SERF studies of mass motions arising in flares

iii~’. ~ Vol.2, No.11. pp.203—219, 1983 I’rinted in Great Britain. All rights reserved.

0273_1177/83/110317$8.5010 copyrLght© COSI’AR

SERF STUDIES OF MASS MOTIONS ARISING IN FLARES William J. Wagner* *High Altitude Observatory, National Center for Atmospheric Research’, Boulder, CO 80307, U.S.A.

ABSTRACT The SERF investigation of mass motions was outlined at a Cambridge meeting in 1979. Mid-course corrections of observing programs and a review of data took place in Palo Alto (1980) and Simferopol (1981). SERF participants at the recent Annecy SMY Workshop studied new mass motions data and noted the difficulty in co-locating Type II burst sources on or in front of loop transients. A model invoking a foreshock analogous to that at the earth’s magnetosphere was suggested. Radio type IVs, co-spatial with dense hot plasmoids. may be the result of a plasma radiation emission mechanism. The injection of mass into the corona was observed in chromospheric and coronal lines recently with magnetic field changes and also at very high speeds into loops. The start time of coronal loop transients, it extrapolated to the chromosphere. usually precedes flare H-alpha or X-ray emission. Observational inferences from polarization and other studies begin to favor the three-dimensional bubble over the planar loop as a description of coronal mass motions. INTRODUCTION Mass motions at the solar surface have been recorded and studied for many years. Even with the advent of space instrumentation and the exciting discovery of coronal transient mass ejections. however, solar physicists are progressing only slowly in their understanding of the phenomenon and its driver. An important class of events on the sun, mass ejections now appear to represent the most energetic transient phenomenon in the solar system. The evaluation of such energies has driven traditional flare researchers to speak currently of the awesome power (energy per unit time) of the classical chromospheric flare (Spicer [52]). Today, however. remaining unanswered are fundamental problems as to the timing of transient mass motions compared to other flare effects, and the origin in the low corona of the mass of a loop transient. Even the basic question of what a transient is, magnetic arch or pressure wave, and its shape (planar loop or bubble) eludes researchers. Such elementary problems have proven too difficult ta solve by merely a single group of observers, either ground-based or spaceborne. Progress in the future will rely on team work and the concerted efforts of multi-discipline consortla. The two dozen active participants in the Annecy Mass Motions Workshop were charged with interpreting the past several years of observations in a physics framework (see other chapters in this volume for results of individual event data analyses). This paper does not represent a review of the mass motions topic (see instead MacQueen [30]. Dryer [7], or Wagner [63]), rather a progress report which has been filtered by some (objective) judgement. The Annecy SERF Workshop saw new information generated in several areas. Section 2 describes new solar surface observations of Mass Motions which hold the hope of providing continuing studies extending beyond the lifetime of their space platform counterparts. Outer corona transients are discussed in Section 3 with particularly noteworthy aspects being their timing vis a vis the chromospheric flare and their movement with respect to radio type 11 burst sources. Evolution of mass ejections proceeds in the interplanetary medium, but Section 4 reports the appearance of transients at 1 AU which, with similarity considerations, may reflect upon their nature at the sun. MASS MOTIONS AT THE SOLAR SURFACE Several participants reported observations of an unusual nature from ground-based telescopes. The development of new-generation facilities (see for example Smartt et al. [49], Mein [36]) has kept apace of the orbiting observatories.

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Mass at Low Temperatures

At the time of flares, various fleeting phenomena are known to appear. Machado [20J has discussed chromospheric Ha halos in association with soft X-ray emission occurring at. the flash phase. Martin described at the Workshop an accelerated emission front which occurred during the rise of a flare on 5 September 1973. The front appeared as emission in Ha and Ca II (x8542) in the shape of a diffuse arc which accelerated away from the flare site, reaching about 300 km s~ at 100000 km. The front preceded an erupting filament, but traced out an analogous height-versus-Lime trajectory. Martin [32] argues that the front represents not a chromospheric wave (Uchida ci al., [58]). but rather material motions because the undisturbed chromosphere is visible through the faint emission, and no Doppler shifts were detected in chromospheric structures. The fuzzy emission front is the birth of a coronal transient, Martin believes, with the same material later appearing (ionized) in the white light loop transient. Jackson [27] notes the elevated departure point of coronal transients above the flare site. A discussion (Section 3 below) of the basic nature of white light loop transients in the outer corona generates considerable controversy. While the pressure input wave model is developing rapidly today, the local expanding magnetic loop (Anzer [2]) or magnetic pressure (Pneuman [43]) pictures remain viable. Mein and Mein showed a meticulous observation from the Meudon Observatory tower telescope which lends support to magnetic expansion as a transient driver. The Meins detected an expansion of Ha features which they interpreted as magnetic flux tubes carrying falling Ha material during a flare-spray at 1100 UT on 29 June 1980. The west limb of the Sun was particularly active on this day, with radio bursts and transients reported at 0245 and 1830 UT. Unfortunately, the SMM C/P experienced an outage during the Mein flare, but the after-event filtergrams, when compared to those before, show distinct outer corona changes, with the limb region at the flare site giving the appearance of radial, striated post-flare transient legs. The 1100 UT flare observed by the Meins was the most impulsive of the day, with GOES Importance M4.2 and interplanetary particles, metric radio bursts, and 7-rays produced (Ryan [44]). Using the multichannel double-pass spectroheliograph at Meudon, the Meins recorded several series of nine simultaneous wavelength-displaced Ha images. Doppler line of sight velocities are combined with proper motion to trace out the rapidly expanding magnetic loops shown in Figure 1 to a height of 135000 km. Mein and Mein [37] find that the local magnetic field in the loop tops increased by 14 percent in ten minutes. Thus, this careful study of mass motion, although indicating velocities slower than those observed in the outer corona, does provide an elusive indicator of expanding flux which may be driving a transient in the inner corona. Such evidence has not been readily available, although today both ground-based facilities, such as the Meudon tower telescope and orbiting coronagraphs using forbidden emission line filters seem to have begun to detect coronal field changes (see House et al. [23]) in mass ejections.

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Fig. 1. Intensity (left) and line of sight velocities (right) in Ha measured at 1059 UT for the 7-ray flare-spray of 29 June 1980. Mein and Mein [37] fit a model of local dipole magnetic field to these observations in which the expanding field increases in strength 14 percent in ten minutes.

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Spectacular examples of cool (neutral Ilydrogen) mass in motion were provided by Rouipult from the coronagraph of the Warsaw Observatory. One particularly striking cine sequence illustrated a mass ejection with a flare-spray behavior which commenced, however, not from ihe chromosphere. but clearly from an elevated segment of a prominence. The escaping Ha material accelerated rapidly to spray-like velocities and followed a path almost tangent to the limb.

Rompolt was successful in recording in Ha several events such as that shown in Figure 2. which the Solwind and SMM C/P coronagraphs later observed in the outer corona (House ci al. [24]). With several examples in hand, Romnpolt reported that for eruptive prominence events, an entire magnetic arch expands outward with the white light transient at the leading edge of it, and the prominence material ‘frozen in” as part of the interior of the arch.

Fig. 2. The eruption at 1022 UT of a west limb prominence on 5 May 1980 was one of several observed by Rompolt at the Warsaw Observatory which were also recorded by the orbiting Solwind and C/P coronagraphs. House et al. [24] report such Ha emission is sustamed to beyond 4 R~. Mass at High Temperatures The Thomson-scattered continuum reveals with little ambiguity the local electron column depth in the corona. Interpretive uncertainties such as optical depth, temperature, ionization, or Doppler shifts, normally present in analyses using emission lines are avoided in white light studies. Unfortunately, today facilities are just beginning to be developed which provide continuum coverage low in the corona (Fisher et aL [13]). Heretofore, instrumental stray light inherent in Lyot coronagraphs precluded their use for other than the stronger emission lines, while externally-occulted coronagraphs vignetted the corona to no less than 1.45 R 0 from sun center (MacQueen et aL [31]). In spite of the complexity of emission line analysis, the inner corona vitally interests us as the birthplace of mass motions. Srnartt presented results from the new Sacramento Peak Observatory Emission Line Coronagraph which records the entire solar limb in Ha, Fe X X6374. and Fe XIV A5303. Series of exposures alternate between these ions (hence temperature) in one-minute interval patrol cadence. Smartt reports that, aside from the occasional coronal transient, young active regions can show almost continuous change occurring in middle-temperature structure emitting X6374 in association with an eruptive prominence. Smaz-tt [50] dismisses the possibility that these minute to minute changes are mass motion of ions. Rather, varying magnetic conditions either on scales less than the resolution limit of the telescope or in the underlying photosphere may be modulating the forbidden line emission. An alternative explanation according to Smartt is that energy in the form of high-energy electrons or waves is irregularly injected into the coronal field which acts to make the existing field structure luminous. These rapid intensity variations are not seen simultaneously in the Fe XIV channel. In work largely attributable to SERF brokerage, Smartt with Sacramento Peak data. Howard from the P78-i Soiwind coronagraph group, and Wagner with the SMM Coronagraph/Polarimeter team collaborated to analyze an eruptive prominence/transient event of 15 - 16 April 1980 (Wagner et aL [63]). Smarit recorded the prominence eruption in unusually close coincidence with the extrapolated departure time of the outer corona white light transient. Sawyer et al. [46] report that for

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C/P the usual sequence of events is for the transient departure time to extrapolate 2 - 4 minutes earlier than the chromospheric activity start (Section 3.3 below). The purpose of the Wagner et al. [63] study was to trace a coronal transient from the chromosphere to 10 ft 0. producing a detailed height versus time record which might show ir1dication of velocity changes. Such was not the case. however, as a constant speed of 257 ±25 km S obtained. The analysis of the 15 - 16 April 1980 event demonstrated the power of collaborative science in its verification for Smartt of the first-ever detected red line transient. Evidence from the orbiting coronagraphs confirmed the A8374 event by placing the fleeting (one minute life-time) emission line enhancement precisely at the white light transient departure time. Images in the electron continuum from as close to the limb as 0.2 R0 have been produced by Fisher at the Mauna Loa Observatory of the High Altitude Observatory. Fisher [12) reports that flareassociated transients in the K-Coronameter field of view show a leading enhanced-density white light transient similar to those seen above 1.7 ft0. Wu and Dryer have been attempting to model the behavior of this inner corona region in which leading depletions of material are observed to precede erupting prominences (Wu et aL [87]). Energy input and the magnitude of the temperature pulse, which is presumed to drive this transient, are inferred from soft X-ray and EUV data from the SMM XRP, HXRBS, and UVSP experiments. Dryer [6] claimed that the MHD code which is used can reproduce leading enhancements for overlying closed fields and depletions for open magnetic structure. The Hard X-Ray Imaging Spectrometer on the SMM spacecraft often sees the development of arches emitting X-rays. Simnett [48] presented data from 13 April 1980 which documented the filling of a coronal arch which linked two active regions with hot material. This may have been material motion or a continuing input of energy for up to 2 hours after a non-impulsive tlare. Integrations over several hours show the maintenance of quasi-permanent structures through the course of several small flares. Antonucci et al. [1] using SMM X-Ray Polychromator Ca XIX and Fe XXV data confirm actual material motion up from the impulsive flare site. These flows of very hot effluent persist for three minutes and reach line of sight speeds of 340 km s~. Such numbers imply that material may reach considerable heights in the corona before the event fades if the velocity does not decrease with height. The energy inferred is far in excess of that available in electron beams. Tandberg-Hanssen showed spectroheiograms in C IV X1548 during an eruptive prominence event of 6 May 1980. The event (Tandberg-Hanssen et aL [55)) marked the initiation of a coronal transient reported later (House et al. [23]) in the C/P field of view. Tandberg-Hanssen noted the resemblance of the eruption to an expanding loop. HIGH CORONA MASS EJECTIONS Approximately ten years ago, orbiting coronagraphs began to reveal the true impact on the interplanetary medium of the well-studied chromospheric mass ejections. Limited to observations in Ha or in the few forbidden visible emission lines, coronal physicists today would remain blissfully ignorant of the magnitude of mass and energy loss represented by coronal transients. Video frames from the OSO-7 coronagraph stunned experimenters with images of diffuse clouds of prominence and spray ejecta passing 10 R0 (Tousey [56]). The loop-like white light transient which surrounded eruptive prominence remnants, or rose alone without Balmer line-emitting ejects during flare events was subsequently captured on film by the ATM coronagraph (MacQueen et aL [29]). Although it took exo-atmospheric coronagraphs to identify coronal transients, it would appear froits the above Section that the greater versatility of ground-based ooronagraphs and the new energy regimes of X-ray telescopes will do much to explain the basic nature and origin of these mass ejections which are discussed here. Statistics The frequency of flares and sunspots varies in a well-known 11-year cycle, It is not clear that eruptive prominences show the same dependence. Eight months of ATM coronagraph data led to speculation that the Solwind and SMM C/P telescopes would be overwhelmed with coronal activity, if an extrapolation were valid from the declining phase of the cycle to the maximum. Using an empirical relation between transient frequency and Wolf number. Hildner et al. [18] predicted 100 transients per month for 1980. Specifying the frequency of transients was admitted to be difficult by the Workshop attendees. The most essential problem is one of definition, and, especially, in carrying a consistent definition for “transient” from one telescope to another. The second complication lies in maintaining a consistent “detectabiLity limit” between the counts of various workers, in the face of differing instrument resolutions, passbands, and data reduction (specifically, the use of direct or differenced images). Considerable discussion between coronagraph experiment teams from the C/P and Solwind led to a general agreement that, with all the above caveats, both instruments were apparently seeing the same frequency of transient events to within perhaps 30 percent (Sawyer et al. [45]). Preliminary

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counts were made by Sawyer of mass ejection events over the 138 days of C/P operation. If correc-

tions are made for instrument duty cycles, outages, and other complications, during spring and summer 1980. the mass ejection frequency was about twice as high as in 1973. Hildner ci al. [ie] would have predicted a C/P transient rate four times as high as the ATM observed. Possible explanations of the breakdown in the Wolf number-transient prediction may lie in a different actual mix of flare-, versus eruptive prominence-associated transients. An alternative explanation may be that the solar maximum transient frequency is low because the sun requires some sort of “recovery” time before a region can produce a second transient (Wagner et at. [62]). Loops or BubbLes?

While mass ejections from the high corona show a wide variety of forms (Munro ci al. [38]), the most distinctive shape belongs to the cohort of loop transients, In addition to being the most common type (the loop comprises about one-third of the ejections observed), this phenomenon attracts modelling efforts by virtue of its conceptual simplicity and its surfeit of measurable parameters. Yet a decade after its discovery, neither theorists nor observers have settled the question as to whether these transients are two-dimensional loops or three-dimensional bubbles (Wagner [64]). The Mass Motions Workshop heard reports which advanced the bubble concept from at least three lines of reasoning. Crib analyzed polarization in the ATM event of 10 August 1973. She was able to relate polarization of each element along the transient to its distance to the plane of the sky. Crifo et al. [5] argue that any bubble shape would show contributions principally from a plane section parallel to the plane of the sky, whereas a loop, if expanding in a direction away from the plane of the sky, would show this angle in its constant polarization signature. Further, as the transient expansion continued in time, these derived orientations would be maintained unchanged. Crifo concluded that the 10 August 1973 event was bubble-shaped. The method was checked by noting the effect of the transient on the displacement of a neighboring streamer. In interplanetary space, transients may be the large three-dimensional bags or clouds of anomalous solar wind that are observed at 1 AU. Schwenn described these as regions 0.25 AU in radial depth by some 30 degrees in azimuthal extent marked by high field strengths and low density and temperature. The magnetic field is inferred by observations in the ecliptic plane to be closed (Burlaga et al. [4]) around these clouds. Further discussions of the interplanetary data are found below and in other chapters of this volume (McKenna-Lawlor [35]. Passes [42]), especially relating to the STIP Workshop (Dryer [8]). For now, these studies at I AU are invoked merely as evidence for the bubble viewpoint.

Further suggestion of the longitudinal extent of such magnetic clouds comes from the HELlOS-I observations. From 12 to 15 April 1981, the actual piston driver gas from a flare 135 degrees away from the HELlOS subsolar longitude streamed past this spacecraft. Such wide-ranging effects near 1 AU argue for a three-dimensional nature for the coronal transients. It is difficult to place a planar loop 135 degrees from the flare site, even considering the refractive and convective effects of the solar wind structure. This remains true even if observations show transient trajectories tilted as much as 40 degrees from radial in the corona (Sawyer et aL [46]). Contrary to the above evidence for a bubble-like nature to the white light loop is the report of Trottet. If a transient truly is a planar loop, observers question why few or no examples of edge-on loops exist. Trottet arid MacQueen [57] studied ATM loop events which were well-associated with eruptive prorninences. They find that such transients are strongly correlated with filaments running northsouth and argue, from X-ray and forbidden emission line observations, that the overlying field also lies predominately north-south. These authors conclude that the ATM loop transients were a special set with few or no examples expected of east-west filament/field/loop plane orientation. Hence, although such mass ejections are indeed loop-shaped, ws have yet to be treated to an edge-on view of the phenomenon. This argument could, of course, still admit to the transients being sphericaL Departure Thn.es Alter work by Jackson and Hildner [28] and Jackson [27] identified forerunners of white light transients, a coronal “chicken or the egg” controversy has ensued with respect to flares and transients. As discussed in the Workshop, the setting of the coronal transient time of departure from the chroniosphere (the result of a time extrapolation back to zero height) is inexorably bound to the problem of spatially locating the transient, the shock, and the type II radio burst. That such is the case will be evident in the next section where it is shown that the wave/mass ejection concept clearly represents as basic a question to the nature of transients as the loop/ bubble controversy. Sawyer began the discussion of flare-transient time correlation by reporting that, in preliminary analyses using Solar-Geophysical Data (Prompt Reports), for about twelve C/P events, the flare start times noticeably lagged behind the extrapolated departure time of the white light mass ejection. The events were loop transients accompanied by several flare manifestations. The general sequence of events was: centimetric radio burst, GOES 1-BA X-ray burst, transient departure from the chromosphere (extrapolated). Ha flare (Sawyer at aL [45]). Some time later, metric radio bursts and erupting prominence motions begin.

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Stewart showed height versus time plots for an expanding loop transient which was followed in the C/P field by a dense ionized plasmoid on 27 April 1980. In Figure 3, all three major white light features clearly extrapolate to zero height at a time six to fifteen minutes prior to the flare. Stewart at al. [53] concentrate on the radio aspects of this event as observed simultaneously with the Culgoora radioheliograph, but report also that the coronal transient was preceded some twenty minutes earlier by a forerunner, not illustrated in Figure 3 (or perhaps another unrelated transient).

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TIME (UT) Fig. 3. A height versus time diagram from the transient and radio event of 27 April 1980. A chromospheric departure time for the coronal features is indicated six to fifteen minutes prior to flare start time. (Data from Stewart et al. [53]). Stewart also produced height-time plots for the 17 April 1980 transient which was observed by C/P and three radio observatories. Culgoora, Clark Lake (University of Maryland), and Fort Davis (Harvard College). Both the loop transient and a dense plasmoid extrapolated to the chromosphere approximately eight minutes earlier than the flare start time. In a parallel STIP Workshop (Sawyer [45]), the event of 12 April 1980 was tracked from the chromosphere to 1 AU. Sawyer ([45], her Figure 12) demonstrates by extrapolation a transient departure time which leads the radiative flare (Ha Importance 1B; GOES 1-8A Importance M2.1) by about ten minutes. The day of 29 June 1980 produced an exceptionally active southwest limb. The first transient of the day has been studied In depth by Gary [15] as one of the best-covered radio events insofar as C/P images were recorded very early of the developing white light transient. In Figure 4 the unusual side-by-side double loop progress is extrapolated to zero height. Departure time of the northern loop precedes the flare by four minutes; the southern loop left the chromosphere about two minutes before flare start. Not shown in Figure 4 (see Gary [15]) is a forerunner, analogous to that found by Stewart et al. [53]. In analyzing the mass motions of 7 April 1980, Wagner et al. [62] concentrated primarily on the energy partition of the matter ejected from the sun. A height-time plot was made which showed the outermost point of the loop extrapolating to the flare site at the time of the flare. However, as explained in Wagner et al. [62]. this simultaneous flare/transient start was forced by definition because only one C/P data frame showed the top of the loop. In view of the evidence from the participants above, perhaps a proper inference of the trajectory of the loop top would be a line parallel to that of the plasmoid on the side of the loop as suggested in Figure 5. Because the 7 April 1980 loop is unusually squat (width greater than height above the C/P occulting disk), the plane of the sky speed of the outermost point of the loop is probably slower than that of the observed blob on the ioop side, In either of these cases, if the transient is not required a priori to start with the flare as in Wagner ci al. [62]. a better guess would be that the 7 April 1980 departure time preceded the flare start time by about ten minutes.

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TIME (UT) Fig. 5. A heieht versus time record for the transient of 7 April 1980. Instead of assuming a start of the outermost loop at the flare time as is done in Wagner et al. [62]. a more reasonable extrapolation (of the single data point) would place the loop start several minutes before the flare. Not all well-studied 1980 transients lead the chromospheric events, it was noted. Wagner ci al. [63] find exact simultaneity in the departure time of the white light loop of 15 April 1980 and that of the underlying eruptive prominence. It is curious that the 15 April 1980 well-timed mass motions event

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is the only eruptive prominence event mentioned in this section, whereas the other four transients were associated (slightly later in time!) with flares. It is probably fair to report that the Mass Motions Workshop participants left these presentations from five specific event studies with the definite impression that the extrapolated transient departure time could not be reconciled to the flare start time, It was noted that straight line extrapolation of the transient trajectory is used to extend information below the occulting disk to the chromosphere. To admit the possibility of a changing transient speed in the inner corona hidden from externally-occulted orbiting coronagraphs only complicates the departure time problem. Fisher [12] reports that only one of four documented trajectories of Mauna Loa Observatory flareassociated transients shows varying speed--and this one case is in the sense of an acceleration in the low corona. Sawyer opined that C/P data may reveal some transients with slow acceleration, but most have constant speed. Howard [25] agreed that Solwind also sees no deceleration for transients in the outer corona, thereby providing consistent observations from I to 10 R 0. Thus the evidence (Figure 6a) for reconciling transient departure time and flare beginning at a common chromospheric site, namely transient deceleration in the inner corona, does, not exist. An alternative model is provided by Jackson [27] who suggested an elevated site, primary to both the subsequent flare and transient (Figure 6b). TRANSIENT DECELERATION

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Fig. 6. Assuming that coronal transients are indeed associated with flares, two conceptual scenarios are illustrated in which the extrapolated departure time of the transient T,, would lead the flare start 7’,.. In a, the transient decelerates in the inner corona, a picture supported by no observational data. In b, an elevated primary activity site as suggested by Jackson [27] generates the transient and flare. Are the Shock/7)jpe Il/Mass Ejection Cospatial? From data generated by orbiting coronagraphs and swept-frequency radio spectrographs and radioheliographs .during the 1970s, several workers determined the relative location of the shockassociated radio type II “Slow-Drift” bursts and coronal mass ejections. MacQueen [30] and Dulk [9] in their reviews conclude that type II radio bursts, which are presumably excited by shocks in situ, originate in the vicinity of the transient forerunner and at an appropriate stand-off distance from the white light front for the shock. Experimenters with plasma instruments and magnetometers on spacecraft observing the interplanetary medium today also detect shocks leading disturbed regions of the solar wind. The observational placement of the transient (usually a loop) and the type II source region (and shock) in the plane of the sky is a challenging task due to the short-lived nature of the radio emission, our observing “pass-bands’ at a mere handful of radioheliograph wavelengths, and the rapidity of passage of the transient through the corresponding plasma levels. In the last two years, with the operation of the C/P and Solwind instruments and the added two-dimensional capabilities of the Clark Lake Radio Observatory and the Nancay Radioheiograph, and the addition of two new observing frequencies to the Culgoora radioheliograph. a new set of observations addresses the shock/type Il/transient linkage question. The Mass Motions team was shown data from five transients occurring in 1980 for which simultaneous white light orbiting coronagraph images and radioheliograph type II burst data were available. Other cases exist, but had not been analyzed at the time of the Workshop. Two aspects of the data stand out as particularly significant. First, in none of the events did the type 11 convincingly lead

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the white light transient through the inner corona. Second, the plane of the sky speeds of the type Ii exciters (determined by onset time at each frequency) was obviously different. than the transient speeds.

Gary [15]. analyzing the 29 June 1980 C/P event, produced preliminary height versus 1.iiiic plots (Figtire 4) together with overlays of successive C,/P images arid CS! RO type It t)tirSl bet lions (shown in Figure 7). As noted in the discussion above of transient departure times. Gory finds that the extrapolated transient start time leads that of the flare, while Figure 4 suggests tIi~t.the type II departure may be simultaneous with the flare beginning. the mean speed of the type II at 160 1) thanFurther, either the northern or southicrii white light MHz 80 s M ), although the error in the II spccd is ±300km s 1, More detail is shown in Figure loops and (650atkm 1Hz is faster (about 900 km s’ 7 wherein one type II source lies roughly near the top of the southern loop at 0244 and 0247 UT, but the other type lilies only one-half way up the northern loop at 0241 and 0244 UT.

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Fig. 7. Superposition of Culgoora radioheliograms on C/P white light corona images at a. 0244 UT, and b, 0247 UT, on 29 June 1980. Corànal loop transient features are shown by thin lines, ‘type II radio burst contours by heavy lines. One type II exciter lies at the leading edge of the southern loop in each C/P frame, the other generates bursts well behind the front of the northern loop. Data from Gary [15]. The STIP Workshop compiled observations of the transient of 12 April 1980. Sawyer ([45]. her Figure 12) shows similar type 11-transient circumstances to those of 29 June 1980. The II was too weak to allow radioheliograph positioning. From the Clark Lake Radio Observatory swept-frequency records. using various reasonable coronal density and radio emission models, the type II is seen in Figure 12 of Sawyer [45] to have departed the chromosphere after the transient but coincident with the flare. and rapidly to have passed all of the white light transient features within 2 R 0. A very brief type II was reported by Stewart to have accompanied the 27 April 1980 mass ejection. Stewart et al. [53] show that simultaneous C/P images of the ioop transient and Culgoora radioheliograph positions of the type 11 place the radio source well behind the leading peak of the loop (Figure 3). Stewart [54] reports no speed measurement for the short-duration type II. Gary [14] exhibited preliminary studies of a type II seen at both 160 MHz and 80 MHz by CSIRO and the passage of a double (side-by-side) loop observed by the C/P on 17 April 1980. At both frequencies, emission was observed (Figure 6) at locations only one-half way up the instantaneous positions of the loops.

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Fig. B. Superposition ci’f Culgoora radioheliograms (bold Lines) on C/P white light images (thin Lines) for the event of 17 April 1980. The type II radio burst exciter is seen to lag the leading edges of both loop transients. Data from Gary [is]. Gergely et al. [17] reported an unusual behavior for the type II which was observed on 9 April 1980 by the Clark Lake Radio Observatory, the Culgoora radioheiograph, and the Coronagraph/Polarimeter. The II was observed to move toward the sun with time, perhaps the effect of foreshortening on a source which may have been moving tangent to the chromosphere. Thus, to review the above five 1980 events, the prima facts evidence is the following. One type II source is cospatial with a C/P transient (29 June. southern loop), while four Us are seen behind the transients (29 June, northern loop: 27 April; 17 April; 12 April). More significantly, for the 29 June event, the type II passes the white light front by 2.1 R 0. for 12 April by 2.0 R0. On 9 April. the TI motion may be orthogonal to the transient. No speed information exists for 17 April or 27 April. What is immediately clear is the fact that a solution to the shock/type Il/transient location problem cannot be simple. The Mass Motions Workshop considered both the above radioheliographcoronagraph data and the transient departure time information together. Recall, the transient was found either to depart the chromosphere earlier than the flare beginning, or to be launched from a site elevated in the corona. The type II, when extrapolated back, may be simultaneous with the flare and be behind the transient until about 2 R0 where, because its speed exceeds that of the transient, the II source rises above the ejecta. In fact, if the type II starts later and lower than the transient. but is faster, then the question of cospatiality is moot. Is the II source behind, on, or ahead of the mass ejection is best answered, yes. Evidence for the type II passing through the white light loop has been available for some time. Nelson [39] showed examples of such behavior in interpreting upward (to lower frequencies) “Jumps” in type II swept-frequency spectrograms from Culgoora. Such breaks in the II dynamic spectra are interpreted by Nelson as the radio source propagating from a dense (post-transient backwash condition) to more rare medium (the undisturbed corona ahead of the transient). One implication of such an independent existence for the Ii source and the transient is to the models which would have the transient intimately connected with, or actually be the shock. In investigating such an implication, however, Vaisberg [611 suggests a more sophisticated outlook. The type II source must be distinguished from its associated exciter shock. Vaisberg offers the example of

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the (,crrestial magnctopause as a salvation for the transient-as-shock viewpoint At. thin how shock of the earth, it is well—known now (see Iloppe et aL, [21]. their Figure 33 especially) that. various particle populations may grow at locations distant to the peak of this foreshock. Vaisberg suggests that the moving solar shock outlining the white light transient accelerates dent runs wlitcti escape into the unperturbed ambient corona. Thus. “up-stream of the advancing shock/transient Ilic criergetic electrons produce plasma oscillations via the two-stream instability. Here, of course. Ihie transient would be expected to have not a loop, but a bubble geometry. This picture has been investi-

gated in situ for the case of the terrestial bow shock, and has recently been confirmed in studies of interplanetary shocks by Soviet and U.S. spacecraft (Obridko [10]). The important point. Vaisberg noted, is that the location of the region where different plasma modes are excited does not necessarily coincide with the shock itself. Varying conditions of ambient density and especially magnetic field orientation which overlie the shock/bubble determine a variety of radio source positions vis a vis the peak of the visible loop. As the shock/bubble rises, these conditions should slowly change producing relative motion between the transient peak and the radio emission. Interestingly, an earlier paper by Smerd et al. [51J presented evidence in the form of “split-band” type 11 radiation for an argument that emission occurs occasionally both upstream and downstream of the shock. Figure 9 shows one possible configuration wherein the shock is cospatial with the Loop front, but which causes a “skirt” of type II emission at the waist of the transient, much like the picture Vaisberg [61] described and which mimics some of the above observations shown the Mass Motions Workshop. Participants were left with two possibilities: either the shock and type 11 have nothing to do with the coronal transient, or a foreshock model such as suggested by Figure 9 is required, in which case the transient leading edge is a shock.

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Fig. 9. The foreshock model of type 11 radio emission from a, a flare-associated transient and, b, a transient accompanied by an eruptive pronunence. As the transient advances, its leading edge shock (shown boLd) intersects the coronal magnetic field. Electrons are accelerated (heavy arrows) to produce plasma oscillations “upstream” of the transient in analogy to the terrestial bow shock. Type II radio sources thus appear at the plasma level in locations determined by the geometry of the shock and ambient field; these may be some distance from the peak of the transient. Vaisberg guesses that the initial forward shock front is at the leading edge of the transient, but is thinner than the limiting resolution of either the C/P or Solwind. thus not observable as separate from the density enhancement of the bubble itself. On the inside edge of the bubble, there should exist a rarefaction much thicker than the forward shock, or perhaps a reverse shock, again, unobservable. Pesses [41] commented that the foreshock model for the transient would indeed predict the generation of electrostatic waves, perhaps through the the two-stream instability. However, Pesses expressed doubt that such waves could result in particle acceleration to the high energies required for production of the herringbone radio emission associated with type us and observed by ISEE-3 at 1 AU (see also Holman and Pesses [20]). House [22] noted the utility of C/P A5303 potarizot.ion analyses in defining the direction of ambient magnetic field, so crucial for confirming that the sun-solar wind shock interactions behave as solar wind-pLanetary shock interactions.

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In summary, the Workshop concluded that the transient starts in the Low corona early, or at the same time, but high. The type II source passes the transient which implies an existence for the radio-generating shock separate from that of the transient, unless a foreshock mechanism is invoked which could give such an illusion. The use of this later foreshock explanation, however. may serve to put the shock with the transient, but it also requires that the shock start ahead of the impulsive phase of the flare. Why did this new picture of shock/type Il/mass ejection only emerge in 1980 observations by C/P? Two explanations are offered, the first noted that this SMM instrument was designed to observe the corona closer to the solar disk than previous spaceborne coronagraphs, and might therefore have been expected to reveal new behavior and test preconceptions of the II and the transient in the crucial heights of C/P overlap with metric wavelength radioheliographs. The second explanation, more physics-based, is that the average nature of the corona was different (with higher densities and field strengths, as in still lower altitudes of the corona) at the maximum of the solar cycle. With solar minimum densities and field structure, once again type Ils may properly Lead mass ejections in the low corona as the transient skirt of radio emission evolves into a transient “hat”.

7ijpe IVrn Hu~rstsfrom Mass Mosti.ons The moving type IV radio burst in its various forms is one of the most reliable non-optical indicators of mass moving through the corona. The Workshop addressed moving type Ns from two aspects, reviewing briefly the current views of the participants on emission mechanisms, and evaluating the possibility of determining magnetic field strengths from observations of these bursts. Moving IVs originally were ascribed by Boischot and Denisse [3] to synchrotron radiation from MeV particles. With the development of the radioheliograph. and the discovery that erupting prominences were often accompanied by IVm radiation, others invoked the gyro-synchrotron emission process. The gyro-synchrotron mechanism is an especially attractive thesis because it suggests that the strength of the local magnetic field may be derived. However, Stewart [54] noted that the extremely high brightness temperatures recorded at 40 MHz imply particles of greater than 1 MeV and unpolarized emission. Stewart et al. [53] suggest the alternate mechanism of plasma radiation at either the fundamental or second harmonic as a result of their studies of the simultaneous transient/lVm event of 27 April 1980. Pick agreed with such a possible mechanism for some of the IVm events, and reported new observations of high frequency oscillations with a moving IV (Figure 10). This evidence for fine structure from the high time resolution Nancay radioheliograph and the Zurich ETH spectrometer argues for plasma emission, according to Trottet et al. [58]. Pick offered this 31 May 1978 pulsating event as an example of plasma radiation giving way later in the same event to gyro-synchrotron.emission. Gergely agreed with Pick and Stewart on admitting the possibility of plasma radiation for moving Ns, and in fact offered the opinion that all Ns seen with erupting loops are due to this mechanisiy. Gergely [16] noted with curiosity that IV bursts seem to display a velocity threshold of 400 km s with slower mass ejecta failing to excite IVs. Participants were cautioned by Dulk [10] against believing that all moving IV bursts represented plasma emission. Gyro-synchrotron emission must still be favored for the long-lived events of Low brightness temperature Tb whose polarization increases when they are high in the corona. From the degree of circular polarization r~observed, the field strengths are obtainable. Low in the corona when the densities are high, Razin suppression can occur and plasma radiation can lead to high Tb. For second harmonic radiation, present theories offer techniques relating r~to magnetic field strength. However, the polarization of radiation at the fundamental plasma frequency can not today be used as a field diagnostic, our theory being too undeveloped. The data for 1980 with simultaneous orbiting coronagraph observations are all on rather short-lived, low Tb events, Unluckily, much of the above discussion on field strength determination is temporarily moot, because all of the C/P events have proven to be essentially unpolarized at radio wavelengths. MASS MOTIONS FROM INTERPLANETARY EVIDENCE Other chapters in this volume by Pesses, Dryer, and McKenna-Lawlor provide more extensive reporting of new interplanetary results than can be offered here. It is useful, however, to review particular lines of interplanetary evidence which have solar Mass Motion implications. The unfolding picture of large magnetic clouds, regions of closed field and low temperatures which extend 0.25 AU by 30 degrees longitude, evoked the model of coronal transients as bubbles rather than planar loops. Although little observational correlation yet exists between such clouds and transients, an association undoubtedly will be discovered, in the writer’s opinion.

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Fig. 11. The interplanetary signature from HELlOS-I of the coronal transient observed by Solwind 10 April 1981. At 0.9 AU. the driver gas from this event had reached some 135 degrees in longitude away from its ascribed solar source. Such wide-ranging effects argue for a three-dimensional shape to coronal mass ejections. Shocks are identified at 0912 and 1000 UT on DOY 103, and 0745 and 1950 UT on DOY 106. Data from Schwenn [47]. In light of the Workshop conclusions above that white light transients start earlier than the flare and type II. and that they appear perhaps to be overtaken by the type II (ignoring the foreshock emission model). interplanetary timing is particularly pertinent. Maxwell [33] reported that over the last dozen years, a velocity dichotomy is apparent at the sun. Equating type II burst sources and shocks, Maxwell and Dryer [34] find that swept-frequency records plus model analyses ¶S well as radioheliograph plus coronagraph work provide ~I/shock velocities of 1000 - 2000 km s . Mass motions, on the other hand, show 300 - 1000 km s . These results are consistent with the Workshop conclusion above that the type II is faster than the mass transient, however, Dryer argued that the visible ejecta could be always behind the shock, a view which requires something like the foreshock emission mechanism to make it consistent with observations. Also, if the two groupings of velocities are maintained through the interplanetary medium, the shock would reach 1 AU much earlier than the piston. Such is not observed. Thus Dryer argues for shock deceleration in the solar wind, a position in which he was joined by Schwenn [47]. Howard [25] held a somewhat dissenting view after studying thirteen shocks at HELlOS-I for which a corresponding coronal transient was apparently ident’~fiedin the Solwind field of view. The averaged sun-earth velocity of these events was 400 - BOO km s , based on transit time. These speeds are the same as those tracked by Solwind to 10 R0. For 9 May 1979. the only event with all three speeds measured (coronal, transit time, and shock at 1 AU), the shock at 720 km was comparable to the other speeds. Thus. Howard concluded, no need existed during the maximum of the activity cycle for invoking deceleration in the interplanetary medium. CONCLUSIONS At the final meeting of the SERF Mass Motions Workshop held 26-3 1 October 1981 in Annecy. France, participants reviewed a number of interesting analyses of mass motion events. Several new pictures emerged as a result of the ensuing discussions. The chromospheric and low corona manifestation of mass ejecta is still unclear. Diffuse emission fronts occasionally appear at the proper time and speed to emulate the white light transient. Fe X A6374 filtergrams show transient coronal heating, perhaps by electrons, at the time of prominence eruptions. EUV and X-ray images show similar ejecta as well as the hot footpoints of the outer corona ioop transient. The pressure impulse model seems to be succeeding in reproducing, through the use of numerical MHD codes, a considerable body of the observable behavior of coronal transients and shocks. Realistic energy inputs are currently being utilized from 3MM EUV data.

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The C/P and Solwind groups agreed that, on the same basis, the frequency of high corona mass ejections at the maximum of the solar cycle was about double that at solar minimum. yet, about a factor of two lower than predicted.

Surprisingly. Sawyer et al. [45] find the extrapolated chromospheriC departure tiiiic of the white light mass ejection (even ignoring the still-earlier forerunners) to lead the flare start. Indeed, for five flare-associated events reported by Co-Investigators of the C/P here and in other SERF/SlIP Annecy Workshops, the transient departure time was 5 to 10 minutes before the flare. The single example presented for an eruptive-associated transient showed simultaneous departure with prom-

inence eruption. The conclusion drawn from these observations is that the flare-associated transient is launched from chromospheric levels before the flare starts, or an elevated source for transients must be operating (Figure 6b). much as Jackson [27] conceived for the forerunner. No observations support deceleration in the inner corona. The Mass Motions Workshop had the advantage of reviewing a number of studies which compared simultaneous radioheliograph and C/P coronal observations. For type II radio burst sources, the collection of evidence was that in one event the type II and transient top were cospatial. but in four other cases the type II positions were behind the white light front at some time during the event. Two of these events had faster Ils which passed the transient by 2 R 0, one type II moved orthogonally to the visible event, and no speed information existed for the remaining case. Other evidence for the type II source moving faster than its associated transient was cited in the occasionally-observed jumps in metric-wave dynamic spectra, the measured interplanetary transit times, and analyses using swept-frequency records plus coronal density modeling which typically find the II speeds higher than those of transients. The important conclusions by the Mass Motions group are that, simplistically, the type 11 source (presumably a shock) seems to behave independently of the transient, The shock-led white light transient remains a viable model, however, if the terrestial magnetopause situation is invoked, Here, a foreshock (Figure 9) would cause radio emission “upstream” from the transient pealc or bow, at a location determined by the ambient corona. Sometimes, in the low corona, this location is observed to be at the waist of the transient. The relative locations of the transient peak and the type II source change as the shock/transient proceeds, with radio emission originating from near the bow of the transient higher in the corona. While this is not the first use of the terrestial bow shock analogy (see the review by Wild and Smerd [66]), it is not clear that the workshop conclusions on the location of the radio source are the same as prior models. Some interesting logical choices may follow from the above, If the transient is identified as the shock front, and if the transient starts before the flare, then the shock must start before the impulsive phase. Further, if the transient is accompanied by a shock and that shock is the type II exciter, then something similar to the foreshock emission model is needed to explain the 11 source moving faster than the transient. Conversely, if the transient is not identified with the shock which is assumed to be the type II exciter1 then these reported observations still permit the shock to be simultaneous with the impulsive phase and no foreshock model is required for the type II emission. Moving type IV radio bursts seem explainable today not only by gyro-synchrotron radiation, but quite possibly also by plasma radiation. If observers are recording second harmonic plasma radiation, then a chance still exists to derive magnetic field strength at the source. Unfortunately, none of the recent spacecraft-radioheliograph lVm events shows polarization. At 1 AU, the plasma in the piston from a mass ejection event is generally preceded by a shock. Spacecraft often detect multiple shocks, an effect not predicted heretofore by solar observations. Interplanetary workers seek evidence of a shock deceleration between the sun and 1 AU, a deceleration which is not evident in the corona. Evidence on the shape of transients seemed to favor the three-dimensional bubble over a more planar loop. Polarization studies in white light and the the foreshock model both suggest that a transient has depth in the line of sight. In addition, if disturbances at 1 AU represent the arrival of coronal transients, these are observed in situ as magnetic clouds of 0.25 AU depth by 30 degrees azimuthal extent, certainly not planar. Without invoking a bubble shape, it is also difficult to explain the wide longitude span at 1 AU over which the effects of coronal transients are detected. ACKNOWLEDGMENTS The participants at the Annecy SERF Mass Motions Workshop whose individual work and group discussions provided the material for this report were the following: J. Arnaud (Pic du Midi Observatory), F. Crifo (Meudon Observatory). M. Dryer (NOAA/ERL). G. Dulk (Colorado U.), D. Gary (Colorado U.). T. Gergely (U. of Maryland), L. House (High Altitude Observatory/NCAR), H. Howard (U.S. Naval Research Labs), B. Jackson (U. Calif. San Diego). A. Kerdraon (Meudon Observatory). M. McCabe (U. of Hawaii). S. McKenna-Lawlor (St. Patrick’s College). S. Martin (San Fernando Observatory). A. Maxwell (Harvard College Observatory), P. Mein (Meudon Observatory). M. Pesses (Goddard Space Flight JASR 2/11—0

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Center/NASA). M. Pick (Meudon Observatory). E. Priest (Si. Andrew’s University), B. Rompolt (Warsaw Observatory), C. Sawyer (High Altitude Observatory/NCAR), R. Schwenn (Max Planck Institute for Aeronomy) C. Simnett (U. of Birmingham), R. Smartt (Sacramento Peak Observatory), H. Stewart (CSIRO Radiophysics Division), E. Tandberg-Hanssen (Marshall Space Flight Center,’NASA), H. Urbarz (Weissenau Radio Observatory). C. D’Uston (U. of Toulouse). 0. Vaisberg (U.S.S.R. Space Research Institute), L. Vlahos (U. of Maryland), W. Wagner (High Altitude Observatory/NCAR), and S. Wu (U. of Alabama). To the above group, the author apologizes for any mis-quotes or omissions which may have occurred. That progress was made in understanding mass ejections and their relation to flares is due principally to the diplomacy of David Rust who provided the impetus forcing together research groups in his role as SERF’ Organizer and SMM Observatory Coordinator. E. Hildner served as chairman of the Mass Motions team at the original Cambridge meeting (Emslie and Rust [11]) which set the goals and definitions of this study. The author is grateful to S. Migliuolo for helpful comments on the Ioreshock model and to G. Dulk for reviewing the radio data. The forebearance and global view of L. House, Principle Investigator for the C/P. provided time for the coronagraph team to participate in this consortium effort, perhaps at the expense of individual C/P experiment studies. Support which allowed the author to attend the various Workshops was generously provided by the French Ministry of Foreign Affairs, by the Soviet Academy of Sciences, and by NASA Contract S55989 with the High Altitude Observatory. REFERENCES (i) E. Antonucci, A.H. Gabriel. and J.G. Doyle, B.A.A.S. 12, 900 (1980) (2) U. Anzer. Solar Phys. 57, 111 (1978) (3) A. Boischot, and J.F.Denisse, Corr&pt. Rend. Acad. Sci. Fhris 245 2194 (1957) (4) L Burlaga, E. Dittler, F. Mariani, and H. Schwenn, J, Geophys. Res. 86, 6673 (1981) (5) F. Crifo. J.P. Picat, M. Cailloux. Submitted to Solar Phys., (1982) (6) M. Dryer, Workshop communication (1981) (7) M. Dryer, to appear in Space Sci. Rev. (1982) (8) M. Dryer, this volume (1983) (9) G.A. Dulk, in Radio Physics of the San (ed. M. Kundu and 1. Gergely), 419 (1980) (10) G.A. Dulk, Workshop communication (1961) (11) A.G. Emslie, and D.M. Rust, Solar Thys. 65, 271 (1980) (12) R.R. Fisher, private communication, to be published (1981) (13) RH. Fisher, R.M. MacQueen, and A.I. Poland, App!. Optics 20, 1094 (1981) (14) D. Gary, Workshop communication, to be published (1981) (15) 0. Gary. to be published (1982) (16) T.E. Gergely, Workshop communication (1981) (17) T.E. Gergely, M.R. Kundu, F.T. Erskine, C. Sawyer, W.J. Wagner, H. Illing, LL House, M.K. McCabe, RI’. Stewart and Nelson. C. J. B.A.A.S. 12, 900 (1980) (18) E. Hildner, J.T. Gosling, RM. MacQueen, RH. Munro. LI. Poland, and C.L. Ross, Solar Thys. 48, 127 (1976) (19) E. Hildner. in Studies of Traveling Interplanetary Phenomena (ed. M. A. Shea, et al.. Dordrecht: 0. Reidel), p. 3. (1977) (20) G.D. Holman. and M. Pesses, to be published (1982) (21) M.M. Hoppe. C.T. Russell, LA. Frank, T.E. Eastman, and E.W. Greenstadt, J. Geophys. l~bs.86, 4471 (1981) (22) LL. House, Workshop communication (1981) (23) LL. House, W.J. Wagner. E. Hildner. C. Sawyer. H.U. Schmidt, Astrophys. J. 244, L117 (1981) (24) L.L. House. C. Sawyer. R.M.E. filing and W.J. Wagner, to be submitted to Astrophys. J. (1982) (25) R.A. Howard. Workshop communication (1981) (26) B.V. Jackson and E. Hildner, Solar Phys. 60. 155 (1978) (27) B.V. Jackson, Solar Phys. 73, 133 (1981) (28) M. Machado. Solar Phys. 60. 341 (1978) (29) R.M. MacQueen. l.A. Eddy, J.T. Gosling, E. Hildner. R.H. Munro, G.A. Newkirk, Jr., A.I. Poland and C.L. Ross, Astrophys. J. 187. L85 (1974) (30) R.M. MacQueen, Ph-il. fraim.s. R. Soc. Lond. .4297605(1980) (31) R.M. MacQueen. A. Csoeke-Poechk. E. Hildner, L.L. House, R. Reynolds. A. Stanger, H. TePoel. and WI. Wagner. Solar Phys. 65, 91 (1980) (32) S.F. Martin, B.A.A.S. 10. 462 (1978)

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(41) (42) (43) (44) (45) (46) (47) (48)

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A. Maxwell, Workshop communication (I 981) A. Maxwell and M. Dryer, Solar Physics 73, 313 (1981) S. McKenna-I,awlor, this volume (1983) P. Mom. Solar Phys~54, 45 (1977) P. Mein and N. Mciii, to appear in Solar I’hys. (1982) R.H. Munro, J.T. Gosling, E. Hitdner, R.M. MacQueen. Al. Poland. C.L. Ross. Solar I’hys. 61. 201 (1979) G.J. Nelson, private communication (1981) V.N. Obridko, in Solar Afaximura Year I (ed V.N. Obridko) (1982) M. Pesses, Workshop communication (1981) M. Pesses, this volume (1983) G.W. Pneuman. Solar Phys. 65. 369 (1980) 1. Ryan. private communication (1982) C.S. Sawyer, this volume (1962) C.S. Sawyer, L.L. House, R.M.E. filing and W.J. Wagner, Workshop communication, to be published (1982) R. Schwenn. Workshop communication (1981) C. Simnett. Workshop communication (1981)

(49) (50) (51) (52) (53)

R.N. Smartt, RB. Dunn and R. R Fisher, Proc. Soc. Photo-Optical Jnstru. Erigrs. 288. 395 (1981) R.N. Smartt. Workshop communication, to be published (1982) S.F. Smerd, K.V. Sheridan. R.T. Stewart. Astrophys. Letters 1623 (1975) D. Spicer, private communication (1980) R.T. Stewart, F.A. Dulk, K.V. Sheridan, LL. House, W.J. Wagner, C.S. Sawyer, and R. liling, to appear in Astron. and Astrophys. (1982) (54) R.T. Stewart, this volume (1982) (55) E. Tandberg-Hanssen, R.G. Athay. J.M. Beckers, J.C. Brandt, E. C. Bruner, R.D. Chapman, C.C. Chang, J.B. Gurman, W. Henze, C.L. Hyder, A.G. Michalitsianos, R.A. Shine, S.A. Schoolman, B.E. Woodgate, Astrophys. .1. 244, L127 (1981) (56) H. Tousey, The Solar Corona (in Space Research XIII, M.J. Rycroft and S.K. Runcorn, ed.). p. 713 (1973) (57) G. Trottet and RM. MacQueen. Solar Thys. 88, 177 (1980) (58) C. Trottet, A. Kerdraon, A.0. Benz and R. Treumann, Astron. and Astrophys. 93, 129 (1981) (59) H. Urbarz, Workshop communication (1981) (60) 0. Vaisberg, Workshop communication (1981) (61) W.J. Wagner. E. Hildner, L.L. House, C. Sawyer. K.V. Sheridan and G.A. Dulk, Astrophys. J~244, L123 (1981) (62) W.J. Wagner, R.M.E. Illing, C.S. Sawyer, LL House. N.H. Sheeley, Jr., R.A. Howard, M.J. Koomen, D.J. Michels. R.N. Smartt and M. Dryer, submitted to Solar Phys. (1982) (63) W.J. Wagner, Ann. Rev. Astron. and Astrophys. 21, to be published (1983) (64) D.F. Webb, C.-C. Cheng, GA. Dulk, S.J. Edberg, S.F. Martin, S. McKenna-Lawlor, Di. McLean, in Solar Flares: A Monograph from. the ,9cylab Solar Workshop I/(ed. P. Sturrock), p. 471. Boulder: University of Colorado Press. (1979) (65) Y. Uchida. M.D. Altschuler and G. Newkirk, Jr., Solar Phys. 28, 495 (1973) (66) J.P. Wild and S.F. Smerd, Ann. Rev. Astron. and Astrophys. 10, 159 (1972) (67) S.T. Wu, S. Wang, M. Dryer, LI. Poland, D. Sime. C.J. Wolfson and LE. Orwig, B.A.A.S. 13862 (1961)