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  • 1
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    On non-local transport processes in the solar atmosphere (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We review two mechanisms which can lend a non-local character to energy transport in the solar atmosphere, heat flux propagating in the form of collisionless electrons, and non-equilibrium ionization of hydrogen driven by ambipolar diffusion. Application of these processes to modelling of the lower transition region and upper chromosphere is considered.
    Keywords: SOLAR PHYSICS
    Type: In: Electromechanical coupling of the solar atmosphere; Proceedings of the OSL Workshop, Capri, Italy, May 27-31, 1991 (A93-39876 15-92); p. 145-153.
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  • 2
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    Non-Maxwellian distribution functions in flaring coronal loops - Comparison of Landau-Fokker-Planck and BGK solutions (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The high-velocity tail of the electron distribution has been calculated by solving the high-velocity form of the Landau equation for a thermal structure representative of a flaring coronal loop. These calculations show an enhancement of the tail population above Maxwellian for electrons moving down the temperature gradient. The results obtained are used to test the reliability of the BGK approximation. The comparison shows that the BGK technique can estimate contributions to the heat flux from the high-energy tail to within an order of magnitude.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 117; 1, 19
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  • 3
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    Intercomparison of numerical models of flaring coronal loops (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The proposed Benchmark Problem consists of an infinitesimal magnetic flux tube containing a low-beta plasma. The field strength is assumed to be so large that the plasma can move only along the flux tube, whose shape remains invariant with time (i.e., the fluid motion is essentially one-dimensional). The flux tube cross section is taken to be constant over its entire length. In planar view the flux tube has a semi-circular shape, symmetric about its midpoint s = s sub max and intersecting the chromosphere-corona interface (CCI) perpendicularly at each foot point. The arc length from the loop apex to the CCI is 10,000 km. The flux tube extends an additional 2000 km below the CCI to include the chromosphere, which initially has a uniform temperature of 8000 K. The temperature at the top of the loop was fixed initially at 2 X 1 million K. The plasma is assumed to be a perfect gas (gamma = 5/3), consisting of pure hydrogen which is considered to be fully ionized at all temperatures. For simplicity, moreover, the electron and ion temperatures are taken to be everywhere equal at all times (corresponding to an artificially enhanced electron-ion collisional coupling). While there was more-or-less unanimous agreement as to certain global properties of the system behavior (peak temperature reached, thermal-wave time scales, etc.), no two groups could claim satisfactory accord when a more detailed comparison of solutions was attempted.
    Keywords: SOLAR PHYSICS
    Type: NASA. Goddard Space Flight Center Energetic Phenomena on the Sun: The Solar Maximum Mission Flare Workshop. Proceedings; 9 p
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  • 4
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    Multiwavelength analysis of a well observed flare from SMM (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations of an M 1.4 flare which began at 17:00 UT on November 12, 1980, are presented and analyzed. Ground based H-alpha and magnetogram data have been combined with EUV, soft and hard X-ray observations made with instruments on-board the Solar Maximum Mission satellite. The preflare phase was marked by a gradual brightening of the flare site in O v and the disappearance of an H-alpha filament. Filament ejecta were seen in O v moving southward at a speed of about 60 km/s, before the impulsive phase. The flare loop footpoints brightened in H-alpha and the Ca XIX resonance line broadened dramatically 2 min before the impulsive phase. Nonthermal hard X-ray emission was detected from the loop footpoints during the impulsive phase, while during the same period blue-shifts corresponding to upflows of 200-250 km/s were seen in Ca XIX. Evidence was found for energy deposition in both the chromosphere and corona at a number of stages during the flare. Two widely studied mechanisms for the production of the high temperature soft X-ray flare plasma in the corona are considered, i.e. chromospheric evaporation, and a model in which the heating and transfer of material occurs between flux tubes during reconnection.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 99; 167-188
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  • 5
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    Heat flux in a non-Maxwellian plasma (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A hybrid numerical scheme is applied to solve the Landau equation for the electron distribution function over all velocity space. Evidence is presented for the first time of the degree and character of the failure of the classical Spitzer-Haerm heat flux approximation in a realistic solar coronal loop structure. In the loop model used, the failure is so severe at some points that the role of the heat flux in the plasma's energy balance is completely misinterpreted. In the lower corona the Spitzer-Haerm approximation predicts that the heat flux should act as an energy source, whereas the more accurate distribution functions calculated here show this to be an energy sink.
    Keywords: SOLAR PHYSICS
    Type: Physical Review A - General Physics, 3rd Series (ISSN 0556-2791); 40; 981-986
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  • 6
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    Electron impact polarization expected in solar EUV lines from flaring chromospheres/transition regions (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We have evaluated lower bounds on the degree of impact Extreme Ultraviolet/Ultraviolet (EUV/UV) line polarization expected during solar flares. This polarization arises from collisional excitation by energetic electrons with non-Maxwellian velocity distributions. Linear polarization was observed in the S I 1437 A line by the Ultraviolet Spectrometer and Polarimeter/Solar Maximum Mission (UVSP/SMM) during a flare on 15 July 1980. An early interpretation suggested that impact excitation by electrons propagating through the steep temperature gradient of the flaring transition region/high chromosphere produced this polarization. Our calculations show that the observed polarization in this UV line cannot be due to this effect. We find instead that, in some flare models, the energetic electrons can produce an impact polarization of a few percent in EUV neutral helium lines (i.e., lambda lambda 522, 537, and 584 A).
    Keywords: SOLAR PHYSICS
    Type: SSL-PREPRINT-90-124 , Alabama Univ., Data Evaluation, Analysis, and Scientific Study; 9 p
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  • 7
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    Updates on CCMC Activities and GSFC Space Weather Services (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: In this presentation, we provide updates on CCMC modeling activities, CCMC metrics and validation studies, and other CCMC efforts. In addition, an overview of GSFC Space Weather Services (a sibling organization to the Community Coordinated Modeling Center) and its products/capabilities will be given. We show how some of the research grade models, if running in an operational mode, can help address NASA's space weather needs by providing forecasting/now casting capabilities of significant space weather events throughout the solar system.
    Keywords: Meteorology and Climatology
    Type: GSFC.ABS.5383.2011
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  • 8
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    Space Weather Products at the Community Coordinated Modeling Center (2010)
    In:  CASI
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    Publication Date: 2019-07-19
    Description: The Community Coordinated Modeling Center (CCMC) is a US inter-agency activity aiming at research in support of the generation of advanced space weather models. As one of its main functions, the CCMC provides to researchers the use of space science models, even if they are not model owners themselves. The second CCMC activity is to support Space Weather forecasting at national Space Weather Forecasting Centers. This second activity involves model evaluations, model transitions to operations, and the development of space weather forecasting tools. Owing to the pace of development in the science community, new model capabilities emerge frequently. Consequently, space weather products and tools involve not only increased validity, but often entirely new capabilities. This presentation will review the present state of space weather tools as well as point out emerging future capabilities.
    Keywords: Space Sciences (General)
    Type: 90th American Meteorological Society Annual Meeting; Jan 16, 2010 - Jan 21, 2010; Atlanta, GA; United States
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  • 9
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    IHY Modeling Support at the Community Coordinated Modeling Center (2005)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The Community Coordinated Modeling Center (CCMC) is a US inter-agency activity aiming at research in support of the generation of advanced space weather models. As one of its main functions, the CCMC provides to researchers the use of space science models, even if they are not model owners themselves. In particular, the CCMC provides to the research community the execution of "runs-onrequest" for specific events of interest to space science researchers. Through this activity and the concurrent development of advanced visualization tools, CCMC provides, to the general science community, unprecedented access to a large number of state-of-the-art research models. CCMC houses models that cover the entire domain from the Sun to the Earth. In this presentation, we will provide an overview of CCMC modeling services that are available to support activities during the International Heliospheric Year. In order to tailor CCMC activities to IHY needs, we will also invite community input into our IHY planning activities.
    Keywords: Solar Physics
    Type: Stereo/Solar-B Science Planning Workshop: Living With a Star; Nov 15, 2005 - Nov 18, 2005; Oahu, HI; United States
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  • 10
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    Ensemble Forecasting of Coronal Mass Ejections Using the WSA-ENLIL with CONED Model (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The combination of the Wang-Sheeley-Arge (WSA) coronal model, ENLIL heliospherical model version 2.7, and CONED Model version 1.3 (WSA-ENLIL with CONED Model) was employed to form ensemble forecasts for 15 halo coronal mass ejections (halo CMEs). The input parameter distributions were formed from 100 sets of CME cone parameters derived from the CONED Model. The CONED Model used image processing along with the bootstrap approach to automatically calculate cone parameter distributions from SOHO/LASCO imagery based on techniques described by Pulkkinen et al. (2010). The input parameter distributions were used as input to WSA-ENLIL to calculate the temporal evolution of the CMEs, which were analyzed to determine the propagation times to the L1 Lagrangian point and the maximum Kp indices due to the impact of the CMEs on the Earth's magnetosphere. The Newell et al. (2007) Kp index formula was employed to calculate the maximum Kp indices based on the predicted solar wind parameters near Earth assuming two magnetic field orientations: a completely southward magnetic field and a uniformly distributed clock-angle in the Newell et al. (2007) Kp index formula. The forecasts for 5 of the 15 events had accuracy such that the actual propagation time was within the ensemble average plus or minus one standard deviation. Using the completely southward magnetic field assumption, 10 of the 15 events contained the actual maximum Kp index within the range of the ensemble forecast, compared to 9 of the 15 events when using a uniformly distributed clock angle.
    Keywords: Space Sciences (General)
    Type: GSFC-E-DAA-TN15042 , Space Weather; 11; 3; 95-106
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