Distribution Of Aurora Research Articles

Овал полярных сияний – прекрасная, но устаревшая парадигма

Being an important region of the polar ionosphere, the auroral oval is considered in many studies on the disturbed magnetosphere. The oval seems to be thoroughly known to all researchers, but there is evidence of misunderstanding in some papers, so it is time to review this matter. Most works describing the auroral position and dynamics were published more than a half-century ago and became a rarity. In this paper, we tell the history of studies on distribution of auroras before the oval was discovered. We also touch upon the discovery of the oval and tell how it changed our viewpoint on the magnetospheric processes. Besides, we describe how the oval paradigm developed and became non-productive (from our point of view) for studying the structure of the magnetosphere and magnetospheric disturbances. Finally we show the position of the aural zone and auroral magnetosphere among the main domains of the magnetosphere.

The planetary distribution of auroras

Aurora studies began relatively recently, slightly more than a century ago. The authors discuss the contribution of Russian scientists to the study of this phenomenon and the recent attempts to explain the nature of this mysterious phenomenon.

Spiral structures and regularities in magnetic field variations and auroras

Abstract. The conception of spiral shaped precipitation regions, where solar corpuscles penetrate the upper atmosphere, was introduced into geophysics by C. Störmer and K. Birkeland at the beginning of the last century. Later, in the course of the XX-th century, spiral distributions were disclosed and studied in various geophysical phenomena. Most attention was devoted to spiral shapes in the analysis of regularities pertaining to the geomagnetic activity and auroras. We review the historical succession of perceptions about the number and positions of spiral shapes, that characterize the spatial-temporal distribution of magnetic disturbances. We describe the processes in the upper atmosphere, which are responsible for the appearance of spiral patterns. We considered the zones of maximal aurora frequency and of maximal particle precipitation intensity, as offered in the literature, in their connection with the spirals. We discuss the current system model, that is closely related to the spirals and that appears to be the source for geomagnetic field variations during magnetospheric substorms and storms. The currents in ionosphere and magnetosphere constitute together with field-aligned (along the geomagnetic field lines) currents (FACs) a common 3-D current system. At ionospheric heights, the westward and eastward electrojets represent characteristic elements of the current system. The westward electrojet covers the longitudinal range from the morning to the evening hours, while the eastward electrojet ranges from afternoon to near-midnight hours. The polar electrojet is positioned in the dayside sector at cusp latitudes. All these electrojets map along the magnetic field lines to certain plasma structures in the near-Earth space. The first spiral distribution of auroras was found based on observations in Antarctica for the nighttime-evening sector (N-spiral), and later in the nighttime-evening (N-spiral) and morning (M-spiral) sectors both in the Northern and Southern Hemispheres. The N- and M-spirals drawn in polar coordinates form an oval, along which one observes most often auroras in the zenith together with a westward electrojet. The nature of spiral distributions in geomagnetic field variations was unabmibuously interpreted after the discovery of the spiral's existence in the auroras had been established and this caused a change from the paradigm of the auroral zone to the paradigm of the auroral oval. Zenith forms of auroras are found within the boundaries of the auroral oval. The oval is therefore the region of most frequent precipitations of corpuscular fluxes with auroral energy, where anomalous geophysical phenomena occur most often and with maximum intensity. S. Chapman and L. Harang identified the existence of a discontinuity at auroral zone latitudes (Φ ∼ 67°) around midnight between the westward and eastward electrojets, that is now known as the Harang discontinuity. After the discovery of the auroral oval and the position of the westward electrojet along the oval, it turned out, that there is no discontinuity at a fixed latitude between the opposite electrojets, but rather a gap, the latitude of which varies smoothly between Φ ∼ 67° at midnight and Φ ∼ 73° at 20:00 MLT. In this respect the term ''Harang discontinuity'' represents no intrinsic phenomenon, because the westward electrojet does not experience any disruption in the midnight sector but continues without breaks from dawn to dusk hours.

Misregulation of mitotic chromosome segregation in a new type of autosomal recessive primary microcephaly

Primary autosomal recessive microcephaly (MCPH) is a congenital disorder characterized by a pronounced reduction of brain size and mental retardation. We present here a consanguineous Turkish family clinically diagnosed with MCPH and without linkage to any of the known loci (MCPH1-MCPH7). Autozygosity mapping identified a homozygous region of 15.8 Mb on chromosome 10q11.23-21.3, most likely representing a new locus for MCPH. Although we were unable to identify the underlying genetic defect after extensive molecular screening, we could delineate a possible molecular function in chromosome segregation by the characterization of mitosis in the patients’ cells. Analyses of chromosome nondisjunction in T-lymphocytes and fibroblasts revealed a significantly elevated rate of nondisjunction in the patients’ cells as compared to controls. Mitotic progression was further explored by immunofluorescence analyses of several chromosome and spindle associated proteins. We detected a remarkable alteration in the anaphase distribution of Aurora B and INCENP, which are key regulators of chromosome segregation. In particular, a fraction of both proteins remained abnormally loaded on chromosomes during anaphase in MCPH patients’ cells while in cells of normal control subjects both proteins are completely transferred to the spindle midzone. We did not observe any other alterations regarding cell cycle progression, chromosome structure, or response to DNA damage. Our observations point towards a molecular role of the underlying gene product in the regulation of anaphase/telophase progression possibly through interaction with chromosomal passenger proteins. In addition, our findings represent further evidence for the proposed role of MCPH genes in the regulation of mitotic progression.

Comment on “The importance of auroral features in the search for substorm onset process” by Syun-Ichi Akasofu, A. T. Y. Lui, and C.-I. Meng

Comment on “The importance of auroral features in the search for substorm onset process” by Syun-Ichi Akasofu, A. T. Y. Lui, and C.-I. Meng

Distribution of Auroras in the Southern Hemisphere. III. Comparison with Northern Hemisphere

While the distribution of auroras in the southern hemisphere is well represented n terms of each of the parameters 81, 82, and 83 (introduced in Part II), the northern emispheres distribution is not satisfactorily represented in terms of 81. In terms of 2 or 83, and within the limits of accuracy of the data, the distributions in the two hemispheres are conjugate. To carry this investigation further, much more accurate data and more refined concepts are required.

The morphology of the auroral displays of 1957-1958: 1. Statistical analyses of Alaska data

A study of the variation of auroral phenomena with local time and geomagnetic latitude has been made using data from a meridional array of all-sky cameras located in Alaska. It is found that the form of the diurnal variation is dependent upon the criteria of auroral activity used: those criteria that are based on the counting of forms peak near local midnight, whereas those based on the total luminosity in the sky show high activity in the morning hours. The maximum incidence of aurora is found to occur near 66½°N geomagnetic latitude, and the distribution of aurora with latitude between 60° and 70°N is determined. Although the southern extent of auroras retreat northward after local magnetic midnight, the southward motion of the individual forms observed south of the auroral zone peak predominates over the northward motion throughout the night.

Distribution of Auroras in the Southern Hemisphere. II. Nightly Probability of Overhead Aurora

The probability P of overhead occurrence of aurora during a night is estimated for 22 southern hemisphere stations during the I.G.Y. The distribution of probability of occurrence is represented in terms of three measures of colatitude: 81 is defined in terms of the eccentric dipole representation of the geomagnetic field; 82 is defined in terms of projections from circles in the equatorial plane, along the geomagnetic lines of force, onto the Earth; 83 is defined in terms of the integral invariant f; (I-F IF m)!dl of charged particle motion in the geomagnetic field.

THE AZIMUTHAL DISTRIBUTION OF ULTRA-HIGH FREQUENCY RADAR ECHOES FROM AURORA

The distribution in range and azimuth of auroral echoes obtained with an ultra-high frequency radar at Prince Albert is examined. Such distributions may be controlled (i) by the effect of volume integration in the auroral configurations, (ii) by the geographical distribution of aurora, and (iii) by aspect sensitivity of the auroral scatterers. With the radar parameters chosen for this experiment, (i) can be neglected. Of the remaining two effects, (ii) appears to be more important in the period immediately before local midnight and (iii) in the period immediately following local midnight.

Distribution of Auroras in the Southern Hemisphere

Several attempts to delineate the southern zone of maximum frequency of visibility of auroras have led to widely discrepant results. That of White and Geddes (1939) suffered through lack of observations; that of Vestine and Snyder (1945) was based on observed relations between morphology of geomagnetic disturbance and auroras in the northern hemisphere, and application to the southern hemisphere using very limited geomagnetic data. It may be, too, that the distribution of auroras changes slowly with solar activity.

Preliminary studies of the distribution of auroras in Alaska

The analysis of auroral observations for 1951–53 from five stations spread over Alaska shows a zone at geomagnetic latitude 68° for which the incidence of auroras is independent of magnetic activity. At geomagnetic latitudes south of 67° the incidence of auroras is markedly dependent upon magnetic activity.

On the α-Ray Theory of Aurora Borealis

IN a letter to NATURE of April 13 (vol. lxxxvi., p. 213) I gave reasons for the view that at least some of the forms of aurora borealis are caused by a type of rays which, as regards absorption by matter, follow the same law as α rays from radio-active substances. In the letter I also mentioned that the diurnal distribution of aurora apparently would require a negative charge of the rays.