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At least 307 records · Page 17
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NASA NTRS2003

CODA: Coordinated Observations of Dynamics in Aurora

The grant funds were provided to carry out chemical tracer wind and turbulence measurements in the mesosphere and lower thermosphere as part of the Coordinated Observations of Dynamics in Aurora (CODA) experiment for which Dr. Andy Christensen of the Aerospace Corp. was the Principal Investigator. Clemson University was a co-investigator institution on the project and was tasked with designing, building, and testing a total of four chemical tracer release payloads which were used to release trimethyl aluminum (TMA) to measure the winds and turbulent diffusion. All four payloads were flown from the rocket range at Poker Flat, Alaska, in support of instrumented payloads flown from the same location. The CODA experiment was designed to investigate the changes in the chemical composition in the lower thermosphere during an auroral substorm event. In particular, the objective was to determine the relative importance of two competing mechanisms. The first mechanism is associated with the advection of air from the polar cap into the auroral oval. A flow in that direction is typical in the postmidnight sector of the oval. As the air moves from the region of negligible forcing in the polar cap to the region of strong forcing and heating in the oval, changes in the composition are expected to occur. Alternatively, enhanced local mixing will also cause such changes. Since the auroral forcing accelerates the neutral winds in the lower E region, but not at lower altitudes, the forcing results in large shears that can be large enough to be unstable in the Richardson number sense. The unstable shears are expected to generate turbulence and therefore enhanced mixing. Such mixing will also create composition changes similar to what is observed. In the CODA experiment an instrumented payload designed and built by the Aerospace Corporation was used to measure the composition and plasma parameters needed to define the auroral forcing. In addition, three chemical tracer payloads were to be flown along three trajectories widely separated in azimuth to map out the winds and wind gradients. The measurements would thus provide information about the local composition changes above the launch site as well as detailed information about the advection and location of stable or unstable shears both locally and over a broader area in the vicinity of the launch site.

Larsen, M. F.↗
NASA NTRS1991

Imaging Jupiter's aurorae from H3+ emissions in the 3-4 micrometers band

Since H3+ was first spectroscopically detected on Jupiter, there has been considerable interest in using this simple molecular ion to probe conditions existing in the planet's auroral regions. Here we present a series of images of Jupiter recorded at wavelengths sensitive to emission by H3+, which reveal the spatial distribution of excited H3+ molecular ions in the jovian ionosphere, as seen from Earth. We believe that they provide high-spatial-resolution images of polar aurorae on Jupiter. They suggest that the intensity of the auroral emission can vary on a timescale of an hour, a shorter period than had previously been noted. We also find that the spatial distribution of H3+ emissions correlates only partially with the loci of auroral activity inferred from ultraviolet and longer-wavelength infrared observations. The H3+ emission may therefore be controlled by auroral processes that are different from those responsible for the ultraviolet and infrared emissions.

Non-NASA Center↗
NASA NTRS2000

Saturn's Hydrogen Aurora as Observed by HST

We describe Saturn's aurora as observed by HST in 10/1994, 10/1995, and 10-12/1997. HST provides access to the auroral emissions due to atomic and molecular hydrogen in the northern and southern auroral zones.

magnetospheres planets auroral↗
NASA NTRS2006

From Auroras to Sea Ice: Views From the International Space Station and Plans for International Polar Year

For more than 40 years astronauts have been observing Earth, taking photographs or digital images from their spacecraft. Today, a robust program of observation from the International Space Station (ISS) has yielded hundreds of thousands of images of the Earth s surface collected since 2001. Seeing Earth through the eyes of an astronaut is exciting to the general public, and the images are popular in classrooms. Because the ISS has an orbital inclination of 51.6 degrees (the north-south limits of the orbit are at 51.6 degrees latitude), high latitude observations are common. Some of the most striking images collected include views of polar phenomena. Astronauts routinely pass above brilliant red and green aurora; view high, wispy clouds at the top of the atmosphere; or look down on glaciers and floating ice rafts. These images, framed and captured by humans, are easily interpreted by students and teachers. Astronaut observations provide a way to visualize complicated polar phenomena and communicate about them to students of all ages. Over the next two years, astronauts aboard the ISS will formally focus their observations on polar phenomena as participants in the International Polar Year (IPY). Imagery acquisition from the ISS will be coordinated with other IPY scientists staging studies and field campaigns on the ground. The imagery collected from the ISS will be cataloged and served on NASA s web-based database of images, http://eol.jsc.nasa.gov . The website allows investigators, students and teachers to search through the imagery, assemble image datasets, and download the imagery and the metadata. We display some of the most spectacular examples of polar imagery and demonstrate NASA s database of astronaut images of Earth.

Evans, Cynthia A.↗
NASA NTRS2007

The Morphology of the X-ray Emission above 2 keV from Jupiter's Aurorae

The discovery in XMM-Newton X-ray data of X-ray emission above 2 keV from Jupiter's aurorae has led us to reexamine the Chandra ACIS-S observations taken in Feb 2003. Chandra's superior spatial resolution has revealed that the auroral X-rays with E > 2 keV are emitted from the periphery of the region emitting those with E < 1 keV. We are presently exploring the relationship of this morphology to that of the FUV emission from the main auroral oval and the polar cap. The low energy emission has previously been established as due to charge exchange between energetic precipitating ions of oxygen and either sulfur or carbon. It seems likely to us that the higher energy emission is due to precipitation of energetic electrons, possibly the same population of electrons responsible for the FUV emission. We discuss our analysis and interpretation.

Elsner, R.↗
NASA NTRS2006

Cassini Observations of Saturn's Dawn-Magnetotail Region and their Relation to Models of Saturn's Aurora: Preliminary Results

Using Cassini plasma and magnetic field observations from the dawn meridian of Saturn s outer magnetosphere to Saturn s magnetotail region, we investigate the applicability of the centrifugal instability model by Sittler et al. [2006] for Saturn s auroral response to the solar wind, versus the reconnection model of Saturn s aurora by Cowley et al. [2005]. We use Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) and Electron Plasma Spectrometer (ELS) observations to characterize the plasma environment. ELS and magnetometer observations are used to map out the morphology of the outer magnetosphere from dawn to midnight local time. IMS observations are used to measure plasma flow velocities from which one can infer rotation versus convective flows. IMS composition measurements are used to trace the source of plasma from the inner magnetosphere (protons, H2 and water group ions) versus an external solar wind source (protons and Heff ions). A critical parameter for both models is the strength of the convection electric field with respect to the rotational electric field for the large scale magnetosphere. Is there a significant return flow from the magnetotail? Pitch angle distributions also play an important role as a discriminator. If the magnetosphere tends to conserve angular momentum as suggested by Sittler et al. [2006], then we expect to see an anti-correlation between rotational flow component and radial flow velocities. All will be investigated.

Sittler, E. C.↗
NASA NTRS2007

The Morphology of the X-ray Emission above 2 keV from Jupiter's Aurorae

The discovery in XMM-Newton X-ray data of X-ray emission above 2 keY from Jupiter's aurorae has led us to reexamine the Chandra ACIS-S observations taken in Feb 2003. Chandra's superior spatial resolution has revealed that the auroral X-rays with E > 2 keV are emitted from the periphery of the region emitting those with E < 1 keV. We are presently exploring the relationship of this morphology to that of the FUV emission from the main auroral oval and the polar cap. The low energy emission has previously been established as due to charge exchange between energetic precipitating ions of oxygen and either sulfur or carbon. It seems likely to us that the higher energy emission is due to precipitation of energetic electrons, possibly the same population of electrons responsible for the FUV emission. We discuss our analysis and interpretation.

Elsner, R.↗
NASA NTRS2010

Flow, Aurora and PI2 Associations Observed by Themis

It has been known for decades that auroral substorm onset occurs on (or at least near) the most equatorward auroral arc, which is thought to map to the near geosynchronous region. The lack of auroral signatures poleward of this arc prior to onset has been a major criticism of flow-burst driven models of sub storm onset. The combined THEMIS 5 spacecraft in-situ and ground array measurements provide an unprecedented opportunity to examine the causal relationship between midtail plasma flows, aurora, and ground magnetic signatures. I first present an event from 2008 using multi-spectral all sky imager data from Gillam and in-situ data from THEMIS. The multispectral data indicate an equatorward moving auroral form prior to sub storm onset. When this forms reaches the most equatorward arc, the arc brightens and an auroral substorm begins. The THEMIS data show fast Earthward flows prior to onset as well. I suggest that the results strongly support flow-burst driven models of magnetospheric activity. I discuss further the association of flow bursts and Pi2 pulsations, and discuss the possibility of using Pi2 waveforms to infer midtail reconnection dynamics

Kepko, E. I.↗
NASA NTRS2011

A Model-Based Study of On-Board Data Processing Architecture for Balloon-Borne Aurora Observation

This paper discusses an application of ISAAC design methodology to a balloon-borne payload electronic system for aurora observation. The methodology is composed of two phases, high level design and low level implementation, the focus of this paper is on the high level design. This paper puts the system architecture in the context of a balloon based application but it can be generalized to any airborne/space-borne application. The system architecture includes a front-end detector, its corresponding data processing unit, and a controller. VisualSim has been used to perform modeling and simulations to explore the entire design space, finding optimal solutions that meet system requirements.

modeling↗
NASA NTRS2012

Ground-Based Observations of Recovery Phase Aurora

This analysis focuses on spatial and temporal forms occurring after substorm breakup. The observations show irregular shapes and nonuniform drifts with respect to relatively stationary pulsating patches. The pulsating patches occur within a diffuse auroral background as a modulation of the auroral brightness in a localized region. The images analyzed show a decrease in the brightness of the diffuse background in the region of the pulsating patch at the beginning of the 'off' phase of the modulation. Throughout the off phase the brightness of the diffuse aurora gradually increases back to the average intensity. The time constant for this increase is measured as the first step toward determining the physical process.

Jones, Sarah L.↗
NASA NTRS2015

Superthermal Electron Magnetosphere-Ionosphere Coupling in the Diffuse Aurora in the Presence of ECH Waves

There are two main theories for the origin of the diffuse auroral electron precipitation: first, pitch angle scattering by electrostatic electron cyclotron harmonic (ECH) waves, and second, by whistler mode waves. Precipitating electrons initially injected from the plasma sheet to the loss cone via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These secondary electrons can escape back to the magnetosphere, become trapped on closed magnetic field lines, and deposit their energy back to the inner magnetosphere. ECH and whistler mode waves can also move electrons in the opposite direction, from the loss cone into the trap zone, if the source of such electrons exists in conjugate ionospheres located at the same field lines as the trapped magnetospheric electron population. Such a situation exists in the simulation scenario of superthermal electron energy interplay in the region of diffuse aurora presented and discussed by Khazanov et al. (2014) and will be quantified in this paper by taking into account the interaction of secondary electrons with ECH waves.

Coupling↗
NASA NTRS2016

Ionosphere-Magnetosphere Energy Interplay in the Regions of Diffuse Aurora

Both electron cyclotron harmonic (ECH) waves and whistler mode chorus waves resonate with electrons of the Earths plasma sheet in the energy range from tens of eV to several keV and produce the electron diffuse aurora at ionospheric altitudes. Interaction of these superthermal electrons with the neutral atmosphere leads to the production of secondary electrons (E500600 eV) and, as a result, leads to the activation of lower energy superthermal electron spectra that can escape back to the magnetosphere and contribute to the thermal electron energy deposition processes in the magnetospheric plasma. The ECH and whistler mode chorus waves, however, can also interact with the secondary electrons that are coming from both of the magnetically conjugated ionospheres after they have been produced by initially precipitated high-energy electrons that came from the plasma sheet. After their degradation and subsequent reflection in magnetically conjugate atmospheric regions, both the secondary electrons and the precipitating electrons with high (E600 eV) initial energies will travel back through the loss cone, become trapped in the magnetosphere, and redistribute the energy content of the magnetosphere-ionosphere system. Thus, scattering of the secondary electrons by ECH and whistler mode chorus waves leads to an increase of the fraction of superthermal electron energy deposited into the core magnetospheric plasma.

Khazanov, G. V.↗
NASA NTRS2017

Chandra's Observations of Jupiter's X-Ray Aurora During Juno Upstream and Apojove Intervals

The Chandra space telescope has recently conducted a number of campaigns to observe Jupiter's X-ray aurora. The first set of campaigns took place in summer 2016 while the Juno spacecraft was upstream of the planet sampling the solar wind. The second set of campaigns took place in February, June and August 2017 at times when the Juno spacecraft was at apojove (expected close to the magnetopause). We report on these upstream and apojove campaigns including intensities and periodicities of auroral X-ray emissions. This new era of jovian X-ray astronomy means we have more data than ever before, long observing windows (up to 72 kiloseconds for this Chandra set), and successive observations relatively closely spaced in time. These features combine to allow us to pursue novel methods for examining periodicities in the X-ray emission. Our work will explore significance testing of emerging periodicities, and the search for coherence in X-ray pulsing over weeks and months, seeking to understand the robustness and regularity of previously reported hot spot X-ray emissions. The periods that emerge from our analysis will be compared against those which emerge from radio and UV wavelengths.

Lunar & Planetary Science & Exploratio↗
NASA NTRS2020

The Formation of Electron Heat Flux in the Region of Diffuse Aurora

Whistler and electrostatic electron cyclotron harmonics waves are responsible for scattering and precipitating the energetic plasma sheet electrons that drive the diffuse aurora. These primary electrons with energies in the kiloelectron volt range, simultaneously precipitating in magnetically conjugate regions, produce the secondary electron population and can be reflected by the atmosphere back through the magnetosphere and precipitate into the conjugate region with additional follow‐up atmospheric backscatter. Primary, degraded, and secondary electrons can be trapped back into the magnetosphere as they travel back and forth between the two magnetically conjugate ionospheres and continuously delivering their energy to the cold plasma sheet electrons and form the electron thermal fluxes that deposit this energy at the upper ionospheric altitudes. We consider the formation of these heat fluxes focusing on the magnetosphere‐ionosphere energy interplay of the entire superthermal electron spectra from 1 eV up to 10 keV and discuss the efficiency of the different spectral energy intervals that contribute to the electron plasma heating at the magnetospheric altitudes. Our parametric studies at L = 6.8, with lower and upper band chorus whistler wave amplitudes of 10 pT and electron cyclotron harmonic wave amplitudes of 1 mVm−1, indicate the dominant role of the whistler mode in the formation of the electron heat flux coming from the magnetosphere to the ionosphere.

George V. Khazanov↗
NASA NTRS2023

Simulating Electron Distribution Function in the Pulsating Aurora Using Particle and Wave Data of ARASE Satellite

Decades lasting research on the pulsating aurora suggested that this phenomenon forms as result of interactions between the magnetospheric keVs electrons and whistler-mode chorus waves. Arase satellite observation reported the direct evidence for this process confirming in situ measurement of highly correlated precipitated electrons and chorus wave activity. This paper presents the theoretical analysis of this observational event based on the SuperThermal Electron Transport (STET) code that simulates the highly dynamic environment of measured waves and particle data. Specifically, the STET code simulated results confirms the delicate loss-cone observation results of this mission and further reveals the broader energy range of precipitated electron fluxes that was not measurable by Arase satellite.

George V Khazanov↗
NASA NTRSDate not supplied

The Electron Heat Fluxes Associated with Electron Precipitation in the Region of Diffuse Aurora

Electron heat flux that comes from the magnetosphere to the upper ionospheric altitudes controls the value of electron temperature in the core plasma, and, as a result, the total electron density content that is required for different kinds of space weather applications. Knowing the thermal electron heat flux at the upper ionospheric boundaries is the Achilles' heel of all ionospheric models. Such a thermal heat flux setting is especially difficult to justify in the region of the diffuse aurora that is connected to a large energy reservoir of electrons with energies of a few kiloelectron volts, the Earth's plasma sheet, where magnetosphere-ionosphere coupling processes are strongly interconnected. We use the simulated heat flux provided by SuperThermal Electron Transport (STET) code to estimate electron temperatures at the upper ionospheric altitudes and compare these results with corresponding observations from the Defense Meteorological Satellite Program satellite during Saint Patrick's Days 2013 and 2015 Geomagnetic Storms.

George V. Khazanov↗
NASA NTRSDate not supplied

Inertia of Ionospheric Conductance During Electron Precipitation Events in Pulsating Aurora and Polar Arcs

Using coupled SuperThermal Electron Transport (STET) and Super-thermal Proton Electron Atomic Hydrogen – tRansport in the Ionosphere and Thermosphere (SPEAH-RIT) codes, we demonstrate that temporal variability of ionospheric conductance is defined by several time scales: magnetospheric source time variations, starting time of electron precipitation, and termination of the corresponding source of magnetospheric origin. In this case, the time scales are defined by dissipation of energetic electrons and effective recombination processes. The results presented in this paper were applied in the regions of pulsating aurora and polar arcs, demonstrating the fact that ionospheric conductance requires some time to form and decay. These time delays constitute an effective “inertia” in the conductance calculation which is not accounted for in many global models which assume an instantaneous connection between precipitation and conductance. Ionospheric conductance inertia influences the temporal variation in ionospheric and magnetospheric electric fields, and as a result, impacts magnetospheric dynamics and ultimately reconfigures the electron precipitation.

Khazanov, George V↗