Understanding the ionosphere and mesosphere are crucial to detailed modeling of the magnetosphere. While many space physics investigations have progressed beyond exploration to quantitative modeling and even to forecasting, it is interesting to note that NASA collects relatively little in-situ information about the global ionosphere with which to use in these models. We cannot accurately model geomagnetic storms or substorms without direct, real time information about the ionosphere. The importance of the ionosphere to magnetospheric dynamics is recognized in principal by NASA by its support of global imagers such as the visible and ultraviolet imagers on POLAR. These remote sensing instruments may provide an idea of where energetic particles are being precipitated, but there is no information of electric fields or current systems from these images. Even the low altitude polar orbiting satellites aloft presently such as the DMSP satellite do not make electric field and current measurements in the ionosphere. Therefore, except for fixed radars (e.g. SuperDARN) or the occasional balloon experiments, there is no continuous, global, in-situ measurement of the ionospheric fields and currents. Such information is needed as a measure of Ohmic heating and large scale convection patterns for input to the global modelers and as "ground truth" (really foot-of-the-field-line truth) for testing global models.
This is a proposal for a workshop review of a program to measure the electric field and energetic photons at the foot-of-the-field-line for direct comparison to ISTP, LEO and Geosynchronous satellite measurements, and to global models. The large scale electric field (convection scale size) can be measured with 1-minute resolution by vector electric field detectors on high altitude balloons [Holzworth and Bering, 1996]. Already flight programs have demonstrated that 8 payloads can be tracked for long durations [Holzworth and Hu, 1994]. Now that flights as long as 4 months [Holzworth et al., 1993] have been demonstrated, it becomes possible to envision a series of 10 to 20 payloads aloft for many months, covering the globe, or focused on specific pieces of the global problem such as polar electrodynamics. This number of payloads almost certainly mandates a coordinated effort involving several nations and working groups. With a dozen, widely spaced polar cap measurements it would be possible to obtain, in real time, the cross polar cap potential drop with 1 minute time resolution from payloads at sub-auroral latitudes up to the pole. Together with other ground based, continuous measurements, such as with radar and optical measurements, this program could provide the in-situ, global convection pattern with a temporal and spatial resolution that is unattainable by any present or planned satellite program. The measurements proposed would provide quantitative model input data in a manner never before available. With a standardized payload package and telemetry system, using existing satellite-linked data collection capabilities, all measurements could be provided in essentially real time. Note that, as with all measurement techniques, balloon-borne sensors have a variety of known limitations. In addition to electronic limitations (such as telemetry rates) there are limitations imposed by the stratospheric medium and by the proximity to local perturbation influences that tend to obscure the global signatures. Therefore, the payloads will have sufficient instrumentation (including X-ray detectors, magnetic field sensors and electric conductivity measurements) to identify when an individual payload is under an auroral feature, or near a thunderstorm to allow identification of these local influences. With 12 to 20 payloads aloft, the localized loss of some of the data will have a minimal influence on the global determinations. This workshop will consider details of the balloon technology, global stratospheric circulation patterns, payload systems (including sensors, power, data and telemetry) and data coordination strategies needed to address a wide variety of present space physics questions relating to the coupled ionosphere-magnetosphere system.
Note that, as an added feature of the data we will be collecting, the auroral and low latitude electric fields could be mapped to the equator assuming that the large-scale, slowly varying electric field maps along magnetic fields (equipotential mapping) for radiation belt dynamical studies such as real-time variations in the highest gain accelerating mechanism in the magnetosphere - namely radial diffusion caused by fluctuating electric fields [Holzworth and Mozer, 1979]. Another benefit of the proposed balloon-borne system would be the addition of atmospheric instruments such as ozone and air temperature which, when coupled with the basic circulation information provided by the balloon trajectories themselves, could be very valuable to atmospheric dynamics investigations. In fact, once our balloon-borne system is functioning, it would be very straight forward to use it as a basis for any number of experiments needing global measurements from the stratosphere.
One major topic of interest to us in this proposal is the ionospheric electric field in the vicinity of the auroral oval. The electric field is associated with the bulk ``convective'' motions of the plasma. As such, it is a sensitive indicator of the magnetospheric dynamics responsible for a host of other observed phenomena. One of the biggest unsolved problems in the study of ionospheric convection is our inability to obtain ``snapshots" of the entire convection pattern at once. We do not as yet know if any of the various techniques that have been developed to infer convection models actually produce results that are ever realized on an instantaneous basis. The best approximation to a global snapshot at present is obtained via the simultaneous operation of a global network of incoherent scatter radars and magnetometers [Richmond et al., 1988; Knipp et al., 1989]. A similar experiment can be performed with multiple balloon launches [Mozer and Manka, 1971; Holzworth et al., 1977]. An opportunity to perform a unique multiple balloon experiment in the Southern Hemisphere occurred in the 1992-93 austral summer. Two campaigns were conducted, the PPB campaign already mentioned and Professor Robert Holzworth's ELBBO campaign of superpressure balloons [Holzworth et al., 1993]. The ELBBO campaign involved five balloons launched from Christchurch. There were at least 5 and sometimes 6 balloons simultaneously aloft making electric field measurements above the Southern Hemisphere during austral summer 1992-93.
There are some new ground-based instruments whose data can be combined with this Southern Hemisphere balloon data to contribute to solving the snapshot problem, particularly in regard to the study of small-scale impulsive events. These instruments are the PACE HF radar at Halley Bay [Greenwald et al., 1990], the PENGUIn array of automatic geophysical observatories (AGO's), one of which was deployed in late 1992 and the vertical current and electric field meters that we have proposed to install at South Pole and Vostok stations. During the period of the proposed 1996-99 campaigns, the AGO network should be fully operational and the PACE HF radar will have been augmented by construction of HF radars at SANAE and Syowa to become the Southern Hemisphere Auroral Radar Experiment (SHARE). The PACE HF radar measures the line-of-sight component of the convection velocity with 80 s resolution over a large area about South Pole when the amplitude of F region plasma irregularities is sufficient. In contrast, the balloon makes a vector measurement of the average electric field over $\sim$100 km with a sampling interval no longer than 1 minute all of the time. The combination of data from these two instruments with data from an array of magnetometers should make it possible to progress in the study of a number of problems concerning convection near the day side oval, such as the structure and role of impulsive events [Lanzerotti et al., 1986, 1990; Southwood, 1987; Friis-Christensen et al., 1988; Lin et al., 1990; Lockwood et al., 1989], and the nature of convection when $B_z$ is northward [Potemra et al., 1984; Clauer et al., 1988; Vasyliunas, 1988].
The day side oval is also known to be a region of high ULF wave activity [Samson et al., 1971; Rostoker et al., 1972; Heacock, 1974; Gupta, 1975; Bol'shakova et al., 1975; Bol'shakova and Troitskaya, 1977; Olson, 1986; Arnoldy et al., 1988a\&b; Glassmeier, 1988, 1989; Lee et al., 1988]. There are at least five possible sources for these waves, including propagation of magnetopause waves to low altitude [Russell et al., 1971; Scarf et al., 1972, 1974; Lee et al., 1988], ion cyclotron instability within the cusp itself [Fredericks and Russell, 1973], Kelvin-Helmholtz instability in the cusp [D'Angelo, 1973; D'Angelo et al., 1974; Kintner, 1976; Potemra et al., 1988], drift wave instabilities within the cusp [Rostoker et al., 1972; D'Angelo, 1973] and the occurrence of flux transfer events on the magnetopause [Bol'shakova and Troitskaya, 1982; Lanzerotti and Maclennan, 1988; Lee et al., 1988]. There is increasing interest in polar latitude ULF pulsations [D'Angelo, 1977, Troitskaya et al., 1980; Fraser-Smith, 1982; Arnoldy et al., 1988a; Glassmeier, 1989], especially impulsive events. Other topics of recent interest include observations of narrow band emissions at 3 MHz [Olson, 1986] and PC 3 waves [Engebretson et al., 1986, 1989a\&b, 1990; Yumoto et al., 1987].