Engineering topics

McCarthy, M.

Publications and source records attributed to McCarthy, M..

22 records · Page 2

NASA NTRS1998

Does the UVI on Polar Detect Cosmic Snowballs?

Frank and Sigwarth [1997a] claim that the dark pixels observed in dayglow images obtained by the Earth sensor of the Visible Imaging System (VIS) are due to bombardment of Earth by 20 to 40 ton cosmic snowballs. We have independently studied the same one hour of VIS data Frank and Sigwarth used and have performed detailed statistical analysis of the dark pixels. The characteristics of the dark pixels from the VIS images have been compared to those obtained from the overlapping images from the Ultraviolet Imager (UVI). We find the occurrence distributions of the dark pixels, single and multiple, from VIS and UVI are nearly identical. This result cannot be explained by a -eophysical source since the two cameras have different pixel resolutions: A search for evidence of of spacecraft "wobble" motion, whose presence would indicate that the source is external to the camera, has found that pairs of dark pixel clusters are uniformly distributed in an-le and no preference is observed in the wobble direction. Instrument artifacts as the source of the dark pixels is the most likely explanation for these results. Probability estimates for the occurrence of dark pixel clusters lead us to expect coincident events of instrumental origin to occur frequently in the two cameras. The conclusion of this study is that neither VIS nor UVI provide any scientific evidence that the origin of dark pixels is geophysical.

Parks, G. K.↗

NASA NTRS1998

Observations of Substorms from the Auroral Ionosphere to the Distant Plasma Sheet

We have been studying how substorms work by examining the global polar Ultraviolet Imager (UVI) images in correlation with observations from the ground, interplanetary space and the geomagnetic tail between 10-20 earth radii. One of the objectives of our study is to better understand the connection among many complex phenomena going on close to Earth and those in the distant plasma sheet. We have studied, for example, how the aurora[ and polar cap boundaries at different local times behave in relation to variations observed in the solar wind and plasma sheet during substorms. Preliminary results indicate that the polar cap and auroral oval boundaries expand and contract in a complicated but systematic way. These variations are correlated to solar wind parameters, and thinning and recovery phenomena in the plasma sheet. These results will be presented and interpreted in terms of directly driven and/or unloading substorm processes.

Parks, G.↗

NASA NTRS1997

Does the Ultraviolet Imager on Polar Detect Cometesimals?

The Earth's dayglow images obtained by the Ultraviolet Imager (UVI) on Polar should show darkened pixels if cometesimals bombard Earth. This darkening occurs because the UV emissions are absorbed by water between the altitude where the dayglow emissions are produced and the Polar spacecraft. We have asked: (1) Does the UVI detect darkened pixels? (2) If so, what are their characteristics? (3) What can the UVI say about the presence/absence of cometesimals? The UVI does see dark pixels, which tend to be clustered. But the calibration data obtained from the same instrument just before the instrument was launched show similarly darkened pixel clusters. After a though statistical analysis of these images, we conclude that the darkened pixels are instrumental artifacts. Therefore, the UVI does not provide evidence for the existence of the cometesimals.

Parks, G. K.↗

NASA NTRS1995

Observations of the 3-D distribution of interplanetary electrons and ions from solar wind plasma to low energy cosmic rays

The 3-D Plasma and Energetic Particle instrument on the GGS Wind spacecraft (launched November 1, 1994) is designed to make measurements of the full three-dimensional distribution of suprathermal electrons and ions from solar wind plasma to low energy cosmic rays, with high sensitivity, wide dynamic range, good energy and angular resolution, and high time resolution. Three pairs of double-ended telescopes, each with two or three closely sandwiched passivated ion implanted silicon detectors measure electrons and ions from approximately 20 keV to greater than or equal to 300 keV. Four top-hat symmetrical spherical section electrostatic analyzers with microchannel plate detectors, a large and a small geometric factor analyzer for electrons and a similar pair for ions, cover from approximately 3 eV to 30 keV. We present preliminary observations of the electron and ion distributions in the absence of obvious solar impulsive events and upstream particles. The quiet time electron energy spectrum shows a smooth approximately power law fall-off extending from the halo population at a few hundred eV to well above approximately 100 keV The quiet time ion energy spectrum also shows significant fluxes over this energy range. Detailed 3-D distributions and their temporal variations will be presented.

Lin, R. P.↗