pictorial

Credits

kolinski — Tue, 18 Jan 2022 20:53:31 +0000

Credits kolinski Tue, 01/18/2022 - 13:53

Assembling a slide set even as small as this one would have been impossible without the numerous colleagues having provided us with their data, and kindly granted us permission to make use of them. In addition to the people listed below, we also wish to thank J. Beer, T.J. Bogdan, J. Burkepile, A.J. Hundhausen, and B. Lites for help and assistance with various aspects of this project. Unless otherwise noted, all image processing is by P. Charbonneau. The High Altitude Observatory is a division of the National Center for Atmospheric Research, which is sponsored by the National Science Foundation.

Eclipse photographs digitized and processed by A. Lecinski, High Altitude Observatory, National Center for Atmospheric Research (Boulder, CO).

Slide 2, 4, 5: Data courtesy of J. Harvey, National Solar Observatory (Tucson/Kitt Peak, AZ)
Slide 3: Data courtesy of P. Brandt (Kiepenheuer Institut für Sonnenphysik, Freiburg, Germany), G. Scharmer (Uppsala, Sweden) and G. Simon (National Solar Observatory). Primary image processing by D. Shine, Lockheed Corporation
Slide 6, 17: Hα image digitized from a photograph provided by the Space Environment Laboratory, National Aeronautic and Oceanic Administration (Boulder, CO), under partial support from the United States Air Force
Slide 7: Image digitized from a photographic print in the archives of the High Altitude Observatory, National Center for Atmospheric Research (Boulder, CO)
Slide 8: Magnetogram data courtesy of J. Harvey, National Solar Observatory (Tucson/Kitt Peak, AZ); Hα image digitized from a photograph provided by the Space Environment Laboratory, National Aeronautic and Oceanic Administration (Boulder, CO), under partial support from the United States Air Force
Slide 9, 10: All eclipse images digitized from photographs in the archives of the High Altitude Observatory. Primary image processing by A. Stanger, High Altitude Observatory, National Center for Atmospheric Research (Boulder, CO)
Slide 11, 15: Data courtesy of the Yohkoh Science Team
Slide 12: Coronameter data from the Mauna Loa Solar Observatory, operated in Hawaii by the High Altitude Observatory. Primary image processing by A. Lecinsky. X-Ray data courtesy of the Yohkoh Science Team
Slide 13, 14: Coronagraph data from the Solar Maximum Mission, archived at the High Altitude Observatory. Primary image processing by J. Burkepile, High Altitude Observatory, National Center for Atmospheric Research (Boulder, CO)
Slide 16: Data from the Advanced Stokes Polarimeter, operated jointly by the High Altitude Observatory and the National Solar Observatory in Sacramento Peak, NM. Data reduction software, primary image processing and graphics by P. Seagraves, High Altitude Observatory, National Center for Atmospheric Research (Boulder, CO)
Slide 17: Historical reconstruction of yearly sunspot groups by D.V. Hoyt, Research and Data Systems Corp. (Greenbelt, MD). Yearly averaged sunspot numbers from Zürich Observatory, Switzerland. Aurorae data for the years 1780---present reconstructed and compiled by J. P. Legrand, CNRS/INSU (France), and by K. Krivsky, Astronomicky Ustav (Czech Republic) for the years 1600–1720
Slide 18: Calcium Image courtesy of J. Harvey, National Solar Observatory (Tucson/Kitt Peak, AZ). Sunspot area coverage data and plot courtesy of D. Hathaway, NASA/Marshall Space Flight Center (Huntsville, AL). Helmet streamer and coronal mass ejection data compiled by J. Burkepile, High Altitude Observatory, National Center for Atmospheric Research (Boulder, CO)
Slide 19: Magnetogram data from the National Solar Observatory (Kitt Peak, AZ), primary image processing by H. Jones
Slide 20: Soft X-ray images courtesy of the Yohkoh Science Team. Average sunspot curves constructed from daily sunspot numbers provided by the Space Environment Laboratory, National Oceanic and Atmospheric Administration (Boulder, CO). Eclipse photographs and SMM coronagraph image from the archives of the High Altitude Observatory, National Center for Atmospheric Research (Boulder, CO)

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Solar-Terrestrial Interactions

kolinski — Tue, 18 Jan 2022 20:39:21 +0000

Solar-Terrestrial Interactions kolinski Tue, 01/18/2022 - 13:39

The correlation between sunspot number and auroral sightings (slide 17) hints at a possible relationship between solar activity and some aspects of geomagnetism and atmospheric dynamics. This important area of research goes under name of solar-terrestrial interactions.

Solar-Terrestrial Interactions

Solar astronomers of the nineteenth century rapidly recognized that strong flares or other intense activity observed on the Sun were often followed, minutes later, by disturbances in magnetic instruments on Earth. Large flares and coronal mass ejections often trigger geomagnetic storms; coronal material blown outward from the Sun at speeds exceeding that of the normal quasi-steady solar wind steepens into shocks, which pass by the Earth, interacting with and perturbing the Earth's magnetosphere. The most common (and spectacular) manifestation of geomagnetic storms is the occurrence of Aurorae Borealis and Aurorae Australis (the so-called Northern and Southern Lights). More disruptive effects include perturbation of radio communications, disruption of power grids, and enhanced orbital decay of low orbiting satellites. However, in view of their transient character, such events are not believed to induce long lasting variations in the climatic system, unless their frequency of occurrence were to change dramatically over extended periods of time.

Changes in the solar luminosity represent the most obvious way to effect climatic variability on Earth. Because sunspots are darker than their surroundings (slide 1 and slide 3), and given the dramatic variations in sunspot area coverage through the solar cycle (slide 18), one may expect a corresponding decrease of the solar luminosity with increased sunspot coverage. In fact, the Sun is very slightly brighter near sunspot maximum, possibly because (darker) sunspots and active regions are often surrounded by (brighter) plages (slide 2). However, certain portions of the solar spectrum, in particular the ultraviolet, vary rather drastically throughout the solar cycle. Even though ultraviolet radiation contributes very little to the total radiative output of the Sun, consequences for the Earth's climate can nevertheless be significant, as the chemistry and energy balance of the upper atmosphere (altitudes of ~ 50 km and up) are largely driven by the flux of solar ultraviolet radiation. As it turns out, the time period 1645–1715 corresponding to the Maunder minimum in sunspot number (slide 17), occurred during an extended time period of severe winters and overall cold weather in western Europe, which is sometimes referred to in the climatic literature as the "little ice age."

There exists a number of less direct way to ascertain the level of solar activity prior to the beginning of telescopic sunspot monitoring in 1610. Comparison of historical records of auroral sightings with sunspot numbers reveal a striking correlation between the amplitude of sunspot cycles and the frequency of (recorded) auroral sightings. In particular, very few aurorae were reported in northern Europe during the time period corresponding to the Maunder minimum. Auroral sightings have been reported as far back as 500 B.C., but the records are extremely sparse up to about 1000 A.D. and are truly reliable only for the last 400 years or so. Nevertheless, if taken at face value these data indicate that prolonged epochs of low auroral activity, similar to the Maunder minimum, have occurred at earlier epochs, in particular in 1420–1500 (the so-called Spörer minimum) and 1290–1340 (the Wolf minimum).

The production of the isotopes beryllium 10 and carbon 14 are known to be sensitive to the intensity of galactic cosmic ray bombardment in the upper atmosphere of the Earth. The flux of cosmic rays at the Earth's orbit, in turn, is known to decrease with increasing solar activity. The abundance of 10Be and 14C, as determined respectively from polar ice cores and tree rings, shows pronounced increases around the times of the Maunder, Spörer and Wolf minima. A significant drop of the 14C abundance in 1100–1250 A.D., possibly associated with a period of abnormally high solar activity, roughly coincides with a period of warming in Medieval Europe, and of generalized drought in North America, as evidenced by the demises of the Anasazi culture in the second half of the 13th century. From the modeling standpoint, the situation is complicated by the need to account for purely geomagnetic effects (the Earth has its own aperiodic magnetic cycle, characterized by epochs of field reversal with period of order 104–105 yr, and other epochs of fixed magnetic polarity lasting 106–107 yr). The situation is further complicated by various uncertainties associated with transport and deposition of contaminants in the Earth's atmosphere, and with the dynamics of the global atmospheric carbon cycle. Nevertheless, while the physical link(s) between the solar cycle and large-scale climatic patterns remains elusive, such striking correlations are suggestive of a causal relationship.

The Sun has been around more or less in its present form for four and a half billion years, and has another five billion years or so to go before it exhausts its supply of Hydrogen to becomes a red giant. In doing so the Sun will inflate to about 50 times its present size, engulfing Mercury and incinerating Venus and Earth in the process. Later evolutionary phases will see the Sun swell up to ~ 300 times its present size, but by then there will most likely be no spectators left on Earth to witness the event. The evidence reviewed above, however, strongly suggests that we should not wait 5 billion years before starting to pay attention to what the Sun is doing.

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The Corona Through the Solar Cycle

kolinski — Tue, 18 Jan 2022 20:15:22 +0000

The Corona Through the Solar Cycle kolinski Tue, 01/18/2022 - 13:15

Not surprisingly, the changes in the surface magnetic field distribution through the solar cycle, as evidenced by the evolving numbers and spatial distributions of sunspots, prominences and filaments (slide 17 and slide 18), are also reflected in the corona.

Soft X-ray images from the Yohkoh satellite.

The top row of images are X-ray images from the Yohkoh satellite, spaced approximately 10 months apart during the descending part of cycle 22. The overall decrease in X-ray luminosity for the solar disk as a whole is in many ways as spectacular as the decrease in the number of active regions seen at a given time on the disk. The bottom row shows a few eclipse photographs spanning the time period 1966–1988, together with a coronal image constructed from Solar Maximum Mission data for 1985, essentially at solar minimum. Note how the corona is reduced to a belt of streamers symmetrically straddling the solar equator. The 1980 eclipse of slide 9 occurred at the very peak of solar cycle 21; contrast the appearance of the white light corona then, with streamers appearing at all latitudes, with the solar minimum corona.

Written By P. Charbonneau and O.R. White–April 18, 1995

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Hale's Sunspot Polarity Law

kolinski — Tue, 18 Jan 2022 20:04:00 +0000

Hale's Sunspot Polarity Law kolinski Tue, 01/18/2022 - 13:04

This slide shows two solar magnetograms taken in the descending phases of cycles 21 and 22. White and black correspond respectively to positive and negative magnetic polarities (i.e., normal magnetic field component pointing toward and away from the observer).

Two solar magnetograms taken in the descending phases of cycles 21 and 22.

The images have been rescaled and the color scale adjusted to emphasize polarity changes (at the expense of dynamic range). As a consequence, sunspots and plages are not as clearly delineated as on slide 5, but show up globally as large regions of a given magnetic polarity. The white lines trace the paths of magnetic neutral lines. The equator runs more or less horizontally across each magnetogram. As noted previously, most regions of strong magnetic fields are grouped in pairs of opposite polarities; furthermore, at any given time the ordering of positive/negative regions with respect to the E - W direction (the direction of rotation, from left to right on these images) is the same in a given hemisphere, but is reversed from northern to southern hemispheres. This was first determined observationally in the first decade of the 20th century by G.H. Hale, and is known as Hale's Polarity Law. Shortly after this discovery, ongoing studies of the magnetic polarities of sunspot pairs by Hale and collaborators revealed yet another intriguing pattern: from one sunspot cycle to the next, the magnetic polarities of sunspot pairs undergo a reversal in each hemisphere. This polarity reversal pattern is apparent on this slide. Hale's Polarity Law is evidence for large-scale order underlying what would otherwise seem to be a purely stochastic phenomena. The source of these regularities is rooted in the solar dynamo, the mechanism leading to the continuous regeneration of the solar magnetic field. This involves the interaction between large-scale flows deep in the solar interior and the existing solar magnetic field, and requires the presence of the rotationally-induced Coriolis force to break the global symmetry that would otherwise characterize those fluid motions. As a discussion of the physical nature and mode of operation of the solar dynamo would entail an overly lengthy digression, we refer the interested reader to some of the textbooks listed at the end of this text. Nevertheless, it should now be apparent that in terms of the global configuration of the large-scale solar magnetic field, it takes two sunspot cycles for the same pattern of magnetic polarities to reappear. From a physical standpoint, the true length of the solar cycle is not 11 years, but rather 22 years. Yet astronomers are creatures of tradition, and solar astronomers are no exception; nearly a century after Hale's discovery of the sunspot polarity law, it remains customary to speak of the "11 year solar cycle."

Written By P. Charbonneau and O.R. White–April 18, 1995

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The Butterfly Diagram

kolinski — Tue, 18 Jan 2022 19:54:28 +0000

The Butterfly Diagram kolinski Tue, 01/18/2022 - 12:54

The lower image in this figure is a butterfly diagram for the time period 1900–1993.

Butterfly diagram for the time period 1900–1993.

The construction of sunspot butterfly diagrams was first carried out by E.W. Maunder in 1904, and proceeds as follows: one begins by laying a coordinate grid on, for example, a solar white light or calcium image, with, as in the case of geographic coordinates on Earth, the rotation axis defining the North-South vector. The visible solar disk is then divided in latitudinal strips of constant projected area, and for each such strip the percentage of the area covered by sunspots and/or active regions is calculated and color coded. This defines a one-dimensional (vertical) array describing the average sunspot coverage at one time. By repeating this procedure at constant time intervals and stacking the arrays one besides the other, one obtains a two-dimensional image of average sunspot coverage as a function of heliospheric latitude (vertical axis) and time (horizontal axis). Tilted 90 degrees to the side, the diagram reminds one of a row of butterflies, thus the name butterfly diagram. Several features of these diagrams are noteworthy; the absence of sunspots at high latitudes (≥ 40 degrees) at any time during the cycle, and the equatorward drift of the sunspot distribution as the cycle proceeds from maximum to minimum are particularly striking here. Note how the latitudinal distribution of sunspots is never exactly the same, and how for certain cycles (for example cycle 20, 1965-1976) there exists a pronounced North-South asymmetry in the hemispheric distributions. Note also how, at solar minima, spots from each new cycle begin to appear at mid-latitudes while spots from the preceding cycle can still be seen near the equator, and how sunspots are almost never observed within a few degrees in latitude of the equator. Sunspot maximum (1991, 1980, 1969, ...) occurs about midway along each butterfly, when sunspot coverage is maximal at about 15 degrees latitude.

The plot on the upper right is a butterfly-like diagram running from the maximum of cycle 21 to one year of cycle 22 maximum. The latitudinal distribution of helmet streamers (blue +'s) illustrates the response of the corona to changes in the surface magnetic field, and can be seen to vary in phase with the sunspot distribution during that time interval. Note, however, that streamers are observed all the way to the poles at solar maximum, and that at any given time in the cycle streamers extend to higher latitudes than sunspots and active regions (see also slide 12). A butterfly-like diagram for the observed latitudes of coronal mass ejections (green 's; see also slide 13 and slide 14) nearly coincides with this diagram, with mass ejections occurring all the way to polar regions near the sunspot maximum phase of the cycle. Note that the absence of mass ejections from 1981 to 1984 is an artifact; the lack of mass ejection data from September 1980 to June 1984 is due to a breakdown of the SMM satellite; it was successfully repaired in space by the crew of the space shuttle Challenger in April 1984. A butterfly-like diagram for the observed latitudes of solar flares (not shown), on the other hand, coincides with the sunspot butterfly diagram. This further supports the notion that the larger-scale coronal manifestations of solar activity (such as coronal mass ejections) are not directly related to flares and other smaller-scale phenomenon confined to active region latitudes. Solar variability and solar activity must then be taken as the totality of processes operating within the Sun and their observed effects over the entire solar surface and at the Earth.

Written By P. Charbonneau and O.R. White–April 18, 1995

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The Sunspot Cycle

kolinski — Tue, 18 Jan 2022 19:48:28 +0000

The Sunspot Cycle kolinski Tue, 01/18/2022 - 12:48

The number of sunspots visible on the solar disk vary continuously at any given time, as sunspots are carried on and off the visible disk by solar rotation. True variations occur following the appearance of new sunspots and sunspot groups via magnetic flux emergence (slide 16), as well as fragmentation and disappearance of existing spots and groups.

Sunspots visible on the solar disk vary continuously at any given time.

At first glance, observations carried out over time periods of weeks/months suggest that the latter two phenomena are stochastic in nature, but observations over time periods of decades reveal an intriguing cyclic pattern of gradual increase and decrease in the average number of sunspots visible on the solar disk. This was first noted in 1843 by H. Schwabe, an amateur solar astronomer, and provided the first hint of the existence of the sunspot cycle, whose period Schwabe estimated to be about 10 years. Further work revealed that the length of successive sunspot cycles is not strictly constant but varies from ~ 9 to 11.5 years, with an average cycle period of about 10.8 years. The plot shown on this slide is a historical reconstruction of yearly-averaged sunspot group counts (yellow curve), extending all the way back to the first telescopic sunspot observations in the early seventeenth century. The purple curve is the Zürich normalized sunspot number. Note how the amplitude of the cycle, or the peak average number of sunspots seen in a given year, varies from one cycle to the next. Note also how cycles are asymmetric, in that the rise from sunspot minimum to maximum occurs more rapidly than the subsequent fall from sunspot maximum to minimum. Another striking feature on this plot is the dramatically reduced number of sunspots observed in the time period spanning the years 1645 - 1715. This was first noticed by G. Spörer, and investigated more systematically by E.W. Maunder. This time period is now usually referred to as the Maunder minimum. Proxies of geomagnetic activity such as aurorae (green crosses) correlate well with the sunspot number, in the sense that lower auroral counts are associated with low amplitude sunspot cycles (e.g., 1940 - 1960), and high counts with high amplitude cycles (1800 - 1822). The Maunder minimum shows up particularly well in the auroral record.

The rise and fall of sunspot numbers are only one manifestation of the solar cycle. Solar astronomers traditionally label solar cycles from one minimum to the next, and assign them numbers starting at one with the 1755 - 1766 cycle. At this writing (January 1995) we are in the descending phase of cycle 22. Remembering that sunspots are associated with magnetic fields, it is tempting to assume that the sunspot cycle is primarily magnetic in origin. This hypothesis is corroborated by turning to other tracers of the solar magnetic field. The sequence of Hα images shown on the slide are spaced one year apart, covering the descending phase of cycle 21 and rising phase of cycle 22. Sunspot minimum occurred in 1985 - 1986. The quality of individual images varies, and no attempt has been made to calibrate the overall intensities; The changes in active region coverage (i.e., bright regions in Hα), and in the number and distribution of filaments and prominences, are nevertheless striking. Filaments and Hα bright regions gradually vanish from 1980 to 1986, and reappear again in 1987. Note how active regions gradually "drift" toward the equator through the descending part of the cycle, and are then first observed at 30 - 40 degrees latitude once the next cycle begins. Observations in white light confirm that sunspots follow the same pattern, a phenomenon first studied in detail and reported in 1858 by another amateur solar astronomer, R.C. Carrington.

Written By P. Charbonneau and O.R. White–April 18, 1995

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White Light and Magnetic Flux

kolinski — Tue, 18 Jan 2022 18:33:51 +0000

White Light and Magnetic Flux kolinski Tue, 01/18/2022 - 11:33

Strong flares are believed to be associated with the emergence of magnetic flux through the photosphere. The figure shows a sequences of white light images (left), and corresponding magnetic inclination maps (right).

Sequences of white light images (left), and corresponding magnetic inclination maps (right).

These latter images are similar to magnetograms, except that the color scale now codes the inclination of magnetic fieldlines with respect to the vertical; light green indicates a vertical magnetic field pointing towards the observer, light blue a vertical field pointing away from the observer, and orange a field parallel to the solar surface. The image is left uncolored wherever the field strength is smaller than about 200 Gauss. Magnetic neutral lines are superimposed on each set of images (in yellow on the left, black on the right). These images were constructed from data obtained with a vector magnetogram, an instrument that allows simultaneous determination of all three components of the magnetic fields at a given point on the solar surface, from the measured intensity of linear and circular polarized light. All images have been rotated so that they are viewed from a direction perpendicular to the solar surface, and tick marks are 10 Megameters (10000 km) apart in all cases.

On June 16 1992 (not shown), this active region had the appearance of a simple sunspot pair, and was hardly visible in X-rays. Five days later (top row), smaller spots and pores began to appear, resulting in a much more complex magnetic field structure in the active region as a whole, as evidenced by the magnetic inclination map and the circuitous paths traced by magnetic neutral lines. By the next day, the coalescence of smaller structures has led to the formation of numerous small sunspots and sunspot groups with well-defined penumbrae. Two days later (bottom row) the active region had grown further, and was again globally bipolar, with a global neutral line running roughly SE - NW. Examination of X-ray image sequences reveals a drastic increase in X-ray brightness on June 21, followed by nearly continuous flaring as the active region is carried over the limb in subsequent days. Note also how the magnetic field is essentially vertical in the umbra of sunspots, while in the penumbra it shows significant inclination with respect to the vertical.

Written By P. Charbonneau and O.R. White–April 18, 1995

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Solar Activity in X-rays

kolinski — Tue, 18 Jan 2022 18:29:57 +0000

Solar Activity in X-rays kolinski Tue, 01/18/2022 - 11:29

This slide shows two examples of solar activity as seen in X-rays. Frames are separated by a time interval of approximately one day. Solar rotation would carry an active region from the East (left) limb to disk center in about seven days.

Two examples of solar activity as seen in X-rays.

Note, in the first row of images, how the active region indicated by a yellow box on July 2nd 1993, brightens dramatically from July 3rd to 4th, and fades back to its original appearance by the next day. In many instances the brightening (and fading) is observed to occur on much shorter timescales, and in its swiftest form represents the most common type of flare. The complexity and multiple timescales characterizing these types of flaring events is best appreciated when viewing animations of X-ray images closely spaced in time.

The sequence shown on the bottom row is an example of a class of less energetic X-ray events occurring on much larger spatial scales, commonly seen following coronal mass ejections. Note how a structure that resembles the base of a helmet streamer (compare with slide 12) develops in the SW (lower right) quadrant. The relatively faint X-ray emission is believed to be associated with the dissipation of magnetic energy, occurring as magnetic fieldlines blown open by the mass ejection reconnect and close up again over the ejection site, eventually leading to the formation of a new helmet streamer.

Written By P. Charbonneau and O.R. White–April 18, 1995

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Two More Coronal Mass Ejections

kolinski — Tue, 18 Jan 2022 18:23:17 +0000

Two More Coronal Mass Ejections kolinski Tue, 01/18/2022 - 11:23

Two more coronal mass ejections observed with the coronagraph on board the Solar Maximum Mission satellite.

April 14, 1980 and Oct 24, 1989: White Light images.

Coronal mass ejections occur at all latitudes, suggesting that they are not directly related to intense localized heating events such as flares, as the latter are restricted to low latitude active regions. In fact few coronal mass ejections are observed to be preceded by large flares or intense activity. Observations also show that the expanding coronal material can be still accelerating a few solar radii away from the Sun, and often moving at velocities in excess of the gravitational escape speed, suggesting that the acceleration process is primarily magnetic in origin. The triggering of a coronal mass ejections is currently believed to be caused by a loss of large-scale magnetostatic equilibrium. The 24 October 1989 coronal mass ejection shown on the lower sequence of images is one of the most powerful recorded by the Solar Maximum Mission Coronagraph; approximately 2 x 1013 kg of material were ejected with peak velocities of nearly 2000 km s-1, blowing a hole nearly 100 degrees wide through the solar corona.

Written By P. Charbonneau and O.R. White–April 18, 1995

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A Coronal Mass Ejection

kolinski — Tue, 18 Jan 2022 18:13:46 +0000

A Coronal Mass Ejection kolinski Tue, 01/18/2022 - 11:13

While helmet streamers are long-lived, their demise often occurs abruptly through one of the larger-scale and perhaps most spectacular manifestation of solar activity: coronal mass ejections.

August 18, 1980: White Light image.

In the larger coronal mass ejections, such as the one depicted on this time sequence of images, up to 1013 kg of coronal material may be ejected outward at speeds as high as 1000 kilometers per second (although average values are closer to ~ 1012 kg and 400 km s-1). Prior to its disruption, this helmet streamer (10:04 frame) had been visible for a few days, during which it showed little change in shape or brightness except for a very gradual rise and/or swelling. The transition to a rapid evolutionary phase defines the onset of the coronal mass ejection proper. As this helmet streamer first swells in the initial stages of the ejection, a dark cavity comes into view, within which an erupting prominence can be seen. The prominence material is blown outward along with the original streamer material; the bright, filamentary structures on the 13:10 frame are in fact the remnants of the prominence. Comparison of Hα images taken before and after a coronal mass ejection often reveal the disappearance of a filament originally located along the magnetic neutral line straddled by the disrupted helmet streamer. Note however that not all filaments disappear this way, and not all mass ejections are accompanied by erupting prominences. The dark disk in the upper right corner of each frame is not the solar disk, but the occulting disk of the Solar Maximum Mission (SMM) coronagraph, used to take these images (on this instrument the occulting disk has a radius 60% larger than the solar disk).

Written By P. Charbonneau and O.R. White–April 18, 1995

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pictorial

Credits

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Solar-Terrestrial Interactions

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The Corona Through the Solar Cycle

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Hale's Sunspot Polarity Law

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The Butterfly Diagram

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The Sunspot Cycle

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White Light and Magnetic Flux

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Solar Activity in X-rays

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Two More Coronal Mass Ejections

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A Coronal Mass Ejection

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