Air navigation in high latitudes

Polar Record ◽  
1950 ◽  
Vol 5 (39) ◽  
pp. 440-449
Author(s):  
A. J. Hagger

Near the Poles, the geographical system of reference by meridians and parallels approaches limiting conditions, and the apparent motion of heavenly bodies is unfamiliar. Accepted routines of navigation break down, and it is therefore necessary to devise new methods for the use of aircraft in polar regions. In addition, the weakness of the magnetic field in these regions forces us to modify or supplement the ordinary method of steering by magnetic compass. It cannot be too much emphasised, however, that the overriding criteria by which any technique must be examined are those which are common to navigation in all latitudes, and which are imposed by the nature of the aircraft itself. They arise chiefly owing to the speed and instability of the machine, and to the conditions of physical and mental strain in which the aerial navigator must work. Techniques and instruments must survive the three-fold test, applicable to any latitude: “Is the manipulative process handy enough to be done accurately by a navigator, tired or under nervous tension?”, “Is it simple enough for him to avoid errors under conditions of stress or mild anoxia?”, and “Is it fast enough?”

2014 ◽  
Vol 44 (4) ◽  
pp. 293-312 ◽  
Author(s):  
Tomáš Šoltis ◽  
Ján Šimkanin

Abstract We present an investigation of dynamo in a simultaneous dependence on the non-uniform stratification, electrical conductivity of the inner core and the Prandtl number. Computations are performed using the MAG dynamo code. In all the investigated cases, the generated magnetic fields are dipolar. Our results show that the dynamos, especially magnetic field structures, are independent in our investigated cases on the electrical conductivity of the inner core. This is in agreement with results obtained in previous analyses. The influence of non-uniform stratification is for our parameters weak, which is understandable because most of the shell is unstably stratified, and the stably stratified region is only a thin layer near the CMB. The teleconvection is not observed in our study. However, the influence of the Prandtl number is strong. The generated magnetic fields do not become weak in the polar regions because the magnetic field inside the tangent cylinder is always regenerated due to the weak magnetic diffusion.


2015 ◽  
Vol 57 (6) ◽  
Author(s):  
Domenico Di Mauro ◽  
Lili Cafarella ◽  
Stefania Lepidi ◽  
Manuela Pietrolungo ◽  
Laura Alfonsi ◽  
...  

<p>A geomagnetic observatory is a permanent facility where magnetic declination and inclination are recorded in conjunction with the temporal evolution of the magnetic field components. Polar regions are scarcely covered by observational points then the contributions from observatories located there are particularly relevant. The geomagnetic observatory at Concordia station, Dome C - Antarctica is located in the inner part of the continent, its position is favorable for two key reasons, i) data are unaltered by the "coastal effect” and ii) crustal effect is negligible due to the thickness, almost 3 km, of ice coverage. Nevertheless, these latter conditions imply an unconsidered aspect which characterizes the entire station and every structure laying on the ice surface: the dome on which Concordia station resides is sliding horizontally and moving vertically with a velocity of few millimeter to centimeters per year as indicated by independent geodetic observations. This slow and continuous movement has a puzzling effect on the trend of horizontal components of the magnetic field, sampled in a time window of a decade since the establishing of the observatory in 2005. During the International Polar Year (2007-2009) the observatory was upgraded with new equipment fulfilling the requirements of the Intermagnet consortium, and becoming an observatory member in 2011. In this paper are illustrated the strategy adopted to track any possible displacement of the observatory reference points (i.e. the azimuth mark, the pillar position) and all the ordinary and extraordinary actions required for collecting high quality data.</p>


2019 ◽  
Vol 47 (1) ◽  
pp. 85-87
Author(s):  
E.V. Maiewski ◽  
R.A. Kislov ◽  
H.V. Malova ◽  
O.V. Khabarova ◽  
V.Yu. Popov ◽  
...  

A stationary axisymmetric MHD model of the solar wind has been constructed, which allows us to study the spatial distribution of the magnetic field and plasma characteristics at radial distances from 20 to 400 radii of the Sun at almost all heliolatitudes. The model takes into account the changes in the magnetic field of the Sun during a quarter of the solar cycle, when the dominant dipole magnetic field is replaced by a quadrupole. Selfconsistent solutions for the magnetic and velocity fields, plasma concentration and current density of the solar wind depending on the phase of the solar cycle are obtained. It is shown that during the domination of the dipole magnetic component in the solar wind heliospheric current sheet (HCS) is located in the equatorial plane, which is a part of the system of radial and transverse currents, symmetrical in the northern and southern hemispheres. As the relative contribution of the quadrupole component to the total magnetic field increases, the shape of the HCS becomes conical; the angle of the cone gradually decreases, so that the current sheet moves entirely to one of the hemispheres. At the same time, at high latitudes of the opposite hemisphere, a second conical HCS arises, the angle of which increases. When the quadrupole field becomes dominant (at maximum solar activity), both HCS lie on conical surfaces inclined at an angle of 35 degrees to the equator. The model describes the transition from the fast solar wind at high latitudes to the slow solar wind at low latitudes: a relatively gentle transition in the period of low solar activity gives way to more drastic when high solar activity. The model also predicts an increase in the steepness of the profiles of the main characteristics of the solar wind with an increase in the radial distance from the Sun. Comparison of the obtained dependences with the available observational data is discussed.


1999 ◽  
Vol 202 (8) ◽  
pp. 891-908 ◽  
Author(s):  
M.E. Deutschlander ◽  
J.B. Phillips ◽  
S.C. Borland

Light-dependent models of magnetoreception have been proposed which involve an interaction between the magnetic field and either magnetite particles located within a photoreceptor or excited states of photopigment molecules. Consistent with a photoreceptor-based magnetic compass mechanism, magnetic orientation responses in salamanders, flies and birds have been shown to be affected by the wavelength of light. In birds and flies, it is unclear whether the effects of light on magnetic orientation are due to a direct effect on a magnetoreception system or to a nonspecific (e.g. motivational) effect of light on orientation behavior. Evidence from shoreward-orienting salamanders, however, demonstrates that salamanders perceive a 90 degrees counterclockwise shift in the direction of the magnetic field under long-wavelength (&gt;=500 nm) light. A simple physiological model based on the antagonistic interaction between two magnetically sensitive spectral mechanisms suggests one possible way in which the wavelength-dependent effects of light on the salamander's magnetic compass response might arise. Assuming that the wavelength-dependent characteristics of the avian magnetic response can be attributed to an underlying magnetoreception system, we discuss several hypotheses attempting to resolve the differences observed in the wavelength-dependent effects of light on magnetic orientation in birds and salamanders. By considering the evidence in the context of photoreceptor- and non-photoreceptor-based mechanisms for magnetoreception, we hope to encourage future studies designed to distinguish between alternative hypotheses concerning the influence of light on magnetoreception.


1958 ◽  
Vol 6 ◽  
pp. 295-311
Author(s):  
V. C. A. Ferraro

The evidence in favour of a corpuscular theory of magnetic storms is briefly reviewed and reasons given for believing that the stream must be neutral but ionized and carry no appreciable current. It is shown that under suitable conditions the stream is able to pass freely through a solar magnetic field; the stream may also be able to carry away with it a part of this field. However, because of geometrical broadening of the stream during its passage from the sun to the earth, the magnetic field imprisoned in the gas may be wellnigh unobservable near the earth.The nature, composition and dimensions of the stream near the earth are discussed and it is concluded that on arrival the stream will present very nearly a plane surface to the earth if undistorted by the magnetic field.Because of its large dimensions, the stream will behave as if it were perfectly conducting. During its advance in the earth's magnetic field the currents induced in the stream will therefore be practically confined to the surface. The action of the magnetic field on this current is to retard the surface of the stream which being highly distortible will become hollowed out. Since the stream surface is impervious to the interpenetration of the magnetic tubes of force, these will be compressed in the hollow space. The intensity of the magnetic field is thereby increased and this increase is identified with the beginning of the first phase of a magnetic storm. This increase will be sudden, as observed, owing to the rapid approach of the stream to the earth.The distortion of the stream surface is discussed and it is pointed out that two horns will develop on the surface, one north and the other south of the geomagnetic equator. Matter pouring through these two horns will find its way to the polar regions.The main phase of a magnetic storm seems most simply explained as due to a westward ring-current flowing round the earth in its equatorial plane. Under suitable conditions such a ring-current would be stable if once set up. The mode of formation of the ring is, however, largely conjectural. The possibility that the main phase may be of atmospheric origin is also briefly considered. It is shown that matter passing through the two horns to the polar regions could supply the energy necessary for the setting up of the field during the main phase. The magnetic evidence in favour of such a hypothesis, however, seems wanting.


2016 ◽  
Vol 13 (118) ◽  
pp. 20151010 ◽  
Author(s):  
Roswitha Wiltschko ◽  
Margaret Ahmad ◽  
Christine Nießner ◽  
Dennis Gehring ◽  
Wolfgang Wiltschko

The Radical Pair Model proposes that the avian magnetic compass is based on spin-chemical processes: since the ratio between the two spin states singlet and triplet of radical pairs depends on their alignment in the magnetic field, it can provide information on magnetic directions. Cryptochromes, blue light-absorbing flavoproteins, with flavin adenine dinucleotide as chromophore, are suggested as molecules forming the radical pairs underlying magnetoreception. When activated by light, cryptochromes undergo a redox cycle, in the course of which radical pairs are generated during photo-reduction as well as during light-independent re-oxidation. This raised the question as to which radical pair is crucial for mediating magnetic directions. Here, we present the results from behavioural experiments with intermittent light and magnetic field pulses that clearly show that magnetoreception is possible in the dark interval, pointing to the radical pair formed during flavin re-oxidation. This differs from the mechanism considered for cryptochrome signalling the presence of light and rules out most current models of an avian magnetic compass based on the radical pair generated during photo-reduction. Using the radical pair formed during re-oxidation may represent a specific adaptation of the avian magnetic compass.


2008 ◽  
Vol 4 (S259) ◽  
pp. 437-438 ◽  
Author(s):  
Thorsten A. Carroll ◽  
Markus Kopf ◽  
Klaus G. Strassmeier ◽  
Ilya Ilyin ◽  
Ilkka Tuominen

AbstractWe present Zeeman-Doppler images of the active K2 star II Peg for the years 2004 and 2007. The surface magnetic field was reconstructed with our new ZDI code iMap which provides a full polarized radiative transfer driven inversion to simultaneously reconstruct the surface temperature and magnetic vector field distribution. II Peg shows a remarkable large scale magnetic field structure for both years. The magnetic field is predominantly located at high latitudes and is arranged in active longitudes. A dramatic evolution in the magnetic field structure is visible for the two years, where a dominant and largely unipolar field in 2004 has changed into two distinct and large scale bipolar structures in 2007.


2002 ◽  
Vol 205 (24) ◽  
pp. 3903-3914 ◽  
Author(s):  
John B. Phillips ◽  
S. Chris Borland ◽  
Michael J. Freake ◽  
Jacques Brassart ◽  
Joseph L. Kirschvink

SUMMARYExperiments were carried out to investigate the earlier prediction that prolonged exposure to long-wavelength (&gt;500 nm) light would eliminate homing orientation by male Eastern red-spotted newts Notophthalmus viridescens. As in previous experiments, controls held in outdoor tanks under natural lighting conditions and tested in a visually uniform indoor arena under full-spectrum light were homeward oriented. As predicted, however,newts held under long-wavelength light and tested under either full-spectrum or long-wavelength light (&gt;500 nm) failed to show consistent homeward orientation. The newts also did not orient with respect to the shore directions in the outdoor tanks in which they were held prior to testing. Unexpectedly, however, the newts exhibited bimodal orientation along a more-or-less `fixed' north-northeast—south-southwest magnetic axis. The orientation exhibited by newts tested under full-spectrum light was indistinguishable from that of newts tested under long-wavelength light,although these two wavelength conditions have previously been shown to differentially affect both shoreward compass orientation and homing orientation. To investigate the possibility that the `fixed-axis' response of the newts was mediated by a magnetoreception mechanism involving single-domain particles of magnetite, natural remanent magnetism (NRM) was measured from a subset of the newts. The distribution of NRM alignments with respect to the head—body axis of the newts was indistinguishable from random. Furthermore, there was no consistent relationship between the NRM of individual newts and their directional response in the overall sample. However, under full-spectrum, but not long-wavelength, light, the alignment of the NRM when the newts reached the 20 cm radius criterion circle in the indoor testing arena (estimated by adding the NRM alignment measured from each newt to its magnetic bearing) was non-randomly distributed. These findings are consistent with the earlier suggestion that homing newts use the light-dependent magnetic compass to align a magnetite-based `map detector'when obtaining the precise measurements necessary to derive map information from the magnetic field. However, aligning the putative map detector does not explain the fixed-axis response of newts tested under long-wavelength light. Preliminary evidence suggests that, in the absence of reliable directional information from the magnetic compass (caused by the 90° rotation of the response of the magnetic compass under long-wavelength light), newts may resort to a systematic sampling strategy to identify alignment(s) of the map detector that yields reliable magnetic field measurements.


2012 ◽  
Vol 490-495 ◽  
pp. 2510-2514
Author(s):  
Yi Bo Feng ◽  
Xi Sheng Li ◽  
Xiao Juan Zhang

In the view of the disadvantages brought by DMC(digital magnetic compass) and gyro when they are used separately, a combined directional instrument composed by a 3-axes digital magnetic compass and a 3-axes MEMS gyro for vehicles is introduced, which is less influenced to the magnetic field interference and random drift. In the abnormal magnetic field, the MEMS gyro is used for correcting the heading angle of DMC. The experiment data shows that this instrument can output a stable and high-precision heading angle. It can be used to provide heading angle for vehicles.


2016 ◽  
Vol 46 (3) ◽  
pp. 221-244 ◽  
Author(s):  
Ján Šimkanin

Abstract Hydromagnetic dynamos are numerically investigated at low Prandtl, Ekman and magnetic Prandtl numbers using the PARODY dynamo code. In all the investigated cases, the generated magnetic fields are dominantly-dipolar. Convection is small-scale and columnar, while the magnetic field maintains its large-scale structure. In this study the generated magnetic field never becomes weak in the polar regions, neither at large magnetic Prandtl numbers (when the magnetic diffusion is weak), nor at low magnetic Prandtl numbers (when the magnetic diffusion is strong), which is a completely different situation to that observed in previous studies. As magnetic fields never become weak in the polar regions, then the magnetic field is always regenerated in the tangent cylinder. At both values of the magnetic Prandtl number, strong polar magnetic upwellings and weaker equatorial upwellings are observed. An occurrence of polar magnetic upwellings is coupled with a regenaration of magnetic fields inside the tangent cylinder and then with a not weakened intensity of magnetic fields in the polar regions. These new results indicate that inertia and viscosity are probably negligible at low Ekman numbers.


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