE EXISTENCE OF CHARACTERISTIC MICROSCALE MAGNETOHYDRODYNAMIC FLUCTUATIONS INSIDE A COROTATING INTERACTION REGION AT 2.5 AU

A detailed analysis of small period (15-900sec) Magnetohydrodynamic (M HD) turbulence of the interplanetary magnetic field (IMF) has been mad e using Pioneer-11 high resolution in time data (0.75 sec) inside a Co rotating Interaction Region (C.I.R.) at a heliocentric distance of 2.5 AU in 1973 (days 284-286). The methods used here are hodogram analysi s, minimum variance matrix analysis and coherence analysis. Inspection of the hodogram analysis gives evidence for finite amplitude non-tran sverse Alfven waves if 2min up to 8min averages of the IMF data are us ed. On the other hand this wave structure disappears if smaller or lon ger averages of the IMF data are taken under consideration. Minimum va riance analysis gives evidence of linear polarized wave modes and cohe rence analysis shows that the field fluctuations are dominated by the magnetosonic fast modes with periods 15sec to 900sec. However it is al so shown that some small amplitude Alfven waves are present in the tra iling edge of this reg ion with characteristic periods of 15 until to 200sec. The results are discussed in terms of several theoretical mech anisms.