Magnetic South Research Articles

Les blackouts ionosphériques observés en terre adélie en 1957 et 1958

During the IGY continuous vertical incidence ionosonde records were obtained at Terre Adélie by the Expéditions Polaires Françaises in collaboration with the Group Ionosphère of CNET. Excellent hourly and, during World Days, quarter hourly, ionograms were obtained during the entire twenty-four month period from January, 1957 to December, 1958. From an examination of the numerous ionograms, the occurrences of complete blackouts was noted at Terre Adélie, which is well within the southern auroral zone and only a few hundred kilometers from the south magnetic pole. Correlation of these high absorption periods was sought with other geophysical phenomena; e.g. local and planetary magnetic indices, cosmic ray fluctuations, proton events, solar radio and ultraviolet bursts and with ionospheric blackouts found at northern high latitude stations. Several conclusions were found: (a) the occurrence, duration and intensity of blackouts in Terre Adélie correlates rather poorly with local magnetic character figures as deduced from the station magnetograms; (b) observed blackouts correlate much better with planetary magnetic character figures, Kp or Ap; (c) good correlation exists with cosmic ray intensity fluctuations both the total component (recorded at Limeil-Brevannes) or the nucleonic component (recorded at Pic du Midi and Kerguelen). Antarctic blackouts in most cases coincide with the main, negative, phase of cosmic ray storms. It was also found that a definite relationship exists between the few proton events which we investigated and the most intense blackouts; the proton events occurred prior to the blackouts. An excellent correlation was noted between the blackouts found at Terre Adélie and those observed at Little America, Thule, Barrow, Churchill, Ottawa, etc. Thus, with the exception of partial absorption of small duration, polar blackouts seem to be global polar phenomena being particularly intense in the auroral zones. Suggestions are made regarding the probable mechanism responsible for producing the polar high absorption periods and their precursors.

The magnetic fields of sunspots

The occurrence of sunspots in pairs with opposite magnetic polarities can be explained if it is assumed that lines of magnetic force encircle the axis of rotation in opposite directions a little below the surface of the Sun. Material moving upwards will carry a loop of field through the surface and give a south magnetic pole on the same circle of latitude. Such a field is to be expected from the interaction of the Sun's non-uniform rotation with a meridional field. The progression of the spots in latitude requires a slow meridional circulation. The dynamics of the non-uniform rotation and the meridional circulation are not understood; it is possible that the equatorial parts of the Sun are coupled magnetically to a more rapidly rotating interior.

THE HARMONIC ANALYSIS OF THE EARTH'S MAGNETIC FIELD, FOR EPOCH 1942

Summary The results are given of the harmonic analysis of the Admiralty magnetic charts of declination, horizontal intensity and inclination for the epoch 1942.5. Within the limits of observational error, the Earth's magnetic field appears to be entirely of internal origin. There is no evidence of a dipole field of external origin greater than 0-1 per cent of the field of internal origin. The intensity of the dipole field is at present decreasing at a rate of about 5 per cent per century. The geomagnetic poles have a westerly drift at a rate of 4°-5 per century; the north magnetic dip pole is moving in a direction a little to the west of north, but the south magnetic dip pole appears to be practically stationary. In consequence of the dearth of magnetic data over the oceans since 1929, magnetic charts are becoming less accurate and there is a great need for airborne magnetic surveys of ocean areas.

The Position and Movement on the Solar Disk of Sources of Radiation at a Frequency of 97 Mc/s. III. Outbursts

The apparent position and polarization of the source of solar radiation at 97 Mc/s. have been measured during six outbursts, for five of which data on the accompanying solar flares are available. Initially the apparent position of outburst and flare almost coincide, the outbursts usually being rather closer to the solar limb than the flare. As the outburst proceeds, its position rapidly changes, the apparent movement usually being towards, and sometimes off, the solar limb. The initial apparent displacement towards the solar limb and the subsequent movement can be explained if we assume that the outburst radiation is excited by some physical agency originating at the same time, and in the same region, as the flare, and moving outward through the corona. The velocity of such an agency would need to be between 500 and 3000 km./sec., and it is suggested that the corpuscular streams associated with sudden-commencement terrestrial magnetic storms are the initiators of outbursts. The polarization of the outbursts in the early stages is random. Often a second increase occurs, with elliptical, usually circular, polarization. On two occasions linear polarization has been observed in this later stage of an outburst. The relation between the changes in polarization and the associated changes in apparent position conform to the rule given in Part II of this series, that right-hand circular polarization arises in the region above a south magnetic pole and left-hand above a north pole, while linear polarization appears to originate above the central region of a bipolar group, the E-vector having a direction approximately along the axis of the spot-group.

Lieut.-Commander L. C. Bernacchi

LIEUT.-COMMANDER Louis CHARLES BERNACCHI was born in 1876 in Tasmania, and spent his early years in Melbourne, where his father was astronomer to the State Government. The call of physics, and especially of magnetism, therefore came naturally to him, and at the age of twenty-two he went as physicist to the first expedition which ever wintered on the Antarctic continent. This was the Newnes Expedition of 1898-99, led by Borchgrevink, which wintered at Cape Adare, within two hundred miles of the south magnetic pole.

Lines of Magnetic Force

PROF. C. COLERIDGE FARH, of Canterbury College, Christehureh, New Zealand, has sent a communication in which he advocates the preparation of accurate charts showing the lines of magnetic force running from the south magnetic pole to the north magnetic pole. Prof. Farr points out that the secular change in declination at any observing station is the parallactic angle subtended by the movement of either pole as viewed along a line of magnetic force, and he considers that the comparison of charts, showing the lines of force at different epochs, would lead to a better understanding of the nature of secular variation. The lines of force could be sketched in on existing declination charts, but there would be obvious difficulties in drawing the lines all the way from pole to pole. In forwarding Prof. Farr's letter, H. F. Skey, director of the Magnetic Observatory, Christchurch, N.Z., directs attention to the smoothed charts of such lines given by A. G. McNish in Terrestrial Magnetism, 41, 37 (1936). The question is whether unsmoothed charts on a large scale would be sufficiently reliable and sufficiently useful to justify the cost of publication.

Cosmic Rays Near the South Magnetic Pole

ADMIRAL R. E. BYBD'S book, “Antarctic Discovery” (Putnam and Co., Ltd.), which has just been published, contains a preliminary note on the cosmic ray records made by his expedition near the South Magnetic Pole. In an aeroplane flight from Little America (828 miles from the magnetic pole), a height of 12,000 ft. was reached and maintained for three hours while A. A. Zuhn made his observations. While the analysis of the records obtained during this flight, and also during regular ground-level observations, has not yet been completed, Admiral Byrd states that he has been informed by Zuhn that the intensity of radiation was fifteen times greater at 12,000 ft. than at ground-level in Little America, and eight times greater than that recorded in any observations made in the United States. It is to be regretted that it was necessary to replace the original argon of the ionisation chamber with carbon dioxide, owing to a leak which developed during thelong transport of the instrument. As, however, a radium capsule was available for standardisation, Admiral Byrd expresses the opinion that the validity of the records obtained will not be affected. He adds that a crucial test of this point is to be made before the records are formally published.

Kennelly‐Heaviside‐Layer measurements on the Byrd Antarctic Expedition, 1929–30

Among the radio scientific measurements conducted on the Byrd Antarctic Expedition at its base, Little America, Antarctica (latitude 78° 35′ south, longitude 163° 48′ west) , particular emphasis was laid upon local echo‐measurements of the Kennelly‐Heaviside layer at a number of different radio frequencies, at several seasons, and over varying times of day. This investigation appeared of especial importance because of the slight diurnal but great seasonal change of darkness and sunlight, and because of the relative proximity of the magnetic south pole (approximate latitude 72°.4 south, longitude 154°.0 east).

Magnetic phenomena in the region of the south magnetic pole

Magnetographs were in operation at Cape Evans, the base station of the British (Terra Nova) Antarctic Expedition (77° 38' S., 166° 24' E.), during 1911 and 1912. A second set was in operation at the base station of the Australasian Antarctic Expedition in Adelie Land (67° 0' S., 140° 40' E.) during 1912 and 1913. There were synchronous records for seven months, April to October, 1912. Having been charged with the discussion of both sets of magnetic curves, a unique opportunity was afforded me of studying magnetic phenomena occurring near the south magnetic pole, which is intermediate in position to the two stations. With the approval of Sir Douglas Mawson and of the Committee for the Publication of the Scientific Reports of the British Antarctic (Terra Nova) Expedition, I propose in the present paper to give some of the prominent results of the intercomparison.

Societies and Academies

Societies and Academies

The South Magnetic Pole

The South Magnetic Pole

Observations in the South Magnetic Pole Area

Observations in the South Magnetic Pole Area

The Heart of the Antarctic : Being the Story of the British Antarctic Expedition, 1907- 1909. By E. H. Shackleton, C.V.O. With an Introduction by Hugh Robert Mill, D.Sc. An Account of the First Journey to the South Magnetic Pole . By Professor T. W. Edgeworth David, F.R.S. 2 vols., ill., plates. Philadelphia, J. B. Lippincott Co. 1909. $10 net.

<i>The Heart of the Antarctic</i> : Being the Story of the British Antarctic Expedition, 1907- 1909. By E. H. Shackleton, C.V.O. With an Introduction by Hugh Robert Mill, D.Sc. <i>An Account of the First Journey to the South Magnetic Pole</i> . By Professor T. W. Edgeworth David, F.R.S. 2 vols., ill., plates. Philadelphia, J. B. Lippincott Co. 1909. $10 net.

The South Magnetic Pole

The South Magnetic Pole

Concerning position of South Magnetic Pole

The position of the South Magnetic Pole referred to in this Journal, vol. XIII, p. 186, is as given by Commander Chetwynd in his discussion of the absolute observations made by the Expedition. “National Antarctic Expedition, Physical Observations,” p. 133, Charts I and II. The position finally obtained by Commander Chetwynd for, say, 1903, “Physical Observations,” p. 156, is 72°51′S., 156°25′E. [The declination observations gave a position, 72°50′ S., 156°20′ E., and the inclinations, 72°52′ S., 156°30′ E.]

Lieut. Shackleton's Antarctic Expedition

(1) Explorations and Results. THE anxiety occasioned by the delay in the return of Lieut. Shackleton's expedition has been relieved by its safe arrival and the news of its supreme success. A cable published in the Daily Mail of March 24 records the magnificent exploits of the expedition, and though there are occasional obvious verbal inaccuracies in regard to some technical points, the report makes clear the main outlines of its great achievements. They unquestionably place it in the front rank of Polar expeditions. Its two most striking achievements were the sledge journeys by which Lieut. Shackleton reached within one hundred geographical miles of the South Pole, and discovered the nature of the very centre of the South Polar region, and by which Prof. David gained the magnetic south pole, and rendered almost certain the continuity of South Victoria Land and Wilkes Land.

Antarctic Exploration 1

THE author began by referring to the results established by Gauss in 1839. Gauss proved: “(1) That the knowledge of Y (the west component of the horizontal component of terrestrial magnetism, called usually X) over the whole earth, along with the knowledge of H (the north component of H) at all points on a line running from one pole to the other, is sufficient for the foundation of a complete theory of the magnetism of the earth. (2) That a finally complete theory was also deducible from the simple knowledge of Z (the component of the earth's magnetism, that is directed to the earth's centre) on the whole earth's surface.” There existed, for a large part of the earth's surface, data for large charts of the normal values of the declination of H and of Z, at the epoch 1880, from which X, Y, and Z could readily be deduced. These charts were accurate for the zone lying between 60° N. and 50° S. lat. (except for some parts of North Asia and of Central Africa); they were less accurate for 60° to 70° N. lat., and 50° to 60° S. Beyond these limits in the south, lay regions almost un-visited since Ross's Expedition in 1840–43; so that the charts were correspondingly weak in those latitudes. The charts show that the Challenger crossed the Antarctic Circle about the meridian 79° E. These and other somewhat recent observations made between 50° and 60° S. lat., show that considerable changes in the magnetic elements have occurred since Ross's time, and therefore the charts for 1880 cannot be completed, especially as our knowledge of the changes is too limited to permit of the use of Ross's observations. Further it is desirable to have actual verification of Gauss's extension by theory of the magnetic elements at places where they are known to places where they are unknown. The position of the south magnetic pole is still undetermined, and magnetic observations are wanted from 40° S. to the geographical pole. For the carrying out of these views, Melbourne Observatory, being furnished with the necessary instruments, would serve admirably as a base station, with subsidiary bases at the Cape, and at Sandy Point, Magellan Strait, for the use of portable absolute instruments. Much of the survey could be done on board ship at sea, observations having now become so trustworthy by the process of “swingingship.” Portable instruments could also be used on ice, where their readings would be specially free from sources of error. The great effect of the ship's iron in high latitudes can be got rid of by experience, as proved in the voyage of the Challenger, an important matter being a proper position on board far the instruments. This position could be chosen immediately after the selection of the ship. The error in the vertical component varies with the “heel” of the ship; the horizontal error can be eliminated by the process of “swinging.”

On the probable position of the south magnetic pole

The recent discovery of the site of the North Magnetic Pole, which has resulted from the experiments of Capt. James Ross, suggested to the author the inquiry whether any similar indications of an approach to the South Magnetic Pole can be gathered from any observations now on record. With this view a table is given of the observations made by Tasman in 1642 and 1643, during his voyage of discovery in the Southern Ocean, extracted from his journal; from which it appears that he on one occasion noticed the continual agitation of the horizontal needle, in south latitude 42° 25', and longitude from Paris 160°. On the presumption that the South Magnetic Pole was at that time near this spot, and that it has since been retrograding towards the East, the author conjectures that it will now be found in or about the 43rd parallel of south latitude; and to the south-east of the Island of Madagascar, a situation extremely convenient for ascertaining its exact position, which he considers as an object of great theoretical as well as practical importance.

XXIII. On the position of the south magnetic pole

XXIII. <i>On the position of the south magnetic pole</i>