NEWKIRK, G.,
R. T. HANSEN and
S. HANSEN

NORTON, R. He,

J. E. GUNN,

W. C. LIVINGSTON,
G. A. NEWKIRK and
H. ZIRIN

PERRY, R. M.

PRICE, S., and
J.C. PALES

WLERICK, G., and
J. AXTELL

1968

1967

1967

1963

1957

Coronal Electron Densities during the Period
of the July 1966 Proton Flare, Annals of the
IQSY, 3, 49-62.

Surveyor I Observations of the Solar Corona,
J.G.R., 72, 815.

Variation in the Appearance of a Coronal
Streamer with Solar Rotation, A. G. Memo
No. 175, High Altitude Observatory, Boulder,
Colorado.

Mauna Loa Observatory: The First Five Years,
Monthly Weather Review, 91, 665.

A New Instrument for Observing the Electron
Corona, Astrophys. J., 126, 253.

- 10 -



OBSERVATIONS OF THE SOLAR ELECTRON CORONA: FEBRUARY 1964 - JANUARY 1968

by

Richard T. Hansen
High Altitude Observatory
Boulder, Colorado and Kamuela, Hawaii

1. OBSERVATIONS

The purpose of this report is to summarize briefly the work with the
High Altitude Observatory's K-coronameter during the period July 1963 to
January 1968. Earlier observations with the same instrument, then operated
at Climax, Colorado, are reproduced in the following publications of the
IGY Solar Activity Data Center:

Report No. 4 by G. Newkirk, Jr., G. W. Curtis and K. Watson
for the period September 1956 - January 1958 (38 days data);

Report No. 16 by Chr. E. Heynekamp for the period January 1958 -
November 1960 (132 days data).

During the summer of 1963 the observing program with the instrument at
Climax was discontinued and in September of that year the K-coronameter was
installed in the Mees Solar Laboratory of the Hawaii Institute of Geophysics's
Haleakala Observatory as a collaborative program between the University of
Hawaii and the High Altitude Observatory with special support from the
National Science Foundation as part of the United States effort for the
International Years of the Quiet Sun. Photometrically useful measurements of
the white light corona began in February 1964 and continued at Haleakala until
November 1965 when the instrument was relocated to its present site at the
Environmental Science Services Administration's Mauna Loa Observatory (11,150)
feet elevation). The physical setting of this mountain laboratory and the
meteorological factors which established its suitability for coronagraphic
observations are described by Price and Pales (1963) and Hansen, Hansen and
Price (1966).

The K-coronameter is a Photoelectric Polarimeter incorporated into a
Lyot coronagraph for the study of the sun's electron corona outside of natu-
ral eclipse (Wlérick and Axtell 1957; Axtell 1958; Lee and Fullerton 1961).
The data reduction and calibration techniques have been described earlier
(Newkirk, Curtis and Watson 1958; Heynekamp 1962) and were continued without
change during the more recent period. Two details are worthy of note: All
of the observations in Hawaii were made with the same scanning aperture of
diameter 0.0292" so that the effective spatial resolution was consistently
1.3 minutes of arc; and second, all observations were calibrated with New-
kirk's filter Number 4 of nominal transmission 1.8 x 107° so any error in
the original calibration or progressive deterioration of the filter would
be directly reflected in the newer data.



Sidereal Rotation Rate (Yday)

20 30 40 50 60 70 80

1s rT Td
—27
14
28
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729
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Or». \
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Latitude
Figure 3. The average rotation rate of K-coronal features

during the years 1964 - 1967 compared with rates
for other solar phenomena, taken from Hansen,
Hansen and Loomis (1969).

Synodic Period (days)



2. ANALYSIS

A detailed description of the evolution of the brightness distribu-
tion from the minimum year 1964 through the ascending phase of cycle 20
is given by Hansen, Garcia, Hansen and Loomis (1969). Their abstract
follows:

Observations of the white light corona were made on
over 900 days during the years 1964-1967 at heights
between 1.125 and 2.0 R, with the K-coronameter at
Mount Haleakala and Mauna Loa, Hawaii. The bright-
ness distribution of the minimum corona was ellip-
tical with average equatorial intensities three times
the polar. Coronal features of the new cycle at
1.125 R. occurred predominantly in the sunspot zones
at 25-30° latitude and in a high latitude zone which
migrated toward the North pole before solar maximum.
The brightness of the inner corona doubled over this
period and a close association is found between the
average corona and 10.7-cm solar radio flux. Elec-
tron densities in the equatorial regions were nearly
twice those of Van de Hulst's model corona, in agree-
ment with the results of recent eclipse observations.

In Figure 2, representative daily measurements at 1.125 Ry are
superposed for each of the four years. They show the relative con~
stancy of the corona during 1964 and then the gradual development of
discrete features, two to three times brighter than the minimum corona,
at preferred latitudes. The Northern hemisphere was distinctly more
active than the Southern in 1966.



The specific dates having K-coronameter observations during the
period February 1964 to January 1968 are enumerated in Appendix. The
amount of data is too great for inclusion in this volume and is further-
more probably too specialized to warrant the expense of complete publi-
cation. Persons with specific interest in this material may contact the
author.

A typical example of a daily coronal survey is shown in Figure 1 in
the form of a polar plot of the brightness as a function of position angle
at successively greater distance from the solar limb. The outermost trace
represents the brightness distribution of the innermost corona because the
corona has a steep gradient. (The representation should not be confused
with the frequently-presented isophote form.) For many days it was possible
to observe only the inner regions of the K-corona (at a distance of 1.125 Ro)
due to any of several unfavorable conditions such as the early formation of
clouds above the observatory or the presence of excessive amounts of smoke,
dust, or insects in the air path between the telescope and the sun. But on
many other days, particularly during the years 1966-1967, it was possible to
extend measurements to 2.0 Rg, a radius above the solar limb.

14 DECEMBER
1967

Figure 1. Typical daily coronal survey.



The differential rotation of the sun's corona was also studied
for the same time period (Hansen, Hansen and Loomis 1969). A principal
result is shown in Figure 3 where the average rotation rate of K-coronal
features as a function of latitude is compared with that found from
other solar phenomena. The agreement is generally quite close at low
latitudes, but in the range 55-65° the corona seems to rotate nearly
2°/day faster than the photosphere, as indicated by studies of the
day-to-day displacement of polar faculae.

Abstract: Autocorrelation analyses of K-coronameter
observations made at Haleakala and Mauna Loa, Hawaii
during 1964-1967 have established average yearly ro-
tation rates of coronal features as a function of
latitude and height above the limb. At low latitudes
the corona was found to rotate at the same rate as
sunspots but at higher latitudes was consistently
faster than the underlying photosphere. There were
differences as large as 3-4% in the rate at specific
latitudes from year to year and between the two hemi-
spheres. In 1967 a nearly constant rotation was found
for heights ranging from 1.125 to 2.0 Ro. For 1966
there was a more complicated pattern of height depend-
ence, with the rate generally decreasing with height
at low latitudes and increasing at high latitudes.

As part of the "Cooperative Study of Solar Active Regions" (CSSAR)
project of the International Years of the Quiet Sun (IQSY), the Haleakala
K-coronameter records for 10 March-30 October 1965 were made available
for a study of the relationship between coronal emission and plage
regions. The analysis was reported by Leroy, Résch and Trellis (1968)
at the International Astronomical Union (IAU) Symposium in Budapest,
and their abstract states:

A study of the development in the solar corona of
active centers born during the CSSAR period leads
to the following remarks: the "enhancement" of
coronal emissions seems to take place first within
a localized "core" close to the plage, then to ex-
tend to a much larger "halo"; the core from which
all the radiations under study originate does not
last much more than the spots, whereas the “halo" is
characterized by the major importance of the emission
at 5303 A, and lasts as long as the K3 plages.

These features can be explained by the assumption
that the enhancement is inhomogeneous during the
first part of its life, then becomes homogeneous
after the core has disappeared.



REPORT UAG -7

WORLD DATA CENTER A

Upper Atmosphere Geophysics

OBSERVATIONS OF THE SOLAR CORONA:
FEBRUARY 1964 - JANUARY 1968

¥

October 1969



could be described by a radially-dependent core den-
sity which decreased as a gaussian in directions per-
pendicular from the core line. Typical 1/e-contour
dimensions were 30° extent in latitude by 40° in
longitude, measured heliocentric. Streamers were
always found in near association with complexes of
solar activity as manifested by sunspots and plages.

Other studies resulting from the K-coronameter work include:
Calculations of the variation in the appearance of an idealized solar
streamer as it rotates around the limb of the sun (Perry 1967); the
association between K-coronal features and other solar phenomena (in
preparation); a description of the evolution of the coronal features
seen at the 12 November 1966 eclipse (Hansen, Hansen and Garcia 1967);
corroboration of Surveyor I observations of the corona (Norton, Gunn,
Livingston, Newkirk and Zirin 1967); and comparison between solar wind
and coronal intensities (in preparation).

3. ACKNOWLEDGEMENTS

The work reported here is the result of specific contributions by
many individuals. Charles Garcia shared with the author responsibility
for daily operation and maintenance of the K-coronameter. Robert Lee
frequently assisted in difficult electronic problems.

Mrs. Shirley Hansen carried out the data reduction with the help
of a number of part-time assistants including Jon Okada, Mike Perry,
Ronald Kwon, Mrs. Joyce Foster, Mrs. Nancy Edwards, Miss Lois Kawabata
and Miss Nadine Kurokawa. The statistical studies were done by Dr.
Harold Loomis with the University of Hawaii's computing facilities.

Installation of the K-coronameter at Haleakala in 1963 was sup-
ported by a grant from the National Science Foundation for purchase of
a Boller and Chivens Equatorial Spar and Photoelectric Guiding system,
duplicating the Sacramento Peak designs of Dr. Richard Dunn and Dr.
Edwin Dennison. Operation of the instrument at Haleakala was made
possible by the cooperation of Dr. Walter Steiger and Dr. John Jefferies
of the University of Hawaii and, at Mauna Loa, by Howard Ellis and
Lothar Ruhnke of the Environmental Science Services Administration.

Dr. John Firor and Dr. Gordon Newkirk gave us their continued enthu-
siasm and support.



Also under IAU and IQSY sponsorship was the Proton Flare Project
(PFP) of 1966. Newkirk, Hansen and Hansen (1968) reported on the analy-
sis of the Mauna Loa data as follows:

K-coronameter observations during the interval June-
September 1966 are used to construct five electron
density models of the corona above the proton flare
region. These models are compared with others for
the corona above active regions. The observations
following the proton flares of 10 July and 5 Septem-
ber show the presence of a unique low elevation con-
densation in the corona. The possibility that this
condensation is the direct contribution of material
expelled by the flares is examined.

The K-coronal measurements were also combined with data obtained
from three stratospheric balloon flights of Coronascope II (5 March 1964,
30 June and 1 July 1965) plus photographs of the corona at the eclipse
of 30 May 1965 in an extensive study of the structure, dynamics and evo-
lution of solar coronal streamers (Bohlin, 1968). The results were re-
ported to a meeting of the National Academy of Sciences (Bohlin, Newkirk
and Hansen 1968) as follows:

Although total solar eclipses have been scientifi-
cally observed for decades, their infrequency and
short duration precluded investigation of the stream~
ers into which the white-light corona is structured.
Even the most rudimentary characteristics of streamers,
such as spatial location, evolutionary patterns, and
associated phenomena, remained largely speculative, or
at best, ambiguous. Unprecedented time resolution
(extending over 32 days) of these streamers was ob-
tained in 1965 using an externally-occulted corona-
graph (the Coronascope II project) operating in the
stratosphere, coupled with the May 1965 total solar
eclipse. These photographic data (out to 6 solar
radii from the sun) were cross-identified with nearly
daily observations of the innermost corona from a
land-based, photoelectric scanning coronagraph to
yield solar disk location of 12 coronal streamers.
These streamers were traced in the K-coronameter data
to show that streamers clearly partake in the general
solar rotation and can have lifetimes as long as 4 or
5 solar rotations (110 to 140 days). Streamers evolve
slowly, appearing almost quasi-stationary over periods
of several months. However, occasionally rapid changes
in just 14 days were found. Their density structure



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1l -


WORLD DATA CENTER A

Upper Atmosphere Geophysics

REPORT UAG-7

OBSERVATIONS OF THE SOLAR CORONA:
FEBRUARY 1964-JANUARY 1968
by

Richard T. Hansen
High Altitude Observatory

Boulder, Colorado and Kamuela, Hawaii

NY
'S

Prepared by Research Laboratories, ESSA, Boulder, Colorado
and published by

U.S. DEPARTMENT OF COMMERCE
ENVIRONMENTAL SCIENCE SERVICES ADMINISTRATION

ENVIRONMENTAL DATA SERVICE
ASHEVILLE, NORTH CAROLINA, USA 28801

S

October 1969

SUBSCRIPTION PRICE: $9.00 a year; $2.50 additional for foreign mailing; single copy
price varies." Checks and money orders should be made payable to the Superintendent of
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*Price of this issue 15 cents


WORLD DATA CENTER A |

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World Data Center A consists of the Coordination Office

and eight subcenters:

World Data Center A
Coordination Office
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Environmental Science Services
Administration
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Notes:

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(2) Communications regarding data interchange matters in general and World Data Center A asa
whole should be addressed to: World Data Center A, Coordination Office (see address above),

(3) Inquiries and communications concerning data in specific disciplines should be addressed to
the appropriate subcenter listed above.



AXTELL, J.

BOHLIN, J. D.

BOHLIN, J. D.,
G. NEWKIRK and
R. T. HANSEN

HANSEN, R. T.,
S. F. HANSEN and
SAUL PRICE

HANSEN, R. T.,
S. F, HANSEN and
C. J. GARCIA

HANSEN, R. T.,
C. J. GARCIA

S. F. HANSEN and
H. LOOMIS

HANSEN, R. T.,
8S. F. HANSEN and
H. LOOMIS

HEYNEKAMP, C, E.

LEE, R. H. and
J. G,. FULLERTON

LEROY, J. L.,
J. ROSCH and
M, TRELLIS

NEWKIRK, G.,
G. W. CURTIS and
D. K. WATSON

1958

1968

1968

1966

1967

1969

1969

1962

1961

1968

1958

REFERENCES

A Study of the Polarized Component of the

Solar Electron Corona (Thesis, University
of Colorado, Boulder, Colorado).

Structure, Dynamics and Evolution of Solar
Coronal Streamers (Thesis, University of
Colorado, Boulder, Colorado).

The Structure, Evolution and Associated
Phenomena of Solar Coronal Streamers.
Paper presented at the autumn meeting of
the National Academy of Sciences, Pasadena,
California.

An Example of Meteorological Considerations
in Selecting an Observatory Site in Hawaii,
P.A.S.P., 78, 14.

The Solar Electron Corona of 12 November
1966, A. G. Memo No. 174, High Altitude
Observatory, Boulder, Colorado.

Brightness Variations of the White Light
Corona during the Years 1964-1967, Solar
Physics (in press).

Differential Rotation of the Solar Electron
Corona, submitted to Solar Physics.

Observations of the Solar Electron Corona:

January 1958-November 1960, IGY Solar Acti-
vity Report Series No. 16, 4 July 1962, High
Altitude Observatory, Boulder, Colorado.

K-Coronameter Observes the Sun's Electron
Corona, Electronics, 34, 58.

Evolution des Emissions Coronales au Cour de

la Vie d'un Centre Actif. Structure and Devel-

opment of Solar Active Regions, Ed. K. 0.
Kiepenheuer (Reidel Publ. Co., Dordrecht,
Holland).

Observations of the Solar Electron Corona:
September 1956-January 1958. IGY Solar
Activity Report Series No. 4, 15 August 1958,
High Altitude Observatory, Boulder, Colorado.



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