INTENSE 2.3-HZ ELECTRIC-FIELD PULSATIONS IN THE STRATOSPHERE AT HIGH AURORAL LATITUDE

A survey has been performed of the power spectra of the electric field measured by stratospheric balloon-borne instruments during the 1985-1 986 South Pole Balloon Campaign. The survey reviewed all 468 hours of available data and covered the frequency range from 0 to 4 Hz. Three e pisodes of narrow-band emissions were detected in this frequency range . These emissions occurred about 5.5% of the time, with intense emissi on occurring about 1% of the time. These narrow-band emissions had fre quencies in the horizontal component between 2 and 2.5 Hz. The frequen cies observed in the vertical component were different, with several b ands present. The fundamental frequency in the vertical component was around 0.8 to 1.4 Hz depending on event, The spectra of the events in the vertical component showed multiple emission bands, not all harmoni cally spaced. The vertical component showed much more pronounced time variations of the frequencies of the emission bands than the horizonta l component showed. The amplitude of the emission in the vertical comp onent was usually but not always larger than that in the horizontal co mponents. The ratio E(V)/E(H) was typically similar to 2-3. The amplit ude of the horizontal component of the emissions was quite large in on e of the three events, with individual bursts having amplitudes of 60 mV/m. The polarization was complicated. in the horizontal plane, there were two narrow bands of opposite-handed circularly polarised emissio ns. Since the vertical axis of the emission had frequency components n ot present in the horizontal plane, the polarization in the zonal plan e was linear, with a quasi-Lissajou character. An extensive list of po ssible explanations for these emissions was considered. Since similar emissions with a similar occurrence rate have been seen by other worke rs, instrumental explanations were ruled out. Local external artifacts were also ruled out. Distant sources associated with tropospheric sto rms were considered in detail. During the most intense of the 2-Hz emi ssion events, the nearest bad weather was more than 1000 km away. It p roved impossible to account for the amplitude and polarization of the horizontal component with any reasonable tropospheric source. Explaini ng the narrow-band tuning was also a problem for any weather source mo del. An ionospheric model based on the concept of the ionospheric Alfv en resonator is capable of accounting for the tuning, amplitude, and p olarization of the horizontal components. However, this model has mode rate difficulty in accounting for the observed vertical component of t he emissions. In the end, no available model proved fully satisfactory .