Search NASA⌕ Search

SEARCH · Search NASA

Results for “solar corona, electron density fluctuations”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

21 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Solar flare produced pulsations in meter and X-ray wavelengths

The mechanism responsible for the modulation of synchrotron radiation in the meter wave range by a solar flare is examined. The proposed explanation is based on the interaction of a flare generated shock front with a magnetic flux tube extending out into the corona over the flare. As the shock wave propagates through the flux tube, Alfven waves are developing and travelling up the tube toward each other, thereby accelerating electrons and protons by the Fermi mechanism and thus filling the top of the flux tube with energetic electrons. Radial oscillations develop as the shock front becomes parallel to the magnetic field direction and the intensity of the synchrotron radiation is modulated by these oscillations. An OSO-5 experiment detected a hard X-ray burst associated with the flare that produced modulated radio emission and X-ray modulations that are attributed to density fluctuations in the X-ray bursts.

Frost, K. J.↗
NASA NTRS2023

Structured Type III Radio Bursts Observed in Interplanetary Space

Context . The last few decades have seen numerous studies dedicated to fine structures of type III radio bursts observed in the meter–decameter wavelengths. Most of the explanations of the structured radio emission involve the propagation of electron beams through the strongly inhomogeneous plasma in the low corona. To date, only a few type III bursts with fine structures, observed at hecto-kilometric wavelengths, have been reported. Aims . We report here the existence of numerous structured type III radio bursts observed during the STEREO era by all three WAVES instruments on board STEREO A, B, and Wind. The aim of the study is to report and classify structured type III bursts, and to present the characteristics of their fine structures. The final goal is to try to understand the physical mechanism responsible for the generation of structured radio emission. Methods . In this study we used data from all available spacecraft, specifically STEREO and Wind. We employed 1D density models to obtain the speed of the source of type III radio emission, the electron beam. We also performed a spectral analysis of the fine structures in order to compare their characteristics with the metric–decametric fine structures. Results . The presented similarities of the type III fine structures in the metric to decametric and interplanetary wavelengths indicate that the physical processes responsible for the generation of structured type III radio bursts could be the same, at heights from the low corona to the interplanetary range. We show that the observed structuring and intermittent nature of the type III bursts can be explained by the variation in the level of density fluctuations, at different distances from the Sun.

Non-thermal radiation mechanisms↗
NASA NTRS2019

Near-Sun Observations of an F-Corona Decrease and K-Corona Fine Structures

Remote observations of the solar photospheric light scattered by electrons (K-corona) and dust (F-corona/Zodiacal light) have been made from the ground during eclipses and from space at 1 AU and as close as 0.3 AU. Previous observations of dust scattering have not confirmed the existence of a theoretically-predicted dust free zone near the Sun. The transient nature of the corona has been well characterized for large events, but questions still remain (e.g. initiation, production of solar energetic particles) and for small events even the structure is uncertain. Here we report on imaging the solar corona, from the Parker Solar Probe spacecraft, during the first two perihelion passes (0.16-0.25 AU), each of ten days duration. The view from these distances is qualitatively similar to the historical view, but there are some significant differences in the details. We have uncovered at short elongations a decrease in the intensity of the F-coronal intensity, which is suggestive of the long-sought dust free zone. Also we have resolved the plasma structure of very small eruptions, which are being frequently ejected from the Sun. They take two forms - the commonly observed magnetic flux ropes or the predicted, but not yet observed, magnetic islands arising from the tearing mode instability in the current sheet. Our observations of the coronal streamer evolution confirm the large-scale topology of the solar corona, but they also reveal that, as recently predicted, streamers are composed of yet smaller sub-streamers channeling continual density fluctuations at all visible scales.

Astronomy and astrophysics↗