Equatorial auroral records reveal dynamics of the paleo-West Pacific geomagnetic anomaly

Localized regions of low geomagnetic intensity such as the South Atlantic Anomaly allow energetic particles from the Van Allen radiation belt to precipitate into the atmosphere and have been linked to a signature in the form of red aurora–like airglow visible to the naked eye. Smoothed global geomagnetic models predict a low-intensity West Pacific Anomaly (WPA) during the sixteenth to nineteenth centuries characterized by a simple time dependence. Here, we link the WPA to an independent database of equatorial aurorae recorded in Seoul, South Korea. These records show a complex fluctuating behavior in auroral frequency, whose overall trend from 1500 to 1800 AD is consistent with the locally weak geomagnetic field of the WPA, with a minimum at 1650 AD. We propose that the fluctuations in auroral frequency are caused by corresponding and hitherto unknown fluctuations in the regional magnetic intensity with peaks at 1590 and 1720 AD, a time dependence that has been masked by the smoothing inherent in regularized global geomagnetic models. A physical core flow model demonstrates that such behavior requires localized time-dependent upwelling flows in the Earth’s core, possibly driven by regional lower-mantle anomalies.

Analysis of Magnetic Anomaly Characteristics of Underground Non-Coplanar Cross-buried Iron Pipelines

The non-coplanar cross-buried pipelines are a common way of pipeline wiring. In order to investigate the magnetic anomaly characteristics of the non-coplanar cross-buried pipelines and guide the site operation, the influences of a series of factors on the magnetic anomaly of the non-coplanar cross-buried pipelines are analyzed. Based on the principle of magnetic dipole construction, a forward model is established for the magnetic anomaly characteristics of the subsurface non-coplanar cross-buried pipelines. The basic characteristics of magnetic anomaly for the non-coplanar cross-buried pipelines are defined. The influences of geomagnetic parameters (geomagnetic intensity, geomagnetic inclination, and geomagnetic declination), pipeline parameters (thickness, magnetic susceptibility), and cross angle of pipelines on the characteristics of magnetic anomalies are analyzed. The results show that the shape of the total magnetic anomaly is mainly affected by the magnetic inclination, and the curve of magnetic anomaly at ± I site shows some symmetry. The amplitude is approximately linearly affected by the total geomagnetic field, magnetic declination, pipeline thickness, material magnetic susceptibility, and pipeline cross angle. There is a periodic change of the amplitude with the increase of geomagnetic inclination (−90°–>90°). The crest-trough distance is mainly affected by geomagnetic inclination, magnetic declination, thickness, magnetic susceptibility, and pipeline cross angle. A more accurate measurement can be achieved if the direction of the pipelines is roughly measured and then the number of measurement points is augmented near the intersection of pipelines and the measurement lines. Present work obtains the equivalent magnetic dipole units by segmenting pipelines. The magnetic anomaly characteristics of non-coplanar crossed iron pipelines are successfully simulated. The numerical results are in accordance with the experimental analysis.

The combined processing of geomagnetic intensity vector projections and absolute magnitude measurements

A method for the combined processing measurements of the projections and the absolute magnitudes of geomagnetic field intensity vectors, based on mathematical technology of local approximation models, is proposed. The approach realized in this paper, based on the proposed method, provides an increase in quality of the measurements of the projections of the geomagnetic intensity vector. An algorithm for the two-stage combined processing of the measurements of projections and absolute magnitudes of geomagnetic field intensity vectors is developed. The operation of the combined processing algorithm was tested on models and observatory measurements. The estimates of the combined processing algorithm errors were obtained using statistical modelling. The reduction of the root-mean-square error values was achieved for the estimates of the projections of geomagnetic field intensity vectors.

Characteristic of Magnetic Fluctuation of Underground Passing Pig Labeled with Magnets

During the pigging process, a pig labeled with magnets can be effectively detected by monitoring the magnetic fluctuation (MF) introduced when the pig passes by. In order to analyze the influence of various factors on the MF, the principle for magnetic fluctuation detection (MFD) is described, and a detection model is established here. The influence of model parameters, such as pipeline geometries, geomagnetic characteristics, as well as permeability of pipeline, on the magnetic anomaly distribution along the measured line is analyzed. The study reveals that with the increase in pipeline parameters (thickness, permeability, and outer diameter), the MF detected decreases. The pipeline length will have little influence on the MF. With an increased number of magnets, the MF increases while remaining almost unchanged at two ends of the measuring line. Attention should be paid to the installation of magnets to ensure the consistency of the magnetic moments. With the increase in geomagnetic intensity and declination, the MF will be almost unaffected, while the change of geomagnetic inclination will introduce an obvious change to the MF. In field application, measuring points can be set along and above the pipeline with a certain interval. From the magnetic anomaly measured, it can be determined whether the pig has passed by the point or not.

The combined processing of geomagnetic intensity vector projections and absolute magnitude measurements

A method for the combined processing measurements of the projections and the absolute magnitudes of geomagnetic field intensity vectors, based on mathematical technology of local approximation models, was proposed. The approach realized in this paper, based on the proposed method, provides the increase of accuracy of the measurements of the projections of the geomagnetic intensity vector. An algorithm for the two-stage combined processing of the measurements of projections and absolute magnitudes of geomagnetic field intensity vectors was developed. The operation of the combined processing algorithm was tested on models and observatory measurements. The estimates of the combined processing algorithm errors were obtained using statistical modelling. The reduction of the root mean square error values was achieved for the estimates of the projections of geomagnetic field intensity vectors.