Geomagnetic Field Variations Research Articles

Solar and lunar tidal variabilities in GPS‐TEC and geomagnetic field variations: Seasonal as well as during the sudden stratospheric warming of 2010

AbstractThe Global Positioning System (GPS) deduced total electron content (TEC) data at 15°N (geomagnetic), which is the northern crest region of equatorial ionization anomaly, are used to study solar and lunar tidal variabilities during the years 2008 and 2009 and also during the 2009–2010 winter, when a major sudden stratospheric warming (SSW) event has occurred. The diurnal and semidiurnal tidal amplitudes show semiannual variation with maximum amplitudes during February–March and September–November, whereas terdiurnal tide is larger during April–September. They show significant longitudinal variability with larger (smaller) amplitudes over 250°E–150°E (200°E–250°E). Lunar semidiurnal tidal amplitudes show sporadic enhancements during northern winter months and negligible amplitudes during northern summer months. They also show notable longitudinal variabilities. The solar migrating tides DW1 and SW2 show semiannual variation with larger amplitudes during spring equinox months, whereas TW3 maximizes during northern summer. DW2 shows larger amplitudes during summer months. During the SSW, except TW3, the migrating tides DW1 and SW2 show considerable enhancements. Among solar nonmigrating tides, SW1, TW2, and DS0 show larger enhancements. Solar tides in TEC and equatorial electrojet strength over Tirunelveli vary with the time scale of 60 days during October 2009–March 2010 similar to ozone mass mixing ratio at 10 hPa, and this confirms the vital role of ozone in tidal variabilities in ionospheric parameters. Lunar tidal amplitudes in changes in horizontal component of geomagnetic field (ΔH) are larger over Tirunelveli, a station near dip equator. Solar semidiurnal tides in ΔH have larger amplitudes than lunar tides over polar stations, Mawson and Godhavn.

Geomagnetic variation peculiarities at middle latitudes of the East European Platform

The results of instrumental observations of geomagnetic variations at the Mikhnevo midlatitudinal observatory of Institute of Geosphere Dynamics of the Russian Academy of Sciences (54.9595° N; 37.7664° E) are presented and discussed. The main periodicities of the local background variations of geomagnetic field are determined. Variations of ~ 27 days have been registered, as well as periodicities with periods of ~6–9, 12–14, 60 days, and a semiannual periodicity. It has been shown that the background geomagnetic variation periodicities have a sporadic and scaling character. An alternating effect of increasing and degradation periods in geomagnetic variation intensity (the intermittency effect) is found.

Six centuries of geomagnetic intensity variations recorded by royal Judean stamped jar handles

Earth's magnetic field, one of the most enigmatic physical phenomena of the planet, is constantly changing on various time scales, from decades to millennia and longer. The reconstruction of geomagnetic field behavior in periods predating direct observations with modern instrumentation is based on geological and archaeological materials and has the twin challenges of (i) the accuracy of ancient paleomagnetic estimates and (ii) the dating of the archaeological material. Here we address the latter by using a set of storage jar handles (fired clay) stamped by royal seals as part of the ancient administrative system in Judah (Jerusalem and its vicinity). The typology of the stamp impressions, which corresponds to changes in the political entities ruling this area, provides excellent age constraints for the firing event of these artifacts. Together with rigorous paleomagnetic experimental procedures, this study yielded an unparalleled record of the geomagnetic field intensity during the eighth to second centuries BCE. The new record constitutes a substantial advance in our knowledge of past geomagnetic field variations in the southern Levant. Although it demonstrates a relatively stable and gradually declining field during the sixth to second centuries BCE, the new record provides further support for a short interval of extreme high values during the late eighth century BCE. The rate of change during this "geomagnetic spike" [defined as virtual axial dipole moment > 160 ZAm2 (1021 Am2)] is further constrained by the new data, which indicate an extremely rapid weakening of the field (losing ∼27% of its strength over ca. 30 y).

A study of geomagnetic field variations along the 80° S geomagnetic parallel

Abstract. The availability of measurements of the geomagnetic field variations in Antarctica at three sites along the 80° S geomagnetic parallel, separated by approximately 1 h in magnetic local time, allows us to study the longitudinal dependence of the observed variations. In particular, using 1 min data from Mario Zucchelli Station, Scott Base and Talos Dome, a temporary installation during 2007–2008 Antarctic campaign, we investigated the diurnal variation and the low-frequency fluctuations (approximately in the Pc5 range, ∼ 1–7 mHz). We found that the daily variation is clearly ordered by local time, suggesting a predominant effect of the polar extension of midlatitude ionospheric currents. On the other hand, the pulsation power is dependent on magnetic local time maximizing around magnetic local noon, when the stations are closer to the polar cusp, while the highest coherence between pairs of stations is observed in the magnetic local nighttime sector. The wave propagation direction observed during selected events, one around local magnetic noon and the other around local magnetic midnight, is consistent with a solar-wind-driven source in the daytime and with substorm-associated processes in the nighttime.

Induction effects of geomagnetic disturbances in the geo-electric field variations at low latitudes

Abstract. In this study we examined the influences of geomagnetic activity on the Earth surface electric field variations at low latitudes. During the International Equatorial Electrojet Year (IEEY) various experiments were performed along 5° W in West Africa from 1992 to 1995. Among other instruments, 10 stations equipped with magnetometers and telluric electric field lines operated along a meridian chain across the geomagnetic dip equator from November 1992 to December 1994. In the present work, the induced effects of space-weather-related geomagnetic disturbances in the equatorial electrojet (EEJ) influence area in West Africa were examined. For that purpose, variations in the north–south (Ex) and east–west (Ey) components of telluric electric field were analyzed, along with that of the three components (H, D and Z) of the geomagnetic field during the geomagnetic storm of 17 February 1993 and the solar flare observed on 4 April 1993. The most important induction effects during these events are associated with brisk impulses like storm sudden commencement (ssc) and solar flare effect (sfe) in the geomagnetic field variations. For the moderate geomagnetic storm that occurred on 17 February 1993, with a minimum Dst index of −110 nT, the geo-electric field responses to the impulse around 11:00 LT at LAM are Ex = 520 mV km−1 and Ey = 400 mV km−1. The geo-electric field responses to the sfe that occurred around 14:30 LT on 4 April 1993 are clearly observed at different stations as well. At LAM the crest-to-crest amplitude of the geo-electric field components associated with the sfe are Ex = 550 mV km−1 and Ey = 340 mV km−1. Note that the sfe impact on the geo-electric field variations decreases with the increasing distance of the stations from the subsolar point, which is located at about 5.13° N on 4 April. This trend does not reflect the sfe increasing amplitude near the dip equator due the high Cowling conductivity in the EEJ belt.

Solar flares and variation of local geomagnetic field: Measurements by the Huancayo Observatory over 2001-2010

We study the local variation of the geomagnetic field measured by the Huancayo Geomagnetic Observatory, Peru, during 2001-2010. Initially, we sought to relate the SFI values, stored daily in the NOAA's National Geophysical Data Center, with the corresponding geomagnetic index; however, no relation was observed. Nonetheless, subsequently, a comparison between the monthly geomagnetic-activity index and the monthly SFI average allowed observing a temporal correlation between these average indices. This correlation shows that the effect of the solar flares does not simultaneously appear on the corresponding magnetic indices. To investigate this, we selected the most intense X-class flares; then, we checked the magnetic field disturbances observed in the Huancayo Geomagnetic Observatory magnetograms. We found some disturbances of the local geomagnetic field in the second and third day after the corresponding solar flare; however, the disturbance strength of the local geomagnetic field is not correlated with the X-class of the solar flare. Finally, there are some disturbances of the local geomagnetic field that are simultaneous with the X-class solar flares and they show a correlation with the total flux of the solar flare.

Quiet Time Correlation Between Geomagnetic Field Variations and the Dynamics of the East African Equatorial Ionosphere

The equatorial ionosphere is highly dynamic and consequently poses serious threats to communication and navigation systems. As a result, proper understanding of ionospheric dynamics is important. The present paper presents the results of an investigation of the correlation between quiet time vertical total electron content (VTEC) and solar quiet variation in the horizontal component of geomagnetic field (Sq(H)) from low solar activity year (2009) to the high solar activity year (2014) within the equatorial East African sector using statistical analysis method. Values of Sq(H) were observed to increase steadily from around 0700LT attaining maximum values around 1100-1200LT, then descending towards zero level and beyond. The magnitudes of (VTEC) increase uniformly from around 0600-1000LT, then gradually, attaining maximum values around 1300-1500LT. The time instants of occurrence of these peaks are mainly controlled by drifts and photo-ionization. The correlation coefficients (ccs) between (VTEC) and Sq(H) were found to be strongest during the ascending phase (0600-1200LT), ranging from 0.69 to 0.98 at Addis Ababa and 0.61 to 0.97 at Nairobi. During the descending phase (1300-1800LT), ccs range from -0.28 to 0.89 at Addis Ababa and-0.06 to 0.76 at Nairobi. A high level of significance (99.98%) of ccs was obtained. The good linear relationship is attributed to the independent increase of the eastward electric field and photo-ionization on (VTEC) while poor relationship is possibly due to domination of photo-ionization over equatorial ionization anomaly (EIA) development. The annual ccs between (VTEC) and Sq(H) exhibit a general dependence on solar activity at Addis Ababa, closer to the dip equator, rather than at Nairobi during the ascending phase of the daytime. This observation suggests that the EEJ changes linearly with change in solar activity, thus streamlining the variations in TEC, through drifts, and Sq(H) by intensifying the eastward equatorial electric field.

Geoinformation system for amplitude-frequency analysis of geomagnetic variations and space weather observation data

We present and describe a method to conduct correlation and amplitude-frequency analysis of the observational data of geomagnetic variations and space weather that is based on the combined use of a concept of single information space, models and methods of wavelet and Fourier analysis, and geo-information technologies. The method includes formalized elements of mathematical and methodological support for conducting amplitude-frequency and correlation analysis of the observations of geomagnetic variations and space weather and is verified by means of a prototype in-house platform-independent web-oriented geoinformation system GEOMAGNET (https:// www.geomagnet.ru). The proposed method is verified using data obtained from the magnetic observatories of the INTERMAGNET network and space weather data from the artificial Earth satellite ACE. Results of the observation, automated correlation and amplitude-frequency analysis of signals that provide information on the geomagnetic field and space weather variations at specified time intervals both on the Earth's surface and in near-Earth space are discussed and evaluated.

Experimental Study on the Localization of Moving Object by Total Geomagnetic Field

In the method of target localization based on magnetic anomalies, the scheme of vector field localization and experimental research are significant. Because more information of magnetic field can be measured by vector sensors, the position of the target can be directly calculated by the equations. However, the vector magnetic anomaly generated by the target is difficult to measure. And the detection range is small due to the low sensitivity of vector sensors. A method for target localization based on the total geomagnetic field is proposed. Its advantages are that the measurement of total magnetic field is not affected by the orientation of the total field sensors and the detection range is large due to their high sensitivity. In this paper, we focus on the localization using the array with the total field magnetometers. And we design an array structure with the total field magnetometers. Then, we obtain the higher order nonlinear equations for the target localization based on this array. The numerical method is used to solve the equations. Meanwhile, we present a method for eliminating the effect of geomagnetic field variations and uneven spatial distribution. In suburban roads, localization experiments were carried out. And the results showed that the relative error of target localization is less than 5% by using the proposed method.

Analysis of magnetic data of ground station network during strong magnetic storms

The paper suggests a new technique for magnetic data analysis to detect and to estimate short-time anomalous increases in geomagnetic disturbance intensity. Based on the technique and applying the data of meridionally arranged stations in the north-east of Russia («Kotel’nyi» KTN, «Tixi» TIX, «Chokurdakh» CHD, «Zyryanka» ZYK, «Mys Shmidta» CPS, «Yakutsk» YAK, «Magadan» MGD, «Paratunka» PET, «Khabarovsk» KHB) and the near equatorial Indian stations (“Hyderabad” HYB and “Choutuppal” CPL), we analyzed the geomagnetic field variations during strong magnetic storms. This approach allowed us to detect simultaneously occurring local increases in geomagnetic activity observed a few hours before events and during the main phases of magnetic storms.

Interactive system for geomagnetic data analysis

The paper suggests the methods for analyzing geomagnetic field variations, which are implemented in “Aurora” software system for complex analysis of geophysical parameters. The software system allows one to perform a detailed magnetic data analysis. The methods allow one to estimate the intensity of geomagnetic perturbations and to allocate increased geomagnetic activity periods. The software system is publicly available (http://aurorasa.ikir.ru:8580, http://www.ikir.ru:8280/lsaserver/MagneticPage.jsp).This research was supported by the Russian Science Foundation (Project Nо. 14-11-00194).

Archaeointensity results spanning the past 6 kiloyears from eastern China and implications for extreme behaviors of the geomagnetic field

Variations of the Earth's geomagnetic field during the Holocene are important for understanding centennial to millennial-scale processes of the Earth's deep interior and have enormous potential implications for chronological correlations (e.g., comparisons between different sedimentary recording sequences, archaeomagnetic dating). Here, we present 21 robust archaeointensity data points from eastern China spanning the past ∼6 kyr. These results add significantly to the published data both regionally and globally. Taking together, we establish an archaeointensity reference curve for Eastern Asia, which can be used for archaeomagnetic dating in this region. Virtual axial dipole moments (VADMs) of the data range from a Holocene-wide low of ∼27 to "spike" values of ∼166 ZAm2 (Z: 1021). The results, in conjunction with our recently published data, confirm the existence of a decrease in paleointensity (DIP) in China around ∼2200 BCE. These low intensities are the lowest ever found for the Holocene and have not been reported outside of China. We also report a spike intensity of 165.8 ± 6.0 ZAm2 at ∼1300 BCE (±300 y), which is either a prelude to or the same event (within age uncertainties) as spikes first reported in the Levant.

Unusually high frequency natural VLF radio emissions observed during daytime in Northern Finland

Geomagnetic field variations and electromagnetic waves of different frequencies are ever present in the Earth’s environment in which the Earth’s fauna and flora have evolved and live. These waves are a very useful tool for studying and exploring the physics of plasma processes occurring in the magnetosphere and ionosphere. Here we present ground-based observations of natural electromagnetic emissions of magnetospheric origin at very low frequency (VLF, 3–30 kHz), which are neither heard nor seen in their spectrograms because they are hidden by strong impulsive signals (sferics) originating in lightning discharges. After filtering out the sferics, peculiar emissions are revealed in these digital recordings, made in Northern Finland, at unusually high frequencies in the VLF band. These recently revealed emissions, which are observed for several hours almost every day in winter, contain short (∼1–3 min) burst-like structures at frequencies above 4–6 kHz, even up to 15 kHz; fine structure on the 1 s time scale is also prevalent. It seems that these whistler mode emissions are generated deep inside the magnetosphere, but the detailed nature, generation region and propagation behaviour of these newly discovered high latitude VLF emissions remain unknown; however, further research on them may shed new light on wave-particle interactions occurring in the Earth’s radiation belts.

Influence of geomagnetic activity and earth weather changes on heart rate and blood pressure in young and healthy population.

There are many references in the literature related to connection between the space weather and the state of human organism. The search of external factors influence on humans is a multi-factor problem and it is well known that humans have a meteo-sensitivity. A direct problem of finding the earth weather conditions, under which the space weather manifests itself most strongly, is discussed in the present work for the first time in the helio-biology. From a formal point of view, this problem requires identification of subset (magnetobiotropic region) in three-dimensional earth's weather parameters such as pressure, temperature, and humidity, corresponding to the days when the human body is the most sensitive to changes in the geomagnetic field variations and when it reacts by statistically significant increase (or decrease) of a particular physiological parameter. This formulation defines the optimization of the problem, and the solution of the latter is not possible without the involvement of powerful metaheuristic methods of searching. Using the algorithm of differential evolution, we prove the existence of magnetobiotropic regions in the earth's weather parameters, which exhibit magneto-sensitivity of systolic, diastolic blood pressure, and heart rate of healthy young subjects for three weather areas (combinations of atmospheric temperature, pressure, and humidity). The maximum value of the correlation confidence for the measurements attributable to the days of the weather conditions that fall into each of three magnetobiotropic areas is an order of 0.006, that is almost 10 times less than the confidence, equal to 0.05, accepted in many helio-biological researches.

Effect of March 9, 2016 Total Solar Eclipse on geomagnetic field variation

During solar eclipse, solar radiation to the Earth is blocked by the Moon. Thus, the ionization process in the ionosphere is disrupted, as well as the variation of geomagnetic field. The disturbance of geomagnetic field is caused by electric current in the E layer of the ionosphere. At low latitude, the current which is dominant in quiet day is the Sq currents. The blocking of solar radiation cause decrement in electron density in the blocked region. The aim of the research is to find the effect of total solar eclipse to the geomagnetic field. The measurement of the geomagnetic field variation during total solar eclipse on March 9, 2016 was carried out at the Meteorological station of BMKG in Ternate (0° 49' 45.20 "N; 127° 22' 54.00" E). By eliminating the geomagnetic disturbance that occurred in a daily geomagnetic field variation, the pattern of quiet day which is usually in a shape of smooth curve became affected. During the total solar eclipse on March 9, 2016 from 00:30 until 02:00 UT, we found that the geomagnetic field variation of the quiet day decreased by -5 nT.

Can the comprehensive model phase 4 (CM4) predict the geomagnetic diurnal field for days away from quiet time?

Abstract. The most recent comprehensive model (CM4) of the geomagnetic field (Sabaka et al., 2004) has been used in conjunction with geomagnetic ground observatory station data to analyse and study the geomagnetic diurnal variation field for days away from quiet time and the CM4 prediction for these times. Even though much has been learnt about many components of the geomagnetic field, the diurnal variation field behaviour for days away from quiet time (moderately disturbed time) has not been intensively studied. Consequently, we analyse these, and the predictive ability of the CM4 for ground variations, and whether the CM4 prediction of the diurnal variation (whether at quiet time or away from quiet time) is valid outside the period of reference that from which the data were used in modelling. In carrying out the study, we compared the observatory station data and the CM4 prediction directly. Using the CM4 code, well-characterised internal and magnetospheric components were subtracted from the data, plots and global maps of the residual field generated and then compared with the CM4 to see how well the model performed in predicting the data at moderately disturbed time (Kp ≤ 5). The results show that the CM4 is valid and produces useful predictions outside the period covering the timespan of the model and during moderately disturbed time, despite the lack of active data in the original model dataset. The model predictability of the data increases as we move to higher spherical harmonic degree truncation, as the model–data misfit is reduced, but with increased roughness as a result of small-scale features incorporated. The observed results show that this relationship between the increase in spherical harmonic degree truncation and reduction in misfit can be restricted by data quality or quantity and global coverage or spread.

Reduced geomagnetic field may affect positive phototaxis and flight capacity of a migratory rice planthopper

The geomagnetic field (GMF) is not constant but changes over space and time. In addition to the current slow decay of GMF, sudden GMF anomalies, mainly characterized by reduced field intensity, and variation in GMF strength between the migration origin and destination areas of migratory animals have attracted growing attention from researchers. We investigated magnetic field effects (MFEs) triggered by the near-zero magnetic field (NZMF), to some extent a proxy for the reduced GMF, on the positive phototaxis and flight capacity of the adult migratory white-backed planthopper, Sogatella furcifera. For the first time, we report the significant enhancement of adult positive phototaxis by the NZMF compared with the GMF. Compared with the GMF, NZMF also affected the flight capacity of adults (with significantly lower body weights) in a sexually dimorphic way. We further found that expression patterns of the multifunctional cryptochromes (genes CRY1 and CRY2) as circadian photoreceptor and magnetoreceptor, along with the genes AKH and AKHR in the adipokinetic hormone (AKH)/AKH receptor (AKHR) signalling system which is related to energy metabolism and antioxidative stress reactions, correlated with phenotypic changes in positive phototaxis and flight endurance of adults. Therefore, potentially acting through an antioxidative stress-related CRYs–circadian clock–AKH/AKHR signalling pathway, we suggest that a reduced field intensity, and even just variation in GMF, may influence positive phototaxis and flight (migratory) behaviour of insects. Our study presents a feasible link between the probable mechanisms underlying MFEs, including cryptochrome-mediated light-dependent magnetosensitivity, cryptochrome-mediated light-dependent magnetosensitivity of the circadian clock and magnetic field-triggered oxidative stress, and provides new insights into the complexity of potential MFEs induced by variation in GMF.

New archaeomagnetic data recovered from the study of celtiberic remains from central Spain (Numantia and Ciadueña, 3rd-1st centuries BC). Implications on the fidelity of the Iberian paleointensity database

Variations of geomagnetic field in the Iberian Peninsula prior to roman times are poorly constrained. Here we report new archaeomagnetic results from four ceramic collections and two combustion structures recovered in two pre-roman (celtiberic) archaeological sites in central Spain. The studied materials have been dated by archaeological evidences and supported by five radiocarbon dates. Rock magnetic experiments indicate that the characteristic remanent manetization (ChRM) is carried by a low coercivity magnetic phase with Curie temperatures of 530–575°C, most likely Ti-poor titanomagnetite/titanomaghemite. Archaeointensity determinations were carried out by using the classical Thellier-Thellier protocol including tests and corrections for magnetic anisotropy and cooling rate dependency. Two magnetic behaviours were depicted during the laboratory treatment. Black potsherds and poor heated samples from the kilns, presented two magnetization components, alterations or curved Arai plots and were therefore rejected. In contrast, well heated specimens (red ceramic fragments and well heated samples from the kilns) show one single well defined component of magnetization going through the origin and linear Arai plots providing successful archaeointensity determinations. The effect of anisotropy of the thermoremanent magnetization (ATRM) on paleointensity analysis was systematically investigated obtaining very high ATRM corrections on fine pottery specimens. In some cases, differences between the uncorrected and ATRM corrected paleointensity values reached up to 86 %. The mean intensity values obtained from three selected set of samples were 64.3±5.8μT; 56.8±3.8 and 56.7±4.6μT (NUS2, CI2andCIA, respectively), which contribute to better understand the evolution of the palaeofield intensity in central Iberia during the 3rd-1st centuries BC. The direction of the field at first century BC has also been determined from oriented samples from CIA kilns (D=357.2°; I=62.2°; N=10, α95=2.7°).The new archaeointensity data disagrees with previous results from Iberian ceramics which were not corrected for the ATRM effect. On the contrary, they are in agreement with the most recent French paleointensity curve and the latest European intensity model; both based on a selection of high quality paleointensity data. This result reinforces the idea that the puzzling scatter often observed in the global paleointensity database is likely due to differences in the laboratory protocols. Further data from well-established laboratory protocols are still necessary to delineate confidently the evolution of the geomagnetic palaeofield during the first millennium BC.

Temporal changes of the secular variations of geomagnetic field in Europe

Temporal changes of the secular variations of geomagnetic field in Europe

Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents

This research focuses on the inversion of geomagnetic variation field measurements to obtain the source currents in the ionosphere and magnetosphere, and to determine the geoelectric fields at the Earth’s surface. During geomagnetic storms, the geoelectric fields create geomagnetically induced currents (GIC) in power networks. These GIC may disturb the operation of power systems, cause damage to power transformers, and even result in power blackouts. In this model, line currents running east–west along given latitudes are postulated to exist at a certain height above the Earth’s surface. This physical arrangement results in the fields on the ground being composed of a zero magnetic east component and a nonzero electric east component. The line current parameters are estimated by inverting Fourier integrals (over wavenumber) of elementary geomagnetic fields using the Levenberg–Marquardt technique. The output parameters of the model are the ionospheric current strength and the geoelectric east component at the Earth’s surface. A conductivity profile of the Earth is adapted from a shallow layered-Earth model for one observatory, together with a deep-layer model derived from satellite observations. This profile is used to obtain the ground surface impedance and therefore the reflection coefficient in the integrals. The inputs for the model are a spectrum of the geomagnetic data for 31 May 2013. The output parameters of the model are spectrums of the ionospheric current strength and of the surface geoelectric field. The inverse Fourier transforms of these spectra provide the time variations on the same day. The geoelectric field data can be used as a proxy for GIC in the prediction of GIC for power utilities. The current strength data can assist in the interpretation of upstream solar wind behaviour.