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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Anomalous resistivity and the evolution of magnetic field topology

This paper explores the topological restructuring of a force-free magnetic field caused by the hypothetical sudden onset of a localized region of strong anomalous resistivity. It is shown that the topological complexity increases, with the primitive planar force-free field with straight field lines developing field lines that wrap half a turn around each other, evidently providing a surface of tangential discontinuity in the wraparound region. It is suggested that the topological restructuring contributes to the complexity of the geomagnetic substorm, the aurora, and perhaps some of the flare activity on the sun, or other star, and the Galactic halo.

Parker, E. N.↗
NASA NTRS1995

Velocity variation in the high-latitude solar wind

The Ulysses spacecraft has been observing the properties of the high-latitude solar wind during a period of declining and minimum solar activity when the Sun displayed well-developed polar coronal holes. Poleward of approximately 40 deg, Ulysses remained continuously within the flow from the polar coronal hole. All was not quiet within that flow, however. In addition to coronal mass ejections seen at latitudes as high as 60 deg, there were mini-high velocity streams with amplitudes as large as 100 km/s and well developed compression regions on their leading edges and there were large-amplitude Alfven waves. The alpha-particles participate in the mini-stream variations, but not in the Alfven waves, which provides a method of separating the two phenomena. The duration of the mini-streams was typically a few days whereas the periods of the Alfven waves were usually less than 12 hours. Other properties of the mini-streams will be summarized.

Neugebauer, M.↗
NASA NTRS1999

Nonthermal Linewidths from Serts: Implications for Coronal Heating Models

Observations from Solar Extreme-ultraviolet Research Telescope and Spectrograph (SERTS) are used to determine the nonthermal velocity in the corona for active and quiet Sun regions in 1991 and 1993. A nonthermal velocity of 20-30 km/s is obtained in all solar structures observed at both observing times. These observations can be used to constrain coronal heating models. The idea that magnetic reconnection could provide energy to heat the non-transient corona is not supported by the data.

Davila, Joseph M.↗
NASA NTRS2002

Large Scale Flows through the Solar Cycle

Large scale flows within the solar convection zone are the primary drivers of the Sun's magnetic activity cycle. Differential rotation amplifies the magnetic field and converts poloidal fields into toroidal fields. Poleward meridional flow near the surface carries magnetic flux that reverses the magnetic poles and converts toroidal fields into poloidal fields. The deeper, equatorward meridional flow carries magnetic flux toward the equator where it must reconnect with oppositely directed fields in the other hemisphere. These axisymmetric flows are themselves driven by large scale convective motions. Given these intimate connections between the large scale flows and solar activity, it would be surprising if there weren't solar cycle variations in the flow characteristics. Some variations, namely the torsional oscillations, are well established. Other variations, namely changes in the meridional flow and in the convective motions themselves, are more controversial. In this presentation I will describe the observed characteristics of the large scale flows and discuss possible variations associated with the solar cycle.

Hathaway, D. H.↗
NASA NTRS2004

Flows in the Solar Convection Zone

Flows within the solar convection zone are the primary drivers of the Sun's magnetic activity cycle. Differential rotation stretches out the magnetic field and converts poloidal fields into toroidal fields. Zones of strong radial shear are found at both the surface and at the base of the convection zone (the tachocline). The poleward meridional flow near the surface transports magnetic flux that is observed to reverse the magnetic poles near the time of cycle maxima. The deeper (and as yet unobserved), equatorward meridional flow should carry magnetic flux toward the equator where it reconnects with oppositely directed fields in the other hemisphere. The non-axisymmetric flows (granules, supergranules, and giant cells) also transport magnetic flux but in a more random, diffusive, manner. Supergranules and giant cells also play significant roles in driving the large-scale, axisymmetric flows themselves. The effect of solar rotation on supergranulation produces the shear layer near the surface and enhances the meridional flow. The effect of solar rotation on giant cells should produce the latitudinal differential rotation, the shear in the tachocline, and the meridional circulation. In this presentation I will describe the observed and theorized characteristics of the flows in the solar convection zone and discuss their connections to the solar activity cycle.

Hathaway, D. H.↗
NASA NTRS2004

Probabilistic Physics-Based Risk Tools Used to Analyze the International Space Station Electrical Power System Output

This paper describes the methods employed to apply probabilistic modeling techniques to the International Space Station (ISS) power system. These techniques were used to quantify the probabilistic variation in the power output, also called the response variable, due to variations (uncertainties) associated with knowledge of the influencing factors called the random variables. These uncertainties can be due to unknown environmental conditions, variation in the performance of electrical power system components or sensor tolerances. Uncertainties in these variables, cause corresponding variations in the power output, but the magnitude of that effect varies with the ISS operating conditions, e.g. whether or not the solar panels are actively tracking the sun. Therefore, it is important to quantify the influence of these uncertainties on the power output for optimizing the power available for experiments.

Patel, Bhogila M.↗
NASA NTRS2006

What Do Our Users Want? Perspectives on Understanding and Meeting User Needs for Multi-Mission Data Services

The Sun-Earth Connection Active Archive (SECAA) project of NASA's Space Physics Data Facility operates a range of unique and heavily used multi-mission data services in support of the large-scale science objectives of the Great Observatory, including services such as CDAWeb, the CDAWeb Plus client, SSCWeb, OMNIweb and the CDF data format. In developing and operating these services, we have encountered and continue to struggle with a wide range of issues such as balancing scope and functionality with simplicity and ease of use, understanding the effectiveness of our choices and identifying areas most important for further improvement. In this paper, we will review our key services and then discuss some of our observations and new approaches to understanding and meeting user data service requirements. Some observations are obvious but may still have substantial implications; e.g. functionality without information content is of little user interest, which has led to our recent emphasis on development of web services interfaces, so the content and functionality we already serve is readily and fully available as a building block for new services. Some observations require careful design and tradeoffs; e.g. users will complain when they are offered interfaces with limited options but users are also easily intimidated and become lost when offered extensive options for customization. Some observations remain highly challenging; e.g. a comprehensive multi-mission, multi-source view of all data and services available easily produces a daunting list, but a more selective view can easily lead users to overlook available and relevant data. It is often difficult to obtain and meaningfully interpret measures of true productive usage and overall user satisfaction, even with a variety of techniques including statistics, citations, case studies, user feedback and advisory committees. Most of these issues will apply to and may even be more acute for distributed implementation architectures.

McGuire, Robert E.↗
NASA NTRS2009

Coronal Transient Ejections and Outflows During the CR 2068 WHI Campaign

The Whole Heliospheric Interval (WHI) campaigns began with a set of coordinated observations over Carrington Rotation (CR) 2068, which was from March~20 to April~16, 2008. An ultimate objective of WHI to understand the 3-D nature of the heliosphere. Activity on the Sun is the engine that drives the dynamics of the heliosphere, and therefore delineation of the characteristics of the Sun's atmosphere and its output over the period of study is vital to the success of WHI\@. Here we discuss the origins of solar structures that can lead to heliospheric effects, with an emphasis on observations during the CR~2068 WHI interval. These structures include both outflows from open-field regions, and transients originating from closed-field regions. Our focus will be mainly on the latter, and we will specifically consider the coronal source regions of coronal mass ejections (CMEs), and other transients that escape out into the heliosphere, for example in the form of slow expansions or as narrow jets. Over the CR~2068 period we have identified about 30 such transients, with about 20\% of them being moderately to very prominent. We will consider these feature s source regions by examining low-coronal data, along with solar surface magnetograms that provide the magnetic setting of the eruptions. Through intercomparisons of these data, we infer the coronal setup for different eruptions, and the implications for models that attempt to describe eruption-onset mechanisms.

Sterling, Alphonse C.↗
NASA NTRS2009

The Lower Solar Atmosphere During the WHI Campaign (20 Apr-16 May 2008)

The Whole Heliospheric Interval (WHI) period of 20 March - 16 April had a "quiet side" of the Sun, and an "active side," with three ARs. At least two of the ARs produced CMEs, but there were several events that may have been "confined eruptions" from these regions too. Examining the magnetic environment of the erupting regions gives insight into the onset and dynamics of the eruptions. Several of the CMEs can be traced back to likely disk sources, but several unmatched cases still remain. More work is needed to sort through these points.

Sterling, Alphonse↗
NASA NTRS2009

Prominence Structure and Dynamics

Nonerupting prominences are not dull, static objects. Rather, they are composed of fine-scale blobs and threads that are highly dynamic, often appearing to travel in opposite directions on adjacent tracks (denoted counterstreaming). Because the plasma is largely constrained to travel along the magnetic field, these cool, dense features can serve as tracers of the prominence magnetic structure, a valuable resource in view of the long-standing difficulty of observing the coronal field. Conversely, greater understanding of the fundamental magnetic geometry of filament channels can provide important constraints on the physical processes governing the accumulation, support, motion, and eruption of the cool plasma. Despite over a century of detailed observations, large gaps remain in our knowledge of filament channel/plasma formation and evolution. Resolving these issues will shed light on the physics of coronal heating, helicity transport throughout the solar cycle, and the origins of eruptive activity on the Sun. I will discuss the leading models for the magnetic and plasma structure, and outline how new observations and theory /modeling could solve long-standing uncertainties regarding this majestic solar phenomenon.

Karpen, Judy T.↗
NASA NTRS2008

Laser Infrared Desorption Spectroscopy to Detect Complex Organic Molecules on Icy Planetary Surfaces

Laser Desorption-Infrared Spectroscopy (LD-IR) uses an IR laser pulse to desorb surface materials while a spectrometer measures the emission spectrum of the desorbed materials (Figure 1). In this example, laser desorption operates by having the incident laser energy absorbed by near surface material (~10 microns in depth). This desorption produces a plume that exists in an excited state at elevated temperatures. A natural analog for this phenomenon can be observed when comets approach the sun and become active and individual molecular emission spectra can be observed in the IR [1,2,3,4,5]. When this occurs in comets, the same species that initially emit radiation down to the ground state are free to absorb it, reducing the amount of detectable emission features. The nature of our technique results in absorption not occurring, because the laser pulse could easily be moved away form the initial desorption plume, and still have better spatial resolution then reflectance spectroscopy. In reflectance spectroscopy, trace components have a relatively weak signal when compared to the entire active nature of the surface. With LDIR, the emission spectrum is used to identify and analyze surface materials.

Laser Desorption-Infrared Spectroscopy↗
NASA NTRS2000

The Preflight Photometric Calibration of the Extreme-Ultraviolet Imaging Telescope EIT

This paper presents the preflight photometric calibration of the Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO). The EIT consists of a Ritchey-Chretien telescope with multilayer coatings applied to four quadrants of the primary and secondary mirrors, several filters and a backside-thinned CCD detector. The quadrants of the EIT optics were used to observe the Sun in 4 wavelength bands that peak near 171, 195, 284, and 304 . Before the launch of SOHO, the EIT mirror reflectivities, the filter transmissivities and the CCD quantum efficiency were measured and these values are described here. The instrumental throughput in terms of an effective area is presented for each of the various mirror quadrant and filter wheel combinations. The response to a coronal plasma as a function of temperature is also determined and the expected count rates are compared to the count rates observed in a coronal hole, the quiet Sun and an active region.

EIT (EXTREME-ULTRAVIOLET IMAGING TELESCOPE)↗
NASA NTRS2016

Simulations of Solar Jets Confined by Coronal Loops

Coronal jets are collimated, dynamic events that occur over a broad range of spatial scales in the solar corona. In the open magnetic field of coronal holes, jets form quasi-radial spires that can extend far out into the heliosphere, while in closed-field regions the jet outflows are confined to the corona. We explore the application of the embedded-bipole model to jets occurring in closed coronal loops. In this model, magnetic free energy is injected slowly by footpoint motions that introduce twist within the closed dome of the jet source region, and is released rapidly by the onset of an ideal kink-like instability. Two length scales characterize the system: the width (N) of the jet source region and the footpoint separation (L) of the coronal loop that envelops the jet source. We find that both the conditions for initiation and the subsequent dynamics are highly sensitive to the ratio L/N. The longest-lasting and most energetic jets occur along long coronal loops with large L/N ratios, and share many of the features of open-field jets, while smaller L/N ratios produce shorter-duration, less energetic jets that are affected by reflections from the far-loop footpoint. We quantify the transition between these behaviors and show that our model replicates key qualitative and quantitative aspects of both quiet Sun and active-region loop jets. We also find that there connection between the closed dome and surrounding coronal loop is very extensive: the cumulative reconnected flux at least matches the total flux beneath the dome for small L/N, and is more than double that value for large L/N.

Wyper, P. F.↗
NASA NTRS2016

Characterizing Cometary Electrons with Kappa Distributions

The Rosetta spacecraft has escorted comet 67P/Churyumov-Gerasimenko since 6 August 2014 and has offered an unprecedented opportunity to study plasma physics in the coma. We have used this opportunity to make the first characterization of cometary electrons with kappa distributions. Two three-dimensional kappa functions were fit to the observations, which we interpret as two populations of dense and warm (density 10 cubic centimeters, temperature 2 times 10 (sup 5) degrees Kelvin, invariant kappa index 10 to 1000), and rarefied and hot (density equals 0.005 cubic centimeters, temperature 5 times 10 (sup 5) degrees Kelvin, invariant kappa index equals 1 to 10) electrons. We fit the observations on 30 October 2014 when Rosetta was 20 kilometers from 67P, and 3 Astronomical Units from the Sun. We repeated the analysis on 15 August 2015 when Rosetta was 300 kilometers from the comet and 1.3 Astronomical Units from the Sun. Comparing the measurements on both days gives the first comparison of the cometary electron environment between a nearly inactive comet far from the Sun and an active comet near perihelion. We find that the warm population density increased by a factor of 3, while the temperature cooled by a factor of 2, and the invariant kappa index was unaffected. We find that the hot population density increased by a factor of 10, while the temperature and invariant kappa index were unchanged. We conclude that the hot population is likely the solar wind halo electrons in the coma. The warm population is likely of cometary origin, but its mechanism for production is not known.

Broiles, T. W.↗
NASA NTRS2018

Coronal Imaging with the Solar Ultraviolet Imager

Coronal imaging capabilities of the Solar UltraViolet Imager (SUVI) on the Geostationary Operational Environmental Satellite-16 (GOES-16) are investigated. Launched in 2016, GOES-16 is stationed at 75.2 deg W longitude and accommodates both terrestrial and space weather instruments. SUVI is one of two instruments observing the Sun, providing solar images in six extreme ultraviolet (EUV) wavelengths: 94A, 131A, 171A, 195A, 284A and 304A. Mounted on a two axis gimballed Sun Pointed Platform (SPP), its 53 arc minute square field of view is nominally Sun-centered to provide high dynamic range images in all six wavelengths every four minutes. Analyses of on-orbit data indicated that SUVI had sufficient dynamic range and sensitivity in the 171A and 195A wavelengths to image the corona to the largest heights above the Sun to date while simultaneously imaging the Sun. The 1.6 megapixel Charge Coupled Device (CCD) detector enables the capture of the fine features of the corona. On-orbit calibration tests requiring movement of the SUVI line-of-sight off the Sun, demonstrated that the resulting dynamic disturbance didn't adversely impact the earth-pointing instrument performance. Combining these factors, we conducted a test to assess the performance of SUVI as an EUV extremely wide-field coronal imager by off-pointing the SPP around the Sun and synthesizing an image that's about 4 times the diameter of the Sun. The capability to perform coronal imaging at these two wavelengths is demonstrated by off-pointing the SUVI boresight to nine locations around the Sun and generating a composite coronal image that extends to approx. 4 solar radii. For this purpose, we exploited the satellite's ability to provide stable, fine pointing, even during the slews. Various exposure durations were considered during the first trial and a composite coronal image is obtained for each wavelength. The results are promising. The off-pointing locations and the exposure duration are being refined for the subsequent trials. The routine use of an ultraviolet solar imager as both an imager and a EUV coronagraph would be the first of its kind and is an exciting development. The on-orbit solar coronagraphs to date provide white light images with fields of view extending from 4-15 solar radii. Earlier, Seaton, et al investigated the evolution of the corona in EUV near the solar surface with the data from the Sun Watcher with Active Pixels and Image Processing (SWAP) EUV solar telescope on board the Project for On-Board Autonomy 2 (PROBA2). The presence of corona in EUV even to 4 solar radii is not known. The results of these experiments will begin to fill this void.

Tadikonda, Sivakumara K.↗
NASA NTRS2018

Coronal Imaging with the Solar Ultraviolet Imager

Coronal imaging capabilities of the Solar UltraViolet Imager (SUVI) on the Geostationary Operational Environmental Satellite-16 (GOES-16) are investigated. Launched in 2016, GOES-16 is stationed at 75.2 deg W longitude and accommodates both terrestrial and space weather instruments. SUVI is one of two instruments observing the Sun, providing solar images in six extreme ultraviolet (EUV) wavelengths: 94A, 131A, 171A, 195A, 284A and 304A. Mounted on a two axis gimballed Sun Pointed Platform (SPP), its 53 arcminute square field of view is nominally Sun-centered to provide high dynamic range images in all six wavelengths every four minutes. Analyses of on-orbit data indicated that SUVI had sufficient dynamic range and sensitivity in the 171A and 195A wavelengths to image the corona to the largest heights above the Sun to date while simultaneously imaging the Sun. The 1.6 megapixel Charge Coupled Device (CCD) detector enables the capture of the fine features of the corona. On-orbit calibration tests requiring movement of the SUVI line-of-sight off the Sun, demonstrated that the resulting dynamic disturbance didn't adversely impact the earth-pointing instrument performance. Combining these factors, we conducted a test to assess the performance of SUVI as an EUV extremely wide-field coronal imager by off-pointing the SPP around the Sun and synthesizing an image that's about 4 times the diameter of the Sun. The capability to perform coronal imaging at these two wavelengths is demonstrated by off-pointing the SUVI boresight to nine locations around the Sun and generating a composite coronal image that extends to approx. 4 solar radii. For this purpose, we exploited the satellite's ability to provide stable, fine pointing, even during the slews. Various exposure durations were considered during the first trial and a composite coronal image is obtained for each wavelength. The results are promising. The off-pointing locations and the exposure duration are being refined for the subsequent trials. The routine use of an ultraviolet solar imager as both an imager and a EUV coronagraph would be the first of its kind and is an exciting development. The on-orbit solar coronagraphs to date provide white light images with fields of view extending from 4-15 solar radii. Earlier, Seaton, et al investigated the evolution of the corona in EUV near the solar surface with the data from the Sun Watcher with Active Pixels and Image Processing (SWAP) EUV solar telescope on board the Project for On-Board Autonomy 2 (PROBA2). The presence of corona in EUV even to 4 solar radii is not known. The results of these experiments will begin to fill this void.

Tadikonda, Sivakumara K.↗
NASA NTRS2018

Very Narrow Coronal Mass Ejections Producing Solar Energetic Particles

Aims. Our main aim is to study the relationship between low-energy solar particles (energies below 1 MeV) and very narrow coronal mass ejections (“jets” with angular width ≤ 20°). Methods. For this purpose, we considered 125 very narrow coronal mass ejections (CMEs) from 1999 to 2003 that are potentially associated with low-energy solar particles (LESPs). These events were chosen on the basis of their source location. We studied only very narrow CMEs at the western limb, which are expected to have good magnetic connectivity with Earth. Results. We found 24 very narrow CMEs associated with energetic particles such as ions (protons and 3He), electrons, or both. We show that arrival times at Earth of energetic particles are consistent with onset times of the respective CMEs, and that in the same time intervals, there are no other potential sources of energetic particles. We also demonstrate statistical differences for the angular width distributions using the Kolmogorov–Smirnov test for angular widths for these 24 events. We consider a coherent sample of jets (mostly originating from boundaries of coronal holes) to identify properties of events that produce solar energetic particles (velocities, widths, and position angles). Our study presents a new approach and result: very narrow CMEs can generate low-energy particles in the vicinity of Earth without other activity on the Sun. The results could be very useful for space weather forecasting.

Bronarska, K.↗
NASA NTRS2022

CME Evolution in the Structured Heliosphere and Effects at Earth and Mars During Solar Minimum

The activity of the Sun alternates between a solar minimum and a solar maximum, the former corresponding to a period of “quieter” status of the heliosphere. During solar minimum, it is in principle more straightforward to follow eruptive events and solar wind structures from their birth at the Sun throughout their interplanetary journey. In this paper, we report analysis of the origin, evolution, and heliospheric impact of a series of solar transient events that took place during the second half of August 2018, that is, in the midst of the late declining phase of Solar Cycle 24. In particular, we focus on two successive coronal mass ejections (CMEs) and a following high-speed stream (HSS) on their way toward Earth and Mars. We find that the first CME impacted both planets, whilst the second caused a strong magnetic storm at Earth and went on to miss Mars, which nevertheless experienced space weather effects from the stream interacting region preceding the HSS. Analysis of remote-sensing and in-situ data supported by heliospheric modeling suggests that CME–HSS interaction resulted in the second CME rotating and deflecting in interplanetary space, highlighting that accurately reproducing the ambient solar wind is crucial even during “simpler” solar minimum periods. Lastly, we discuss the upstream solar wind conditions and transient structures responsible for driving space weather effects at Earth and Mars.

Space weather↗