SMITHSONIAN

CONTRIBUTIONS

to

ASTROPHYSICS

Smithsonian Institution

Astrophysical Observatory

Volume 8, Number 2

The Relative Positions

of Sunspots and Flares

by John G. Wolbach

Washington, D.C.

Smithsonian

Contributions to Astrophysics

VOLUME 8, NUMBER 2

THE RELATIVE POSITIONS

OF SUNSPOTS AND FLARES

by JOHN G. WOLBACH

i

SMITHSONIAN INSTITUTION

Washington, D.C.

1963
Publications of the Astrophysical Observatory

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Smithsonian Institution.

Cambridge, Mass.

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington 25, D.C. - Price 20 cents
The Relative Positions of Sunspots and Flares

John G. Wolbach

It is well known that solar flares occur near

sunspots, usually within the area of the surrounding calcium plage. There is very little

detailed information, however, on the relative

location of sunspot and flare elements within

an active region. This paper presents a study

of 11 actively flaring sunspots and the positional

relation between flare and spot elements. Nine

of the sunspots occurred in 1950, two in 1955.

Current attention to flares associated with

polar cap absorption (PCA) and ground-level

cosmic-ray events lends particular interest to

this question of flare-spot positional relationships. Dodson and Hedeman (1960) noted a

conspicuous difference in the location of two

importance-3 flares occurring on 16 July 1959,

one with and one without intense type-IV radio

emission and a PCA. Ellison, McKenna, and

Reid (1961) have presented evidence that

cosmic-ray flares characteristically cross and

obscure one or more spot umbras of high

magnetic-field strength, but little information

is available about the extent to which noncosmic-ray flares may also obscure spot umbras.

From the present data an estimate is made of

the frequency with which a flare may be expected to cover a spot umbra.

Observational data

Daily maps of the solar disc, 40 cm in diameter,

from drawings made routinely at the 150-foot

tower telescope of the Mount Wilson Observa1

 Harvard College Observatory, Cambridge, Mass.

tory, provided the data on sunspots and calcium

plages. The flare observations in the form of

35-mm time-lapse photographs of the solar disc

in the light of Ha for 1950 came from the

High Altitude Observatory and for 1955 from

the Sacramento Peak Observatory. I combined

the data by projecting the Ha film onto the corresponding Mount Wilson map and drawing the

flares on the map. Using additional sunspots

and the sun's limb, I was able to superimpose

the projected image with sufficient accuracy to

show the relative positions of the flares with

errors small relative to the dimensions of the

sunspots.

The elevation of a flare above the surface of

the sun introduces into the determination of

its position an error that increases with distance

from the center of the solar disc. To investigate this error, working both from maps of some

of the spots presented here and from maps of

additional spots near the limb, I traced on a

single diagram as many spot-flare maps as

possible. The flares showed foreshortening,

and up to about 75° from the sun's central

meridian (CM) there was no obvious concentration of flares on the limbward side of the

spots. For spots at 80° from the CM, the

flares extended to the limb and beyond and did

appear to concentrate on the limbward side of

the spot. Foreshortening did not appear to

increase beyond 80°, probably because at this

distance the apparent areas arise in part from

the vertical extent of the flare.

101
102 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

FIGURE 1.—The apparent displacement of a flare owing to its height above the solar surface: a= angular distance of flare F and

spot S from center of disc. The sightline EF from the earth cuts disc at A so that the flare appears to be at an angular distance a' from the sun's center. The angle e is formed by the sightlines EF and EO to the center of the sun's disc.

From the quantities diagrammed in figure 1,

the height h=SF and apparent displacement

6= (a'—a) are related by the expression

&_sin (a'—e)— sin

R sin (a-\-e) (1)

For practical purposes the angle e may be

neglected; and for small 8, equation (1) may be

written as

n«-zr-f-S cot aIt £,

(2)

We have noted that the displacement of

flares toward the limb becomes apparent at

about 80°. From this fact, employing a'=90°

and a=80°, we obtain a flare height of 10,000

km. This procedure, of course, gives only an

order of magnitude.

J. W. Warwick (1955) found the most frequent height of flares to be less than 10,000

km and obtained a smooth distribution of

flare heights up to 70,000 km. His values were

determined statistically from measurements of

flare area at different distances from the sun's

center. C. S. Warwick (1955) found similar

heights from a study of limb flares. J. W.

Warwick also determined that the sides of the

flare contribute to the area, thus explaining the

lack of foreshortening of the flare area very

near the limb.

A few flares that had a noticeable appearance

of extreme vertical extension were omitted from

the analysis. All those discussed here were

within 63° of the CM. Statistical results presented below indicate that flaring occurred

preferentially in the following component of

sunspot groups, whether this component was

toward or away from the CM. Since about an

equal number of flares occurred east and west

of the CM, no systematic errors should be

introduced into the statistics by flare heights,

although sometimes the height may have caused

considerable error.

Figures 2 through 12 show schematically the

composite spot-flare and magnetic diagrams for
RELATIVE POSITION OF SUNSPOTS AND FLARES WOLBACH 103

each of 11 spot groups. In each case, all the

observed activity of a given spot group has been

projected to the center of the disc. I made

both sections of the diagrams for a given spot

group by superposing each day's observations of the main umbras on the center of the

disc. Other features—penumbras, flares, and

lesser umbras—for each day were oriented on

the composite diagram about the position of

the principal umbra. The appropriate Stonyhurst disc was used to estimate the foreshortening and the relative positions of these features

at the center of the disc. Any area that was

occupied by an umbra on one or more days is

shown on the composite map by dense dots.

If a region was occupied by penumbra on one

day and umbra on another day, it is shown as

umbra, but if it was occupied by flaring at any

time, the flaring is shown in preference to either

umbra or penumbra. The composite map thus

aims to provide a general picture of the locations

of each type of activity during the disc passage

of the spot group.

The upper section of the composite diagram,

showing the data on magnetic field strengths

and polarities (underlined) was made in the

same way, with the lesser elements positioned

relative to the superposed main elements. The

location of a measured field strength is marked

by a small circle. To simplify the diagrams,

clusters of small circles were enclosed by a line,

with only the average field strength of the elements given. Southern polarities are distinguished by underlining. Figures 2 and 3 do not

have adequate magnetic diagrams because of

insufficient data.

Table 1 summarizes information on the 11

sunspots.

Discussion of observations

Before figures 2 through 12 are discussed, it

would be useful to review the Mount Wilson

classification of sunspots according to their

magnetic properties (Hale and Nicholson, 1938).

This classification recognizes four basic categories of sunspot groups: unipolar (a), bipolar

(/3), semicomplex (0y) and complex (7). Unipolar (a) groups are single spots or clusters of

spots having the same magnetic polarity. If

the unipolar cluster lies in the preceding or

following part of its plage the classification is

ap or af, respectively. (The terms preceding

and following are defined with reference to the

rotation of the sun, so that the preceding comFigure

no.

2

3

4

5

6

7

8

9

10

11

12

Mount

Wilson

no.

10359

10324

10434

10350

10303

10344

11267

11266

10384

10332

10373

TABLE 1.—Summary of data on 1

CMP date

1 June 1950

3 May 1950

4 Aug 1950

26 May 1950

13 April 1950

22 May 1950

7 July 1955

5 July 1955

25 June 1950

12 May 1950

15 June 1950

Latitude

5 S

14 N

10 S

8 N

15 N

17 S

32 N

34 S

9 N

6 N

18 S

Avg.

mag.

class

dpi

lyl

Wyl

Wpl

lyl

lapd

Wpl

lapl

dppl

lapl

Wpl

Max.

field

strength

2000

2200

3400

3600

4200*

3000*

2500

2600

4200*

3800

3600

t selected flaring spots

Avg.

area

302

615

770

924

1527

65

193

222

373

511

913

Max.

area

549

1119

1126

1115

2000

116

305

357

631

821

982

Total

flares of

importance

1 2 3

21 4 -

14 7 -

34 7 -

35 6 -

44 8 3

10 2 -

25 1 —

10 1 —

14 2 -

15 7 -

16 2 -

Climax

and Sacramento

Peak

flares of

importance

1 2 3

4 1 —

5 1 —

21 5 —

15 1 —

25 2 3

5 2 —

16

10

5 2 —

8 3 —

7 2 —

Magnetic

regions

b-b

b-c

b-c

c-b

b-c

b-c

b-a

b-a

b-b

b-a

b-a

•Dr. Seth Nicholson reports that these field strengths are probably too high, perhaps by as much as a factor of 2.
104 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

ponent of a spot group is the part first to become visible at the east limb, to cross the CM,

etc.) Bipolar groups in their simplest form

consist of two spots of opposite polarity;

often, however, a bipolar group is a stream of

spots, those in the preceding and those in the

following clusters having opposite polarities.

The group is called 0 if the two clusters are of

approximately equal size. If the preceding or

following cluster dominates, the classification is

fip or j8/, respectively. The complex y groups

have polarities so irregularly distributed that

they cannot be classed as bipolar; the polarities

may be mixed even within a single penumbra.

The fiy groups have bipolar characteristics but

lack the /3's clearly marked division between

regions of opposite polarities; the preceding or

following cluster may contain small spots of the

"wrong" polarity. The fiy and y groups have

been shown to produce a disproportionately

large percentage of solar flares (Giovanelli,

1939; Bell and Glazer, 1959).

Figures 2 through 6 show the complex sunspots form 0 to 7, while figures 7 through 12

show those of simpler magnetic configuration.

In each case the preceding cluster is projected

to the center of the disc. Although ap and

some fip groups have only small spots to define

the position of the following component during

the transit, this region is well defined by flare

activity. For /3 and 0y groups the following

region is well occupied by substantial spots.

When, as in figures 2 and 3, the spotted and

flaring regions intermingle, it is because of the

drifting of spots within these groups. The

spot and flare regions tend to be well separated

when there is less activity and drifting of the

spots. In the figures both simple and complex

groups are presented in order of increasing size

to emphasize the more defined separation of the

spot and the flare regions as the size of the complex spot groups increases. While this trend is

not statistically significant because of the small

number of spots, it seems worth noting in view

of the spot-flare relationships associated with

cosmic-ray flares (discussed in the concluding

section).

Examination of figures 2 through 12 shows

that nearly all sunspot and flare activity during

the transit occurred in an area only one-fourth

to one-half as great as the total areas occupied

by the calcium plage on one or another day.

Occasionally a large flare may extend to the

limits of the plage, leaving the flaring region

asymmetrical. The composite plage with its

peninsular variations is more extended in longitude than in latitude and is roughly symmetrical

about an east-west axis that extends through

the preceding and following component clusters

of the spot group. In a /3 or y group the

spotted area is similarly extended in longitude.

The flaring area is external to the spots and

often appears to curl about them symmetrically.

Apparent penetration of the spot clusters by

flares can be seen when flaring on one day occupied space in the region that on another day

was occupied by sunspots. Less often a flare

apparently covered a sunspot.

In ap spot groups the position of the following

cluster, often marked by small transient spots

of opposite polarity, seems a favored location

for flaring. Other flares, appearing as curved

filaments, surround the main spot cluster or

even partially invade it. In bipolar and complex groups the flares tend to surround the spot

clusters.

Magnetic regions

Examination of the composite magnetic diagrams reveals further spot-flare relationships

that can be most readily described by a classification of magnetic regions within sunspot

groups as follows: a regions containing only

weak fields, usually of both polarities and including the boundary separating them; b regions in which one polarity is represented by

strong magnetic fields of a major umbra in

either the preceding or the following component,

the other polarity being represented at most by

weak fields of small transient spots; c regions

containing strong magnetic fields of both polarities in the same cluster, often within the same

penumbra, and usually found only in fiy and y

spot groups.

A given spot group will contain at least one,

and usually two magnetic regions, which can

be recognized on the magnetic composite dia-
RELATIVE POSITION OF SUNSPOTS AND FLARES—WOLBACH 105

10359

LEGEND

PENUMBRA

UMBRA

FLARE REGIONS! DAY

FLARE REGIONS Z DAY

FLARE REGIONS 4 DAY

0,

ft/

FIGURE 2.—Spot 10359, dpi. All flaring originates from b regions. Magnetic data are inadequate for analysis. Considerable

activity of drifting, merging, and breakup of spot components resulted in intermingling of spot and flare regions, and a

scattered appearance of the umbras on this composite diagram. Legend also applies to figures 3-12.
SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

FIGURE 3.—Spot 10324, / 7/ . Most of the flaring is centered in the c region (center of the diagram). The drift, merging, and

breakup of spots in this region produces interpenetration of flares as in figure 2. (The small spots to the right are another

group.)
RELATIVE POSITION OF SUNSPOTS AND FLARES WOLBACH 107

FIGURE 4.—Spot 10434, I fiy I . Flaring occurred almost equally in the b and c regions. The preceding cluster, at first a b region, became a c region and broke into pieces, separating its northern and southern magnetic polarities. A bridge of sunspots

of southern polarity developed from the following to the preceeding cluster, producing an east-west boundary between polarities. Distribution of spots then produced a b region, and a- c region extended from the following component into the northeast of the preceding component.

680448 O—63 2
SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

FIGURE 5.—Spot 10350, Iffpl. For the first three days this spot was /37, with a c and a b region, the former responsible for

most of the flaring. Spots of northern polarity that extended into the preceding position intermingled with those of southern

polarity. Magnetic measures are few. A few spots drifted to the preceding end of the plage as the intruding north polarity

died out. The spot then became 0p, with the two polarities well separated, and little flaring occurred during the rest of the

transit.
RELATIVE POSITION OF SUNSPOTS AND FLARES—WOLBACH 109

FIGURE 6.—Spot 10303, I y I. Most of the flaring surrounds the following component, in the c region. The fields of southern

polarity were declining in this component toward the end of the transit.
110 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

FIGURE 7.—Spot 10344, / apd. For two days the central area is classified as a c region because umbras up to 2500 gauss of both

polarities existed in the same penumbra (although Mount Wilson called it 0p). Most of the flaring occurred in the c region. The southern polarities disappeared by central meridian passage, and the spot group then became ap with a single b

region and little flaring.
RELATIVE POSITION OF SUNSPOTS AND FLARES—WOLBACH 111

FIGURE 8.—Spot 11267, I0pl . The larger preceding component grew and spread into a spot stream. The following component, a recurring transient small spot, lay in an a region. The majority of the flaring occurred in the b region.
112 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

TABLE 2.— The usual relation between Mount Wilton

sunspot classes and types of magnetic regions in the

preceding and following parts of the plage

FIGURE 9.—Spot 11266, laf I. The principal flaring occurred in the a region. The preceding cluster (b region)

remained stable during transit. Only small transient spots

occurred in the following a region.

grams. Table 2 shows the usual relations between these magnetic regions and the Mount

Wilson classes of sunspots.

After classifying the magnetic regions by

means of the composite diagrams, I re-examined

the daily maps and assigned a daily classification to the magnetic regions of each spot group.

Some cases had to be omitted because of insufficient magnetic data. In 64 of 70 observing

days, my classification was related to the

Mount Wilson class as shown in table 2. In

the remaining six cases, I assigned a c classification to regions in sunspots listed as (3p by

Mount Wilson. According to explanations in

the Publications of the Astronomical Society of

the Pacific for 1920-1927, when the preceding

or following cluster contains a small spot of

opposite polarity that plays a transient minor

Mount

Wilson

class

a

ap

«f

Pp

PP

P

Pf

Pf

py, y

Type of magnetic

region

Preceding

b

a

b

b

b

b

a

b or c*

Following

b

a

b

a

b

b

b

b

b or c*

* th has at least two regions, y at least one region, of which one ore

more is a e, the other a 6 type region. The position in the plage Is not

relevant.

part in the cluster the Mount Wilson classification disregards it. However, in the six cases I

found a spot of sufficient field strength and

closeness to the main umbras such as to demand a c-region classification.

For each flare day I determined which magnetic region (of the two in the spot group) had

the greater flare area. In most cases the choice

was obvious. Table 3 gives the number of

Table 3.—Number of days on which flaring occurred

preferentially in magnetic regions of type a, b, and c;

and the probability P that the observed differences are

due to chance

Mount

Wilson

class

ap

PP

Total

PP

P

Total

All classes

Magnetic

regions

b-a

b-a

b-a

b-c

b-c

b-c

b-c

No. of days on

which flaring

favored

magnetic

regions

a b c

8 1

7 4

15 5

1 3

1 11

0 5

2 19

b a,c

7 34

P

0.02

0.4

0.03

0.3

0.004

0.024

0. 0002

0.00003
RELATIVE POSITION OF SUNSPOTS AND FLARES—WOLBACH 113

FIGURE 10.—Spot 10384, dppl. Flaring surrounds both spot clusters. The spot grew during transit, and the separation of the

components increased.
114 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

FIGURE 11.—Spot 10332, la.pl. The principal flaring occurred in the a region, occupied by only transient spots. Some flaring

encircles the forward end of the b region and covered a small part of the main umbra.
RELATIVE POSITION OF SUNSPOTS AND FLARES—WOLBACH 115

FIGURE 12.—Spot 10373, / fip I. Most flaring occurred in the a region around the small spots of mixed polarity to the northeast of the major component. The small spots of southern polarity at the following end of the plage have little flaring

importance.
116 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

days on which each of two types of magnetic

region contained a clear preponderance of flare

activity. On the assumption that each region

had an equal probability of being the more

flare-active each day, I computed the probability P that the flare distribution observed

between each pair of regions was due to chance.

The standard deviation is given by a=^Jnpq,

where p=q=0.5, and n is the total number of

flare days; the observed deviation from a uniform distribution is k—n/2, where k is the

number of days on which the flares favored the

more active region. From the ratio of the

observed to standard deviation and a table of

the normal curve of error I determined the

values of P in table 3.

Table 3 shows, even with the small amount

of data, that the main area of flaring tends to

occur with statistically significant preference

in zones of mixed polarities, that is, in c and a

regions. When magnetic regions b and c were

present, the flaring occupied the c region with

striking preference, tending to surround the

spot cluster with the mixed polarities. With

the a and b configuration, when the daily class

of the spot group was ap, the flaring tended to

prefer the a region with borderline significance.

With /8p spots the difference between a and b

regions is not statistically significant.

Within a c or a region the boundary separating the polarities of opposite sign appeared

a favored location for flaring. However, the

boundary between two b regions of opposite

polarity, as between the components of a /3

spot group, did not appear to be a favored

location for flaring. In /3 groups the fl»ring

seemed to surround the spot clusters rather

than occupy the region between them. Spot

components of a single polarity were often

surrounded by flares, except when a c region

was present. In one case (spot no. 10434,

fig. 4) when the 6-type lead cluster was surrounded by bright flares, it became a c region

on the next day as portions of the disintegrating

follower spot drifted into the lead component

and became an integral part of it. Probably

the preference of flaring for c regions is real and

may be related to the greater flare productivity

of complex spots found by Bell and Glazer

(1959).

I attempted to correlate flaring with change

or disappearance of magnetic and visual configurations, including the transformation from

a c to a 6 field. The data were too few for

meaningful results.

With additional data I looked for a relation

between flare activity and spot activity as

manifested by a change in the Mount Wilson

magnetic class. From the Greenwich (1954)

list of spots with average area greater than

500 millionths of the visible hemisphere, I

selected those in the years 1946 through 1957

which, according to the I.A.U. Quarterly

Bulletin oj Solar Activity, produced at least

10 flares. Of these I retained only the 47 that

showed one or more major changes in the daily

magnetic classification. A major change was

one from simple (a or 0) to complex (0y or 7),

or vice versa. I divided the flare days into two

main groups: (1) pairs of days between which

a change of magnetic class occurred, and (2)

the remaining days on which the magnetic

classification was steady. I determined the

average number of flares per day for a, /3, and 7

spots when the classification was steady, and

the average number of flares per day on the

pairs of days bracketing a change from /8 to 7,

and so on. The steady 7 classification produced more flares per day than any changing

or less complex classification. The greater

flare productivity of the 7 class was most

striking for importance-2 and especially for

importance-3 flares. The data provided no

evidence that a change in the magnetic class is

accompanied by an outburst of flaring.

Frequency of umbra coverage and cosmic-ray

flares

Evidence presented by Dodson and Hedeman

(1960) and by Ellison, McKenna, and Reid

(1961) that cosmic-ray flares may characteristically cover a large spot umbra led me to

examine my data in an effort to estimate the

frequency of this phenomenon. Is the coverage

of a large umbra a rare or a common event?

The cosmic-ray flares discussed by these

writers are of importance 3 and 3 +; most of

them were followed by a great magnetic storm;

and the more recent of them have been found

to be associated with a radio noise outburst of
RELATIVE POSITION OF SUNSPOTS AND FLARES—WOLBACH 117

exceptional intensity. By contrast, the flares

discussed here are mostly of importance 1 and

of little or no geomagnetic significance. Only

one flare (22 May 1950) was followed within

three days by even a small geomagnetic storm.

Table 4 gives data on the frequency with

which elements of flares in my sample covered

a spot umbra, divided according to the importance of the flare and the area of the umbra.

TABLE 4.—Number and percentage of flares extending

over a sunspot umbra

Flare

importance

3

2

1

1,2,3

No.

3

14

120

137

No. of flares

extending over

Maior Small

umbra umbra

1 1

3 1

2 1

6 3

Doubtful

cases

4

4

8

Percent of flares

extending over

Major

umbra

33

21

2

4

Small

umbra

33

7

1

2

Doubtful

cases

29

3

6

Umbras with an area over 20 millionths of a

hemisphere were called large; those between 10

and 20 millionths, small. Umbras of less than

10 millionths were ignored. The data indicate

that umbra coverage by importance-1 flares is

relatively rare, but that it may be fairly common

among more important flares. However, flares

of importance 2 and 3 are too few to permit

definite conclusions.

While umbra coverage by the more important

flares may be common, there is a marked difference between the pattern observed in my

sample and that described by Ellison el al.

The cosmic-ray flares appeared as broad,

elongated, curved, and sometimes double filaments. In the Ellison paper, tracings of the

axes of the flare filaments on Mount Wilson

magnetic maps of the sunspots show that the

main body of the flares passed directly over

one or more major umbras of the spot group.

The flare elements were elongated in a direction

roughly paralleling the boundary between the

north and south polarities.

On the other hand, all the coverings listed

in table 4 were accomplished by only a small

segment of the flare whose main body lay outside the penumbra of the spot. I found no

case in which the main body of the flare lay

over a major spot component in the manner of

the cosmic-ray flares, an indication that these

may be a rather rare configuration.

My observations of spot coverings resembling

those described by Ellison et al. appeared in

the a regions, where flares often crossed directly

over small (<10 millionths) spots, and lay

along the boundaries separating opposite polarities. Larger spot components, whether

centers of b or c regions, were surrounded

rather than covered by flares. The flares

curved around the spots, occasionally projecting

over an umbra. Sometimes an isolated fragment of a flare would lie across a portion of a

spot. Since most of the c regions were occupied

by flares, the associated sunspot of y or (3y type

was most likely to be thus partially covered.

I found five flares that had the form of a

double filament, but none passed over the main

body of a spot. Only one was followed by as

much as a small geomagnetic storm.

Six of the seven cosmic-ray spots had areas

similar to those in figures 5 and 6, while the

spot of July 1946 had an area in excess of 4000

millionths on the flare day. With the exception

of the November 1949 spot, which was /3f, all

the cosmic-ray spots have been y or JST- It is

noteworthy that most of the cosmic-ray spots

maintained their magnetic type unchanged

during their disc passage, in contrast to the

variability of the 11 spots studied here. A

study of flare positions in steady spots is needed

to determine whether such spots are also likely

to be encircled rather than invaded by importance-2 and importance-3 flares. Also the

cosmic-ray flares were all importance-3+, in

contrast to the lesser importance of those with

the glancing coverage here described.

In conclusion, it would appear that the umbra

coverage seen in cosmic-ray flares may represent

a striking singularity of solar activity. Although

chosen for flare activity, the spots investigated

here presumably give a more representative

picture of spot-flare relationships.

Acknowledgments

This work was started in the summer of 1956

while I was a guest investigator at the National
118

SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

Bureau of Standards, Boulder, Colo.; it was completed at Harvard under the sponsorship of contracts AF19(6O4)-146, -1394, and -i962 with

the Geophysics Research Directorate of the

Air Force Cambridge Research Laboratories,

Office of Aerospace Research.

I am indebted to Dr. Walter O. Roberts,

director of the High Altitude Observatory, and

to Dr. John W. Evans, director of the Sacramento Peak Observatory, for the use of their

flare films; and to Dr. Roberts also for the

opportunity to use the excellent film projection

facilities at the High Altitude Observatory.

Through the cooperation of Mrs. Marion Wood

Haurwitz the Mount Wilson maps were obtained from copies on file at the National

Bureau of Standards. Dr. Seth B. Nicholson

kindly provided me with the daily magnetic

classifications of the sunspots. Dr. James W.

Warwick and Dr. Constance S. Warwick gave

generous encouragement to this work. I especially thank Dr. Barbara Bell for valuable

suggestions in the preparation of the final

manuscript.

References

BELL, BM and GLAZEB, H.

1959. Some sunspot and flare statistics. Smithsonian Contr. Astrophys., vol. 3, no. 4,

pp. 25-38.

DODSON, H. W., and HEDEMAN, E. R.

1960. Flares of July 16, 1959. Astron. Journ.,

vol. 65, p. 51.

ELLISON, M. A.; MCKENNA, S. M. P.; and REID, J. H.

1961. Cosmic ray flares. Dunsink Obs. Publ.,

vol. 1, no. 3, pp. 53-88.

GlOVANELLI, R. G.

1939. The relations between eruptions and sunspots. Astrophys. Journ., vol. 89, pp.

555-567.

GREENWICH, ROYAL OBSERVATORY

1955. Sunspot and geomagnetic-storm data, 1874-

1954. Her Majesty's Stationery Office,

London, 107 pp.

HALE, G. E., and NICHOLSON, S. B.

1938. Magnetic observations of sunspots. Carnegie Inst. Publ. no. 498, 692 pp.

WARWICK, C. S.

1955. Flare height and association with SID's.

Astrophys. Journ., vol. 121, pp. 385-390.

WARWICK, J. W.

1955. Heights of solar flares. Astrophys. Journ.,

vol. 121, pp. 378-384.

Abstract

This paper describes a study of 11 flaring sunspots, for which on flare days the relative positions of flares and

sunspots have been determined from data provided by the Climax and the Mount Wilson Observatories. For each

spot group all data, including the magnetic polarities and field strengths, were projected to the center of the sun's

disc and combined.

The maps show that flaring tends to prefer regions containing both polarities rather than unipolar areas within

a spot group. The favored zone may be a spot cluster containing both polarities, as within fly and y groups, or a

region occupied by transient spots of both polarities, as in the following component of some fip and ap groups.

Statistical analysis shows that flares preferred these regions more often than would be expected by chance.

A supplementary investigation including additional sunspots revealed no correlation between frequency of flaring

and internal spot activity such as the breakup or merging or small components.

A count of spot umbras covered by flares was made. About 10 percent of the flares show clear or possible

coverage of some part of a spot umbra. The flares observed here covered the spots only partially or along the edges,

a positional relation markedly different from that found by Ellison et al. for cosmic-ray flares where the main body

of the flare passed directly over the sunspot.

U.S. GOVERNMENT PRINTING OFFICE: 1963 O—680448