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Steven R. Cranmer - One of the best experts on this subject based on the ideXlab platform.
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statistical study of network jets observed in the solar transition region a comparison between Coronal Holes and quiet sun regions
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Nancy Narang, Steven R. Cranmer, Dipankar Banerjee, Rebecca T Arbacher, Hui Tian, E E Deluca, Sean MckillopAbstract:Recent IRIS observations have revealed a prevalence of intermittent small-scale jets with apparent speeds of 80 - 250 km s$^{-1}$, emanating from small-scale bright regions inside network boundaries of Coronal Holes. We find that these network jets appear not only in Coronal Holes but also in quiet-sun regions. Using IRIS 1330A (C II) slit-jaw images, we extract several parameters of these network jets, e.g. apparent speed, length, lifetime and increase in foot-point brightness. Using several observations, we find that some properties of the jets are very similar but others are obviously different between the quiet sun and Coronal Holes. For example, our study shows that the Coronal-hole jets appear to be faster and longer than those in the quiet sun. This can be directly attributed to a difference in the magnetic configuration of the two regions with open magnetic field lines rooted in Coronal Holes and magnetic loops often present in quiet sun. We have also detected compact bright loops, likely transition region loops, mostly in quiet sun. These small loop-like regions are generally devoid of network jets. In spite of different magnetic structures in the Coronal hole and quiet sun in the transition region, there appears to be no substantial difference for the increase in foot-point brightness of the jets, which suggests that the generation mechanism of these network jets is likely the same in both regions.
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statistical study of network jets observed in the solar transition region a comparison between Coronal Holes and quiet sun regions
Solar Physics, 2016Co-Authors: Nancy Narang, Steven R. Cranmer, Dipankar Banerjee, Rebecca T Arbacher, Hui Tian, E E Deluca, Sean MckillopAbstract:Recent IRIS observations have revealed a prevalence of intermittent small-scale jets with apparent speeds of \(80\,\mbox{--}\,250~\mbox{km}\,\mbox{s}^{-1}\), emanating from small-scale bright regions inside network boundaries of Coronal Holes. We find that these network jets appear not only in Coronal Holes but also in quiet-sun regions. Using IRIS 1330 A (C II) slit-jaw images, we extracted several parameters of these network jets, e.g. apparent speed, length, lifetime, and increase in foot-point brightness. Using several observations, we find that some properties of the jets are very similar, but others are obviously different between the quiet Sun and Coronal Holes. For example, our study shows that the Coronal-hole jets appear to be faster and longer than those in the quiet Sun. This can be directly attributed to a difference in the magnetic configuration of the two regions, with open magnetic field lines rooted in Coronal Holes and magnetic loops often present in the quiet Sun. We also detected compact bright loops that are most likely transition region loops and are mostly located in quiet-Sun regions. These small loop-like regions are generally devoid of network jets. In spite of different magnetic structures in the Coronal hole and quiet Sun in the transition region, there appears to be no substantial difference for the increase in footpoint brightness of the jets, which suggests that the generation mechanism of these network jets is very likely the same in both regions.
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Coronal Holes
Living Reviews in Solar Physics, 2009Co-Authors: Steven R. CranmerAbstract:Coronal Holes are the darkest and least active regions of the Sun, as observed both on the solar disk and above the solar limb. Coronal Holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. This paper reviews measurements of the plasma properties in Coronal Holes and how these measurements are used to reveal details about the physical processes that heat the solar corona and accelerate the solar wind. It is still unknown to what extent the solar wind is fed by flux tubes that remain open (and are energized by footpoint-driven wave-like fluctuations), and to what extent much of the mass and energy is input intermittently from closed loops into the open-field regions. Evidence for both paradigms is summarized in this paper. Special emphasis is also given to spectroscopic and coronagraphic measurements that allow the highly dynamic non-equilibrium evolution of the plasma to be followed as the asymptotic conditions in interplanetary space are established in the extended corona. For example, the importance of kinetic plasma physics and turbulence in Coronal Holes has been affirmed by surprising measurements from the UVCS instrument on SOHO that heavy ions are heated to hundreds of times the temperatures of protons and electrons. These observations point to specific kinds of collisionless Alfvén wave damping (i.e., ion cyclotron resonance), but complete theoretical models do not yet exist. Despite our incomplete knowledge of the complex multi-scale plasma physics, however, much progress has been made toward the goal of understanding the mechanisms ultimately responsible for producing the observed properties of Coronal Holes.
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Low-latitude Coronal Holes during solar maximum
Advances in Space Research, 2004Co-Authors: Mari Paz Miralles, Steven R. Cranmer, J. L. KohlAbstract:Abstract The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO has been used to observe large low-latitude Coronal Holes during solar maximum that produced fast solar wind streams. UVCS observations show that large low-latitude Coronal Holes at solar maximum, Coronal Holes of at least 10° in longitude, have plasma properties that seem to bridge the gap between solar minimum polar Coronal Holes and streamers. The ion kinetic perpendicular temperatures in equatorial Coronal Holes are about 2 times larger than those in a solar minimum equatorial streamer, and about a factor of 2 smaller than those in polar Coronal Holes above 2 R ⊙ . The outflow speeds for the large equatorial Coronal Holes observed by UVCS are 3–4 times lower than those in polar Coronal Holes between 2 and 3 R ⊙ . The values for high- and mid-latitude Coronal Holes are in between those. In all these cases, the in situ data corresponding to these Coronal Holes showed high-speed wind streams with asymptotic speeds of 600–750 km s −1 . These wind speeds approach those observed over polar Coronal Holes at solar minimum, but the outflow speeds in these Coronal Holes between 2 and 3 R ⊙ are different. In contrast to the polar Coronal Holes, the bulk of the solar wind acceleration must occur above 3 R ⊙ for large low-latitude Coronal Holes at solar maximum. These observations provide detailed empirical constraints for theoretical models and may be key to understanding how the various types of solar wind plasma are heated and accelerated.
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Coronal Holes and the High-Speed Solar Wind
Space Science Reviews, 2002Co-Authors: Steven R. CranmerAbstract:Coronal Holes are the lowest density plasma components of the Sun's outer atmosphere, and are associated with rapidly expanding magnetic fields and the acceleration of the high-speed solar wind. Spectroscopic and polarimetric observations of the extended corona, coupled with interplanetary particle and radio sounding measurements going back several decades, have put strong constraints on possible explanations for how the plasma in Coronal Holes receives its extreme kinetic properties. The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft has revealed surprisingly large temperatures, outflow speeds, and velocity distribution anisotropies for positive ions in Coronal Holes. We review recent observations, modeling techniques, and proposed heating and acceleration processes for protons, electrons, and heavy ions. We emphasize that an understanding of the acceleration region of the wind (in the nearly collisionless extended corona) is indispensable for building a complete picture of the physics of Coronal Holes.
Dipankar Banerjee - One of the best experts on this subject based on the ideXlab platform.
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statistical study of network jets observed in the solar transition region a comparison between Coronal Holes and quiet sun regions
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Nancy Narang, Steven R. Cranmer, Dipankar Banerjee, Rebecca T Arbacher, Hui Tian, E E Deluca, Sean MckillopAbstract:Recent IRIS observations have revealed a prevalence of intermittent small-scale jets with apparent speeds of 80 - 250 km s$^{-1}$, emanating from small-scale bright regions inside network boundaries of Coronal Holes. We find that these network jets appear not only in Coronal Holes but also in quiet-sun regions. Using IRIS 1330A (C II) slit-jaw images, we extract several parameters of these network jets, e.g. apparent speed, length, lifetime and increase in foot-point brightness. Using several observations, we find that some properties of the jets are very similar but others are obviously different between the quiet sun and Coronal Holes. For example, our study shows that the Coronal-hole jets appear to be faster and longer than those in the quiet sun. This can be directly attributed to a difference in the magnetic configuration of the two regions with open magnetic field lines rooted in Coronal Holes and magnetic loops often present in quiet sun. We have also detected compact bright loops, likely transition region loops, mostly in quiet sun. These small loop-like regions are generally devoid of network jets. In spite of different magnetic structures in the Coronal hole and quiet sun in the transition region, there appears to be no substantial difference for the increase in foot-point brightness of the jets, which suggests that the generation mechanism of these network jets is likely the same in both regions.
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statistical study of network jets observed in the solar transition region a comparison between Coronal Holes and quiet sun regions
Solar Physics, 2016Co-Authors: Nancy Narang, Steven R. Cranmer, Dipankar Banerjee, Rebecca T Arbacher, Hui Tian, E E Deluca, Sean MckillopAbstract:Recent IRIS observations have revealed a prevalence of intermittent small-scale jets with apparent speeds of \(80\,\mbox{--}\,250~\mbox{km}\,\mbox{s}^{-1}\), emanating from small-scale bright regions inside network boundaries of Coronal Holes. We find that these network jets appear not only in Coronal Holes but also in quiet-sun regions. Using IRIS 1330 A (C II) slit-jaw images, we extracted several parameters of these network jets, e.g. apparent speed, length, lifetime, and increase in foot-point brightness. Using several observations, we find that some properties of the jets are very similar, but others are obviously different between the quiet Sun and Coronal Holes. For example, our study shows that the Coronal-hole jets appear to be faster and longer than those in the quiet Sun. This can be directly attributed to a difference in the magnetic configuration of the two regions, with open magnetic field lines rooted in Coronal Holes and magnetic loops often present in the quiet Sun. We also detected compact bright loops that are most likely transition region loops and are mostly located in quiet-Sun regions. These small loop-like regions are generally devoid of network jets. In spite of different magnetic structures in the Coronal hole and quiet Sun in the transition region, there appears to be no substantial difference for the increase in footpoint brightness of the jets, which suggests that the generation mechanism of these network jets is very likely the same in both regions.
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Propagating MHD Waves in Coronal Holes
Space Science Reviews, 2010Co-Authors: Dipankar Banerjee, G. R. Gupta, Luca TeriacaAbstract:Coronal Holes are the coolest and darkest regions of the upper solar atmosphere, as observed both on the solar disk and above the solar limb. Coronal Holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. During the years of the solar minima, Coronal Holes are generally confined to the Sun’s polar regions, while at solar maxima they can also be found at lower latitudes. Waves, observed via remote sensing and detected in-situ in the wind streams, are most likely responsible for the wind and several theoretical models describe the role of MHD waves in the acceleration of the fast solar wind. This paper reviews the observational evidences of detection of propagating waves in these regions. The characteristics of the waves, like periodicities, amplitude, speed provide input parameters and also act as constraints on theoretical models of Coronal heating and solar wind acceleration.
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propagating mhd waves in Coronal Holes
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: Dipankar Banerjee, G. R. Gupta, Luca TeriacaAbstract:Coronal Holes are the coolest and darkest regions of the solar atmosphere, as observed both on the solar disk and above the solar limb. Coronal Holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. During the years of the solar minima, Coronal Holes are generally confined to the Sun's polar regions, while at solar maxima they can also be found at lower latitudes. Waves, observed via remote sensing and detected in-situ in the wind streams, are most likely responsible for the wind and several theoretical models describe the role of MHD waves in the acceleration of the fast solar wind. This paper reviews the observational evidences of detection of propa- gating waves in these regions. The characteristics of the waves, like periodicities, amplitude, speed provide input parameters and also act as constraints on theoretical models of Coronal heating and solar wind acceleration.
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Waves in Polar Coronal Holes
Magnetic Coupling between the Interior and Atmosphere of the Sun, 2009Co-Authors: Dipankar BanerjeeAbstract:The fast solar wind originates from polar Coronal Holes. Recent observations from SoHO suggest that the solar wind is flowing from funnel-shaped magnetic fields anchored in the lanes of the magnetic network at the solar surface. Using the spectroscopic diagnostic capability of SUMER on SoHO and of EIS on HINODE, we study waves in polar Coronal Holes, in particular their origin, nature, and acceleration. The variation of the width of spectral lines with height above the solar surface supplies information on the properties of waves as they propagate out of the Sun.
David Falconer - One of the best experts on this subject based on the ideXlab platform.
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magnetic untwisting in solar jets that go into the outer corona in polar Coronal Holes
The Astrophysical Journal, 2015Co-Authors: Ronald L. Moore, Alphonse C Sterling, David FalconerAbstract:We study 14 large solar jets observed in polar Coronal Holes. In EUV movies from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), each jet appears similar to most X-ray jets and EUV jets that erupt in Coronal Holes; but each is exceptional in that it goes higher than most, so high that it is observed in the outer corona beyond 2.2 RSun in images from the Solar and Heliospheric Observatory/Large Angle Spectroscopic Coronagraph (LASCO)/C2 coronagraph. From AIA He ii 304 A movies and LASCO/C2 running-difference images of these high-reaching jets, we find: (1) the front of the jet transits the corona below 2.2 RSun at a speed typically several times the sound speed; (2) each jet displays an exceptionally large amount of spin as it erupts; (3) in the outer corona, most of the jets display measureable swaying and bending of a few degrees in amplitude; in three jets the swaying is discernibly oscillatory with a period of order 1 hr. These characteristics suggest that the driver in these jets is a magnetic-untwisting wave that is basically a large-amplitude (i.e., nonlinear) torsional Alfven wave that is put into the reconnected open field in the jet by interchange reconnection as the jet erupts. From the measured spinning and swaying, we estimate that the magnetic-untwisting wave loses most of its energy in the inner corona below 2.2 RSun. We point out that the torsional waves observed in Type-II spicules might dissipate in the corona in the same way as the magnetic-untwisting waves in our big jets, and thereby power much of the Coronal heating in Coronal Holes.
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magnetic untwisting in solar jets that go into the outer corona in polar Coronal Holes
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Ronald L. Moore, Alphonse C Sterling, David FalconerAbstract:We study 14 large solar jets observed in polar Coronal Holes. In EUV movies from SDO/AIA, each jet appears similar to most X-ray jets and EUV jets that erupt in Coronal Holes, but each is exceptional in that it goes higher than most, so high that it is observed in the outer corona beyond 2.2 RSun in images from the SOHO/LASCO/C2 coronagraph. From AIA He II 304 {\AA} movies and LASCO/C2 running-difference images of these high-reaching jets, we find: (1) the front of the jet transits the corona below 2.2 RSun at a speed typically several times the sound speed; (2) each jet displays an exceptionally large amount of spin as it erupts; (3) in the outer corona, most of the jets display measureable swaying and bending of a few degrees in amplitude; in three jets the swaying is discernibly oscillatory with a period of order 1 hour. These characteristics suggest that the driver in these jets is a magnetic-untwisting wave that is basically a large-amplitude (i.e., non-linear) torsional Alfven wave that is put into the reconnected open field in the jet by interchange reconnection as the jet erupts. From the measured spinning and swaying we estimate that the magnetic-untwisting wave loses most of its energy in the inner corona below 2.2 RSun. We point out that the torsional waves observed in Type-II spicules might dissipate in the corona in the same way as the magnetic-untwisting waves in our big jets and thereby power much of the Coronal heating in Coronal Holes.
Sean Mckillop - One of the best experts on this subject based on the ideXlab platform.
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statistical study of network jets observed in the solar transition region a comparison between Coronal Holes and quiet sun regions
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Nancy Narang, Steven R. Cranmer, Dipankar Banerjee, Rebecca T Arbacher, Hui Tian, E E Deluca, Sean MckillopAbstract:Recent IRIS observations have revealed a prevalence of intermittent small-scale jets with apparent speeds of 80 - 250 km s$^{-1}$, emanating from small-scale bright regions inside network boundaries of Coronal Holes. We find that these network jets appear not only in Coronal Holes but also in quiet-sun regions. Using IRIS 1330A (C II) slit-jaw images, we extract several parameters of these network jets, e.g. apparent speed, length, lifetime and increase in foot-point brightness. Using several observations, we find that some properties of the jets are very similar but others are obviously different between the quiet sun and Coronal Holes. For example, our study shows that the Coronal-hole jets appear to be faster and longer than those in the quiet sun. This can be directly attributed to a difference in the magnetic configuration of the two regions with open magnetic field lines rooted in Coronal Holes and magnetic loops often present in quiet sun. We have also detected compact bright loops, likely transition region loops, mostly in quiet sun. These small loop-like regions are generally devoid of network jets. In spite of different magnetic structures in the Coronal hole and quiet sun in the transition region, there appears to be no substantial difference for the increase in foot-point brightness of the jets, which suggests that the generation mechanism of these network jets is likely the same in both regions.
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statistical study of network jets observed in the solar transition region a comparison between Coronal Holes and quiet sun regions
Solar Physics, 2016Co-Authors: Nancy Narang, Steven R. Cranmer, Dipankar Banerjee, Rebecca T Arbacher, Hui Tian, E E Deluca, Sean MckillopAbstract:Recent IRIS observations have revealed a prevalence of intermittent small-scale jets with apparent speeds of \(80\,\mbox{--}\,250~\mbox{km}\,\mbox{s}^{-1}\), emanating from small-scale bright regions inside network boundaries of Coronal Holes. We find that these network jets appear not only in Coronal Holes but also in quiet-sun regions. Using IRIS 1330 A (C II) slit-jaw images, we extracted several parameters of these network jets, e.g. apparent speed, length, lifetime, and increase in foot-point brightness. Using several observations, we find that some properties of the jets are very similar, but others are obviously different between the quiet Sun and Coronal Holes. For example, our study shows that the Coronal-hole jets appear to be faster and longer than those in the quiet Sun. This can be directly attributed to a difference in the magnetic configuration of the two regions, with open magnetic field lines rooted in Coronal Holes and magnetic loops often present in the quiet Sun. We also detected compact bright loops that are most likely transition region loops and are mostly located in quiet-Sun regions. These small loop-like regions are generally devoid of network jets. In spite of different magnetic structures in the Coronal hole and quiet Sun in the transition region, there appears to be no substantial difference for the increase in footpoint brightness of the jets, which suggests that the generation mechanism of these network jets is very likely the same in both regions.
K Mursula - One of the best experts on this subject based on the ideXlab platform.
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automated identification of Coronal Holes from synoptic euv maps
Solar Physics, 2018Co-Authors: Amr Hamada, Timo Asikainen, Ilpo Virtanen, K MursulaAbstract:Coronal Holes (CHs) are regions of open magnetic field lines in the solar corona and the source of the fast solar wind. Understanding the evolution of Coronal Holes is critical for solar magnetism as well as for accurate space weather forecasts. We study the extreme ultraviolet (EUV) synoptic maps at three wavelengths (195 A/193 A, 171 A and 304 A) measured by the Solar and Heliospheric Observatory/Extreme Ultraviolet Imaging Telescope (SOHO/EIT) and the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) instruments. The two datasets are first homogenized by scaling the SDO/AIA data to the SOHO/EIT level by means of histogram equalization. We then develop a novel automated method to identify CHs from these homogenized maps by determining the intensity threshold of CH regions separately for each synoptic map. This is done by identifying the best location and size of an image segment, which optimally contains portions of Coronal Holes and the surrounding quiet Sun allowing us to detect the momentary intensity threshold. Our method is thus able to adjust itself to the changing scale size of Coronal Holes and to temporally varying intensities. To make full use of the information in the three wavelengths we construct a composite CH distribution, which is more robust than distributions based on one wavelength. Using the composite CH dataset we discuss the temporal evolution of CHs during the Solar Cycles 23 and 24.
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automated identification of Coronal Holes from synoptic euv maps
arXiv: Space Physics, 2017Co-Authors: Amr Hamada, Timo Asikainen, Ilpo Virtanen, K MursulaAbstract:Coronal Holes (CH) are regions of open magnetic field lines in the solar corona and the source of fast solar wind. Understanding the evolution of Coronal Holes is critical for solar magnetism as well as for accurate space weather forecasts. We study here the extreme ultraviolet (EUV) synoptic maps at three wavelengths (195A/193A, 171A and 304A) measured by Solar and Heliospheric Observatory/Extreme Ultraviolet Imaging Telescope (SOHO/EIT) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) instruments. The two datasets are first homogenized by scaling the SDO/AIA data to the SOHO/EIT level by means of histogram equalization. We then develop a novel automated method to identify CHs from these homogenized maps by determining the intensity threshold of CH regions separately for each synoptic map. This is done by identifying the best location and size of an image segment, which optimally contains portions of Coronal Holes and the surrounding quiet Sun allowing us to detect the momentary intensity threshold. Our method is thus able to adjust itself to the changing scale size of Coronal Holes and to temporally varying intensities. To make full use of the information in the three wavelengths we construct, a composite CH distribution, which is more robust than distributions based on one wavelength. Using the composite CH dataset we discuss the temporal evolution of CHs during the solar cycles 23 and 24.
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centennial evolution of monthly solar wind speeds fastest monthly solar wind speeds from long duration Coronal Holes
Journal of Geophysical Research, 2017Co-Authors: Lauri Holappa, Renata Lukianova, K MursulaAbstract:High-speed solar wind streams (HSSs) are very efficient drivers of geomagnetic activity at high latitudes. In this paper we use a recently developed ΔH parameter of geomagnetic activity, calculated from the nightside hourly magnetic field measurements of the Sodankyla observatory, as a proxy for solar wind (SW) speed at monthly time resolution in 1914–2014 (solar cycles 15–24). The seasonal variation in the relation between monthly ΔH and solar wind speed is taken into account by calculating separate regressions between ΔH and SW speed for each month. Thereby, we obtain a homogeneous series of proxy values for monthly solar wind speed for the last 100 years. We find that the strongest HSS-active months of each solar cycle occur in the declining phase, in years 1919, 1930, 1941, 1952, 1959, 1973, 1982, 1994, and 2003. Practically all these years are the same or adjacent to the years of annual maximum solar wind speeds. This implies that the most persistent Coronal Holes, lasting for several solar rotations and leading to the highest annual SW speeds, are also the sources of the highest monthly SW speeds. Accordingly, during the last 100 years, there were no Coronal Holes of short duration (of about one solar rotation) that would produce faster monthly (or solar rotation) averaged solar wind than the most long-living Coronal Holes in each solar cycle produce.