AURORAE AND MAGNETIC STORMS 
vide possibilities for more reliable determinations of 
the auroral frequency curves. 
A detailed morphological study of auroral phenomena 
has hitherto been carried on mainly over Scandinavia. 
It would be of the greatest interest to extend this de- 
tailed study of types of aurorae and their position in 
space to other places along the auroral zone. In this 
connection it would be of great mterest to study the 
horizontal extension of a single quiet auroral form, such 
as a homogeneous are or band, along the auroral zone. 
From a single station one can determine the extension 
of such a form up to 600-700 km, but it is still an un- 
solved question whether or not such a form may have 
even greater extension, or may even cover a greater 
part of the auroral zone. The question could perhaps 
be solved most conveniently by using a series of air- 
planes flying at fixed distances from each other along 
the auroral zone. 
The spectrum of the aurorae shows an increasing 
number of lmes with each new improvement in the 
spectrographic equipment used [17]. The most impor- 
tant new features of the spectra are the number of 
faint atomic lines from N and O which seem to be 
present. Further, the hydrogen lines Ha and Hg show 
great changes in intensity together with a strong broad- 
ening of the line width, which indicate Doppler move- 
ments of the emitting atoms. 
A new and promising field of research on ionization 
processes within the aurorae is the study of the scat- 
tering of radio waves from aurorae in the VHF -region. 
In this case, the ion clouds within an auroral display 
would act as scattering centers, and a detailed study 
would give information about the dimensions of these 
centers. 
REFERENCES 
1. Aurvén, H., Cosmical Electrodynamics. Oxford, Clarendon 
Press, 1950. 
2. BIRKELAND, Kr., Norwegian Aurora Polaris Expedition, 
1902-08. Christiania, Vol. 1, Part 1, 1908; Part 2, 1913. 
3. CHapmMan, S., and Barrens, J., Geomagnetism, Vol. II. 
Oxford, Clarendon Press, 1940. (See pp. 850-890) — 
Oo 
10. 
ll. 
12. 
13. 
14. 
15. 
16. 
Al, 
309 
. Fritz, H., Das Polarlicht. Leipzig, Brockhaus, 1881. 
. Harana, L., The Aurorae. London, Chapman (in press). 
. —— und Srorrrecen, W., “Echoversuche auf Ultra- 
kurzwellen.”’ Hochfrequenztech. u. Elektroakust., 55: 105- 
108 (1940). 
. Havens, R., Kou, R. T., and Lacow, H., Pressures and 
Temperatures in the Earth’s Upper Atmosphere. Naval 
Res. Lab. Rep., Washington, D. C., March, 1950. 
. Lovett, A. C. B., Crmee, J. A., and Extyert, C. D., 
“Radio Echoes from the Aurora Borealis.’? Nature, 
160: 372 (1947). 
. McNisu, A. G., “Heights of Electric Currents near the 
Auroral Zone.’ Terr. Magn. atmos. Elect., 43: 67-75 
(1938). 
Photographic Atlas of Auroral Forms, 24 pp. Oslo, Inter- 
national Union of Geodesy and Geophysics, 1930. 
SrusBEE, H. B., and Vestine, EH. H., ‘‘Geomagnetic Bays, 
Their Frequency and Current-Systems.”’ Terr. Magn. 
atmos. Elect., 47: 195-208 (1942). (See also Vestine, H. 
H., “On the Analysis of Surface Magnetic Fields by 
Integrals.” bid., 46: 27-41 (1941).) 
STorMeER, C., ‘‘Résultats des mesures photogrammétriques 
des aurores boréales observées dans la Norvége méri- 
dionale de 1911 4 1922.” Geofys. Publ., Vol. 4, No. 7 
(1926). 
— ‘Sonnenbelichtete Nordlichtstrahlen.”” Z. Geophys., 
5: 177-194 (1929). 
—— ‘Uber die Probleme des Polarlichtes.” Bectr. Geophys., 
Supp. 1: 1-84 (1931). 
Veacarp, L., ‘Die Deutung der Nordlichterscheinungen 
und die Struktur der lonosphire.” Hrgebn. exakt. Naturw., 
17: 229-281 (19389). 
—— “The Aurora Polaris and the Upper Atmosphere,”’ 
Chap. XI, in Terrestrial Magnetism and Electricity, 
J. A. Fuemrne, ed. New York, McGraw, 1939. 
—— New Important Facts Relating to the Composition and 
State of the Ionosphere Derived from Auroral Studies. 
Report to the Sec. Meeting of the Mixed Commission 
on the Ionosphere, URSF, Ziirich, 1950. 
. VestinE, E. H., and CHApMAN, S., ‘‘The Electric Current 
System of Geomagnetic Disturbance.’’ Verr. Magn. 
atmos. Hlect., 48: 351-3882 (1938). 
. Ware, F. W. G., and Geppzs, M., “‘Ihe Antarctic Zone 
of Maximum Auroral Frequency.” Terr. Magn. atmos. 
Elect., 44: 367-377 (1939). 
