ON ION-ACOUSTIC TURBULENCE AND THE NONLINEAR EVOLUTION OF KINETIC ALFVEN WAVES IN AURORA

Wave data from the recently launched Freja satellite, show a close rel ationship between Alfven wave activity and ion acoustic wave activity within auroral energization regions. The Alfven wave activity becomes especially strong (several 100 mV/m) in localized regions with horizon tal scales of a few hundred meters to a km (few tens of Hz in the S/C reference system). In some cases these signatures become more electros tatic-like and filled with broadband, high frequency electrostatic tur bulence up to 15 kHz. This broadband electrostatic turbulence has an a mplitude comparable to the larger scale electric signatures, and is id entified as ion acoustic waves. We argue that these signatures have ev olved from solitary kinetic Alfven waves (SKAW), and may be important for auroral energization processes.