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Diagnostics of Coronal Magnetic Fields through the Hanle Effect in UV and IR Lines  

Nour E. Raouafi   Submitted: 2016-07-06 15:39

The plasma thermodynamics in the solar upper atmosphere, particularly in the corona, are dominated by the magnetic field, which controls the flow and dissipation of energy. The relative lack of knowledge of the coronal vector magnetic field is a major handicap for progress in coronal physics. This makes the development of measurement methods of coronal magnetic fields a high priority in solar physics. The Hanle effect in the UV and IR spectral lines is a largely unexplored diagnostic. We use magnetohydrodynamic (MHD) simulations to study the magnitude of the signal to be expected for typical coronal magnetic fields for selected spectral lines in the UV and IR wavelength ranges, namely the H I Ly-α and the He I 10830 Å lines. We show that the selected lines are useful for reliable diagnosis of coronal magnetic fields. The results show that the combination of polarization measurements of spectral lines with different sensitivities to the Hanle effect may be most appropriate for deducing coronal magnetic properties from future observations.

Authors: Nour E. Raouafi, Pete Riley, Sarah Gibson, Silvano Fineschi and Sami K. Solanki
Projects: None

Publication Status: Published in Frontiers in Astronomy and Space Sciences, 22 June 2016. doi: doi: 10.3389/fspas.2016.00020
Last Modified: 2016-07-07 09:18
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Solar Coronal Jets: Observations, Theory, and Modeling  

Nour E. Raouafi   Submitted: 2016-07-06 15:34

Coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of significant mass and energy input to the upper solar atmosphere and the solar wind. While the energy involved in a jet-like event is smaller than that of "nominal" solar flares and coronal mass ejections (CMEs), jets share many common properties with these phenomena, in particular, the explosive magnetically driven dynamics. Studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. On the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients close or at the limit of the current spatial resolution such as spicules. Furthermore, jet phenomena may hint to basic process for heating the corona and accelerating the solar wind; consequently their study gives us the opportunity to attack a broad range of solar- heliospheric problems.

Authors: N.E. Raouafi, S. Patsourakos, E. Pariat, P.R. Young, A.C. Sterling, A. Savcheva, M. Shimojo, F. Moreno-Insertis, C.R. DeVore, V. Archontis, T. Török, H. Mason, W. Curdt, K. Meyer, K. Dalmasse, Y. Matsui
Projects: GOES X-rays ,Hinode/EIS,Hinode/SOT,Hinode/XRT,IRIS,Nobeyama Radioheliograph,RHESSI,SDO-AIA,SDO-HMI,SoHO-EIT,SoHO-MDI,SoHO-CDS,SoHO-LASCO,SoHO-SUMER,STEREO,TRACE,Yohkoh-HXT,Yohkoh-SXT

Publication Status: Published in Space Science Reviews. doi: 10.1007/s11214-016-0260-5
Last Modified: 2016-07-07 09:18
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Dynamics of High-Velocity Evanescent Clumps [HVECs] Emitted from Comet C/2011 L4 as Observed by STEREO  

Nour E. Raouafi   Submitted: 2015-07-16 07:24

High-quality white-light images from the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) HI-1 telescope on board STEREO-B reveal high-velocity evanescent clumps (HVECs) expelled from the coma of the C/2011 L4 (PanSTARRS) comet. The observations were recorded around the comet?s perihelion (i.e., ∼ 0.3 AU) during the period 9?16 March 2013. Animated images provide evidence of highly dynamic ejecta moving near radially in the antisunward direction. The bulk speed of the clumps at their initial detection in the HI1-B images range from 200 to 400 km s-1 followed by an appreciable acceleration up to speeds of 450?600 km s-1, which are typical of slow to intermediate solar wind speeds. The clump velocities do not exceed these limiting values and seem to reach a plateau. The images also show that the clumps do not expand as they propagate. The white-light images do not provide direct insight into the composition of the expelled clumps, which could potentially be composed of fine, submicron dust particles, neutral atoms and molecules, and/or ionized atomic/molecular cometary species. Although solar radiation pressure plays a role in accelerating and size sorting of small dust grains, it cannot accelerate them to velocities >200 km s-1 in the observed time interval of a few hours and distance of <106 km. Further, order of magnitude calculations show that ionized single atoms or molecules accelerate too quickly compared to observations, while dust grains micron sized or larger accelerate too slowly. We find that neutral Na, Li, K, or Ca atoms with 𝛽>50 could possibly fit the observations. Just as likely, we find that an interaction with the solar wind and the heliospheric magnetic field can cause the observed clump dynamical evolution, accelerating them quickly up to solar wind velocities. We thus speculate that the HVECs are composed of charged particles (dust particles) or neutral atoms accelerated by radiation pressure at 𝛽>50 values. In addition, the data suggest that clump ejecta initially move along near-radial, bright structures, which then separate into HVECs and larger dust grains that steadily bend backward relative to the comet?s orbital motion due to the effects of solar radiation and gravity. These structures gradually form new striae in the dust tail. The near-periodic spacing of the striae may be indicative of outgassing activity modulation due to the comet nucleus? rotation. It is, however, unclear whether all striae are formed as a result of this process.

Authors: Raouafi, N.-E.; Lisse, C. M.; Stenborg, G.; Jones, G. H.; Schmidt, C. A.
Projects: STEREO

Publication Status: JGR-Space Physics. In press.
Last Modified: 2015-07-19 18:45
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Abstracts by Author
Diagnostics of Coronal Magnetic Fields through the Hanle Effect in UV and IR Lines
Solar Coronal Jets: Observations, Theory, and Modeling
Dynamics of High-Velocity Evanescent Clumps [HVECs] Emitted from Comet C/2011 L4 as Observed by STEREO

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