Robert M. Candey

Structure within Jovian hectometric radiation

Observations of Jovian hectometric radio emission (HOM) by the Voyager planetary radio astronomy (PRA) experiment at frequencies from 300 kHz to 1.3 MHz indicate persistent dynamic spectral features that had not been previously studied. The features of interest appear as “lanes” of decreased emission intensity within the otherwise persistent HOM. The lanes are apparent in intensity and occurrence probability spectrograms of frequency versus Jovian System III (1965) longitude. In the investigation of the morphology of these features, we use inbound and outbound Voyager 2 data at Jupiter to show that the lane occurrence and characteristics do not depend on local time over the range sampled. Occurrence probability spectrograms of frequency versus magnetic latitude are created from the portion of the data when the spacecraft was between 0° and +10° magnetic latitude. These spectrograms represent both the inbound and outbound passes and are quite similar despite the different longitude ranges. A simple extension of decametric (DAM) arc features into the HOM wavelength does not account for all the lane features, giving further evidence that HOM is an independent emission component. Polarization signatures for the data show that the polarization is predominantly right-hand circular and that it does not reverse across the lanes, suggesting the emission is from the same hemisphere. In addition, we investigate possible effects due to solar wind variations and find that the occurrence of the lanes appears to be independent of times of low and high solar wind densities. The intensity of the HOM emission on either side of the lanes is comparable, implying that the lane is probably not a result of a gap between fundamental and second harmonic emission regions. We present these data and analyses as a morphological study to establish that the lane features are an important part of the HOM emission and should be considered in HOM emission models. At this time, no theory of the source of the lanes explains all the observed features.

Latitudinal structure within Jovian hectometric radiation

Jovian hectometric radio emission (HOM: 300–3000 kHz) has a number of persistent structural features associated with it as observed by the Voyager 1, Voyager 2, Ulysses, and Galileo spacecraft for specific jovigraphic latitudes (−4° to +7.1°) and local times (0.3 to 10.5 hours). Most notable are the presence of HOM emission between 270° and 120° central meridian longitude (CML) and the region of reduced emission intensity (a “gap”) between 120° and 270°. We displayed the Ulysses and Galileo data using time-frequency occurrence probability spectrograms and show that the observed HOM emission features are nearly identical to those observed by the Voyager spacecraft. This implies that the HOM structure is long-lived and fixed in its longitudinal position within the Jovian magnetosphere. HOM structure depends on small changes in the observers jovigraphic latitude, so the different jovigraphic latitudes of the spacecraft were used to probe the HOM beam structure. Prom this analysis we found that the CML width of the main HOM gap is directly correlated to the latitude of the spacecraft. We conclude that the latitudinal thickness of the HOM beam is about 12°, extending from −5° to +7° magnetic latitude.

Jovian dual-sinusoidal HOM lane features observed by Galileo

A well defined sinusoidal-shaped “band” of reduced emission intensity exists within Jovian HOM from 500 kHz to 3 MHz at all Jovian longitudes as observed by the Galileo spacecraft. A less prominent sinusoidal-shaped band feature exists in the same frequency range but is 180° out of phase with the more prominent feature. We used a multiple Jovian rotation spectrogram technique to fully display both bands and found that these sinusoidal-shaped features are the source of the “lanes” previously studied in Voyager and Ulysses data. Our extension of the simple straight-line ray model by Gurnett et al. [1998] provides a qualitative explanation for the observed features. We found that the two sinusoidal bands show an asymmetry about the longitude of the northern tip of the magnetic dipole (202° CML). Enhancements of emission can be seen along the edges of the bands which may be interpreted as caustic surfaces.

Simple ray tracing of Galileo-observed hectometric attenuation features

Observations of persistent structural features within Jovian hectometric (HOM) radio emission have been made with the Galileo spacecraft. Two well-defined sinusoidal-shaped “band” features of reduced emission intensity and occurrence probability exist at all Jovian longitudes and nearly cover the entire spectrum of HOM radio emission from ∼500 kHz to 3000 kHz. These two sinusoidal lanes have a bandwidth of 200–400 kHz and are 180° out of phase with one another, suggesting that they are a result of HOM radio emission propagation processes from opposite hemispheres. These features become more apparent when presented as intensity or occurrence probability spectrograms added together over multiple Jovian rotations. Enhancements in the HOM intensity and occurrence are seen along the edges of one of the observed sinusoidal lane features which may indicate caustic surfaces due to refraction along the propagation path. We present some simple ray tracing analyses to show that refraction from density enhancements in the Io torus flux tube may explain some of the observations. Using this simple method, we approximate the density enhancements in the Io flux tube to be 100 cm−3.

Sonification of Astronomical Data

Instituut voor Sterrenkunde, Leuven, BelgiumAbstract.This document presentsJava -based software calledxSonify that uses a sonificationtechnique (the adaptation of sound to convey information) to promote discovery in astronomicaldata. The prototype is designed to analyze two-dimensional data, such as time-series data. Wedemonstrate the utility of the sonification technique with examples applied to X-ray astronomyand solar data. We have identified frequencies in theChandra X-Ray observations of EX Hya,a cataclysmic variable of the intermediate polar type. In another example we study the impactof a major solar flare, with its associated coronal mass ejection (CME), on the solar wind plasma(in particular the solar wind between the Sun and the Earth), and the Earth’s magnetosphere.Keywords.Solar Wind, Sonification, xSonify, Variable Stars

Web-based sonification of space science data

is the use of non-speech audio to convey information 1 (with sonar and Geiger counters, for example). The best example in space physics was the use of sound for detecting micro-meteoroids that impaced Voyager 2 as it traversed Saturns rings; these impacts were obscured in the plotted data but were clearly evident as hailstorm sounds. 2 We are extending the Coordinated Data Analysis Web (CDAWeb) data browsing system (cdaweb.gsfc.nasa.gov/) to display space science data as sounds in addition to its existing plot capability (line plots, spectrograms, images, etc.). In CDAWeb, the user selects spacecraft, instruments, datasets, and time periods of interest and is then presented with a list of variables to display. PERL and Interactive Data Language (IDL) routines on the CDAWeb server interactively create the selection pages and then read the data from Common Data Format (CDF) files (used for its portability and self-describing meta-information), plot the data (automatically selecting reasonable plot types and scaling), and return the plots as GIF images. We are extending CDAWeb to provide an alternative display type for certain variables where an IDL routine writes the data out in a JavaScript routine that calls the Beatnik (www.headspace.com/) plug-in to the users Web browser. When the user clicks on the sound data icon, the Beatnik plug-in plays the data array as varying pitches, loudnesses, or drumbeat rhythms. Sonification Background Sonification is useful for monitoring some data while looking at something else, for complex or rapidly/temporally changing visualizations, for data exploration of large datasets (particularly multi-dimensional datasets), and for exploring datasets in frequency rather than spatial dimensions. A good reference to research on the use of audio representation of data is the International Conferences on Auditory Display Complex datasets (e.g., particle measurements varying in energy, look direction, time, and particle species such as electrons and ions) are usually only examined in a subset of dimensions at a time, forcing researchers to build up a picture in their minds of the whole dataset. Sound can be used to represent these other dimensions, using pitch, loudness, rhythm, damping or attack/decay rate, direction, duration and repetition, timbre and harmonics, phase, and rest periods. 4 Audio can also be used to reinforce the visual displays as alternative ways of looking at or hearing the data, particularly where visual patterns are hidden until identified by other means. An additional benefit of sound for visualization is that the ear is more sensitive …

Low background gamma‐ray spectrometer

The next generation gamma‐ray spectrometer after the planned Nuclear Astrophysics Explorer (NAE) could be based on the Moon to use the lunar regolith for shielding the detectors from cosmic rays and neutrons. This increased shielding over what could reasonably be put in low‐Earth orbit would provide a narrow line sensitivity (3σ) of ∼2×10−7 photons cm−2 s−1 at 1 MeV in 106 s, which is about 10 times better than the NAE and 100 times better than GRO/OSSE.