Solar Radio Spike Bursts

Thesis (Ph.D.) University of Alaska Fairbanks, 197

The spectral difference between solar flare HXR coronal and footpoint sources due to wave-particle interactions

Investigate the spatial and spectral evolution of hard X-ray (HXR) emission from flare accelerated electron beams subject to collisional transport and wave-particle interactions in the solar atmosphere. We numerically follow the propagation of a power-law of accelerated electrons in 1D space and time with the response of the background plasma in the form of Langmuir waves using the quasilinear approximation.}{We find that the addition of wave-particle interactions to collisional transport for a transient initially injected electron beam flattens the spectrum of the footpoint source. The coronal source is unchanged and so the difference in the spectral indices between the coronal and footpoint sources is \Delta \gamma > 2, which is larger than expected from purely collisional transport. A steady-state beam shows little difference between the two cases, as has been previously found, as a transiently injected electron beam is required to produce significant wave growth, especially at higher velocities. With this transiently injected beam the wave-particle interactions dominate in the corona whereas the collisional losses dominate in the chromosphere. The shape of the spectrum is different with increasing electron beam density in the wave-particle interaction case whereas with purely collisional transport only the normalisation is changed. We also find that the starting height of the source electron beam above the photosphere affects the spectral index of the footpoint when Langmuir wave growth is included. This may account for the differing spectral indices found between double footpoints if asymmetrical injection has occurred in the flaring loop.Comment: 10 pages, 10 FIgures, accepted for publication in A&

High-sensitivity observations of solar flare decimeter radiation

A new acousto-optic radio spectrometer has observed the 1 - 2 GHz radio emission of solar flares with unprecedented sensitivity. The number of detected decimeter type III bursts is greatly enhanced compared to observations by conventional spectrometers observing only one frequency at the time. The observations indicate a large number of electron beams propagating in dense plasmas. For the first time, we report weak, reversed drifting type III bursts at frequencies above simultaneous narrowband decimeter spikes. The type III bursts are reliable signatures of electron beams propagating downward in the corona, apparently away from the source of the spikes. The observations contradict the most popular spike model that places the spike sources at the footpoints of loops. Conspicuous also was an apparent bidirectional type U burst forming a fish-like pattern. It occurs simultaneously with an intense U-burst at 600-370 MHz observed in Tremsdorf. We suggest that it intermodulated with strong terrestrial interference (cellular phones) causing a spurious symmetric pattern in the spectrogram at 1.4 GHz. Symmetric features in the 1 - 2 GHz range, some already reported in the literature, therefore must be considered with utmost caution.Comment: Astronomy and Astrophysics, in pres

TELEMETRY MODERNIZATION AT THE KWAJALEIN MISSILE RANGE

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, NevadaTelemetry support has been a component of the instrumentation test support structure at Kwajalein Missile Range (KMR) for nearly 40 years. From a limited initial suite of manually pointed telemetry antennas, the Range has grown to include nine tracking antennas and four fixed receiving antennas. This paper describes the current modernization program at KMR that will include nine new telemetry trackers and five fixed antennas that will be networked and controlled via fiber optic links from a newly established telemetry control center on the island of Kwajalein. These upgrades will reduce operational cost and institute efficiencies, while continuing to meet Range Users’ growing requirements.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection

A Catalog of proton events, 1966-1976, having non-classical solar radio burst spectra /

A catalog of about 118 proton events, 1966-1976, not included in an earlier catalog of 81 events (AFGL TR-77-0081) for the same period is presented. These 118 events combined with the earlier 81 provide the basis for summarizing solar radio burst/high-energy proton correlation and prediction signature work. In the earlier effort, hereafter called Catalog I, the starting point was the identification of all solar radio bursts having the classical U-shape spectrum, and then establishing proton event association for the purpose of devising a reliable 'false-alarm' free predictor of the major proton events (equivalent PCA 2-2. 5dB). In the present effort, the starting point is the identification of all other proton events not included in Catalog I (misses by the U-shape spectrum criteria), and then searching for the establishing solar radio correlations and possible predictions of weaker proton events. There are very few real misses of principal proton events.Research supported by the Air Force Geophysics Laboratory, Air Force Systems Command, United States Air Force, Hanscom AFB, Massachusetts.Space Physics Division Project 4643.ADA060816 (from http://www.dtic.mil)."16 May 1978."Includes bibliographical references (pages 35-37).A catalog of about 118 proton events, 1966-1976, not included in an earlier catalog of 81 events (AFGL TR-77-0081) for the same period is presented. These 118 events combined with the earlier 81 provide the basis for summarizing solar radio burst/high-energy proton correlation and prediction signature work. In the earlier effort, hereafter called Catalog I, the starting point was the identification of all solar radio bursts having the classical U-shape spectrum, and then establishing proton event association for the purpose of devising a reliable 'false-alarm' free predictor of the major proton events (equivalent PCA 2-2. 5dB). In the present effort, the starting point is the identification of all other proton events not included in Catalog I (misses by the U-shape spectrum criteria), and then searching for the establishing solar radio correlations and possible predictions of weaker proton events. There are very few real misses of principal proton events.Mode of access: Internet

Effect of turbulent density-fluctuations on wave-particle interactions and solar flare X-ray spectra

Aims. The aim of this paper is to demonstrate the effect of turbulent background density-fluctuations on flare-accelerated electron transport in the solar corona. Methods. Using the quasi-linear approximation, we numerically simulated the propagation of a beam of accelerated electrons from the solar corona to the chromosphere, including the self-consistent response of the inhomogeneous background plasma in the form of Langmuir waves. We calculated the X-ray spectrum from these simulations using the bremsstrahlung cross-section and fitted the footpoint spectrum using the collisional “thick-target” model, a standard approach adopted in observational studies. Results. We find that the interaction of the Langmuir waves with the background electron density gradient shifts the waves to a higher phase velocity where they then resonate with higher velocity electrons. The consequence is that some of the electrons are shifted to higher energies, producing more high-energy X-rays than expected if the density inhomogeneity is not considered. We find that the level of energy gain is strongly dependent on the initial electron beam density at higher energy and the magnitude of the density gradient in the background plasma. The most significant gains are for steep (soft) spectra that initially had few electrons at higher energies. If the X-ray spectrum of the simulated footpoint emission are fitted with the standard “thick-target” model (as is routinely done with RHESSI observations) some simulation scenarios produce more than an order-of-magnitude overestimate of the number of electrons  >50 keV in the source coronal distribution