G. J. Byrne

Ground‐based instrumentation for measurements of atmospheric conduction current and electric field at the South Pole

We have constructed instruments to measure the atmospheric conduction current and the atmospheric electric field: two fundamental parameters of the global-electric circuit. The instruments were deployed at the Amundsen-Scott South Pole Station in January 1991 and are designed to operate continuously for up to one year without operator intervention. The atmospheric current is measured by a sensor that uses a split-hemispheric conducting shell of 17.8-cm radius, separated by a thin Teflon insulating disk. The detection electronics are inside the sphere. In principle, the atmospheric current flows into one hemisphere, through the electronics where it is measured, and out the other hemisphere. The electric field is measured by a field mill of the rotating dipole type. The electric field sensing elements are two 30-cm-long antennas, driven to rotate in the vertical plane at 1800 rotations per minute. Two arrays of identical instruments have been deployed, separated by 600 m, in order to distinguish between atmospheric electrical signals of local and global origin. The separation distance of the arrays was determined by the climatology of the Antarctic plateau. Sample data from the first days of operation at the South Pole indicate variations in the global circuit over time scales from minutes, to hours, to days.

Balloon observations of stratospheric electricity above the South Pole: vertical electric field, conductivity, and conduction current

Abstract This paper summarizes the results of measurements of the electrical conductivity σ and vertical component of the vector electric field Ez acquired from eight stratospheric balloon flights launched from Amundsen-Scott Station, South Pole, in the austral summer of 1985–1986. The major findings of this research are as follows 1. (1) The data contribute to the set of global atmospheric electricity measurements and extend the work of COBB [(1977), Atmospheric electric measurements at the South Pole. In Electrical Processes in Atmospheres, Dolezalek H. and Reiter R. (eds), pp. 161–167. Steinkopf, Darmstadt, F.R.G.] to determine the electrical environment of the south polar region 2. (2) The average vertical profile of the conductivity at the South Pole, when compared with profiles obtained at other Antarctic locations, suggests that the conductivity scale height may increase with increasing geomagnetic latitude across the polar cap. 3. (3) The conductivity profiles measured at the South Pole and other Antarctic locations differ significantly from polar cap model profiles. On the basis of these measurements, the model profiles appear to require modification 4. (4) The magnitudes of the Ez profiles were observed to vary from day-to-day by a factor of > 2 5. (5) In all of the flights the air-Earth conduction current Jz, calculated as the product of Ez and σ, decreased with altitude in agreement with previous direct measurements of the air-Earth current by Cobb [( 1977), Atmospheric electric measurements at the South Pole. In Electrical Processes in Atmospheres, Dolezalek H. and Reiter R. (eds), pp. 161–167. Steinkopf, Darmstadt, F.R.G.] 6. (6) The magnitude of Jz was 2–3 times larger than the global average, which can be attributed to the lower columnar resistance of the atmosphere above the high-elevation Antarctic plateau. The magnitude of Jz agrees with that observed by Cobb, if the Cobb measurements are multiplied by the Few and Weinheimer [(1986), Factor of 2 error in balloon-borne atmospheric conduction current measurements. J. geophys. Res.91, 10937] correction factor of 2 7. (7) Ez from all of the flights during times of balloon float demonstrates characteristics of the classical ‘Carnegie’ diurnal variation, which is indicative of global influences on the ionospheric potential 8. (8) The influence of geomagnetic activity was observed as a decrease in the amplitude of the diurnal variation of Ez with increasing geomagnetic activity index Kp, which is the predicted effect at the South Pole of the magnetospheric polar-cap potential superimposed on the ‘Carnegie’ potential variation.

Balloon measurements above the South Pole: Study of ionospheric transmission of ULF waves

We report here an experimental study of the Hughes and Southwood model of the transmission of electromagnetic signals from the ionosphere/magnetosphere to the lower atmosphere. The electric field data were obtained from one of eight high-latitude balloon payloads launched above the south geographic pole during the South Pole Balloon Campaign in the 1985–1986 austral summer. The magnetic field data are from the South Pole magnetometer. The balloon payloads were instrumented with double-probe electric field detectors and bremsstrahlung X ray detectors. One of the events from flight 7 (January 8, 1986, at 1500–1800 UT (1130–1430 MLT)) had an amplitude in the range of 10–20 mV/m and a period of several minutes. In the magnetosphere, the wave was probably an Alfven mode. The wave event was superimposed on background fluctuations that can be attributed to turbulence. The results agree with the predictions of the model in that the best coherence is observed between parallel components of E versus B. The results disagree with the predictions of the model in two respects. First, we find a frequency structure not predicted by the model, and second, we find intervals where the electric and magnetic field polarizations are of opposite handedness. The first discrepancy was modeled by taking account of the measured electrostatic turbulence. The second problem remains a puzzle.

The effect of mid-latitude electron precipitation on the geoelectric field

Abstract A simple model is outlined to describe electron precipitation from the population of charged particles trapped in the Earths magnetic field; almost all of the precipitation is shown to occur in the region of the South Atlantic Anomaly (SAA). When the effect of a dawn-to-dusk electric field across the magnetosphere is included in the model, a diurnal modulation of the precipitated electron flux is predicted. Experimental evidence which supports the diurnal modulation model is described; the measurements which are discussed are principally those from University of Houston rocket payloads flown in the region dominated by the SAA. The resulting diurnal variation in atmospheric conductivity in the SAA is shown to be such that it could account for part of the daily UT variation in the geoelectric field. The observed seasonal variation in the pattern of geoelectric field modulation is also shown to be consistent with the proposed source of the daily variation. The difficulty of altering global conductivity by intense ionization of the mesosphere is discussed and the point is made that further in situ investigation of the Antarctic mesosphere is needed.

Long term changes in the electrical conductivity of the stratosphere

Abstract Stratospheric electrical conductivity measurements have been made from high altitude research balloons at various locations around the world for more than 30 years. In the stratosphere, conductivity is affected by a number of things, including changes in aerosol or water vapor content. In this paper, we compare data taken in the last five years at mid latitude locations with data taken in the previous three decades at both mid and high latitude from a total of more than 40 balloon flights. Existing models for the effects of geomagnetic latitude, temperature, and other factors have been used to normalize the conductivity data for comparison. Low noise background has permitted the observation of a solar cycle dependence in the equatorial data. Otherwise, this limited statistical sample exhibits short term variations that completely obscure any long term climatic trends that may have occurred during the past three decades.

Summertime stratospheric wind measurements above the South Pole

Abstract Observations of the mean wind flow and wave motions in the stratosphere at the South Pole are presented. The atmospheric motions are determined from the tracking of a high altitude, zero-pressure balloon launched from Amundsen-Scott Station during the austral summer of 1985–1986. The balloon position was precisely monitored by an optical theodolite for a large portion of the flight so that small scale motions could be resolved. The mean flow above the pole was approximately 3ms −1 . Atmospheric motions characteristic of internal gravity waves were observed with an intrinsic period of approximately 4.5 h and vertical and horizontal wavelengths of approximately 2.5km and 125km, respectively. The horizontal perturbation velocity of the observed waves was large compared to the mean horizontal flow velocity. The implication is that wave motions play a dominant role in the transport of stratospheric constituents in regions where the mean winds are light, such as over the South Pole during austral summer.

Balloon Observations of the Electric Field Over South Pole: Convection Patterns

During the 1985–86 austral summer, eight balloon flights were launched from Amundsen-Scott Station, South Pole, Antarctica by the University of Houston in order to measure the ionospheric electric field in the vicinity of the polar cusp and the polar cap. One objective of this work was to determine the average daily ionospheric plasma convection patterns near the polar cusp as measured by the balloon experiment. The solar wind and interplanetary magnetic field conditions during the campaign period have been obtained using IMP 8 satellite data. IMP 8 was in the solar wind during four of the balloon flights. The balloon data have been binned separately as functions of Kp, interplanetary magnetic field (IMF) B z and IMF B y . The intent is to determine if there are any differences between data obtained in this way and data obtained from other techniques. The overall patterns show the expected two-cell convection pattern. In detail, the various individual patterns show subtle but interesting departures from previous results.