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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 73 records · Page 4
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NASA NTRS2023

Parker Solar Probe Observations of High Plasma β Solar Wind From the Streamer Belt

In general, slow solar wind from the streamer belt forms a high plasma β equatorial plasma sheet around the heliospheric current sheet (HCS) crossing, namely, the heliospheric plasma sheet (HPS). Current Parker Solar Probe (PSP) observations show that the HCS crossings near the Sun could be full or partial current sheet (PCS) crossings, and they share some common features but also have different properties. In this work, using the PSP observations from encounters 4–10, we identify streamer belt solar wind from enhancements in plasma β, and we further use electron pitch angle distributions to separate it into HPS solar wind around the full HCS crossings and PCS solar wind in the vicinity of PCS crossings. Based on our analysis, we find that the PCS solar wind has different characteristics as compared with HPS solar wind: (a) the PCS solar wind could be non-pressure-balanced structures rather than magnetic holes, and the total pressure enhancement mainly results from the less reduced magnetic pressure; (b) some of the PCS solar wind is mirror-unstable; and (c) the PCS solar wind is dominated by very low helium abundance but varied alpha–proton differential speed. We suggest that the PCS solar wind could originate from coronal loops deep inside the streamer belt, and it is pristine solar wind that still actively interacts with ambient solar wind; thus, it is valuable for further investigations of the heating and acceleration of slow solar wind.

Slow solar wind↗
NASA NTRS1979

Negative streamer development in FEP teflon

A computational model is developed which describes the evolution and propagation of an ionizing front (negative streamer) in solid materials. The ionization front consists of drifting avalanching electrons moving self-consistently under the influence of their own space-charge field together with an applied external field. The required input information for the model consists of the functional dependence of the macroscopic transport coefficients on the local electric field, the initial conditions for beginning the calculation, and the strength of the applied field. A computational approach for specifying the transport coefficients and initional conditions is also described. The approach has been implemented by constructing three computer codes which sequentially interface, beginning with single electron scattering, and ending with streamer development. Computational results are presented for model calculations in Teflon. The overall model is perceived to provide a picture of the initiation phase of a propagating discharge in electron-irradiated dielectrics.

Beers, B. L.↗
NASA NTRS1981

Solar wind helium and hydrogen structure near the heliospheric current sheet - A signal of coronal streamers at 1 AU

Solar wind flow properties associated with very low helium to hydrogen abundance ratios have been observed with Los Alamos instruments on IMP 6, 7, and 8 during 1971-1978. A characteristic pattern has been discovered consisting of correlated interplanetary field reversals, high plasma density, low and nearly identical H(+) and He(2+) bulk velocities, low H(+) and He(2+) kinetic temperatures, and minima in their ratios. Because coronal streamers straddle the current sheet close to the sun, the pattern discovered is the 'signal' of a coronal streamer at 1 AU. A superposed epoch analysis of 74 well-defined sector boundary crossings provides verification of the above correlation featuring a pronounced minimum in the helium to hydrogen abundance ratio at the sector boundary passage.

Borrini, G.↗
NASA NTRS1981

The solar origins of solar wind interstream flows - Near-equatorial coronal streamers

A class of low-speed solar wind flows with velocities of 450 km/s and less, ion temperatures of 40,000 K and less, and heavy ion distributions indicating moderate coronal freezing in temperatures in the range from 1 million to 2.5 millions K is considered. For brevity this class is termed interstream. Interstream flows have as yet, not firm identification with a coronal origin. The considered investigation is concerned with the identification of the coronal origins of interstream flows. It is found that major sources of low speed solar wind are the quiescent, near-equatorial coronal streamers. Such an identification provides a natural explanation for the long term variations of solar wind electron temperature and density observed at 1 AU by Feldman et al. (1979) in terms of the concurrent long term morphological variation in the coronal equatorial streamer belt observed using the Mauna Loa K-coronameters.

Feldman, W. C.↗
NASA NTRS1987

A type IV burst associated with a coronal streamer disruption event

A type IV burst was observed on February 17, 1985 with the Clark Lake Radio Observatory multifrequency radioheliograph operating in the frequency range 20-125 MHz. This burst was associated with a coronal streamer disruption event. From two-dimensional images produced at 50 MHz, evidence of a type II burst and a slow moving type IV burst are shown. The observations of the moving type IV burst suggests that a plasmoid containing energetic electrons can result from the disruption of a coronal streamer.

Kundu, M. R.↗
NASA NTRS1990

A three-dimensional simulation of a coronal streamer

A time-dependent MHD simulation was used to investigate the magnetic topology of an idealized streamerlike configuration in three dimensions. Starting from an initially current-free multipole field and a transonic flow, a quasi-steady, streamerlike configuration forms. The simulated streamer exhibits a closed magnetic field region bounded by a current layer and surrounded by open fields. This helmet region is surmounted by a current layer, with an enhanced density in the closed field and current sheet regions. The simulated streamer has a finite longitudinal extent, with the closed field region primarily confined to the center of the structure.

Linker, Jon A.↗
NASA NTRS1992

Shapes of strong shock fronts propagating through the coronal streamer belt

The effect of the coronal streamer belt on the propagation of a shock front in the solar wind is modeled. The model predicts a meridional deviation in the shock normal, resulting in a tendency for the shock normals to point toward the current sheet, which is straddled by the coronal streamer belt. Normals of eight shocks indpendently assessed to be within the expected range of influence of the belt are presented. Six of the eight shocks showed the predicted distortion. The null hypothesis would yield the same result in one out of 14 tries. The dimple shape induces a postshock confluence in the center of the belt of material pushed centerward from the top and bottom of the belt. It is suggested that this confluence of material might drive field line reconnection at the heliospheric current sheet in the center of the belt, as MHD simulations have observed.

Burton, M. E.↗
NASA NTRS1993

Multiple heliospheric current sheets and coronal streamer belt dynamics

The occurrence of multiple directional discontinuities in the coronal streamer belt at sector boundary crossings in the heliosphere, often ascribed to waves or kinks in the heliospheric current sheet, may alternatively be attributed to a network of extended current sheets from multiple helmet streamers with a hierarchy of sizes at the base of the corona. Frequent transient outflows from these helmets can account for a variety of signatures observed at sector boundaries, including ordered field rotations, planar magnetic structures and sandwichlike plasma structure.

Crooker, N. U.↗
NASA NTRS1993

Ulysses observations of a recurrent high speed solar wind stream and the heliomagnetic streamer belt

Near-ecliptic solar wind observations by Ulysses on its way to the polar regions of the Sun, compared with those from IMP 8 at 1 AU, showed that high-speed streams decay and broaden with heliocentric distance from IMP 8 to Ulysses, as expected. In July 1992 while traveling south at approximately 13 deg S and 5.3 AU, Ulysses encountered a recurrent high-speed stream, that may also have been observed at IMP 8. The stream has been observed a total of 14 times, once in each solar rotation through June 1993 at approximately 34 deg S. The source of the high-speed stream is an equatorward extension of the south polar coronal hole. From July 1992 through June 1993, averages of solar wind peak speed increased while density decreased with heliographic latitude. Both the stream and a low-speed, high-density flow, presumably associated with the heliomagnetic (coronal) streamer belt encircling the heliomagnetic equator, crossed Ulysses with the solar rotation period until April 1993 when the spacecraft was at approximately 29 deg S heliographic latitude. After this time, as the spacecraft climbed to higher latitudes, the central portion of the streamer belt with lowest speed and highest density disappeared. Therefore, at its maximum inclination, the belt was tilted at approximately 29 deg to the heliographic equator at this point in the solar cycle.

Bame, S. J.↗
NASA NTRS1995

An estimate of solar wind velocity profiles in an coronal hole and a coronal streamer area (6-40 solar radius)

Using the total electron content data obtained by the Ulysses Solar Corona Experiment during the superior solar conjunction in summer 1991, we selected two data sets, one associated with a coronal hole and the other one with coronal streamer crossings. By doing this data splitting, we find two entirely different density profiles varying as r(exp -2.7) and r(exp -2.3) for the coronal hole and coronal streamers, respectively. Assuming mass flux conservation from the inner corona to one AU, an estimate for the velocity profiles or acceleration in these two different regions can be determined. The more negative exponent of the coronal hole density profile indicates a more extended heating and acceleration region or more flaring, or both. Various possible explanations will be discussed.

Paetzold, M.↗
NASA NTRS1994

Magnetohydrodynamic Simulation of a Streamer Beside a Realistic Coronal Hole

Existing models of coronal streamers establish their credibility and act as the initial state for transients. The models have produced satisfactory streamer simulations, but unsatisfactory coronal hole simulations. This is a consequence of the character of the models and the boundary conditions. The models all have higher densities in the magnetically open regions than occur in coronal holes (Noci, et al., 1993).

Suess, S. T.↗
NASA NTRS1999

Streamer Brightness Boundary

Flow tubes adjacent to closed magnetic field lines on the boundaries of streamers can have spreading factors which change rapidly with height. Numerical models in this thin layer are subject to uncertainties. Here we use an analytic model of magnetically closed and adjacent open regions to analyze the spreading factor close to the closed field lines. The model is based on the one-temperature, isothermal flow model of Pneuman (1968), extended to calculate spreading factors and plasma beta, and to better explain streamer evolution with increasing temperature.

Suess, S. T.↗
NASA NTRS2003

A Slow Streamer Blowout at the Sun and Ulysses

On 10 June 2000 a streamer on the southeast limb slowly disappeared from LASCO/C2 over a period of 17 hours. Within this interval, a small CME was reported in C2. Nothing was reported in C3. The ejecta was later detected at Ulysses, which was at quadrature with the Sun and SOHO at the time. The interplanetary CME (ICME) displayed all the properties of a typical ICME. Slow streamer blowouts such as this have long been known but are little studied.

Suess, S. T.↗
NASA NTRS2020

Source and Propagation of a Streamer Blowout Coronal Mass Ejection Observed by the Parker Solar Probe

In the first orbit of the Parker Solar Probe (PSP), in situ thermal plasma and magnetic field measurements were collected as close as 35RSun from the Sun, an environment that had not been previously explored. During the first orbit of PSP, the spacecraft flew through a streamer blowout coronal mass ejection (SBO-CME) on 2018 November 11 at 23:50 UT as it exited the science encounter. The SBO-CME on November 11 was directed away from the Earth and was not visible by L1 or Earth-based telescopes due to this geometric configuration. However, PSP and the STEREO-A spacecraft were able to make observations of this slow (v ≈ 380 kms−1) SBO-CME. Using the PSP data, STEREO-A images, and Wang–Sheeley–Arge model, the source region of the CME is found to be a helmet streamer formed between the northern polar coronal hole and a mid-latitude coronal hole. Using the YGUAZU-A model, the propagation of the CME is traced from the source at the Sun to PSP. This model predicts the travel time of the flux rope to the PSP spacecraft as 30 hr, which is within 0.33 hr of the actual measured arrival time. The in situ Solar Wind Electrons Alphas and Protons data were examined to determine that no shock was associated with this SBO-CME. Modeling of the SBO-CME shows that no shock was present at PSP; however, at other positions along the SBO-CME front, a shock could have formed. The geometry of the event requires in situ and remote sensing observations to characterize the SBO-CME and further understand its role in space weather.

Kelly Elizabeth Korreck↗
NASA NTRS2020

High-resolution Near-infrared Polarimetry and Submillimeter Imaging of FS Tau A: Possible Streamers in Misaligned Circumbinary Disk System

We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2–1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to ~240 au from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an local standard of rest kinematic (LSRK) velocity of 1.19–5.64 km s−1. Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17–16.43 km s−1. From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems.

Yi Yang↗
NASA NTRS1995

An Estimate of Solar Wind Velocity Profiles in a Coronal Hole and a Coronal Streamer Area (6-40 R(radius symbol)

Total electron content data obtained from the Ulysses Solar Corona Experiment (SCE) in 1991 were used to select two data sets, one associated with a coronal hole and the other with coronal streamer crossings. (This is largely equatorial data shortly after solar maximum.) The solar wind velocity profile is estimated for these areas.

solar corona solar wind coronal streamer Ulysses↗