Component Of Geomagnetic Field Research Articles

Annual and semiannual variations of the lunar semidiurnal geomagnetic field components at North American locations.

Annual and semiannual variations of the lunar semidiurnal geomagnetic field components at North American locations.

Conditions for the geomagnetic induction relationship

A sufficient condition for the linear relationship between the vertical and horizontal components of the time-varying geomagnetic field is that the primary field can be expressed as a linear sum of two fields, each of which has a consistent morphology. This is approximately fulfilled if local induction is predominant and the primary field is approximately horizontal.

Magnetic contour maps at the core-mantle boundary.

Contour maps of the northward, eastward, and downward components of the main geomagnetic field and of the field intensity at the surface of earth's liquid core are presented and compared with similar maps at earth's surface. The mantle is assumed to be an insulator for purposes of the extrapolation. Maximum values of the individual field components are found to be amplified by factors of order 10-20 and the maximum field intensity by 12 over the value at earth's surface and the increase in small scale structure is evident. By comparing maps of places where Br=0 at different truncation levels, we find that even for a recent magnetic model which best fits the data quite well, contours of the field extrapolated to the core are quite sensitive to truncation level. This suggests a need to develop nonlinear data-fitting procedures if one's interest is in precise location of field contours rather than in estimating field values.

Geomagnetic disturbances and associated phase anomalies of a VLF radio wave at midlatitudes.

Phase anomalies of VLF radio waves were investigated in relation to geomagnetic disturbances, using data obtained from the reception of the NLK station during 37 months from August 1970 to December 1974. The horizontal component of geomagnetic field observed at Memambetsu (Japan) together with the Ap index is used as an index of intensity of a geomagnetic disturbance. Primary storm effects on the phase anomalies during nighttime with an average value of 8μsec have a tendency to occur 2 hours later than the decrease of horizontal component of geomagnetic field with an average value of 70 gammas (hourly mean value). Storm after-effects which are the main features at midlatitudes continue for 3 days with large phase anomalies and further continue for about 5 days with small ones. Phase anomalies were observed during the daytime when the solar zenith angle was about 70° and observed during severe storm periods even with a solar zenith angle of 30°. Sudden phase anomalies were observed just after magnetic Pi pulsations.

An important statistical consideration, and the effect of the interplanetary magnetic field on the quiet time variation of the geomaganetic field

We present an analysis of some interplanetary and geomagnetic field data and at the same time attempt to show that erroneous conclusions may be drawn if the effects of autocorrelation are not taken into account in standard least squares regression methods. We found the following conclusions survived the autocorrelation corrections to simple correlation tests (i) that the directed z component of the interplanetary magnetic field (IMF) affects the first few Fourier terms in the daily variation of the vertical component of the quiet geomagnetic field (ii) ΣK p correlates with the daily mean magnitude of the IMF.

Solar flare effects in equatorial counter electrojet currents

THE solar flare effect on the horizontal component of the geomagnetic field (H) during the period of counter equatorial electrojet current is characterised by a negative crochet (decrease of the H field) at an equatorial electrojet station and a positive crochet (increase of H field) at a low latitude station outside the electrojet belt. During the period of partial counter electrojet, the crochet in H may be positive at all low latitude stations but the amplitude decreases at stations nearer to the equator. We explain this as the combined effect of the solar flare on the normal eastward currents over the Equator associated with Sq current system (around 107–110 km) as well as on the westward counter electrojet current (∼ 100 km) both flowing simultaneously over the low latitude stations, while at stations outside the equatorial region the solar flare effect is due to only the eastward Sq currents. (The Sq currents are currents in the upper atmosphere arising from convective motion through the geomagnetic field1,2.)

Geomagnetic effect associated with X-ray flare from Sco X-1

THE effect on the night-time lower ionosphere of X radiation from celestial sources is a topic of some controversy1–4. An X-ray flare from Sco X-1 has been shown to have a daytime effect on the ionosphere5 and it has also been reported6 that celestial X-ray sources have a nocturnal effect on the lower ionosphere in certain conditions. Galactic X-ray ionisation has been shown7–9 to affect night-time geomagnetic field components.

Galactic X-ray ionization effects in geomagnetic horizontal field

Examination of the night-time geomagnetic horizontal field component at Alibag for international quiet-days of solar minimum epochs, show effects of galactic X-ray ionization as depressions in the field approximately corresponding to transit times of individual sources.

Measurement of the geomagnetic field using parametric resonances in optically pumped He<sup>4</sup>

A single-axis vector magnetometer which can be used to measure changes in geomagnetic field components has been constructed using a parametric resonance in the optically pumped 23S 1 level of He4. The principle of operation for the n=1, p=1 parametric resonance is described. This resonance has a peak amplitude-to-noise ratio of 1.2 \times 10^{4} in a 0.5 Hz noise bandwidth and a 14.9 \times 10^{-4} G linewidth. The performance of the instrument is demonstrated by observing changes in the earth's field and 1.0μG calibration signals. Sensitivity is established to be 1.0 \times 10^{-7} G in a 5 Hz noise bandwidth.

科学衛星“しんせい”のスピン速度の減衰に対する地磁気の影響について

The spin decay of our first scientific satellite (1971-080 A) seems to give a clear evidence to the statement that a spin-stabilized earth satellite suffers the spin decay resulting from energy losses in the form of eddy currents and/or magnetic hysteresis. The analysis of the spin decay is presented in this paper, together with the observed data. A close corelation is found between the rate of spin decay and the magnitude of geomagnetic field component normal to the spin axis. With the aid of the torque measurement using a torque-meter, it is concluded that the torque due to the magnetic hysteresis is negligibly small as compared to the one due to the eddy currents. The average torque acting on Shinsei in its orbit is estimated to be roughly 12 dyne-cm.

Longitudinal spread of equatorial Sq variability

The quiet day daily range ΔH = H max − H min of the H component of geomagnetic field at the Equator is known to have a large day-to-day variability which is intimately connected with equatorial ionospheric upheavals. Its longitudinal extent is studied here by comparing ΔH at different longitudes. It is shown that the longitudinal extent is often restricted to less than 180° corresponding to less than 12 hr.

Coordinate system for use with high-latitude energetic-particle phenomena

The coordinate system generally used to describe the structure of solar-particle profiles over the polar caps is based on invariant latitude and magnetic local time. By using trajectory integrations in a model geomagnetic field a new coordinate system is developed that is not based on internal geomagnetic-field components alone but also takes into account the currents flowing in the magnetopause and the neutral sheet. It is shown that the new coordinate system is more relevant for the interpretation of high-latitude energetic-particle data than the old system and that its use makes it possible to calculate reconnection rates and scattering mean free paths in the tail. In a companion paper the results of the calculations performed here are applied to observations first to decide which magnetosphere model (open or diffusive) is appropriate and second to use the solar-particle data for making measurements of important magnetospheric parameters.

Day-to-day variability of the quiet-day daily range of equatorial geomagnetic field and its relationship with ionospheric dynamics

To study the day-to-day variability of the daily range ΔH = H max − H min of the H component of geomagnetic field at the Equator, quiet days ( A p = 0–8) in the quiet sun year 1964 were divided into four ranges viz. 0–69 gamma, 70–89 gamma, 90–109 gamma and 110 or more gamma of ascending ΔH values at Trivandrum for the three seasons J, D, E separately. Average daily variation patterns of several parameters for these 12 groups were studied. It was found that enhanced ΔH at Trivandrum was well correlated with the northern S q current strength only in winter when the latter was weak. ΔH at Trivandrum was poorly correlated with ΔH at Alibag as also with solar radiation parameters (10.7 cm and X-ray fluxes) in all seasons, and moderately correlated with the southern component of interplanetary magnetic field B z t. In contrast, ΔH at Alibag was moderately correlated with the B x and B v components. Sevral other peculiarities of corresponding ΔY and ΔZ components and associated upheavals in ionospheric F-region parameters at equatorial and middle latitudes are presented and discussed. It is concluded that the day-to-day variability of ΔH at equatorial and middle latitudes is primarily connected with ionospheric upheavals which seem to be connected with different interplanetary parameters for different latitudes.

The disappearance of equatorial E s and the reversal of electrojet current

Based on simultaneous observations of the horizontal geomagnetic field component H, sporadic E (E s ) and E-W electron drifts at stations close to the dip equator within the equatorial electrojet region, it has been found that on quiet days and sometimes on disturbed days, when there is an abnormal large decrease in H during daytime, there is a simultaneous disappearance of E s and a reversal of the direction of drift of electrons from westward to eastward. This suggests that the disappearance of equatorial E s during day-time is due to a temporary reversal of the electrojet current, which is caused by the imposition of an additional electrostatic field opposite in direction to that of normal S a field.

Enhancements in electron content at Arecibo during geomagnetic storms

A phenomenon has been observed at Arecibo, Puerto Rico in which the total electron content of the ionosphere, in a column nearly parallel to the geomagnetic field, is enhanced in the afternoon or night during a magnetic disturbance. The enhancement is associated with the large negative excursion in the H component of the local geomagnetic field induced by the ring current. The enhancements which occur at night begin simultaneously with a downward motion of the F layer. This motion however is not a disturbance phenomenon as it is observed on 85 per cent of all nights at Arecibo regardless of magnetic activity. The downward motion and the enhancement in electron content which accompanies it on disturbed nights commence later in local time at higher latitudes. Neither north-south nor east-west motions of ionization appear to be able to explain the nighttime enhancements unless in the latter case eastward winds with velocities greater than 500 m/sec exist. Diffusion of ionization from the protonosphere and direct ionization have also been excluded as possible mechanisms.

Frequency variations of Schumann resonances

The resonances of the earth-to-ionosphere cavity are analyzed by considering the different propagation characteristics of day and night hemispheres. The azimuthal unsymmetries cause mode splitting, but the amplitudes of these additional split modes appear to be negligible for normal conditions. Diurnal variations of the resonance frequencies of the vertical electric field differ from the frequency variations of the horizontal magnetic field. The electric field resonance frequencies can explain the complete diurnal variation of the measured fundamental resonance if local equatorial thunderstorm activity, which peaks in late afternoon over land, is changed to a variation, which peaks at night for sources over the Pacific. The frequency variations are caused by the interaction of adjacent resonance modes. An eccentric geomagnetic field may cause comparable frequency changes if the nighttime phase velocity is decreased with an increasing magnitude of the radial geomagnetic field component. Such a phase velocity variation is not observed for nighttime ionosphere models that account for various F-layer altitudes.

Flayer reflections and ion effects in the propagation of terrestrial ELF waves

At night, ELF waves penetrate above the D layer, and propagation parameters of the earth to ionosphere wave guide are dependent on the detailed ionospheric structure below the F layer. The propagation characteristics are dependent on the altitude of the F layer, the electron density below this layer, the magnitude of the radial geomagnetic field component, and also on ions that tend to increase the absorption of the penetrating magneto-ionic mode. The propagation parameters of individual ionosphere models appear to be too erratic to explain long distance or global wave propagation, but the average of the propagation parameters derived for a number of different propagation geometries becomes comparable to the parameters deduced from a simpler isotropic ionosphere model, where waves are confined to altitudes below 100 km.

Time and latitude variations of blanketing sporadicEof different intensities

An in-depth study of blanketing sporadic E (Es) layers at temperate latitudes has been carried out with the purpose of clearly establishing many pertinent details of their temporal and latitudinal variations. A new method of analysis has been used in which blanketing Es layers have been separated into four groups according to their intensity, which is defined in terms of the ratio (ƒbEs/ƒoE). From an analysis of eight-years' (1958–1965) data of hourly ƒbEs, values at ten stations, it has been possible to establish, for the first time, that (1) Es layers of different intensities show different daytime variations with regard to their occurrence, and (2) there is a clear-cut change from higher to lower midlatitudes in the pattern of these daytime variations. It is shown that the daytime Es occurrence does not go through two maxima at all latitudes and in all seasons. The seasonal and solar cycle variations in the average ƒbEs and in the percentage occurrence of Es layers in each group are also shown. The ƒbEs values of intense Es layers show a marked decrease with decreasing solar activity, and this indicates the existence of solar cycle variation in the neutral wind shears and possibly in other relevant parameters in the E region. On the other hand, the occurrence of ‘intense’ and ‘moderately strong’ Es layers shows an increase with decreasing solar activity. Both features are shown to be consistent with the conclusions of wind-shear theory. A careful analysis of the Es variations with geographic latitude and with H (the horizontal component of geomagnetic field) has produced no unambiguous evidence for the dependence of Es occurrence or ƒbEs on H; and the inability of the present analysis to bring out this theoretically predicted dependence is attributed to the possibility that significant variations of neutral wind shears with latitude and geographic location can easily obscure the dependence on H. It is shown that the abnormally high incidence of ‘intense’ Es layers at Kokubunji is a purely summertime phenomenon. It is pointed out that this high incidence at Kokubunji cannot be explained in terms of the large H value alone, but the occurrence of very strong wind shears at this station has to be assumed. It is emphasized that much self-restraint is needed against making simplistic statements about the observed morphological characteristics of sporadic E.

The electrojet phenomenon

Abstract The term ‘electrojet’ is frequently used to describe the intense bands of electric curent which flow at certain times in the earth's ionosphere at an altitude of about 100 km. Two main forms of electrojet current are distinguished; an equatorial electrojet which flows during the daylight hours in a narrow band of latitudes centred on the magnetic equator, and an auroral electrojet which flows during the main phese of magnetic storms in auroral regions. Both are accompanied by abnormally large changes in the geomagnetic field components as measured at the earth's surface. This article reviews the main features of the two forms of electrojet and discusses the present theories for their origin. Ionospheric irregularities are associated with both types of electrojet, and the experimental evidence so far accumulated indicates that these are produced by plane plasma waves generated by a two-stream instability in the plasma and travelling with the acoustic velocity of about 360 m s−1.

Measurements of Components of Geomagnetic Field with Proton Precession Magnetometers

Measurements of Components of Geomagnetic Field with Proton Precession Magnetometers