SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 10 - MAY 19, 2006
92 SOLAR PHYSICS
Includes solar activity, solar flares, solar radiation and sunspots.
For related information see 93 Space Radiation.
20060012310 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Dynamical Changes Induced by the Very Large Solar Proton Events in October-November 2003
Jackman, Charles H.; Roble, Raymond G.; January 2006[2006]; 1 pp.; In English; Copyright; Avail.: Other Sources; Abstract Only
The very large solar storms in October-November 2003 caused solar proton events (SPEs) at the Earth and impacted the upper atmospheric polar cap regions. The Thermosphere Ionosphere Mesosphere Electrodynamic General Circulation Mode (TIME-GCM) was used to study the atmospheric dynamical influence of the solar protons that occurred in Oct-Nov 2003, the fourth largest period of SPEs measured in the past 40 years. The highly energetic solar protons caused ionization and hanges in the electric field, which led to Joule heating of the mesosphere and lower thermosphere. This heating led to temperature increases up to 4K in the upper mesosphere. The solar proton-induced ionization, as well as dissociation processes, led to the production of odd hydrogen (HO(x)) and odd nitrogen (NO(y)). Substantial (\g40%) short-lived ozone decreases followed these enhancements of HO(x) and NO(y) and led to a cooling of the mesosphere and upper stratosphere. This cooling led to temperature decreases up to 2.5K. The solar proton-caused temperature changes led to maximum meridional and zonal wind variations of +/- 2 m/s on background winds up to +/- 30 m/s. The solar proton-induced wind perturbations were computed to taper off over a period of several days past the SPEs. Solar cycle 23 was accompanied by ten very large SPEs between 1998 and 2005, along with numerous smaller events. These solar proton-driven atmospheric variations need to be carefully considered when examining other polar changes. Author
Solar Storms; Solar Protons; Polar Caps; Hydrogen Compounds; Ionization; Solar Atmosphere; Solar Cycles; Thermosphere
20060012344 NASA Goddard Space Flight Center, Greenbelt, MD, USA
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Determination of Low-Energy Cutoffs and Total Energy of Nonthermal Electronics in a Solar Flare on 2002 April 15
Sui, Linhui; Holman, Gordon D.; Dennis, Brian R.; The Astrophysical Journal; June 20, 2005; Volume 626, pp. 1102-1109; In English; Original contains black and white illustrations; Copyright; Avail.: Other Sources
The determination of the low-energy cutoff to the spectrum of accelerated electrons is decisive for the estimation of the total nonthermal energy in solar flares. Because thermal bremsstrahlung dominates the low-energy part of flare X-ray spectra, this cutoff energy is difficult to determine with spectral fitting alone. We have used anew method that combines spatial, spectral, and temporal analysis to determine the cutoff energy for the M1.2 flare observed with RHESSI on 2002 April 15. A low-energy cutoff of 24 +/- 2 keV is required to ensure that the assumed thermal emissions always dominate over nonthermal emissions at low energies (\h20 keV) and that the spectral fitting results are consistent with the RHESSI light curves and images. With this cutoff energy, we obtain a total nonthermal energy in electrons of (1.6 +/- 1) x 10(exp 30) ergs that is comparable to the peak energy in the thermal plasma, estimated from RHESSI observations to be (6 +/- 0.6) x 10(exp 29) ergs assuming a filling factor of 1. Author
Solar Flares; X Ray Spectra; Gamma Rays; Bremsstrahlung; Thermal Plasmas; Thermal Emission
20060012345 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Si XII X-ray Satellite Lines in Solar Flare Spectra
Phillips, K. J. H.; Dubau, J.; Sylwester, J.; Sylwester, B.; [2006]; 1 pp.; In English; No Copyright; Avail.: Other Sources; Abstract Only
The temperature dependence of the Si XII n=3 and n=4 dielectronic satellite line features at 5.82A and 5.56A respectively, near the Si XIII 1s(sup 2)-1s3p and 1s(sup 2)-1s4p lines (5.681A and 5.405A), is calculated using atomic data presented here. The resulting theoretical spectra are compared with solar flare spectra observed by the RESIK spectrometer on the CORONAS-F spacecraft. The satellites, like the more familiar n=2 satellites near the Si XIII 1s(sup 2)-1s2p lines, are formed mostly by dielectronic recombination, but unlike the n=2 satellites are unblended. The implications for similar satellite lines in flare Fe spectra are discussed. Author
Temperature Dependence; Satellite Temperature; Solar Flares; Coronas
20060012346 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Dynamic Features in and nearby a Prominence
Kucera, T.; Landi, E.; [2006]; 1 pp.; In English; PROM Workshop, 26-30 Oct. 2005, Denver, CO, USA; Copyright; Avail.: Other Sources; Abstract Only
We will discuss the thermal and dynamic properties of dynamic structures in and around a prominence channel observed on the limb on 17 April 2003. Observations were taken with the Solar and Heliospheric Observatory's Solar Ultraviolet Measurements of Emitted Radiation (SOHO/SUMER) in lines formed at temperatures from 80,000 to 1.6 million K. The instrument was pointed to a single location and took a series of 90 s exposures. Two-dimensional context was provided by the Transition Region and Coronal Explorer (TRACE) in the UV and EUV and by the Kanzelhohe Solar Observatory in H-alpha. Two dynamic features were studied in depth: a prominence activation and repeated motions in a loop nearby the prominence. We were able to calculate three-dimensional geometries and trajectories, differential emission measure, and limits on the average density, kinetic and thermal energies. These observations provide important tests for models of dynamics in prominences and cool (approx.10(exp 5) K) loops. Author
Solar Prominences; Thermodynamic Properties; Solar Observatories; Dynamic Characteristics; H Alpha Line; Thermal Energy; Transition Region and Coronal Explorer
20060012347 NASA Goddard Space Flight Center, Greenbelt, MD, USA
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Multiwavelength Analysis of a Solar Flare on 2002 April 15
Sui, Linhui; Holman, Gordon D.; White, Stephen M.; Zhang, Jie; The Astrophysical Journal; [2005]; Volume 633; 1 pp.; In English; Copyright; Avail.: Other Sources
We carried out a multiwavelength analysis of the solar limb flare on 2002 April 15. The observations all indicate that the flare occurred in an active region with an asymmetric dipole magnetic configuration. The earlier conclusion that magnetic reconnection is occurring in a large-scale current sheet in this flare is M e r supported by these observations: (1) Several bloblike sources, seen in RHESSI 12-25 keV X-ray images later in the flare, appeared along a line above the flare loops. These indicate the continued presence of the current sheet and are likely to be magnetic islands in the stretched sheet produced by the tearing-mode instability. (2) A cusplike structure is seen in Nobeyama Radioheliogiaph (NoRH) 34 GHz microwave images around the time of the peak flare emission.We quantitatively demonstrate that the X-ray-emitting thermal plasma seen with RHESSI had a higher temperature than the microwave-emitting plasma seen with NoRH. Since the radio data preferentially see cooler thermal plasma, this result is consistent with the picture in which energy release occurs at progressively greater heights and the hard X-rays see hot new loops while the radio sees older cooling loops. The kinetic energy of the coronal mass ejection (CME) associated with this flare was found to be about 1 order of magnitude less than both the thermal energy in the hot plasma and the nonthermal energy carried by the accelerated electrons in the flare, as deduced from the RHESSI observations. This contrasts with the higher CME kinetic energies typically deduced for large flares. Author
Solar Flares; Magnetic Field Reconnection; Coronal Mass Ejection; Energy Transfer; Magnetohydrodynamic Stability; Thermal Energy; X Rays
20060013026 NASA Goddard Space Flight Center, Greenbelt, MD, USA
EIT and the Popular Imagination
Gurman, J. B.; [2005]; 1 pp.; In English; Scientific Meeting, Institut d'Astrophysique Spatiale, 19-21 Oct. 2005, Orsay,, France; No Copyright; Avail.: Other Sources; Abstract Only
The Extreme ultraviolet Imaging Telescope on board SOHO, designed and built by Principal Investigator Jean-Pierre Delaboudiniere and his French/Belgan/US team, has produced numerous scientific breakthroughs, and has become both the standard coronal finder telescope and the determinant of whether halo coronal mass ejections are earthward-directed. Due to the dramatic nature of the images produced by EIT over the last nearly ten years, those images have been adopted worldwide in a manner no one could have foreseen before the launch of SOHO. I examine a small sample of the many scientific, commercial, and cultural uses of EIT imagery from the last decade in order to demonstrate how well-visualized, scientific imagery can first penetrate and then become an accepted part of the popular imagination. Author
Imaging Techniques; Ultraviolet Telescopes; Soho Mission
20060013072 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Virtual Observatories for Space Physics Observations and Simulations: New Routes to Efficient Access and Visualization
Roberts, Aaron; [2005]; 1 pp.; In English; Calspace-TGPP Numerical Modeling of Space Plasma Flows, 27-31 Mar. 2005, Palm Springs, CA, USA; No Copyright; Avail.: Other Sources; Abstract Only
New tools for data access and visualization promise to make the analysis of space plasma data both more efficient and more powerful, especially for answering questions about the global structure and dynamics of the Sun-Earth system. We will show how new existing tools (particularly the Virtual Space Physics Observatory-VSPO-and the Visual System for Browsing, Analysis and Retrieval of Data-ViSBARD; look for the acronyms in Google) already provide rapid access to such information as spacecraft orbits, browse plots, and detailed data, as well as visualizations that can quickly unite our view of multispacecraft observations. We will show movies illustrating multispacecraft observations of the solar wind and magnetosphere during a magnetic storm, and of simulations of 3 0-spacecraft observations derived from MHD simulations of the magnetosphere sampled along likely trajectories of the spacecraft for the MagCon mission. An important issue remaining to be solved is how best to integrate simulation data and services into the Virtual Observatory environment, and this talk will hopefully stimulate further discussion along these lines. Author
Scientific Visualization; Simulation; Atmospheric Physics; Observatories
20060013111 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The Mysterious Origins of Solar Flares: New observations are beginning to reveal what triggers these hughes explosions of the sun's atmosphere
Holman, Gordon D.; Scientific American; January 2006, pp. 38-45; In English; Original contains color illustrations; Copyright; Avail.: Other Sources
Solar flares can release the energy equivalent of billions of atomic bombs in the span of just a few minutes. These explosions give off a burst of x-rays and charged particles, some of which may later hit Earth, endangering satellites and causing power outages. The sun's tumultuous magnetic fields provide the fuel of flares. The sudden release of energy in a flare results from a process called reconnection, whereby oppositely directed magnetic field lines come together and partially annihilate each other. Although theoretical studies of magnetic reconnection on the sun have been carried out for decades, only recently have space probes uncovered observational evidence for this phenomenon. The telltale signs include pointed magnetic loops located below the spot where magnetic reconnection is taking place. Derived from text
Magnetic Field Reconnection; Solar Flares; Sun; Solar Physics; Stellar Evolution
20060013115 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Solar Probe: Close Encounter with the Sun
Sittler, E. C., Jr.; [2006]; 1 pp.; In English; No Copyright; Avail.: Other Sources; Abstract Only
The Solar Probe Science and Technology Definition Team (STDT) recently completed a detailed study of the Solar Probe Mission based on an earliest launch date of October 2014. Solar Probe, when implemented, will be the first close encounter by a spacecraft with a star (i.e., 3 Rs above the Sun s photosphere). The report and its executive summary were published by NASA (NASA/TM-2005-212786) in September 2005 and can be found at the website http://solarprobe.gsfc.nasa.gov/. A description of the science is being prepared for publication in Reviews of Geophysics by McComas et al. [2006]. For this talk, we will be presenting the consensus view of the STDT including a brief description of the scientific goals, a description of the overall mission, including trajectory scenarios, spacecraft description and proposed scientific payload. We will discuss all these topics and the importance of flying the Solar Probe mission both with regard to understanding fundamental issues of solar wind acceleration and coronal heating near the Sun and Solar Probe s unique role in understanding the acceleration of Solar Energetic Particles (SEPs), which is critical to future Human Exploration. Author
Solar Probes; Solar Physics; Geophysics; Solar Wind; Payloads; Energetic Particles
20060013135 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Flux Transfer Event in the Subsolar Region and Near the Cusp: Simultaneous Polar and Cluster Observations
Le, G.; Zheng, Y.; Russell, C. T.; Pfaff, R. F.; Slavin, J. A.; Lin, N.; Mozer, F.; Parks, G.; Petrinec, S. M.; Lucek, e. A.; Reme, Henri; [2005]; 1 pp.; In English; 2005 American Geophysical Union (AGU) Fall Meeting, 3-10 Dec. 2005, San Francisco, CA, USA; Copyright; Avail.: Other Sources; Abstract Only
The phenomenon called flux transfer events (FTEs) is widely accepted as the manifestation of time-dependent reconnection. In this paper, we present an observational evidence of a flux transfer event observed simultaneously at low-latitude by Polar and high-latitude by Cluster. This event occurred on March 21, 2002, when both Cluster and Polar were located near the local noon but with large latitudinal distance. Cluster was moving outbound from polar cusp to the magnetosheath, and Polar was in the magnetosheath near the equatorial magnetopause. The observations show that a flux transfer event was formed between the equator and the northern cusp. Polar and Cluster observed the FTE's two open flux tubes: Polar saw the southward moving flux tube near the equator; and Cluster the , northward moving flux tube at high latitude. Unlike low-latitude FTEs, the high-latitude FTE did not exhibit the characteristic bi-polar BN signature. But the plasma data clearly showed its open flux tube configuration. Enhanced electric field fluctuations were observed within the FTE core, both at low- and high-attitudes. This event provides us a unique opportunity to understand high-latitude FTE signatures and the nature of time-varying reconnection. Author
Magnetic Flux; Flux Transfer Events; Bipolarity; Time Dependence; Plasmas (Physics)
20060013150 NASA Goddard Space Flight Center, Greenbelt, MD, USA
A Statistical Analysis of Loop-Top Motion in Solar Limb Flares
Holman, Gordon D.; Sui, Linhui; Brosius, D. G.; Dennis, Brian R.; [2005]; 1 pp.; In English; American Geophysical Union, 5-8 Dec. 2005, San Francisco, CA, USA; Copyright; Avail.: Other Sources; Abstract Only
Previous studies of hot, thermal solar flare loops imaged with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) have identified several flares for which the loop top shrinks downward early in the impulsive phase and then expands upward later in the impulsive phase (Sui & Holman 2003; Sui, Holman & Dennis 2004; Veronig et al. 2005). This early downward motion is not predicted by flare models. We study a statistical sample of RHESSI flares to assess how common this evolution is and to better characterize it. In a sample of 88 flares near the solar lin$ that show identifiable loop structure in RHESSI images, 66% (58 flares) showed downward loop-top motion followed by upward motion. We therefore conclude that the early downward motion is a frequent characteristic of flare loops. We obtain the distribution of the timing of the change from downward to upward motion relative to flare start and peak times. We also obtain the distributions of downward and upward speeds. Author
Solar Flares; Solar Limb; Statistical Analysis; Motion
Source: NASA
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