The Relationship Between the Interannual Variation of Earth’s Rotation and El Niño Events

We analyzed the relationship between the earth’s rotational variation and sea-surface temperature anomaly. By means of using Fast Fourier Transform (FFT) bandpass filter on the change of length-of-day (ΔLOD) data, the interannual variation series having time periods greater than 1.5-year and less than 8-year was obtained. Time series analyses of the interannual variation, which corresponds to the El Niño period, reveal a close linkage between the earth’s rotation and El Niño. A detailed comparison suggests, that six of seven El Niño events are nearly synchronous with the interannual variation of the earth’s rotation, and all ΔLOD peak are in El Niño years except 1991–92, which means the interannual variation of the earth’s rotation in these years is relatively slow. The correlation between ΔLOD and sea-surface temperature is about 0.517 (1 month-lag), which far exceeds the 99% significance level.     

Comparison of Earth’s magnetospheric magnetic field models in the context of cosmic ray physics

Over the last two decades, models of the Earth’s magnetospheric magnetic field have been continuously improved to describe more precisely the different magnetospheric current systems (magnetopause current, symmetric and partial ring currents, tail currents and field aligned currents). In this paper we compare the different Tsyganenko models and the Alexeev and Feldstein model in the context of cosmic ray physics. We compare the vertical cutoff rigidity and asymptotic direction of vertical incidence obtained with these models for the January 20, 2005, ground level enhancement and for the big magnetic storm of April 6, 2000. For the event of January 20, 2005, we study the impact of the differences in asymptotic direction obtained with the models on the radiation dose computation at aircraft altitude. For the magnetic storm of April 6, 2000, we discuss the importance of the different magnetospheric current systems in causing cutoff rigidity variations. Finally we summarise the advantages and drawbacks of the different models in the context of space weather.     

Variation of the intensity of the Earth’s magnetic field in Portugal in the 1st millennium BC

The study of magnetization of the ceramic material from 21 archeological monuments of Portugal (the Evora province), dated archeologically from the Bronze Age to the end of the Iron Age has been carried out. For the purpose of more detailed timing of the material from the monuments the method of ceramic age dating on the basis of its porosity has been used. In order to take into account the distorted factors in the determination of the parameters of the ancient geomagnetic field with the aim of the maximal approximation to the actual values the diagnostic features of magnetite weathering have been considered and the level of weathering of the magnetic fraction in the ceramics from archeological monuments has been determined. The data of geomagnetic field-strength variation in the time interval of the 12th century BC to the beginning of the Common Era have been obtained. The field-strength at this time interval varied in the range of 60–90 micro Tesla with the maximal values in the 9th, 8th, and the second half of the 5th to the beginning of the 4th century BC. In addition, the timing of the ceramic material from the urns of the megalithic complex Monte de Tera of the Evora province has been clarified.     

An integrated magnetic,geochemical and archeointensity investigation of casting debris from ancient metallurgical sites of Michoacán,Western Mesoamerica

The ability of baked clay-elaborated objects to record the temporal variations of both direction and intensity of the geomagnetic field at the time of their elaboration or last use has been widely used during the last decades to fill the gaps left by available time-discrete volcanic-rock logs for a better knowledge of the evolution of the geomagnetic field. Further refinement of the secular variation curves has motivated the search for alternative non-conventional materials as attractive targets for archeomagnetic studies. Both clay and copper have been used since pre-Hispanic times for the elaboration of a wide variety of ornamental and utilitarian objects in Mesoamerica. Previous studies carried out in Europe and Israel have shown the usefulness of copper slags as one of these non-conventional materials. We present the results of an integrated study carried out on ten copper slags from seven ancient metallurgical sites of Michoacán. The analysis included a series of rock magnetism experiments, scanning electron microscope analysis, archeointensity determinations following the Thellier-Coe method and their corresponding dating. Based on the results obtained the slag-set analyzed can be divided in two main groups: low Fe concentrations (associated with high Cu concentrations) for slags comprising the first group, and high Fe concentrations (associated with low Cu concentrations) for slags from second group. Slags from the first group are characterized by almost reversible thermomagnetic curves, while those corresponding to the second group show a quite irreversible behavior. A crystalline (vitreous) structure within the massive surface of the slags is observed for those coming from the second (first) group. These striking features could reflect significant differences in the metallurgical process followed at these sites, which according to archeological and historical evidences correspond to Colonial and pre-Hispanic usage metallurgical sites; first and second group, respectively. The good experimental behavior exhibited by these materials demonstrates the suitability of copper slag to obtaining absolute archeointensity data which can be used to improve the existing Mesoamerican archeomagnetic record. This in turn, can be used both for geomagnetic field modelling purposes and archeomagnetic dating.     

Holocene Earth’s magnetic field variations recorded in marine sediments of the NW African continental margin

Holocene records documenting variations in direction and intensity of the geomagnetic field during the last about seven and a half millennia are presented for Northwest Africa. High resolution paleomagnetic analyses of two marine sediment sequences recovered from around 900 meter water depth on the upper continental slope off Cape Ghir (30°51′N, 10°16′W) were supplemented by magnetic measurements characterizing composition, concentration, grain size and coercivity of the magnetic mineral assemblage. Age control for the high sedimentation rate deposits (∼60 cm/kyr) was established by AMS radiocarbon dates. The natural remanent magnetization (NRM) is very predominantly carried by a fine grained, mostly single domain (titano-)magnetite fraction allowing the reliable definition of stable NRM inclinations and declinations from alternating field demagnetization and principal component analysis. Predictions of the Korte and Constable (2005) geomagnetic field model CALS7K.2 for the study area are in fair agreement with the Holocene directional records for the most parts, yet noticeable differences exist in some intervals. The magnetic mineral inventory of the sediments reveals various climate controlled variations, specifically in concentration and grain size. A very strong impact had the mid-Holocene environmental change from humid to arid conditions on the African continent which also clearly affects relative paleointensity (RPI) estimates based on different remanence normalizers. To overcome this problem the pseudo-Thellier RPI technique has been applied. The results represent the first Holocene record of Earth’s magnetic field intensity variations in the NW Africa region. It displays long term trends similar to those of model predictions, but also conspicuous millennium scale differences.     

Estimation of the temperature in the Earth’s interior from surface measurements of the electromagnetic field

The possibility of contactless remote estimation of the temperature in the Earth’s interior from surface magnetotelluric (MT) measurements is examined. The neuronet analysis of MT and temperature measurements in the Bishkek geodynamic research area (the Northern Tien Shan) showed that a contactless electromagnetic geothermometer can in principle be realized. An optimal method including MT measurements and treatment of available thermograms is developed. The method minimizes uncertainties of the remote temperature estimation. The use of six to eight thermograms for calibration of electromagnetic data is shown to provide a 12% relative error of prediction, and a priori geological information available for the region under study can reduce this error. Areas of practical application of a contactless electromagnetic geothermometer are outlined.     

Role of atmospheric circulation in the baric field response to the Earth’s crossing of the interplanetary magnetic field sector boundaries

The Earth’s crossings of the magnetic sector boundaries are accompanied by changes in the magnetosphere, ionosphere, and troposphere. We considered the baric field’s response to the crossing of the inter-planetary magnetic field (IMF) sector boundaries during a geomagnetically quiet period. The IMF sign is shown to affect atmospheric pressure in high-latitude regions. The efficiency and sign of the relationship vary during the year. The baric field response to the Earth’s crossing of the IMF sector boundaries is most distinct during equinoxes. It is shown that, during a geomagnetically quiet period, the circulation processes in the atmosphere drive the changes in the atmospheric pressure when the Earth passes from one IMF sector into another.     

Volume Currents of Present-Day Magnetic Dipole in the Earth’s Core

Izvestiya, Physics of the Solid Earth - Abstract—Perhaps for the first time, we obtained the distributed volume electric currents determined by the observed geomagnetic dipole. To do that,...     

Intensity of geomagnetic field in the Precambrian and evolution of the Earth’s deep interior

Reliable data on the paleointensity of the geomagnetic field can become an important source of information both about the mechanisms of generation of the field at present and in the past, and about the internal structure of the Earth, especially the structure and evolution of its core. Unfortunately, the reliability of these data remains a serious problem of paleomagnetic research because of the limitations of experimental methods, and the complexity and diversity of rocks and their magnetic carriers. This is true even for relatively “young” Phanerozoic rocks, but investigation of Precambrian rocks is associated with many additional difficulties. As a consequence, our current knowledge of paleointensity, especially in the Precambrian period, is still very limited. The data limitations do not preclude attempts to use the currently available paleointensity results to analyze the evolution and characteristics of the Earth’s internal structure, such as the age of the Earth’s solid inner core or thermal conductivity in the liquid core. However, such attempts require considerable caution in handling data. In particular, it has now been reliably established that some results on the Precambrian paleointensity overestimate the true paleofield strength. When the paleointensity overestimates are excluded from consideration, the range of the field strength changes in the Precambrian does not exceed the range of its variation in the Phanerozoic. This result calls into question recent assertions that the Earth’s inner core formed in the Mesoproterozoic, about 1.3 billion years ago, triggering a statistically significant increase in the long-term average field strength. Instead, our analysis has shown that the quantity and quality of the currently available data on the Precambrian paleointensity are insufficient to estimate the age of the solid inner core and, therefore, cannot be useful for solving the problem of the thermal conductivity of the Earth’s core. The data are consistent with very young or very “old” inner core ages and, correspondingly, with high or low values of core thermal conductivity.     

Effect of the magnetic field on measurements of the electron density and temperature by cylindrical probes in the Earth’s ionosphere

In the 1960s and 1970s, quite simply produced cylindrical Langmuir probes were used in the USSR both on satellites (Kosmos-378, Intercosmos-2, -4, -8, -10, -19) and to measure the electron density and temperature on vertical launched rockets (Vertical’-4, -6, -10) within the Intercosmos program. These measurements were first made at middle latitudes. With increasing inclination of the orbits of launched satellites (satellites had no stabilization), falling sections were sometimes observed on probe characteristics in the electron saturation region. The Intercosmos-Bulgaria-1300 satellite, which was stabilized along three axes and was equipped with a cylindrical probe whose longitudinal axis was always directed downward to the Earth, was launched in 1981. This satellite allowed definite conclusions on the effect of the geomagnetic field on the form of the probe characteristic and, hence, on the determination of the electron density and temperature. Probe characteristics with falling sections are presented. These measurements are compared with those performed in a laboratory plasma. The appearance of negative sections on the probe characteristics is shown to be due to the effect of the geomagnetic field. The degree of this effect depends both on the electron density and temperature and on the probe voltage.     

Motion of the Earth’s magnetic poles in the last decade

Based on vector magnetic data from the CHAMP German satellite, average daily spherical harmonic models of the main geomagnetic field to n = m = 10 have been constructed for the period from May 2001 to the end of 2009 at an interval of 4 days. The obtained 16 models, which were averaged over half a year, have been used to calculate the coordinates of the north and south magnetic poles (the points where magnetic field lines are vertical). The changes in these coordinates during these eight and a half years have been traced. Both poles continue moving northward and westward. The north magnetic pole has traveled 400 km during this period. The velocity of its motion has increased up to the year 2003, reaching 62.5 km yr⁻¹, and then started decreasing and reached 45 km yr⁻¹ by the end of 2009. In addition, the direction of motion changed from north-northwestward to northwestward; i.e., the pole started turning slightly towards Canada. The south magnetic pole moved slower by an order of magnitude and has traveled 42 km during this period. The coordinates of the geomagnetic (dipole) poles and the eccentric dipole parameters have also been calculated. The dynamics of these poles has been traced.     

Magnetic record of El Niño Southern Oscillation in Late Pleistocene sediments from Mucubají lake (western Venezuela)

El Niño Southern Oscillation (ENSO) is an internal forcing of the climate system. This event has an actual frequency of 2 to 8 years. Evidence from a paleoclimate proxy database of gray scale (GS), in samples from Pallcacocha lake in Ecuador, indicates that the ENSO had a frequency of 35 to 75 years during the Late Pleistocene. In this work we explored the possible relationship between the ENSO proxies (GS) from Pallcacocha and magnetic parameters from sediments sampled at the Mucubají lake in Mérida, Venezuela (i.e. mass-specific magnetic susceptibility, magnetic remanence S ratio and susceptibilitynormalized saturation isothermal remanent magnetization). After applying a Lanczos bandpass filter to the rock magnetic and the GS data, in order to remove, as much as possible, frequencies associated to any periodic event other than ENSO, we found significant correlations between GS and magnetic parameters for the period between 12450 and 10560 cal. yrs BP. These relationships were obtained using an Adaptive Neuro Fuzzy Inference System (ANFIS), a hybrid algorithm that combines fuzzy logic with neural networks. The results show that the magnetic parameters obtained in Mucubají are able to explain 50.5% of the total variance of the ENSO proxy in a range of 35 to 75 years in Pallcacocha, which is roughly the same percentage of the total variance of the temperature in the Venezuelan Andes, explained by the ENSO at present times. In this way we have inferred a possible influence of the ENSO in the Venezuelan Andes during the Late Pleistocene.     

Latitudinal and Longitudinal Variations of Earth’s Magnetic Force on Electrified Hydrometeors

Geomagnetism and Aeronomy - In this study, a hypothesis is proposed about the possible effect of Geomagnetic field (GMF) on the charge structure of a thundercloud based on Lorentz force equation...     

Perturbation of the magnetic field in the Earth’s magnetosphere due to plateau creation in the radial distribution of plasma pressure

The nonlinear perturbation of a dipole field by a system of transverse currents, which arises due to the radial pressure distribution when the pressure is almost independent of the radial distance, is analyzed. This distribution of pressure was observed in the experiment. The radial dependences of the magnetic field depression, transverse current density, and volumes of magnetic flux tubes have been obtained at different values of the plasma parameter via nonlinear simulation. It is shown that a dependence of the volume of magnetic flux tube on the radial distance can change and a region of the negative gradient of volume can appear at some plasma-parameter values.     

Harmonic sources of the main geomagnetic field in the Earth’s core

The large-scale harmonic magnetic-convective sources of the main geomagnetic field in the Earth’s core have been determined for the first time. The determination is based on a complete system of eigenfunctions of the magnetic diffusion equation in a homogeneously conducting sphere, which is surrounded by an insulator. The sources of the main geomagnetic field observed, which is responsible for the distribution of the electric currents generating this field in the core, are expressed in terms of large-scale eigenfunctions. In this case, the dipole sources are directly related to the observed geomagnetic dipole, whereas the quadrupole sources are related to the quadrupole, etc. The time variations in the obtained sources are responsible for individual spatiotemporal features in the generation or suppression of each Gaussian component of the observed geomagnetic field. When the commonly accepted observational international geomagnetic reference field (IGRF) models were used to partially reveal these time variations, it became possible to specify the estimate of the Earth’s core conductivity and determine the minimum period that can separate us from the commencement of further inversion or excursion.     

Regional differences in the effects of El Niño and La Niña on low flows and floods

Abstract

The response of monthly 7-day low flow, monthly instantaneous peak flow, and monthly frequency of flood events to El Niño and La Niña episodes is investigated for 18 rivers that represent a diverse range of climatic types throughout New Zealand. A significant positive or negative deviation from the long-term average was observed in over half the possible combinations of river, streamflow index, and type of ENSO episode; significant deviations were most frequent in the case of low flow, especially during La Niña episodes. Patterns of streamflow response differ widely between rivers, and the response of a given river to individual ENSO episodes is very variable. The patterns of streamflow response to ENSO are consistent to some extent with the climatic effects of ENSO already identified by meteorologists. Two core regions can be defined in which streamflow tends to respond in the same way. These are in the northeast of the North Island, and in the axial ranges of the South Island, where there are significant effects of ENSO on the frequency and duration of rain-bearing northeasterly and westerly winds respectively. The patterns of response strongly reflect topography, and the exposure of catchments to predominant air masses.     

Determination of Specific Time Variations in the Energy of the Earth’s Magnetic Potential Field from the IGRF Model

Geomagnetism and Aeronomy - A method is proposed for the analysis of time series based on a logarithmic derivative or a specific variation. As compared to conventional analyses based on the Fourier...     

Certain spectral properties of cyclonic turbulence in the Earth’s liquid core

Rapid diurnal rotation of planets results in the appearance of cyclonic thermal turbulence in liquid cores, which is the source of generation of the observed magnetic fields. The model that makes it possible to reproduce characteristic features of small-scale geostrophic flows in the physical and wave spaces is considered in the work. The flows of energy and hydrodynamic helicity as a function of the wavenumber have been estimated. Joint existence of direct and inverse cascades has been indicated. The consequences for the Earth’s core and geodynamo problems have been considered.     

Analysis of Current Movements and Deformations of the Earth’s Crust in Fennoscandia from GNSS Data

Izvestiya, Physics of the Solid Earth - Abstract—An analysis of the displacement rates of GNSS points indicates that the values of current deformations gradually decrease from the center of...     

The relation between solar activity and orientation of the solar wind electric field relative to the Earth’s magnetic moment

The relation of the Kp index of geomagnetic activity to the solar wind electric field (E _SW) and the projection of this field onto the geomagnetic dipole has been estimated. An analysis indicated that the southward component of the IMF vector (B _z < 0) is the main geoeffective parameter, as was repeatedly indicated by many researchers. The presence of this component in any combinations of the interplanetary medium parameters is responsible for a high correlation between such combinations and geomagnetic activity referred to by the authors of different studies. Precisely this field component also plays the main role in the relation between the Kp index and the relative orientation of E _SW and the Earth’ magnetic moment.