scholarly journals Measurements of vector magnetic anomalies on board the icebreaker Shirase and the magnetization of the ship

1999 ◽  
Vol 42 (2) ◽  
Author(s):  
Y. Nogi ◽  
K. Kaminuma
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Magnetic Anomalies ◽  
The Other ◽  
South Indian Ocean ◽  
Permanent Magnetic Field ◽  
South Indian ◽  
Antarctic Research ◽  
Permanent Magnetization ◽  
Made In

Vector measurements of the geomagnetic field have been made in the South Indian Ocean since 1988 when a Shipboard Three Component Magnetometer (STCM) was installed on board the icebreaker Shirase by the 30th Japanese Antarctic Research Expedition (JARE-30). Twelve constants related to the ship's induced and permanent magnetic field were determined by the data obtained from the JARE-30 to the JARE-35. The constants related to the ship's magnetic susceptibility distribution are almost stable throughout the cruise and mostly depend on the ship's shape. On the other hand, the constants related to the ship's permanent magnetization are variable. However, absolute values of total intensity geomagnetic field calculated from vector geomagnetic field is possible to use, if the constraints from total intensity geomagnetic field measured by the proton magnetometer and/or satellite derived magnetic anomalies are applied.

Sea surface temperatures, salinity and pH reconstructions over the last 1,2 Ma in South Indian Ocean using the unique combination of Mg/Ca, d18O and ∆47 in planktonic foraminifera

2021 ◽  
Author(s):  
Marion Peral ◽  
Thibaut Caley ◽  
Bruno Malaizé ◽  
Erin McClymont ◽  
Thomas Extier ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Transfer Function ◽  
Planktonic Foraminifera ◽  
The Other ◽  
Unique Combination ◽  
South Indian Ocean ◽  
Term Evolution ◽  
South Indian ◽  
Clumped Isotope

<p>The Mid-Pleistocene transition (MPT) took place between 1,200 Ma and 800 ka (still debated). During this transition, the Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40 000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical while Earth’s orbital variations remained unchanged. Although orbital variations constitute the first order forcing on glacial-interglacial oscillations of the late Quaternary, they cannot explain alone the shifts in climatic periodicity and amplitude observed during the MPT. In order to explain the MPT, long-term evolution of internal mechanisms and feedbacks have been called upon, in relation with the global cooling trend initiated during the Cenozoic, the expansion of Antarctic and Greenland Ice Sheet and/or the long-term decline in greenhouse gases (particularly CO2). A key point is therefore to accurately reconstruction of oceanic temperatures to decipher the processes driving climate variations.</p><p>In the present work, we studied the marine sediment core MD96-2048 taken from south Indian Ocean (26*10’482’’ S, 34*01’148’’ E) in the region of the Agulhas current. We compared 5 paleothermometers: alkenone, TEX86, foraminiferal- transfer function, Mg/Ca and clumped isotope. Among these approaches, carbonate clumped-isotope thermometry (∆<sub>47</sub>) only depends on crystallization temperature, and the ∆<sub>47</sub> relationship with planktonic foraminifer calcification temperature is well defined. Since Mg/Ca is not only controlled by temperature but is also affected by salinity and pH. The classical d<sup>18</sup>O in planktic is dependent on SST and d<sup>18</sup>Osw, which is regionally correlated with the salinity in the present-day ocean. Assuming that the present-day d<sup>18</sup>O<sub>sw</sub>-salinity relation was the same during the MPT, we are able to separate changes in d<sup>18</sup>O<sub>sw</sub> from temperature effects and reconstruct past salinity. Combining d<sup>18</sup>O, Mg/Ca and ∆<sub>47</sub> on planktonic foraminifera allow in theory to reconstruct SST, SSS and pH.</p><p>Here, we measured d<sup>18</sup>O, Mg/Ca and ∆<sub>47</sub> on the shallow-dwelling planktonic species Globigerinioides ruber ss. at the maximal of glacial and interglacial periods over the last 1.2 Ma. Our set of data makes it possible to estimate the long-term evolution of SST, salinity and pH (and thus have an insight into the atmospheric CO<sub>2</sub> concentration) across the MPT. Frist, strong differences are observed between the 5 derived-SST: the alkenone and TEX86 recorded the higher temperatures than the other SST proxies. Alkenone derived-SST do not show glacial-interglacial variations within the MPT. The Mg/Ca and transfer function derived-SST show a good agreement each other, while the clumped-isotope derived-SST are systematically colder than the other derived-SST. Then, our ∆<sub>47</sub>-SST, salinity and pH results clearly show that amplitude of glacial-interglacial variations was insignificant between 1.2 and 0.8 Ma (within the MPT) and increased after the MPT. Finally, we also discussed the potential to use this unique combination of proxies to reconstruct changes of atmospheric CO<sub>2</sub> concentration.</p>

Are There Different Kinds of Rogue Waves?

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Paul C. Liu ◽  
Keith R. MacHutchon
Keyword(s):  
Rogue Wave ◽  
Rogue Waves ◽  
Rayleigh Distribution ◽  
The Other ◽  
South Indian Ocean ◽  
Gas Drilling ◽  
Wave Measurements ◽  
South Indian ◽  
Theoretical Considerations

There is clearly no immediate answer to the question posted by the title of this paper. Inasmuch as that there are not much definitively known about rogue waves and that there is still no universally accepted definition for rogue waves in the ocean, we think there might just be even more than one kind of rogue waves to contend with. While the conventional approach has generally designated waves with Hmax∕Hs greater than 2.2 as possible rogue waves, based on Rayleigh distribution considerations, there is conspicuously no provision as to how high the ratio of Hmax∕Hs can be and thus not known how high can a rogue wave be. In our analysis of wave measurements made from a gas-drilling platform in South Indian Ocean, offshore from Mossel Bay, South Africa, we found a number of cases that indicated Hmax∕Hs could be valued in the range between 4 and 10. If this were to be the case, then these records could be considered to be “uncommon” rogue waves, whereas a record of Hmax∕Hs in the range between 2 and 4 could be considered to comprise “typical” rogue waves. On the other hand, the spikes in the Hmax data could have been caused by equipment malfunction or some other phenomenon. Clearly, the question of whether or not there are different kinds of rogue waves cannot be readily answered by theoretical considerations alone and there is a crucial need for long-term wave time-series measurements for studying rogue waves.

scholarly journals Experimental Study on the Localization of Moving Object by Total Geomagnetic Field

2017 ◽  
Vol 2017 ◽  
pp. 1-7
Author(s):  
Chong Kang ◽  
Liming Fan ◽  
Quan Zheng ◽  
Xiyuan Kang ◽  
Jian Zhou ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
High Sensitivity ◽  
Magnetic Anomalies ◽  
Target Localization ◽  
Total Field ◽  
Detection Range ◽  
Vector Sensors ◽  
Field Localization ◽  
Low Sensitivity

In the method of target localization based on magnetic anomalies, the scheme of vector field localization and experimental research are significant. Because more information of magnetic field can be measured by vector sensors, the position of the target can be directly calculated by the equations. However, the vector magnetic anomaly generated by the target is difficult to measure. And the detection range is small due to the low sensitivity of vector sensors. A method for target localization based on the total geomagnetic field is proposed. Its advantages are that the measurement of total magnetic field is not affected by the orientation of the total field sensors and the detection range is large due to their high sensitivity. In this paper, we focus on the localization using the array with the total field magnetometers. And we design an array structure with the total field magnetometers. Then, we obtain the higher order nonlinear equations for the target localization based on this array. The numerical method is used to solve the equations. Meanwhile, we present a method for eliminating the effect of geomagnetic field variations and uneven spatial distribution. In suburban roads, localization experiments were carried out. And the results showed that the relative error of target localization is less than 5% by using the proposed method.

Are There Different Kinds of Rogue Waves?

2006 ◽  
Author(s):  
Paul C. Liu ◽  
Keith R. MacHutchon
Keyword(s):  
Time Series ◽  
Rogue Waves ◽  
Rayleigh Distribution ◽  
The Other ◽  
South Indian Ocean ◽  
Gas Drilling ◽  
Wave Measurements ◽  
South Indian ◽  
Theoretical Considerations

Inasmuch as there is as yet still no universally accepted definition for rogue waves in the ocean, we think there might just be more than one kind of rogue waves to contend with. While the conventional approach has generally designated waves with Hmax/Hs greater than 2.2 as possible rogue waves, based on Rayleigh distribution considerations, there is conspicuously no provision as to how high the ratio of Hmax/Hs can be. In our analysis of wave measurements made from a gas-drilling platform in South Indian Ocean, offshore from Mossel Bay, South Africa, we found a number of cases that indicated Hmax/Hs could be valued in the range between 4 and 10. If this were to be the case these records could be considered to be “uncommon” rogue waves, whereas a record of Hmax/Hs in the range between 2 and 4 could be considered to comprise “typical” rogue waves. On the other hand the spikes in the Hmax data could have been caused by equipment malfunction or some other phenomenon. Clearly the question of whether or not there are different kinds of rogue waves can not be readily answered by theoretical considerations alone and there is a crucial need for long-term wave time series measurements for studying rogue waves.

Observations of the Earth's magnetic field made in Edinburgh from 1670 to the present day

1994 ◽  
Vol 85 (4) ◽  
pp. 239-252 ◽  
Author(s):  
D. R. Barraclough
Keyword(s):  
Magnetic Field ◽  
Mathematical Models ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Upper Atmosphere ◽  
The Difference ◽  
Time Changes ◽  
Relative Measurements ◽  
Magnetic North ◽  
Made In

AbstractMagnetic observations made at the same site give valuable information about the time changes (the secular variation) of the geomagnetic field. This paper gives details of all known measurements of the geomagnetic field in and around Edinburgh since the earliest observation of magnetic declination (the difference between true and magnetic north) by George Sinclair in 1670. Early observations of the strength of the field were only relative measurements. Approximate conversion factors are derived to enable these data to be expressed in modern absolute units (nanoteslas). Observed values of declination, inclination and the horizontal intensity of the geomagnetic field are plotted and compared with values computed from mathematical models of the field covering the interval 1690 to 1990, inclusive. The earlier observations were not corrected for the effects of the rapidly varying magnetic fields caused by electric currents in the upper atmosphere. The consequences of this are estimated.

scholarly journals A taxonomic and distributional survey of marine benthonic Ostracoda off Kerguelen and Heard Islands, South Indian Ocean

2004 ◽  
Vol 23 (1) ◽  
pp. 15-38 ◽  
Author(s):  
Michael A. Ayress ◽  
Patrick De Deckker ◽  
Graham P. Coles
Keyword(s):  
Deep Sea ◽  
The Other ◽  
Intermediate Water ◽  
Kerguelen Plateau ◽  
South Indian Ocean ◽  
Sw Pacific ◽  
South Indian ◽  
Two New Species ◽  
The Common ◽  
Ostracod Species

Abstract. From an examination of 34 grab and dredge samples ranging from 110 m to 3584 m water depth, collected during Eltanin cruise 47 across the Kerguelen Plateau, 26 shallow-water and 35 deep-sea benthonic ostracod species have been identified. Systematic notes and illustrations of the common and some of the rare species are presented. Two new species are described: Philoneptunus cassidyi n. sp. and Taracythere abyssora n. sp. Comparisons made with the Atlantic and SW Pacific Oceans and circum-Antarctic regions indicate that the fauna comprises dominantly cosmopolitan deep-sea species while most of the other species have close affinities with the SW Pacific. In the Kerguelen material, seven distinct depth assemblages appear to correspond well with differing watermasses and there is evidence that the relatively shallow position of Antarctic Intermediate Water permits elevation of the upper depth limits of some deep-sea species. Some species have developed ornament of fine reticulation, features not previously seen in those species outside the Kerguelen region.

7. The Earth’s magnetic field

2018 ◽  
pp. 106-126
Author(s):  
William Lowrie
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Plate Tectonics ◽  
Magnetic Anomalies ◽  
Earth’S Magnetic Field ◽  
The Earth ◽  
Earth's Magnetic Field ◽  
Reversed Polarity ◽  
Harmful Radiation ◽  
The Magnetic Field

The Earth is surrounded by a magnetic field, which originates inside its molten core, and which for centuries has helped travellers to navigate safely across uncharted regions. The magnetic field protects life on the Earth by acting as a shield against harmful radiation from space, especially from the Sun. ‘The Earth’s magnetic field’ explains that the magnetic field at the Earth’s surface is dominantly that of an inclined dipole. The Sun’s deforming effect on the magnetic field outside the Earth is described, as are the magnetic fields of other planets. The magnetism of rocks forms the basis of palaeomagnetism, which explains how plate tectonics displaced the continents and produced oceanic magnetic anomalies whenever the geomagnetic field reversed polarity.

scholarly journals The pressure upon the poles of metallic and composite arcs, including an enquiry into the reactions consequent upon electron emission

1920 ◽  
Vol 97 (685) ◽  
pp. 326-348 ◽  
Keyword(s):  
Magnetic Field ◽  
Electron Emission ◽  
The Other ◽  
Earth’S Magnetic Field ◽  
Rapid Melting ◽  
Silver Copper ◽  
Single Arc ◽  
Earth's Magnetic Field ◽  
Carbon Arc ◽  
Made In

Experiments upon the pressure experienced by the poles of a carbon arc led to the theory, which was put forward tentatively, that it was due to the recoil consequent upon the projection of electrons from the poles. Experiments have subsequently been made upon metallic arcs, using poles of iron, silver, copper, and an alloy of silver and copper, and also upon a composite arc in which one pole was of silver and the other of carbon. In dealing with the carbon arc it was found possible to eliminate the effects of the electromagnetic influence of the rest of the circuit and of the earth’s magnetic field, by employing what was called the double-arc method; but in the present set of experiments the rapid melting of the metal rods made it expedient in the majority of cases to employ the less direct single-arc method, which had also been used in the carbon investigation, the necessary allowances for the disturbing influences being made in the manner already described. In the case of the copper arc a satisfactory series was also obtained by using the two arcs.

scholarly journals IV. The action of magnetised electrodes upon electrical discharge phenomena in rarefied gases

1901 ◽  
Vol 197 (287-299) ◽  
pp. 135-150 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Induction ◽  
Royal Society ◽  
Electrical Discharge ◽  
Rarefied Gas ◽  
The Other ◽  
Rarefied Gases ◽  
Rapid Rotation ◽  
First Case ◽  
Made In

In two previous communications which I have had the honour to lay before the Royal Society, reference is made to the action of a magnetic field, either constant or changing, upon the distribution of ions within a highly evacuated space. The chief result dealt with in the first case was the formation of a luminous ring which appeared to be in rapid rotation about the lines of magnetic induction. The other note described a case in which a positively electrified body placed in a rarefied gas became diselectrified when a magnetic field was created in its neighbourhood. I now beg to submit an account of some further experiments which have been made in this matter, with a view to obtaining evidence as to the cause of both these phenomena. The Luminous Ring . A detailed account of the apparatus most suitable for the production of the luminous ring in rarefied gases has already been given in the first of the papers just referred to; nor has it so far been found possible to materially improve upon the method there described.

On: “Application of Gauss’s method to magnetic anomalies of dipping dikes” by I. J. Won (GEOPHYSICS, February 1981, p. 211–215).

Geophysics ◽  
1982 ◽  
Vol 47 (2) ◽  
pp. 266-267
Author(s):  
K. Kunaratnam
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Transverse Component ◽  
The Other ◽  
Infinite Depth ◽  
Dip Angle ◽  
Depth Extent ◽  
Permanent Magnetization

In a recent paper, Won discussed the application of Gauss’s method for obtaining the parameters of a dipping dike from its magnetic anomaly. He assumed the magnetization to be entirely induced and did not consider the effect of the presence of any permanent magnetism. In view of the reported agreement of the calculated dip angles with drilled results, the assumption seems to be valid in this particular case. If permanent magnetization in an unknown direction is present, neither the dip angle of the dike nor the susceptibility can be determined, although the other parameters of the dike (i.e., depth to the top, horizontal location, and thickness) can be deduced from the magnetic anomaly. The dip angle of the dike and the angle made by the transverse component of the resultant intensity of magnetization combine to form a single angle which alone can be determined uniquely from the magnetic anomaly. If the transverse component of the resultant intensity of magnetization is J and it dips at an angle α below the horizontal, then using the other notations given by Won it can be shown that [Formula: see text] and [Formula: see text] (Bruckshaw and Kunaratnam, 1963). For this reason, the magnetic anomaly due to an inclined dike of infinite depth extent and horizontal top surface is the same as that due to a vertical dike having the same top surface but for a modified direction and intensity of magnetization. The inclined dike anomalies can, therefore, be analyzed using the vertical prism models as well. If the magnetization is entirely induced, the dip angle of the inclined dike can be deduced from the direction of magnetization of the equivalent vertical dike.

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