Mar 1, 1998 - 2 m long booms and gives the full three-dimensional vec- ... 9 MLT, 66%70 Ñ MLat, on March 7, 1994, near an al- titude of 1700 km. The 1550 ...
JOURNAL. OF GEOPHYSICAL RESEARCH, VOL. 103, NO. A3, PAGES 4343-4375, MARCH 1, 1998
Broadband ELF plasma emission during auroral energization 1. Slow ion acoustic waves J.-E. Wahlund, •,2A. I. Eriksson, • B. Holback, • M. H. Boehm, 3 J. Bonnell, 4 4j I-I Clemmons • L Eliasson 6 P.M. Kintner,4 C. E. Seyler, . . , . , D. J. Knudsen, 7 P. Norqvist, s andL. J. Zanetti9 Abstract.
High-resolution measurementsby the Frej• spacecraftof broadband
extremelylow frequency(BB-ELF) emissionfrom dc up to the lower hybrid frequency(• few kHz) •re reportedfrom regionsof transverseion •cceler•tion (TAI) •nd bro•d-energysupr•thermMe!ectronbursts(STEB) occuringin the topsideionospheric•urorM regions.A gradualtransitionof the broadbandemission
occursnearthe locMO+ cyclotronfrequency (fo+ • 25 Hz) frompredominantly electromagneticbelow this frequencyto mostly e_lectrostatic •bove this frequency.
The emissionbelow200 Hz oftenreach•mplitudesup to severMhundredmV/m and densityperturbations(6n/n) of tensof %. An improved•nMysistechniqueis presented,basedon the quantityI6E/(6n/n)l versusfrequencyand appliedto the Freja plasma wave measurements.The method can be used to infer the dispersion relation for the measuredemissionas well as give estimatesof the thermal plasma temperatures. The BB-ELF emissionis found to consistpartly of p!asma waves with an ion Boltzmann response,which is interpreted as originating from the
so-calledslow ion acousticwave mode (SIA). This emissionis associatedwith
largebulk ion (O+) temperatures of up to 30 eV and lowelectrontemperatures (!-2 eV) and thereforeoccursduringconditions whenTe/Ti
