An inertial wave-driven stratospheric horizontal electric field: New evidence

We report our recent measurements of horizontal electric fields from multiple stratospheric balloon platforms during the Extended Life Balloon-Borne Observatories (ELBBO) experiment. The ELBBO project involved launches of five superpressure balloons into the stratosphere from Dunedin, New Zealand, during November and December 1992. Most of the balloons floated at a constant altitude of 26 km for over 3 months, covered a wide range of latitudes from the south pole to 281°S, and circled around the southern hemisphere several times. The electric field measurements from the ELBBO experiment have confirmed the earlier discovery of a new source of stratospheric horizontal electric fields [Holzworth, 1989], with wider latitude coverages than the original finding. This newly found horizontal electric field has an average magnitude of 10 to 20 mV/m at night and 100 to 150 mV/m in the daytime. Its field vector has a unique characteristic of counterclockwise rotation in the southern hemisphere, with the rotation period near the atmospheric inertial wave period. The horizontal scale size of this new-source E field was found to be near 500 km, of the order of the horizontal wavelength of the inertial wave in the stratosphere. This new-source E field is a steady background feature of the stratosphere, with local disturbance from underlying thunderstorms or other sources. At high latitude, a dawn-to-dusk electric field mapped down from the magnetosphere was observed at the local midnight, with a larger amplitude than that of the new-source E field. One of the implications of the new-source E field is that the neutral dynamic processes are strongly coupled into the electrodynamic processes in the stratosphere, making this region electrically active and not passive as previously thought by many.