Y. T. Chiu

Whistler‐mode chorus and morningside aurorae

Quasi-electrostatic ELF/VLF chorus emissions immediately above the equatiorial half-gyrofrequency, observed to propagate with wave normal angle (Ψ) within 0.4–1.2° of the resonance cone (Ψr) [Muto et al., 1987], are shown to efficiently resonate with 0.1–10 keV electrons. These waves may thus be important in driving the relatively low energy (<10 keV) component of pulsating aurorae and the morning-side diffuse aurorae (∼1 keV).

Imaging of ionospheric plasma outflow in the magnetosphere: Verification of a new concept

The distribution of He+, O+, and charge-exchanged auroral protons can be obtained by tomographic deconvolution of resonantly scattered solar 304, 834 and 1216 A signals, respectively, by these ions in the sunlit magnetosphere. The Doppler shifts of the emission features, if any, can be used to infer the energies of these ions. This concept have been verified for the case of plasmaspheric He+ ions by the Extreme Ultraviolet telescope on board the Apollo-Soyuz mission. Our calculations for the OII834A line are in agreement with the observations by the STP78-1 satellite experiment. One Spacelab I experiment has observed “hot emissions” near 1216A which are predicted by the charge exchange of auroral protons with geocoronal neutral hydrogen atoms. We discuss results of a simulation of expected intensities from various observing conditions and describe the design of an instrument capable of verifying the hypothesis.

Theoretical aspects of heavy ion injections in the magnetosphere: A review

Abstract The theoretically expected effects of active heavy ion injections in the magnetosphere are reviewed according to their chemical state (plasma or neutral) and their kinetic state (explosion or beam injection) of release. The early-phase effects of such injections (such as ionospheric heating, wave-particle interactions, radiation belt and ring current modifications and anomalous ionization) are briefly discussed. The need for understanding the magnetospheric modification aspects of heavy ion injections becomes more acute in the next decades when the transportation and construction of large-scale space structures would inject increasing volumes of heavy ions in the magnetosphere by both chemical and ion engines. Ion engine exhaust, in the form of a dense relatively cool plasma beam of high drift speed, represents a new regime of heavy ion magnetospheric modification, the effects of which have not been thoroughly investigated either theoretically or observationally. We envisage that the ion engine can be modified into a useful tool for scientific studies of magnetospheric dynamics since it is a source of a variety of ionic species independent of the need for photoionization.

Origin of auroral electric potential structures

Abstract Careful analyses during the past 5–6 years of particle and electric field signatures observed in association with the evening discrete arc have led to major advances in the basic understanding of the structure of the auroral electric potential. The origin of this basic potenital structure, which is inherent in the principle of kinetic plasma distributions in globally inhomogeneous magnetic configurations, is reviewed and examined. It is shown that, once the discrete arc potential structure is understood, this principle of arc formation can be applied to other geomagnetic configurations. In this way, a comprehensive theory of discrete auroral arcs of general configuration, including the theta aurora, can be constructed. Furthermore, completion of the auroral field-aligned current circuit in this theory leads to the hypothesis of downward parallel electric fields in the return current region away from the central portion of the discrete arc potential. Such downward parallel electric fields accelerate ionospheric electrons upward to form the return current and trap low-energy ions at the foot of the field line. It is shown that such trapping of ionospheric ions between the magnetic mirror below and the electric reflection above plays a crucial role in the heating and acceleration of ionospheric ions, which have been found to be an important source of magnetospheric plasma. Evidence for such downward parallel electric field signatures have been found in the last year or so.