Severe Magnetic Storms Research Articles

Cheltenham Magnetic Observatory July to September, 1947

(Latitude 38° 44′.0 N., longitude 76° 50′.5, or 5h 07m.4 W. of Gr.)July 17–20—A moderately severe magnetic storm began with a sudden commencement in all three elements at 17h 49m GMT, July 17, the severest part of the storm occurring within the first eight hours. Initial H‐motion was rapid and of large amplitude. After soon reaching a low value of 18,1777γ at 18h 06m, H then increased 265γ in a rapid although erratic manner until 20h 22m. After about 03h, July 18, H exhibited rapid pulsations of moderate amplitude. After 03h, July 19, long‐period motion of comparatively small amplitude predominated until the end of the storm at 17h July 20. Minimum H of 18,074γ occurred at 14h 36m, July 18. Following the sudden commencement Z decreased until 18h 01m, after which a rapid steady increase set in until 00h 08m, July 18, a change of 288γ being recorded. Z then decreased until 04h, when normal values were resumed. Z showed a rather rapid rise between 16h and 20h, July 18, and was erratic between 01h and 07h, July 19.

Huancayo Magnetic Observatory, July to September, 1941

(Latitude 12° 02′.7 S., longitude 76° 20′.4 or 5h 01m.4 W. of Gr.)July 4–5—Beginning suddenly at 03h 45m GMT, July 4, with an increase of 45 gammas in H in three minutes and followed by almost twenty‐four hours of only very mild disturbance, a very severe magnetic storm was recorded on July 5. It began approximately at midnight and developed its maximum at about noon and then fell off again by the end of the day. It was marked by several peaks and bays with particularly large ones at about 12h and 13.5h. Both D and Z were also markedly effected.

Tucson Magnetic Observatory, July to September, 1941

(Latitude 32° 14′.8 N., longitude 110° 50′.1 or 7h 23m.3 W. of Gr.)July 4–8—The storm began with a sudden increase in H of 41 gammas at 03h 42m GMT, July 4, with evidence of mild activity until 00h, July 5. During the following five hours there was a gradual increase of activity. At 05h 00m, July 5, another sudden increase in H marked the beginning of a severe magnetic storm. The extreme activity of the storm ended at 15h, July 5. Moderate disturbance with considerable short‐period and some long‐period variations continued until about 09h July 8. Approximate ranges: H, 393 gammas; Z, 156 gammas; D, 36′.

Sitka Magnetic Observatory April to June, 1939

April 16–17—A severe magnetic storm began with abrupt movements of all elements at 21h 28m GMT, April 16, and at 0lh 57m, April 17. Thereafter the storm increased rapidly with large bays and short‐period vibrations. The storm ended about 23h GMT, April 17; but the trace remained moderately disturbed for several days. Ranges: D, 238″; H, 1569 gammas; Z, 910 gammas.April 23—A moderate disturbance of large bays, began gradually and was followed by an abrupt motion of the elements at 05h 52m GMT, April 23. After the 15th hour the disturbance gradually subsided and ended about 02h, April 24. The H‐maximum was too great to be recorded. Ranges: D, 158″; H, 1304 gammas (estimated); Z, 590 gammas.

Sitka Magnetic Observatory October to December, 1938

October 6–8—A sudden commencement at 18h 43 m GMT, October 6, marked the beginning of a severe magnetic storm. The three components remained very quiet until 07h, October 7, when the activity began to increase. With a sudden decrease of 520 gammas in H the principal part of the storm began. Until 18h, October 7, the three components moved with such rapid motion that the exact changes could not be determined.

Correlation of magnetic activity with disturbance of radio transmission

Owing to their mutual dependence on conditions in the ionosphere a close connection between magnetic activity and radio transmission is expected. This connection is revealed by impairment of transmission on high frequencies during magnetic storms, ranging from complete failure of certain channels of communication during severe magnetic storms to minor vitiation during periods of lesser activity.The first experimental evidence on the nature of the changes taking place in the reflecting properties of the ionosphere during a magnetic storm were supplied by Hafstad and Tuve (see 1 under “References” at end of this article) in 1929. Limitations in technique at that time prevented comprehensive observation of the changes taking place. Subsequent developments in methods of ionospheric research at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington and elsewhere, particularly the introduction of automatic multifrequency methods [2, 3] have afforded a clearer understanding of the phenomena.

Severe Magnetic Storms Disturb Telegraph and Radio

Severe Magnetic Storms Disturb Telegraph and Radio

Huancayo Magnetic Observatory, March to April, 1929

March 11, 1929—A severe magnetic storm began at 13h 53m on March 11 with a sharp decrease of 18γ in horizontal intensity and an immediate increase of 193γ the following four minutes. The declination and vertical‐intensity traces also showed distinct increases within the next three or four minutes. The storm was distinguished by rapid but moderate fluctuations in horizontal intensity during the daily maxima of March 11 and 12, and by subnormal horizontal intensities with much slower changes during the rest of the time. Declination and vertical‐intensity traces showed only moderate fluctuations during the storm, which ended at about 5h on March 13, at which time the horizontal‐intensity trace became practically normal again.

The relation of radio‐wave propagation to disturbances in Terrestrial Magnetism

From a study of the variation in long‐wave daylight signal‐intensity observed at the Laboratory for Special Radio Transmission Research, Bureau of Standards, and of the disturbances in terrestrial magnetism, it is concluded that there is a marked increase in the intensity of long‐wave signals following severe magnetic storms. In the case of long‐distance reception from European stations, there is a general tendency for the signal‐intensity to be below normal for several days before the maximum of the magnetic disturbance and to show a definite increase from one to three days after the passage of the storm. Observations taken on stations at moderate distances, that is, the Radio Corporation stations at Tuckerton and New Brunswick, New Jersey, and Rocky Point, Long Island, give somewhat different results. While the intensity of signal from these stations is high from two to four days after the storm, as in the case of the distant stations, there is also a decided increase in signal‐strength from two to four days before the magnetic disturbance. The complete paper is published elsewhere (Bur. Stan. J. Res., v. 2, 1201–1211, 1929; Inst. Radio Eng., v. 17, 1206–1213, 1929).

Watheroo Magnetic Observatory July, 1928

(Latitude 30° 19′.1 S.; longitude 115° 52′.6 or 7h 44m E. of Gr.)July 7, 1928—This was a severe magnetic storm. Between 22h and 23h (G.M.T.) on July 7 the magnetic elements began to depart markedly from the normal curve, and within an hour all three elements showed large and rapid fluctuations. From 23h.5 on July 7 to 7h on the following day was the period of greatest severity of the storm, the oscillations of all three elements being so rapid as to scarcely leave a record on the photographic trace. The declination was especially disturbed and the H‐trace was greatly depressed during the last half of the period.

Principal magnetic storms recorded at the Cheltenham Magnetic Observatory, April to December, 1927

The most severe magnetic storm of the year was recorded at the Cheltenham Magnetic Observatory on October 12, 1927. It began abruptly at 5h 26m Eastern (75th meridian) standard time, and continued until 19h 15m. The extreme values occurred at the following times: West declination, maximum at 6h 34m, minimum at 8h 06m, range 2° 17′; horizontal intensity, maximum at 13h 43m, minimum at 6h 31m, range 519γ; vertical intensity, maximum at 6h 38m, minimum at 14h 26m, range 344γ. The most active portion of the storm corresponded with the period during which there was reported to be interference with telegraphic communication.

Principal magnetic storms recorded at the Cheltenham Magnetic Observatory, April to June, 1926

(Lat. 38° 44′.0 N.; long., 76° 50′.5, or 5h 07.4mW. of Gr.)

List of recent publications

1. Renewed interest was aroused by the remarkable earth‐current disturbances of May 14 to May 20, 1921, and, as will be recalled, there were also at the time brilliant displays of polar lights, severe magnetic storms, and manifestations of pronounced solar activity. These disturbances and accompanying phenomena occurred over the entire Earth. Northern lights were observed in lower northerly latitudes than usual, and southern lights were seen as far north in the Southern Hemisphere as Apia, Samoa—a very unusual occurrence. In certain respects the disturbances, during the period mentioned, were similar to those which occurred August 29 to September 4, 1859.

Some results of recent earth‐current observations and relations with solar activity, terrestrial magnetism, and atmospheric electricity

1. Renewed interest was aroused by the remarkable earth‐current disturbances of May 14 to May 20, 1921, and, as will be recalled, there were also at the time brilliant displays of polar lights, severe magnetic storms, and manifestations of pronounced solar activity. These disturbances and accompanying phenomena occurred over the entire Earth. Northern lights were observed in lower northerly latitudes than usual, and southern lights were seen as far north in the Southern Hemisphere as Apia, Samoa—a very unusual occurrence. In certain respects the disturbances, during the period mentioned, were similar to those which occurred August 29 to September 4, 1859.

Solar‐constant values at Calama, Chile, March‐April, 1920

[The following values of the solar constant observed at the Smithsonian Institution station, Calama, Chile, as communicated by Dr. Abbot, are of special interest in connection with the severe magnetic storm of March 22–23, and the marked solar activity of that period.1 It is very gratifying that Dr. Abbot has devised a method of observation and reduction which makes it possible to obtain a value of the solar constant within a few hours after the observations have been made and to receive the data at Washington as promptly as the mail service permits. The values from July, 1918, to January, 1920, inclusive, will be found in various issues of the Monthly Weather Review, January, 1919, to February, 1920. The values from January to March, 1920, Dr. Abbot states, “were all high—of the order of 1.96 to 2.00”. It will be observed from the. table that the lowest value (1.866) since January was observed on March 23—Ed.]

The magnetic storm of August 11–12, 1919, at Lukiapang, China

There was a severe magnetic storm recorded at Lukiapang from August 11 to 13, 1919. It seems to have been more violent than the great storm of September 25, 1909, certainly the perturbations were sharper if not of greater magnitude. The storm started quite suddenly at 14h 58m (China Central Time) on August 11 simultaneously for the three elements, west declination decreasing, horizontal intensity increasing, and vertical intensity decreasing. The movements were so rapid that no visible trace was obtained for the horizontal intensity.

The magnetic storm of August 11–12, 1919, as observed at the Apia Magnetic Observatory, Samoa

[From a blue print transmitted to the Journal by Dr. G. Angenheister, the observer‐in‐charge, the following information has been obtained respecting the chief characteristics of the severe magnetic storm of August 11–12—the severest registered at the Apia Magnetic Observatory since the one of September 26, 1909. All the times given refer to Greenwich civil mean time; they are to be regarded as approximate, as also the absolute value of the magnetic elements; the scalings were made by the Department of Terrestrial Magnetism.]Declination (D). No large perturbations occurred and there was no marked “sudden commencement” near 7h August 11. At about 7h 58m, there is a sharp rise of a few minutes, signifying diminishing east declination (D); the value of D at this point is about 10° 14′ E. A minimum D of about 10° 02′ E is reached at about 9h 53m August 11. The total range in D for August 11–12 is thus about 12′.