Mining metrics for buried treasure

The same but different: That might describe two metrics. On the surface CLASSI may show two metrics are locally equivalent, but buried beneath one may be a wealth of further structure. This was beautifully described in a paper by M.A.H. MacCallum in 1998. Here I will illustrate the effect with two flat metrics -- one describing ordinary Minkowski spacetime and the other describing a three-parameter family of Gal'tsov-Letelier-Tod spacetimes. I will dig out the beautiful hidden classical singularity structure of the latter (a structure first noticed by Tod in 1994) and then show how quantum considerations can illuminate the riches. I will then discuss how quantum structure can help us understand classical singularities and metric parameters in a variety of exact solutions mined from the Exact Solutions book.Comment: 16 pages, no figures, minor grammatical changes, submitted to Proceedings of the Malcolm@60 Conference (London, July 2004

Anthropogenic Space Weather

Anthropogenic effects on the space environment started in the late 19th century and reached their peak in the 1960s when high-altitude nuclear explosions were carried out by the USA and the Soviet Union. These explosions created artificial radiation belts near Earth that resulted in major damages to several satellites. Another, unexpected impact of the high-altitude nuclear tests was the electromagnetic pulse (EMP) that can have devastating effects over a large geographic area (as large as the continental United States). Other anthropogenic impacts on the space environment include chemical release ex- periments, high-frequency wave heating of the ionosphere and the interaction of VLF waves with the radiation belts. This paper reviews the fundamental physical process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure

VLF wave injection experiments from Siple Station, Antarctica

The background of VLF wave-particle experiments from Siple Station, Antarctica, including wave-induced precipitation is briefly reviewed. Single frequency ducted signals that exceed a certain \u27threshold\u27 intensity are observed at the conjugate point (Roberval, Quebec) to be amplified 30-50dB, with temporal growth rates of 30-200dB/s. Following saturation, variable frequency emissions are triggered. When a second signal is added to the first, with a frequency spacing Df<100Hz, signal growth is reduced and sidebands are generated at frequencies separated from the carriers by integer multiples (up to seven) of Df. The sidebands are attributed to short emissions triggered by the beats between the two input carriers. Mid-latitude magnetospheric hiss is crudely simulated by a sequence of 10ms pulses whose frequencies are chosen randomly within a 400Hz band. Results show that certain combinations of 10ms pulses link together to form chorus-like elements, suggesting a common origin for hiss and chorus. Under conditions of strong echoing, emissions may form into lines; a recent example, started by the Siple Station transmitter, exhibits interline spacings of about 45Hz. These lines, called magnetospheric line radiation (MLR), vary slowly in frequency and show no simple connection to the harmonics of the Canadian power grid. Interline suppression may play a role in determining the spacing of MLR lines and the absence of discrete triggered emissions

Recent research on magnetospheric wave-particle interactions

Highlights of recent Stanford University VLF research in the Antarctic include new observations of wave-induced particle precipitation and controlled experiments on nonlinear wave growth phenomena. Higher-than-expected levels of burst precipitation have been discovered inside the plasmasphere, near L=2,using subionospheric signal perturbations called "Trimpi events". Studies of burst precipitation have been extended to the region poleward of the plasmapause using the Siple transmitter signal as a waveguide probe. Experiments on the "coherent wave instability", using the amplitude and frequency modulation capability of the new Siple transmitter, have produced exciting new results. Examples are : 1) better definition of the power threshold for the stimulation of temporal wave growth, 2) generation of strong sidebands by unamplified "beat" waves and 3) generation of chorus-like elements within a band of simulated hiss. Using a new digital processing technique developed at Stanford, new features of the phase behavior of growing waves have been found. Opportunities for extending these experiments are discussed

Variable frequency VLF signals in the magnetosphere: Associated phenomena and plasma diagnostics

Coherent variable frequency signals (ramps) extending from 1 to 8 kHz, injected into the magnetosphere from Siple Station, Antarctica (L=4.3) exhibit upper and lower cutoffs when received at the conjugate station, Roberval, Quebec. Ramp group delay measurements and ionospheric sounding data are used for the first time to determine the cold plasma density and L shell of the propagation path. Relationships among f, df / dt, and the “phase equator” for gyroresonance are calculated using second‐order resonance equations generalized to relativistic electrons. Observed upper cutoff characteristics are interpreted in terms of off‐equatorial gyroresonant interaction regions and ducted propagation limited to frequencies below half the local gyrofrequency. The observed lower cutoff frequencies varied systematically with transmitted ramp slope, suggesting a threshold in the resonant electron number density above which rapid temporal wave growth and saturation can occur. This concept is used to develop a hot plasma diagnostic technique which, for an assumed g(α)υ−n electron distribution, provides an estimate of the energy dependence n. A test of this technique is given using the data and a simplified wave‐particle interaction simulation. Additional aspects of the magnetospheric response to ramp injection, including emission triggering, are discussed