Leslie C. Hale

Middle atmosphere electrical structure, dynamics and coupling

Abstract The ram current to ion traps and the insensitivity of ion conductivity to compressibility provide the basis of robust techniques for middle atmosphere measurements. Gerdien condensers are more difficult to implement but provide more information. Mesospheric electrical conductivity shows many orders of magnitude variability, with depressions below gas phase model values indicating dominance by aerosol particles. The mobility of these ions has been directly measured and indicates particles of thousands of AMU. Large mesospheric fields have come into question, and diagnostic measurements show that many such measurements may be artifacts. However, some measurements of V/m fields with symmetrical and redundant sensors appear to be real. These fields complicate the “mapping” picture of electrical coupling and may also modulate the transport of aerosol particles. They are probably related to neutral atmosphere dynamics and/or the aerosol particles. Lightning couples much more energy to the middle atmosphere and above than previously suspected, primarily in the ELF-ULF range. There are many important unanswered questions in this relatively unexplored frontier area which may be answered with low cost balloon and sounding rocket experiments.

Electrical stratification in the middle atmosphere

Abstract Stratification of the electrical structure of the middle atmosphere (MA) has been observed under a wide range of conditions. “Ledges” in charged particle density at the bottom of Chapman-like layers are accentuated in conductivity profiles due to the atmospheric density gradients effect on mobility, but the steepest gradients yet observed occurred in conjunction with the horizontal magnetic field at the equator. High-latitude conductivity ledges are produced by steeply declining energy distributions. Measurements in a noctilucent cloud showed that the free electrons essentially vanished (presumably due to attachment to cloud particles) but the positive ion conductivity remained virtually unchanged.

ELECTRICAL CONDUCTIVITY MEASUREMENTS IN THE STRATOSPHERE USING BALLOON AND PARACHUTE-BORNE BLUNT PROBES

Blunt probe electrical conductivity measurements from three balloon flights are reported in this paper. Rocket-launched, parachute-borne blunt probe experiments were conducted in conjunction with two of the flights. The float altitude balloon data were useful for studying electrical conductivity and its associated temperature and sunrise variations. The altitude dependence for the balloon conductivity data was observed to be in good agreement with the corresponding rocket measurements.

Ion properties of the high-latitude middle atmosphere

Abstract Investigations of high-latitude, middle-atmosphere ion properties have been conducted using rocket probe techniques. Electrodynamics studies have addressed: mesospheric dynamics and small-scale structure (the MAC/EPSILON Campaign during October–November 1977); ionization effects associated with highly energetic (≥1 MeV) precipitating electrons (the MAC/REP Program during May 1990); and the characteristics of noctilucent cloud (NLC) and polar mesosphere summer echo (PMSE) regions (the NLC-91 Campaign during July–August 1991). Recent developments in Gerdien condenser probe theory, using computational fluid dynamics to model ion collection, have resulted in more accurate evaluation of the ion mobilities and number densities. Measurements of very small ion mobilities are thought to indicate an aerosol ion presence in the upper mesosphere.

Electrodynamics payloads for small rockets

Abstract Totally integrated design facilitates electrical cleanliness and light weight, which are necessary in subsonic parachute-borne payloads for electrodynamics investigations. “Blunt” probes measure ion conductivity, as do Gerdien condensers. Recent finite-element computer analyses combining find electrodynamics have resolved problems in determining ion densities and mobilities from Gerdien data. Three-axis electric fields are measured with deployable boom-mounted electrodes from DC through VLF. Splitting the cylinrical payload with an insulator and measuring the current between halves has provided a vertical Maxwell current detector mechanically rigid enough to measure, at ELF, energy related to coupling. A nose tip “Smith” probe turbulence measurement is usually performed on ascent. Other instrumentation, such as photo-ionization sources and X-ray detectors, can also be included. These electrodynamic measurement payloads are about one meter in length and have a mass of about 9 kg. They can be launched with an Orion-class or smaller vehicle.