THE DIURNAL PROBLEM IN AEROMAGNETIC SURVEYING IN CANADA

Geophysics ◽  
1961 ◽  
Vol 26 (2) ◽  
pp. 211-228 ◽  
Author(s):  
K. Whitham ◽  
E. R. Niblett
Keyword(s):  
Direct Methods ◽  
Magnetic Activity ◽  
Auroral Zone ◽  
Aeromagnetic Survey ◽  
Autocorrelation Functions ◽  
Frequency Distributions ◽  
Practical Applications ◽  
Field Fluctuations ◽  
Survey Results ◽  
Time Variations

Errors introduced into aeromagnetic survey results because of geomagnetic time variations have been analyzed in two ways. In the first, statistical properties of average magnetic disturbance have been calculated for five locations well distributed in latitude in Canada. The autocorrelation functions of vertical magnetic field fluctuations have been used to estimate errors in aeromagnetic surveying as a function of the length of the base loop and the length of the traverse lines or profiles, for five latitudes. In practical applications, the r.m.s. errors are proportional to the square root of elapsed time. These results can be explained in terms of the shape of the autocorrelation functions, and models of disturbance which might produce them are discussed. In the second part experimental results are presented of a comparison of total field intensity fluctuations measured with recording proton precession magnetometers at two pairs of stations, one pair 26 miles apart and the other 94 miles apart. The measurements were taken in Western Canada south of the auroral zone. The r.m.s. differences in the time variations have been determined quantitatively for each hour for both pairs of stations; statistically, it was found that these differences were proportional to the r.m.s. level of magnetic activity and, in this region, to the separation of the stations. The frequency distributions of the r.m.s. differences between the two pairs of stations for the month of September 1959 have been determined. A comparison of the indirect and direct methods of correction indicates that scientifically, in this region, there is little to choose between them in terms of accuracy. Operational considerations are mentioned.

IRREGULAR MAGNETIC ACTIVITY IN NORTHERN CANADA WITH SPECIAL REFERENCE TO AEROMAGNETIC SURVEY PROBLEMS

Geophysics ◽  
1957 ◽  
Vol 22 (3) ◽  
pp. 646-659 ◽  
Author(s):  
K. Whitham ◽  
E. I. Loomer
Keyword(s):  
Magnetic Activity ◽  
Auroral Zone ◽  
Maximum Activity ◽  
High Latitudes ◽  
Aeromagnetic Survey ◽  
Northern Canada ◽  
K Index ◽  
Seasonal Characteristics ◽  
Short Period ◽  
Two Peaks

An investigation of the diurnal and seasonal characteristics of irregular magnetic activity in northern Canada, using two indices of disturbance, shows that in general the K index provides a reliable but smoothed measure of short period activity. Two peaks of activity are evident, a day‐time peak, dominant inside the polar cap, and a night peak, dominant south of the auroral zone. The latter occurs within one hour of local geomagnetic midnight at four Canadian observatories, whereas the day‐time peak occurs progressively later at higher latitudes. The maximum activity occurs in the equinoxes at latitudes near the auroral zone, and during the summer solstice at very high latitudes. Measurements of range at the most disturbed observatory suggest that aeromagnetic surveying in high latitudes is in general feasible, but that for accurate reconnaissance work it is very advantageous to plan operations, so far as conditions permit, taking account of the systematic diurnal variation of disturbance. It is shown that errors of about one half the assumed diurnal change between base lines will occur and sufficient data is given to allow approximate predictions of the optimum length of flight lines.

scholarly journals SABRE observations of Pi2 pulsations: case studies

1997 ◽  
Vol 15 (1) ◽  
pp. 40-53 ◽  
Author(s):  
E. G. Bradshaw ◽  
M. Lester
Keyword(s):  
Case Studies ◽  
Magnetic Activity ◽  
Auroral Zone ◽  
Field Of View ◽  
Ionospheric Currents ◽  
Pi2 Pulsation ◽  
First Case ◽  
Pi2 Pulsations ◽  
Generation Region

Abstract. The characteristics of substorm-associated Pi2 pulsations observed by the SABRE coherent radar system during three separate case studies are presented. The SABRE field of view is well positioned to observe the differences between the auroral zone pulsation signature and that observed at mid-latitudes. During the first case study the SABRE field of view is initially in the eastward electrojet, equatorward and to the west of the substorm-enhanced electrojet current. As the interval progresses, the western, upward field-aligned current of the substorm current wedge moves westward across the longitudes of the radar field of view. The westward motion of the wedge is apparent in the spatial and temporal signatures of the associated Pi2 pulsation spectra and polarisation sense. During the second case study, the complex field-aligned and ionospheric currents associated with the pulsation generation region move equatorward into the SABRE field of view and then poleward out of it again after the third pulsation in the series. The spectral content of the four pulsations during the interval indicate different auroral zone and mid-latitude signatures. The final case study is from a period of low magnetic activity when SABRE observes a Pi2 pulsation signature from regions equatorward of the enhanced substorm currents. There is an apparent mode change between the signature observed by SABRE in the ionosphere and that on the ground by magnetometers at latitudes slightly equatorward of the radar field of view. The observations are discussed in terms of published theories of the generation mechanisms for this type of pulsation. Different signatures are observed by SABRE depending on the level of magnetic activity and the position of the SABRE field of view relative to the pulsation generation region. A twin source model for Pi2 pulsation generation provides the clearest explanation of the signatures observed.

scholarly journals Physics of the Applegate mechanism: Eclipsing time variations from magnetic activity

2018 ◽  
Vol 620 ◽  
pp. A42 ◽  
Author(s):  
M. Völschow ◽  
D. R. G. Schleicher ◽  
R. Banerjee ◽  
J. H. M. M. Schmitt
Keyword(s):  
Binary Systems ◽  
Theoretical Work ◽  
Magnetic Activity ◽  
Close Binary ◽  
Magnetic Fluctuations ◽  
Common Envelope ◽  
Stellar Parameter ◽  
Low Mass ◽  
Time Variations ◽  
Binary Separations

Since its proposal in 1992, the Applegate mechanism has been discussed as a potential intrinsical mechanism to explain transit-timing variations in various types of close binary systems. Most analytical arguments presented so far focused on the energetic feasibility of the mechanism while applying rather crude one- or two-zone prescriptions to describe the exchange of angular momentum within the star. In this paper, we present the most detailed approach to date to describe the physics giving rise to the modulation period from kinetic and magnetic fluctuations. Assuming moderate levels of stellar parameter fluctuations, we find that the resulting binary period variations are one or two orders of magnitude lower than the observed values in RS-CVn like systems, supporting the conclusion of existing theoretical work that the Applegate mechanism may not suffice to produce the observed variations in these systems. The most promising Applegate candidates are low-mass post-common-envelope binaries with binary separations ≲1 R⊙ and secondary masses in the range of 0.30 M⊙ and 0.36 M⊙.

scholarly journals Magnetic local time dependence of geomagnetic disturbances contributing to the AU and AL indices

2011 ◽  
Vol 29 (4) ◽  
pp. 673-678 ◽  
Author(s):  
S. Tomita ◽  
M. Nosé ◽  
T. Iyemori ◽  
H. Toh ◽  
M. Takeda ◽  
...  
Keyword(s):  
Local Time ◽  
Geomagnetic Field ◽  
Field Data ◽  
Geomagnetic Latitude ◽  
Magnetic Activity ◽  
Auroral Zone ◽  
Magnetic Local Time ◽  
Geomagnetic Disturbances ◽  
Current Systems ◽  
Local Time Dependence

Abstract. The Auroral Electrojet (AE) indices, which are composed of four indices (AU, AL, AE, and AO), are calculated from the geomagnetic field data obtained at 12 geomagnetic observatories that are located in geomagnetic latitude (GMLAT) of 61.7°–70°. The indices have been widely used to study magnetic activity in the auroral zone. In the present study, we examine magnetic local time (MLT) dependence of geomagnetic field variations contributing to the AU and AL indices. We use 1-min geomagnetic field data obtained in 2003. It is found that both AU and AL indices have two ranges of MLT (AU: 15:00–22:00 MLT, ~06:00 MLT; and AL: ~02:00 MLT, 09:00–12:00 MLT) contributing to the index during quiet periods and one MLT range (AU: 15:00–20:00 MLT, and AL: 00:00–06:00 MLT) during disturbed periods. These results are interpreted in terms of various ionospheric current systems, such as, Sqp, Sq, and DP2.

scholarly journals ROMA (Rank-Ordered Multifractal Analyses) of intermittency in space plasmas – a brief tutorial review

2010 ◽  
Vol 17 (5) ◽  
pp. 545-551 ◽  
Author(s):  
T. Chang ◽  
C. C. Wu ◽  
J. Podesta ◽  
M. Echim ◽  
H. Lamy ◽  
...  
Keyword(s):  
Large Scale ◽  
Auroral Zone ◽  
Space Plasmas ◽  
Dynamic Interactions ◽  
Stochastic Media ◽  
Mhd Simulations ◽  
Field Fluctuations ◽  
In Situ Observations ◽  
Magnetospheric Cusp

Abstract. Intermittent fluctuations are the consequence of the dynamic interactions of multiple coherent or pseudo-coherent structures of varied sizes in the stochastic media (Chang, 1999). We briefly review here a recently developed technique, the Rank-Ordered Multifractal Analysis (ROMA), which is both physically explicable and quantitatively accurate in deciphering the multifractal characteristics of such intermittent structures (Chang and Wu, 2008). The utility of the method is demonstrated using results obtained from large-scale 2-D MHD simulations as well as in-situ observations of magnetic field fluctuations from the interplanetary and magnetospheric cusp regions, and the broadband electric field oscillations from the auroral zone.

scholarly journals The effect of stellar activity on the spectroscopic stellar parameters of the young solar twin HIP 36515

2019 ◽  
Vol 490 (1) ◽  
pp. L86-L90 ◽  
Author(s):  
Jhon Yana Galarza ◽  
Jorge Meléndez ◽  
Diego Lorenzo-Oliveira ◽  
Adriana Valio ◽  
Henrique Reggiani ◽  
...  
Keyword(s):  
Effective Temperature ◽  
Signal To Noise Ratio ◽  
Activity Cycle ◽  
Magnetic Activity ◽  
Resolving Power ◽  
Strongly Correlated ◽  
Chemical Abundances ◽  
Stellar Activity ◽  
Time Variations ◽  
First Time

ABSTRACT Spectroscopic equilibrium allows us to obtain precise stellar parameters in Sun-like stars. It relies on the assumption of the iron excitation and ionization equilibrium. However, several works suggest that magnetic activity may affect chemical abundances of young active stars, calling into question the validity of this widely used method. We have tested, for the first time, variations in stellar parameters and chemical abundances for the young solar twin HIP 36515 (∼0.4 Gyr), along its activity cycle. This star has stellar parameters very well established in the literature and we estimated its activity cycle in ∼6 yr. Using HARPS spectra with high resolving power (115 000) and signal-to-noise ratio (∼270), the stellar parameters of six different epochs in the cycle were estimated. We found that the stellar activity is strongly correlated with the effective temperature, metallicity, and microturbulence velocity. The possibility of changes in the Li i 6707.8 Å line due to flares and star-spots was also investigated. Although the core of the line profile shows some variations with the stellar cycle, it is compensated by changes in the effective temperature, resulting in a non-variation of the Li abundance.

scholarly journals Applegate mechanism in post-common-envelope binaries: Investigating the role of rotation

2018 ◽  
Vol 615 ◽  
pp. A81 ◽  
Author(s):  
F. H. Navarrete ◽  
D. R. G. Schleicher ◽  
J. Zamponi Fuentealba ◽  
M. Völschow
Keyword(s):  
Orbital Period ◽  
Rotation Rate ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Main Sequence Star ◽  
Common Envelope ◽  
Rotation Rates ◽  
Critical Rotation ◽  
Period Variations ◽  
Time Variations

Context. Eclipsing time variations are observed in many close binary systems. In particular, for several post-common-envelope binaries (PCEBs) that consist of a white dwarf and a main sequence star, the observed-minus-calculated (O–C) diagram suggests that real or apparent orbital period variations are driven by Jupiter-mass planets or as a result of magnetic activity, the so-called Applegate mechanism. The latter explains orbital period variations as a result of changes in the stellar quadrupole moment due to magnetic activity. Aims. In this work we explore the feasibility of driving eclipsing time variations via the Applegate mechanism for a sample of PCEB systems, including a range of different rotation rates. Methods. We used the MESA code to evolve 12 stars with different masses and rotation rates. We applied simple dynamo models to their radial profiles to investigate the scale at which the predicted activity cycle matches the observed modulation period, and quantifiy the uncertainty. We further calculated the required energies to drive the Applegate mechanism. Results. We show that the Applegate mechanism is energetically feasible in 5 PCEB systems. In RX J2130.6+4710, it may be feasible as well considering the uncertainties. We note that these are the systems with the highest rotation rate compared to the critical rotation rate of the main-sequence star. Conclusions. The results suggest that the ratio of physical to critical rotation rate in the main sequence star is an important indicator for the feasibility of Applegate’s mechanism, but exploring larger samples will be necessary to probe this hypothesis.

Helicopter AFMAG (ZTEM) and aeromagnetic survey results over epithermal gold and gold-skarn deposits in the Guerrero Gold Belt, Mexico

2014 ◽  
Author(s):  
Jean M. Legault* ◽  
Shengkai Zhao ◽  
Nasreddine Bournas ◽  
Geoffrey Plastow ◽  
Gillian Kearvell
Keyword(s):  
Epithermal Gold ◽  
Aeromagnetic Survey ◽  
Survey Results ◽  
Skarn Deposits
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