Partnering to Enhance Education and Public Engagement Programs

Collaborating with partners is a fundamental aspect of the Lunar and Planetary Institute's (LPI) educational and public engagement efforts. Such partnerships enable scientists and educators to include members of the audience in program planning and execution. Ultimately, partnerships strengthen programs by providing diverse resources, expertise, and expanding the potential audience

Time-dependent electron transport and optical emissions in the aurora

Thesis (Ph.D.) University of Alaska Fairbanks, 2000This thesis presents the first time-dependent transport model of auroral electrons. The evolution of the spherical electron intensity in phase space is studied for a variety of incident electron intensities. It is shown that the secondary electrons with energies 150 km can take over 300 ms to reach steady state in phase space. Since there are bright optical emissions in this region, such a time dependence in the auroral electrons is important. The emissions of N2(2PG) 3371 A and N+2 (1NG) 4278 A are studied for time-varying electron pulses to show for the first time that this ratio will change until the secondary electrons reach steady state in the ionosphere. The way in which the 3371A/4278A ratio changes with time-varying precipitation depends on the precipitating electron spectra. The changes in the emission ratio can be used to learn more about the auroral acceleration region and the role of the ionosphere in auroral emissions. Field-aligned bursts (FABs), often observed in electron spectra of instruments flying over flickering aurora, are modeled with the time-dependent transport model. How the ionosphere modifies these electrons is shown. The 3371 and 4278 A emissions of flickering FABs are modeled to study the optical effects of modulated electron intensities in time. A study of 4278 A emissions for electron source regions from 630 to 4,000 km are studied along with frequency variations from 5 to 100 Hz. This study shows that the percent variation of the maximum to the minimum column brightness is less for higher frequencies and more distant source regions. It is shown that with an accurate time-dependent transport calculation and 4278 A emission observations of flickering aurora it should be possible to deduce the source altitude of the modulated electrons creating the optical flickering

Evaluation of the electron-TO-phonon interaction in polar crystals from experimental data

The aim of this study was to determine the strengths of the coupling of electrons with the polar long-wavelength transverse optical (TO) vibrations from infrared spectroscopy data. This determination is made by means of a simple relationship between the electron-TO-phonon interaction constant and material parameters, based on a parametrization of the electron-TO-phonon coupling in terms of the long-range dipole-dipole interaction. The combination of experimental data employed here allowed us to calculate directly the relevant constants for a number of representative polar insulators and to show that in ferroelectrics the interband electron-TO-phonon interaction at the Gamma point is essentially strong. In these calculations, infrared spectroscopy methods proved to be an effective tool for study of the main properties of electron interaction with polar long-wavelength TO phonons.Comment: 8 pages, 3 tables, 1 figur

On wind-driven electrojets at magnetic cusps in the nightside ionosphere of Mars

Mars has a complex magnetic topology where crustal magnetic fields can interact with the solar wind magnetic field to form magnetic cusps. On the nightside, solar wind electron precipitation can produce enhanced ionization at cusps while closed field regions adjacent to cusps can be devoid of significant ionization. Using an electron transport model, we calculate the spatial structure of the nightside ionosphere of Mars using Mars Global Surveyor electron measurements as input. We find that localized regions of enhanced ionospheric density can occur at magnetic cusps adjacent to low density regions. Under this configuration, thermospheric winds can drive ionospheric electrojets. Collisional ions move in the direction of the neutral winds while magnetized electrons move perpendicular to the wind direction. This difference in motion drives currents and can lead to charge accumulation at the edges of regions of enhanced ionization. Polarization fields drive secondary currents which can reinforce the primary currents leading to electrojet formation. We estimate the magnitude of these electrojets and show that their magnetic perturbations can be detectable from both orbiting spacecraft and the surface. The magnitude of the electrojets can vary on diurnal and annual time scales as the strength and direction of the winds vary. These electrojets may lead to localized Joule heating, and closure of these currents may require field-aligned currents which may play a role in high altitude acceleration processes

General Morgan’s Grand March

80.7568.398 – “General Morgan’s Grand March”: C. L. Peticolas: Geo. Dunn & Company: 1864: Piano Solo

On the nature of ULF wave power during nightside auroral activations and substorms: 2. temporal evolution

We present a statistical analysis of the time evolution of ground magnetic fluctuations in three (12–48 s, 24–96 s and 48–192 s) period bands during nightside auroral activations. We use an independently derived auroral activation list composed of both substorms and pseudo-breakups to provide an estimate of the activation times of nightside aurora during periods with comprehensive ground magnetometer coverage. One hundred eighty-one events in total are studied to demonstrate the statistical nature of the time evolution of magnetic wave power during the ∼30 min surrounding auroral activations. We find that the magnetic wave power is approximately constant before an auroral activation, starts to grow up to 90 s prior to the optical onset time, maximizes a few minutes after the auroral activation, then decays slightly to a new, and higher, constant level. Importantly, magnetic ULF wave power always remains elevated after an auroral activation, whether it is a substorm or a pseudo-breakup. We subsequently divide the auroral activation list into events that formed part of ongoing auroral activity and events that had little preceding geomagnetic activity. We find that the evolution of wave power in the ∼10–200 s period band essentially behaves in the same manner through auroral onset, regardless of event type. The absolute power across ULF wave bands, however, displays a power law-like dependency throughout a 30 min period centered on auroral onset time. We also find evidence of a secondary maximum in wave power at high latitudes ∼10 min following isolated substorm activations. Most significantly, we demonstrate that magnetic wave power levels persist after auroral activations for ∼10 min, which is consistent with recent findings of wave-driven auroral precipitation during substorms. This suggests that magnetic wave power and auroral particle precipitation are intimately linked and key components of the substorm onset process

Simple geometric algorithms to aid in clearance management for robotic mechanisms

Global geometric shapes such as lines, planes, circles, spheres, cylinders, and the associated computational algorithms which provide relatively inexpensive estimates of minimum spatial clearance for safe operations were selected. The Space Shuttle, remote manipulator system, and the Power Extension Package are used as an example. Robotic mechanisms operate in quarters limited by external structures and the problem of clearance is often of considerable interest. Safe clearance management is simple and suited to real time calculation, whereas contact prediction requires more precision, sophistication, and computational overhead