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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 NTRS1973

The initial stage of development of type IV radio bursts and the relation to expanding magnetic bottles

Using the observed data for wideband type IV solar radio bursts, the onset time differences between the microwave and metric frequencies and the peak flux intensities of the metric component are analyzed as a function of the longitudinal position of the associated flares on the solar disk. It is shown that this time difference is dependent on the position of the associated flare and that the peak flux intensity reaches maximum when a flare occurs in the region from 10 to 40 deg west of the central meridian of the solar disk. These results are explained by taking into account the eastward expansion of magnetic bottles which trap mildly relativistic electrons responsible for type IV bursts. The relation between these magnetic bottles and shock waves which excite type II radio bursts is discussed.

Sakurai, K.↗
NASA NTRS1973

The relationship of solar flare electrons to the flare flash phase and type 3 radio bursts

The energy spectrum and temporal behavior of the 10 to 100 keV solar flare electrons observed at 1 AU are interpreted in terms of: (1) the location of the acceleration region, (2) the time of acceleration and duration of the injection into the interplanetary medium, and (3) type 3 radio burst origin at the sun and at 1 AU. For at least some and possibly the majority of electron flare events the density of the acceleration region is approximately 2 X 10 to the 9th power cu/cm, the time of acceleration and release coincides to within minutes of the flash phase as indicated by the type 3 radio burst, and the duration of the release less than or approximately 3 minutes. Evidence for the origin of type 3 radio bursts in 10 to 100 keV electron streams is shown and discussed.

Lin, R. P.↗
NASA NTRS1974

Motion of the sources for type II and type IV radio bursts and flare-associated interplanetary disturbances

Shock waves are indirectly observed as the source of type II radio bursts, whereas magnetic bottles are identified as the source of moving metric type IV radio bursts. The difference between the expansion speeds of these waves and bottles is examined during their generation and propagation near the flare regions. It is shown that, although generated in the explosive phase of flares, the bottles behave quite differently from the waves and that the bottles are generally much slower than the waves. It has been suggested that the waves are related to flare-associated interplanetary disturbances which produce SSC geomagnetic storms. These disturbances may, therefore, be identified as interplanetary shock waves. The relationship among magnetic bottles, shock waves near the sun, and flare-associated disturbances in interplanetary space is briefly discussed.

Sakurai, K.↗
NASA NTRS2011

Front-Side Type II Radio Bursts Without Shocks Near Earth

Type II radio bursts are due to shocks driven by coronal mass ejections (CMEs), so the shocks are expected to arrive at Earth in 2-3 days if the source is on the front-side of the Sun. However, a significant fraction of front-side CMEs producing type II bursts did not result in shocks at 1 AU. On can think of several possibilities for the lack of shocks: (1) CMEs originating at large central meridian distances may be driving a shock, but the shock may not be extended sufficiently to reach to the Sun-Earth line. (2) CME cannibalism results in the merger of shocks so that one observes a single shock at Earth even though there are two type II bursts near the Sun. (3) CME-driven shocks may become weak and dissipate before reaching 1 AU. We examined a set of 30 type II bursts observed by the Wind/WAVES experiment that had the solar sources very close to the disk center (within a CMD of 15 degrees), but did not have shock at Earth. We find that the near-Sun speeds of the associated CMEs average to approx.600 km/s, only slightly higher than the average speed of CM Es associated with radio-quiet shocks. However, the fraction of halo CMEs is only -28%, compared to 40% for radio-quiet shocks and 72% for all radio-loud shocks. We conclude that the disk-center radio loud CMEs with no shocks at 1 AU are generally of lower energy and they drive shocks only close to the Sun.

Gopalswamy, N.↗
NASA NTRS2010

Type III Radio Burst Duration and SEP Events

Long-duration (>15 min), low-frequency (<14 MHz) type III radio bursts have been reported to be indicative of solar energetic particle events. We measured the durations of type III bursts associated with large SEP events of solar cycle 23. The Type III durations are distributed symmetrically at 1 MHz yielding a mean value of approximately 33 min (median = 32 min) for the large SEP events. When the SEP events with ground level enhancement (GLE,) are considered, the distribution is essentially unchanged (mean = 32 min, median = 30 min). To test the importance of type III bursts in indicating SEP events, we considered a set of six type III bursts from the same active region (AR 10588) whose durations fit the "long duration" criterion. We analyzed the coronal mass ejections (CMEs), flares, and type II radio bursts associated with the type III bursts. The CMEs were of similar speeds and the flares are also of similar size and duration. All but one of the type III bursts was not associated with a type II burst in the metric or longer wavelength domains. The burst without type II burst also lacked a solar energetic particle (SEP) event at energies >25 MeV. The 1-MHz duration of the type III burst (28 rein) is near the median value of type III durations found for gradual SEP events and ground level enhancement (GLE) events. Yet, there was no sign of SEP events. On the other hand, two other type III bursts from the same active region had similar duration but accompanied by WAVES type 11 bursts; these bursts were also accompanied by SEP events detected by SOHO/ERNE. This study suggests that the type III burst duration may not be a good indicator of an SEP event, consistent with the statistical study of Cliver and Ling (2009, ApJ ).

Gopalswamy, N.↗
NASA NTRS1973

Pulsating type IV solar radio bursts

Several models for pulsating type IV radio bursts are presented based on the assumption that the pulsations are the result of fluctuations in the synchrotron emission due to small variations in the magnetic field of the source. It is shown that a source that is optically thick at low frequencies due to synchrotron self-absorption exhibits pulsations that occur in two bands situated on either side of the spectral peak. The pulsations in the two bands are 180 deg out of phase and the band of pulsations at the higher frequencies is the more intense. In contrast, a synchrotron source that is optically thin at all frequencies and whose low-frequency emission is suppressed due to the Razin effect develops only a single band of pulsations around the frequency of maximum emission. However, the flux density associated with the latter model would be too small to explain the more intense pulsations that have been observed, unless the source area is considerably larger than presently seems reasonable.

Gotwols, B. L.↗
NASA NTRS1973

The initial stage of development of type 4 radio bursts and the relation to expanding magnetic bottles

Using observed data for wide-band type IV solar radio bursts, the onset time differences between the microwave and metric frequencies and the peak flux intensities of the metric component were analyzed as a function of the longitudinal position of associated flares on the solar disk. It is shown that this time difference is dependent on the position of associated flares and that the peak flux intensity reaches maximum when a flare occurs in the region 10 to 40 deg west of the central meridian of the solar disk. These results are explained by taking into account the eastward expansion of magnetic bottles which trap mildly relativistic electrons responsible for type IV bursts. Discussion is also made of the relation between these magnetic bottles and shock waves which excite type II radio bursts.

Sakurai, K.↗
NASA NTRS1985

Correlation of solar decimetric radio bursts with X-ray flares

Several hundred radio bursts in the decimetric wavelength range (300-1000 MHz) have been compared with simultaneous soft and hard X-ray (HXR) emission. Long lasting (type IV) radio events have been excluded. The association of decimetric emission with hard X-rays has been found to be surprisingly high (48 percent). The association rate increases with bandwidth, duration, number of structural elements, and maximum frequency. Type III-like bursts are observed up to the upper limit of the observed band. This demonstrates that the corona is transparent up to densities of about 10 to the 10th/cu cm, contrary to previous assumptions. This can only be explained in an inhomogeneous corona with the radio source being located in a dense structure. The short decimetric bursts generally occur during the impulsive phase, i.e., simultaneously with hard X-rays. The times of maximum flux are well correlated (within 2 s). The HXR emission lasts 4 times longer than the radio emission in the average. This work finds a close relationship between decimetric and HXR emission, with sufficient statistics offering additional information on the flare process.

Aschwanden, M. 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 NTRS1990

Statistical study of the correlation of hard X-ray and type III radio bursts in solar flares

A large number of hard X-ray events which occurred during the maximum of solar cycle 21 have been analyzed in order to study their correlation with type III bursts. It is found that the distribution of occurrences of hard X-ray bursts correlated with type III radio bursts is significantly different from the distribution of all hard X-ray bursts. This result is consistent with the assumption that the hard X-ray and type III intensities are somewhat correlated. A bivariate distribution function of the burst intensities is fitted to the data and is used to determine that the typical ratio of X-ray intensity to type II intensity is about 10 and that the ratio of the number of X-ray producing-electrons to type III-producing electrons is about 1000. Three models which have been proposed to explain the relation between the accelerated hard X-ray and type III-producing electrons are examined in the context of these observations.

Hamilton, Russell J.↗
NASA NTRS1980

Plasma oscillations and the emissivity of type III radio bursts

Plasma wave electric field measurements with the solar orbiting Helios spacecraft have shown that intense electron plasma oscillations occur in association with type III solar radio bursts, thereby confirming a well known mechanism for generating solar radio emissions first proposed by Ginzburg and Zhelezniakov in 1958. In this paper the principal characteristics of these plasma oscillations are reviewed and the observed plasma oscillation intensities are compared with recent measurements of the emissivity of type III radio bursts. The observed emissivities are shown to be in good agreement with two current models for the conversion of electrostatic plasma oscillations to electromagnetic radiation.

Gurnett, D. A.↗
NASA NTRS2005

Microsat and Lunar-Based Imaging of Radio Bursts

No present or approved spacecraft mission has the capability to provide high angular resolution imaging of solar or magnetospheric radio bursts or of the celestial sphere at frequencies below the ionospheric cutoff. Here, we describe a MIDEX-class mission to perform such imaging in the frequency range approx. 30 kHz to 15 MHz. This mission, the Solar Imaging Radio Array (SIRA), is solar and exploration-oriented, with emphasis on improved understanding and application of radio bursts associated with solar energetic particle (SEP) events and on tracking shocks and other components of coronal mass ejections (CMEs). SIRA will require 12 to 16 micro-satellites to establish a sufficient number of baselines with separations on the order of kilometers. The constellation consists of microsats located quasi-randomly on a spherical shell, initially of approx. 10 km diameter. The baseline microsat is 3-axis stabilized with body-mounted solar arrays and an articulated, earth pointing high gain antenna. The constellation will likely be placed at L1, which is the preferred location for full-time solar observations. We also discuss briefly follow-on missions that would be lunar-based with of order 10,000 dipole antennas.

interferometry↗
NASA NTRS2003

Energetic Particle Propagation in the Inner Heliosphere as Deduced from Low Frequency (less than 100 kHz) Observations of Type III Radio Bursts

Solar energetic particle (SEP) events are well-associated with solar flares. It is observed that the delay between the time of the flare and the first-arriving particles at a spacecraft increases with increasing difference between the flare longitude and the footpoint of the field line on which the spacecraft is located. This difference we call the "connection angle" and can be as large as approximately 120 deg. Recently it has been found that all SEP events are preceded by type III radio bursts. These bursts are plasma emission caused by the propagation of 2-50 keV flare electrons through the solar corona and into the solar wind. The drift of these type III radio bursts to lower and lower frequencies enables the propagation of the flare electrons to be traced from the Sun to about 1 AU. We have made an extensive analysis of the type III bursts associated with greater than 20 MeV proton events and find that, in most cases, the radio emission extends to the local plasma frequency when the energetic particles arrive within a few hours of the flare. We conclude that this emission at the lowest possible frequency is generated close to the spacecraft. We then use the time from when the burst started at the Sun to when it reached the local plasma frequency to infer the time it took the radio producing electrons to travel to the spacecraft. We find that these delay times are organized by the connection angle and correlate with the proton delay times. We also find that the differences between the radio delays at Wind and Ulysses are matched by differences in the relative arrival times of the energetic particles at the two spacecraft. The consistent timing between the relative arrival times of energetic electrons and protons and the start of the lowest frequency radio emissions suggests that the first arriving particles of both species are accelerated as part of the flare process and that they propagate to the spacecraft along trajectories similar to those of the lower energy flare electrons. To be detected by observers at locations distant from the nominal field lines originating in the flaring regions the particles must undergo lateral transport. The continuity of the radio bursts suggests that the cross-field transport may occur in the interplanetary medium.

Cane, H. V.↗
NASA NTRS2012

High Angular Resolution Imaging of Solar Radio Bursts from the Lunar Surface

Locating low frequency radio observatories on the lunar surface has a number of advantages, including positional stability and a very low ionospheric radio cutoff. Here, we describe the Radio Observatory on the lunar Surface for Solar studies (ROLSS), a concept for a low frequency, radio imaging interferometric array designed to study particle acceleration in the corona and inner heliosphere. ROLSS would be deployed during an early lunar sortie or by a robotic rover as part of an unmanned landing. The preferred site is on the lunar near side to simplify the data downlink to Earth. The prime science mission is to image type II and type III solar radio bursts with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Secondary science goals include constraining the density of the lunar ionosphere by measuring the low radio frequency cutoff of the solar radio emissions or background galactic radio emission, measuring the flux, particle mass, and arrival direction of interplanetary and interstellar dust, and constraining the low energy electron population in astrophysical sources. Furthermore, ROLSS serves a pathfinder function for larger lunar radio arrays. Key design requirements on ROLSS include the operational frequency and angular resolution. The electron densities in the solar corona and inner heliosphere are such that the relevant emission occurs below 10 M Hz, essentially unobservable from Earth's surface due to the terrestrial ionospheric cutoff. Resolving the potential sites of particle acceleration requires an instrument with an angular resolution of at least 2 deg at 10 MHz, equivalent to a linear array size of approximately one kilometer. The major components of the ROLSS array are 3 antenna arms, each of 500 m length, arranged in a Y formation, with a central electronics package (CEP) at their intersection. Each antenna arm is a linear strip of polyimide film (e.g., Kapton(TradeMark)) on which 16 single polarization dipole antennas are located by depositing a conductor (e.g., silver). The arms also contain transmission lines for carrying the radio signals from the science antennas to the CEP. Operations would consist of data acquisition during the lunar day, with data downlinks to Earth one or more times every 24 hours.

MacDowall, Robert J.↗
NASA NTRS2010

Observing Solar Radio Bursts from the Lunar Surface

Locating low frequency radio observatories on the lunar surface has a number of advantages. Here, we describe the Radio Observatory for Lunar Sortie Science (ROLSS), a concept for a low frequency, radio imaging interferometric array designed to study particle acceleration in the corona and inner heliosphere. ROLSS would be deployed during an early lunar sortie or by a robotic rover as part of an unmanned landing. The prime science mission is to image type II and type III solar radio bursts with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Secondary science goals include constraining the density of the lunar ionosphere by searching for a low radio frequency cutoff of the solar radio emissions and constraining the low energy electron population in astrophysical sources. Furthermore, ROLSS serves a pathfinder function for larger lunar radio arrays. Key design requirements on ROLES include the operational frequency and angular resolution. The electron densities in the solar corona and inner heliosphere are such that the relevant emission occurs below 10 MHz, essentially unobservable from Earth's surface due to the terrestrial ionospheric cutoff. Resolving the potential sites of particle acceleration requires an instrument with an angular resolution of at least 2 deg, equivalent to a linear array size of approximately 500 meters. Operations would consist of data acquisition during the lunar day, with regular data downlinks. The major components of the ROLSS array are 3 antenna arms arranged in a Y shape, with a central electronics package (CEP). Each antenna arm is a linear strip of polyimide film (e.g., Kapton (TM)) on which 16 single polarization dipole antennas are located by depositing a conductor (e.g., silver). The arms also contain transmission lines for carrying the radio signals from the science antennas to the CEP.

MacDowall, R. J.↗
NASA NTRS2011

Observing Solar Radio Bursts from the Lunar Surface

Locating low frequency radio observatories on the lunar surface has a number of advantages, including fixes locations for the antennas and no terrestrial interference on the far side of the moon. Here, we describe the Radio Observatory for Lunar Sortie Science (ROLSS), a concept for a low frequency, radio imaging interferometric array designed to study particle acceleration in the corona and inner heliosphere. ROLSS would be deployed during an early lunar sortie or by a robotic rover as part of an unmanned landing. The prime science mission is to image type II and type III solar radio bursts with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Secondary science goals include constraining the density of the lunar ionosphere by searching for a low radio frequency cutoff of the solar radio emissions and constraining the low energy electron population in astrophysical sources. Furthermore, ROLSS serves a pathfinder function for larger lunar radio arrays designed for faint sources.

MacDowall, R. J.↗