Polarization Anomalies Research Articles

The Mesozoic Subduction Zone over the Dongsha Waters of the South China Sea and Its Significance in Gas Hydrate Accumulation

The Mesozoic subduction zone over the Dongsha Waters (DSWs) of the South China Sea (SCS) is a part of the westward subduction of the ancient Pacific plate. Based on the comprehensive interpretation of deep reflection seismic profile data and polar magnetic anomaly data, and the zircon dating results of igneous rocks drilled from well LF35-1-1, the Mesozoic subduction zone in the northeast SCS is accurately identified, and a Mesozoic subduction model is proposed. The accretion wedges, trenches, and igneous rock zones together form the Mesozoic subduction zone. The evolution of the Mesozoic subduction zone can be divided into two stages: continental subduction during the Late Jurassic and continental collision during the late Cretaceous. The Mesozoic subduction zone controlled the structural pattern and evolution of the Chaoshan depression (CSD) during the Mesozoic and Neogene eras. The gas source of the hydrate comes from thermogenic gas, which is accompanied by mud diapir activity and migrates along the fault. The gas accumulates to form gas hydrates at the bottom of the stable domain; BSR can be seen above the mud diapir structure; that is, hydrate deposits are formed under the influence of mud diapir structures, belonging to a typical leakage type genesis model.

Connection between Winter East Asia Flow Patterns and Stratospheric Polar Vortex Anomalies

Using a reanalysis dataset, this work investigates the possible connection of winter East Asia (EA) flow patterns to stratospheric polar vortex (SPV) anomalies. Cluster analysis is performed on the principal components of daily 500 hPa geopotential height fields to identify five distinct flow patterns. SPV anomalies are considered in terms of the occurrence of major sudden stratospheric warmings (MSSWs). The results reveal that for the 15 days before the MSSWs, one of the five patterns occurs more frequently than usual, whereas another occurs less frequently. The former constructively interferes with the climatological EA trough in the troposphere and strengthens the planetary wave activity (heat flux) in the extratropical troposphere and stratosphere. It has a similar pattern in the 500 hPa height to the composite leading to the MSSWs, implying that such strengthening can contribute to the forcing of the MSSWs. The latter is in the opposite sense (destructive interference) and is disadvantageous before the MSSWs. Evidence of a stratospheric downward influence on the five flow patterns is relatively unclear. These results suggest a potential coupling between flow patterns or weather regimes in different regions through the SPV, as well as warrant further investigation of the downward influence on EA weather regimes.

Refinement of Different Frequency Bands of Geomagnetic Vertical Intensity Polarization Anomalies before M > 5.5 Earthquakes.

Geomagnetic vertical intensity polarization is a method with a clear mechanism, mature processing methods, and a strong ability to extract anomalous information in the quantitative analysis of seismogenic geomagnetic disturbances. The existing analyses of geomagnetic vertical intensity polarization are all based on the 5~100 s frequency band without refinement of the partitioning process. Although many successful results have been obtained, there are still two problems in the process of extracting anomalies: the geomagnetic anomalies that satisfy the determination criteria are still high in occurrence frequency; and the anomalies are distributed over too large an area in space, which leads to difficulties in determining the location of the epicenter. In this study, based on observations from western China, where fluxgate observation points are positioned in areas with frequent, densely distributed medium-strength earthquakes, we refined the frequency bands of geomagnetic vertical intensity polarization, recalculated the spatial and temporal evolution characteristics of geomagnetic disturbances before earthquakes, and improved the crossover frequency anomaly prediction index while promoting the application of the method in earthquake forecasting.

The Role of the Stratosphere in Teleconnections Arising From Fast and Slow MJO Episodes

AbstractThe Madden‐Julian Oscillation (MJO) can influence the extratropical circulation on timescales up to several weeks, with a dependence on the MJO characteristics: MJO episodes that propagate slowly across the Maritime Continent have a stronger impact on Euro‐Atlantic weather than fast MJO episodes. While the tropospheric pathway for MJO teleconnections with varying phase speeds is well understood, in this study, we investigate the contribution of the Northern Hemisphere stratospheric pathway for fast versus slow MJO episodes. During slow MJO episodes, Phases 5–6 lead to increased upward wave propagation in the North Pacific sector, and subsequently enhanced heat flux at 100 hPa, leading to the weakening of the polar vortex. The results suggest a clear role of stratosphere‐troposphere coupling for slow MJO episodes, which is proposed as a mechanism for anomalously strong positive polar cap height anomalies in MJO Phases 7–8.

SKS Polarization Anomalies Due to the Coriolis Force

ABSTRACT The Earth’s Coriolis force has been well-known to impact surface waves and normal modes, which is essential to accurately interpret these waves. However, the Coriolis force on body waves has been assumed to be negligible and mostly ignored. It has been previously shown that the Coriolis force impacts polarizations of shear waves, whereas the wavefronts remain unaffected. We expand on the potential influences of Earth’s Coriolis force on shear-wave polarization measurements by conducting 3D numerical simulations for elastic waves generated by earthquake and explosive sources in a radially symmetric, and 3D mantle and crustal models. The Coriolis force can produce polarization anomalies of mantle shear waves up to 7° and core phases, such as SKS and SKKS, up to 4°. Uncorrected shear-wave polarizations due to the Coriolis force can cause an additional source of error (5°–10° in fast direction, and 0.2–0.3 s delay time depending on the method and seismic phase), inaccurate interpretation of station misalignments, and imprecise estimates of the core–mantle boundary topography. We show how to correct for the Coriolis force on teleseismic shear waves using 1D ray tracing for well-isolated phases. We recommend the use of full waveform simulations to accurately account for earthquake sources parameters, poorly isolated phases that could include interfering phase arrivals within the measurement time window, and the effect of the Coriolis force on the polarizations of shear waves.

Self-Potential as a Tool to Monitor Redox Reactions at an Ore Body: A Sandbox Experiment

Ore bodies generate natural electrical fields that are measurable at the ground surface. The ground surface signature of this electrical field is called a self-potential anomaly. We developed a sandbox experiment to monitor the evolution of a self-potential anomaly associated with redox processes mediated by bacterial activity at the surface of a buried metallic object crossing the water table. A Bio-Electrochemical Cell (BEC) is formed by a metal bar connecting the upper, oxygen-rich, part of the tank and an aquifer containing an electron donor in the form of acetate. The self-potential response was observed during a period of 327 days. The tomography of the self-potential signature confirms that self-potential tomography is able to locate the metallic target acting as a BEC. In addition, we performed redox potential, pH, and electrical potential measurements over a vertical cross-section of the tank at several time steps to obtain an idea of where the redox front is located. The distributions of the redox potential and pH further demonstrated the development of the oxidation-reduction chemical processes facilitated by the BEC as bacterial communities developed around the metallic bar. The electrical potential anomaly shows that the bacterial communities followed a short period of exponential growth, then a longer period of a sustained population. These results demonstrate the usefulness of the self-potential method in monitoring redox processes at the surface of a buried ore body. Further works will need to combine such self-potential anomalies with induced polarization anomalies through joint inversion.

A study of volcanic rocks and ferromanganese crusts through marine geophysical methods integration in the north portion of Cruzeiro do Sul Rift in the Rio Grande Rise

The Rio Grande Rise (RGR) is an extensive structural high located in the South Atlantic Ocean, target of increasing exploratory interest. During the last decades, considerable attention has been given to its genesis, dynamic, regional tectonic, and composition. Some studies indicate the presence of volcanic rocks, mainly basaltic, related to their volcanic origin and Ferromanganese Crusts, boosting the research and economic interest. This study suggests the location of volcanic rocks and FeMn crusts at the north portion of Cruzeiro do Sul Rift within the RGR, characterizing the local geology and distribution pattern. We used multibeam bathymetry, sidescan sonar, dredges, and magnetic field data to integrate and better constrain the results. The magnetic field data highlighted the location of probable basaltic rocks, agreeing with the published literature, which was afterward confirmed by dredge samples. Their magnetic anomalies displayed the predominance of reverse polarization and less frequent normal polarization anomalies. FeMn crusts need a large volume of magnetite to cause anomalies in the local magnetic field, which does not happen in the RGR. There, they have reduced thickness and are frequently eroded, as displayed by the bathymetry, sidescan sonar, and geological data. Magnetic lineaments at the Rift margin defined a zone with a series of normal faults. During the Rift formation, transcurrent movements caused an intense fracturing, providing pathways for magma intrusion. Therefore, the fault zone could be related to the primary magnetic anomalies as a function of the magma intrusion and the occurrence of the rifting process and seafloor spreading. The new data presented in this paper brings valuable data for the comprehension and exploration effort of the RGR.

Simulation of Northern Winter Stratospheric Polar Vortex Regimes in CESM2-WACCM

The possible impact of various Arctic polar vortex regimes for the stratosphere on the Northern Hemisphere extratropics has not been fully understood. Previous study has classified the stratospheric Arctic vortex to six regimes using the k-mean clustering algorithm based on the ERA5 reanalysis. The stability and robustness of the classification is further verified with a much longer model dataset and historical integrations from CESM2-WACCM. Consistent with the reanalysis, we clustered the Arctic stratospheric polar vortex forms into six patterns, named as homogeneously-intensified and -weakened regimes (HI, HW), North America-intensified and -weakened regimes (NAI, HAW), and Eurasia-intensified and -weakened regimes (EUI, EUW). A zonally uniform positive (negative) Northern Annular Mode (NAM) pattern develops during the HI (HW) regime from the stratosphere to troposphere. The NAM-like pattern shifts toward the western hemisphere with the largest negative (positive) anomalous height center shifting to North America during the NAI (NAW) regime. In contrast, the maximum polar anomaly center moves towards polar Eurasia during the EUI (EUW) regime. The HI, NAI, and EUW regimes are accompanied with weakened wave activities, while the HW, NAW, and EUI regimes are preceded by enhanced planetary waves. Accordingly, persistent anomalies of warmth (coldness) exist over midlatitude Eurasia and North America during the HI (HW). Anomalous warmth (coldness) centers exist in northern Eurasia, while anomalous coldness (warmth) centers exist around the Mediterranean Sea during the NAI (NAW) regime. Anomalous warmth (coldness) centers develop in East Asia in the EUI (EUW) periods. The rainfall anomaly distributions also vary with the stratospheric polar vortex regime. The frequency for stratospheric regimes during SSWs and strong vortex events is also assessed and consistent with previous findings.

Driving mechanisms for the El Niño–Southern Oscillation impact on stratospheric ozone

Abstract. While the impact of the El Niño–Southern Oscillation (ENSO) on the stratospheric circulation has been long recognized, its effects on stratospheric ozone have been less investigated. In particular, the impact on ozone of different ENSO flavors, eastern Pacific (EP) El Niño and central Pacific (CP) El Niño, and the driving mechanisms for the ozone variations have not been investigated to date. This study aims to explore these open questions by examining the anomalies in advective transport, mixing and chemistry associated with different El Niño flavors (EP and CP) and La Niña in the Northern Hemisphere in boreal winter. For this purpose, we use four 60-year ensemble members of the Whole Atmospheric Community Climate Model version 4. The results show a significant ENSO signal on the total column ozone (TCO) during EP El Niño and La Niña events. During EP El Niño events, TCO is significantly reduced in the tropics and enhanced at middle and high latitudes in boreal winter. The opposite response has been found during La Niña. Interestingly, CP El Niño has no significant impact on extratropical TCO, while its signal in the tropics is weaker than for EP El Niño events. The analysis of mechanisms reveals that advection through changes in tropical upwelling is the main driver for ozone variations in the lower tropical stratosphere, with a contribution of chemical processes above 30 hPa. At middle and high latitudes, stratospheric ozone variations related to ENSO result from combined changes in advection by residual circulation downwelling and changes in horizontal mixing linked to Rossby wave breaking and polar vortex anomalies. The impact of CP El Niño on the shallow branch of the residual circulation is small, and no significant impact is found on the deep branch.

Exploring the link between austral stratospheric polar vortex anomalies and surface climate in chemistry-climate models

Abstract. Extreme events in the stratospheric polar vortex can lead to changes in the tropospheric circulation and impact the surface climate on a wide range of timescales. The austral stratospheric vortex shows its largest variability in spring, and a weakened polar vortex is associated with changes in the spring to summer surface climate, including hot and dry extremes in Australia. However, the robustness and extent of the connection between polar vortex strength and surface climate on interannual timescales remain unclear. We assess this relationship by using reanalysis data and time-slice simulations from two chemistry-climate models (CCMs), building on previous work that is mainly based on observations. The CCMs show a similar downward propagation of anomalies in the polar vortex strength to the reanalysis data: a weak polar vortex is on average followed by a negative tropospheric Southern Annular Mode (SAM) in spring to summer, while a strong polar vortex is on average followed by a positive SAM. The signature in the surface climate following polar vortex weakenings is characterized by high surface pressure and warm temperature anomalies over Antarctica, the region where surface signals are most robust across all model and observational datasets. However, the tropospheric SAM response in the two CCMs considered is inconsistent with observations. In one CCM, the SAM is more negative compared to the reanalysis after weak polar vortex events, whereas in the other CCM, it is less negative. In addition, neither model reproduces all the regional changes in midlatitudes, such as the warm and dry anomalies over Australia. We find that these inconsistencies are linked to model biases in the basic state, such as the latitude of the eddy-driven jet and the persistence of the SAM. These results are largely corroborated by models that participated in the Chemistry-Climate Model Initiative (CCMI). Furthermore, bootstrapping of the data reveals sizable uncertainty in the magnitude of the surface signals in both models and observations due to internal variability. Our results demonstrate that anomalies of the austral stratospheric vortex have significant impacts on surface climate, although the ability of models to capture regional effects across the Southern Hemisphere is limited by biases in their representation of the stratospheric and tropospheric circulation.

On the Relative Importance of Stratospheric and Tropospheric Drivers for the North Atlantic Jet Response to Sudden Stratospheric Warming Events

Abstract Roughly two-thirds of the observed sudden stratospheric warming (SSW) events are followed by an equatorward shift of the tropospheric jet in the North Atlantic, while the other events generally show a poleward shift. It is however not resolved which drivers lead to the large inter-event variability in the surface impact. Using an intermediate complexity atmospheric model, we analyze the contribution of different factors to the downward response: polar cap geopotential height anomalies in the lower stratosphere, downstream influence from the northeastern Pacific, and local tropospheric conditions in the North Atlantic at the time of the initial response. As in reanalysis, an equatorward shift of the North Atlantic jet is found to occur for two-thirds of SSWs in the model. We find that around 40% of the variance of the tropospheric jet response after SSW events can be explained by the lower stratosphere geopotential height anomalies, while around 25% can be explained by zonal wind anomalies over the northeastern Pacific region. Local Atlantic conditions at the time of the SSW onset are also found to contribute to the surface response. To isolate the role of the stratosphere from tropospheric variability, we use model experiments where the zonal mean stratospheric winds are nudged toward climatology. When stratospheric variability is suppressed, the Pacific influence is found to be weaker. These findings shed light on the contribution of the stratosphere to the diverse downward impacts of SSW events, and may help to improve the predictability of tropospheric jet variability in the North Atlantic.

Multistationary Geomagnetic Vertical Intensity Polarization Anomalies for Predicting M ≥ 6 Earthquakes in Qinghai, China

Single-stationed geomagnetic vertical intensity polarization (GVIP) anomalies have demonstrated good predictions of the occurrence of large earthquakes in Japan. Nonetheless, due to the lack of a previously densified geomagnetic network, how the multistationary GVIP anomaly (MGVIPA) corresponds to impending earthquakes remains poorly understood. Based on the newly constructed geomagnetic network from 2014 in Qinghai, China, which is composed of 23 electromagnetic stations, we suggested an MGVIPA method to analyze the correlation with large earthquakes since 2015. The results show that (1) the occurrence of MGVIPA is characterized by clusters in time that continue in a short period; (2) the spatial distribution of MGVIPA usually occurs with high values synchronously at several places over the same period; and (3) the Mw ≥ 6 earthquakes occurred in the regions indicated by MGVIPA within a period ranging from 3 months to 1 year from 2015 to 2021 in Qinghai, China.

Detecting resistivity and induced polarization anomalies of galena veins in the presence of highly chargeable and conductive geological units at Daryan barite deposit in Iran

Assessment of resistivity and induced polarization (IP) data for metallic sulfide ore explorations is considered a routine task in the mining industry. The success in these surveys would be challenging if the sulfide ore lies within conductive and chargeable geological units. In this study, the resistivity and IP data of the Daryan area in northwestern Iran were examined for the detection of high-grade galena veins hosted by the Kahar Formation, a complex geological formation with several conductive and chargeable geological units. To facilitate the geophysical interpretations, a simple approach was adopted to solve the problem, and it was shown that a combination of correct geophysical modeling and approximate clustering of physical properties can help to check and revise (if necessary) the geological model or geophysical interpretations. In the Daryan area, the barite mineralization had high resistivity and low IP anomalies. More importantly, it was found that the highest IP and the lowest resistivity values were not the responses of galena mineralization but the graphite-rich shale. Thus, in complicated situations, the data should be treated and interpreted carefully because the “rules of thumb” may not work. This fact highlighted that prioritization of anomalies based on geophysical models alone is not an appropriate strategy in mineral exploration, and the interpretations must always be evaluated with geology. Moreover, it was discussed that both volume concentration and style of conductive minerals can be vital for creating elusive electrical responses, thus caution should be taken while interpreting electrical models in areas with complicated geology.

An audit of geomagnetic field in polar and south atlantic anomaly regions over two centuries

There are several reports about the decrease of the magnetic field of our planet. Here, we present a detailed investigation of the geomagnetic field over past 200 years using magnetic field models (IGRF+gufm1) and ground magnetic field observations until 2020. There are two prominent regions of consistently decreasing geomagnetic field namely: the South Atlantic Anomaly (SAA) and the southern pole region. The SAA region with field decreasing at 30 nT/year drifting to the south-west, whereas, the southern pole region with field decreasing at the rate 13 nT/year steadily drifting to the north-west. The Earth’s polar (66°–90°) magnetic field was invariably higher around the south pole as compared to the field around the north pole. However, it is found that over the past few decades (since 1950), the average magnetic field in the southern polar region has decreased to such an extent that presently it is weaker than the northern polar magnetic field. This tendency of cross-over in the magnitudes of average polar magnetic field strength is also evident in the ground magnetic field observations. On the ground at Hermanus (station in the SAA region), the rate of decrease of the magnetic field is found to be much higher (98 nT/year) during 1950–2020. Such a significant decrease in the magnetic field at Hermanus could be associated with the splitting of the SAA as it is situated close to the second minima in the SAA region. It is found that the magnetic field gradients around the center of the SAA become shallower as we move towards the higher altitudes. Also, the center of the SAA steadily moves in the north-east direction with increasing altitude. Though the weakening of the geomagnetic field is not an impulsive phenomenon but can invoke serious concerns to our life, satellites, and climate in near future.

Observation of magnetoelectric effect in the S = 1/2 spin chain compound CoSe2O5 single crystal

The antiferromagnetic structure in the S = 1/2 zigzag spin chain compound CoSe2O5 was recently revealed by neutron scattering. Herein, we provide clear evidence for the linear ME coupling through systematic investigations on magnetic, dielectric, and ferroelectric properties. The simultaneous responses of the b-axis electric polarization (Pb) and dielectric anomaly (εb) against magnetic stimuli along the c-axis are revealed. In addition, both the ferroelectric transition and dielectric anomaly shift from the magnetic Néel temperature TN ∼ 8.5 K toward the low temperature under increasing H applied along the c-axis, providing clear evidence for the magnetism-driven ferroelectricity. The observed off diagonal linear ME effect is in accordance with the prediction based on ME tensor analysis for the magnetic space group Pb′cn. Consequently, our results may allow an interesting opportunity to further exploration of intriguing phenomena and physics of ferrotoroidicity in this linear-ME compound CoSe2O5 due to the existence of the off diagonal term in the ME tensor, similar to the case for LiCoPO4.

Decoupling of the Arctic Oscillation and North Atlantic Oscillation in a warmer climate

The North Atlantic Oscillation and the Arctic Oscillation are modes of climate variability affecting temperature and precipitation in the mid-latitudes. Here we use reanalysis data and climate model simulations of historical and warm climates to show that the relationship between the two oscillations changes with climate warming. The two modes are currently highly correlated, as both are strongly influenced by the downward propagation of stratospheric polar vortex anomalies into the troposphere. When considering a very warm climate scenario, the hemispherically defined Arctic Oscillation pattern shifts to reflect variability of the North Pacific storm track, while the regionally defined North Atlantic Oscillation pattern remains stable. The stratosphere remains an important precursor for North Atlantic Oscillation, and surface Eurasian and Aleutian pressure anomalies precede stratospheric anomalies. Idealized general circulation model simulations suggest that these modifications are linked to the stronger warming of the Pacific compared with the slower warming of the Atlantic Ocean. The Arctic Oscillation and North Atlantic Oscillation are modes of Northern Hemisphere climate variability with high temporal and spatial correlation. With strong warming, climate models suggest their link breaks down due to a divergent response to the Pacific and Atlantic oceans and stratosphere.

Geomagnetic anomaly associated with Fukushima earthquake on February 13th, 2021

In this study, we performed research on electromagnetic anomalies related to earthquakes as early signs (precursors) that occurred in Fukushima, Japan on February 13th, 2021. The research focused on the utilization of geomagnetic field data which was derived from the Kakioka (KAK), Kanoya (KNY), and Memambetsu (MMB) observatories, particularly in the ultra-low frequency (ULF) to detect earthquake precursors. The method of electromagnetic data processing was conducted by applying a polarization ratio. In addition, we improved the methodology by splitting the ULF data (which ranged from 0.01-0.1 Hz) into 9 central frequencies and picking up the highest value from each central frequency to get the polarization ratio. The anomaly of magnetic polarization was identified 2-3 weeks before the mainshock in a narrowband frequency in the range of 0.04-0.05 Hz.

Composite Vertical-Motion Patterns near North American Polar–Subtropical Jet Superposition Events

AbstractA polar–subtropical jet superposition is preceded by the development of a polar cyclonic potential vorticity (PV) anomaly at high latitudes and a tropical anticyclonic PV anomaly at subtropical latitudes. A confluent large-scale flow pattern can lead to the juxtaposition of these respective PV anomalies at middle latitudes, resulting in the addition of the nondivergent circulations induced by each PV anomaly and an increase in upper-tropospheric wind speeds at the location of jet superposition. Once these PV anomalies become juxtaposed, vertical motion within the near-jet environment facilitates the advection and diabatic redistribution of tropopause-level PV, and the subsequent formation of the steep, single-step tropopause structure that characterizes a jet superposition. Given the importance of vertical motion during the formation of jet superpositions, this study adopts a quasigeostrophic (QG) diagnostic approach to quantify the production of vertical motion during three types of jet superposition events: polar dominant, eastern subtropical dominant, and western subtropical dominant. The diagnosis reveals that the geostrophic wind induced by polar cyclonic QGPV anomalies is predominantly responsible for QG vertical motion in the vicinity of jet superpositions. The QG vertical motion diagnosed from the along-isotherm component of the Q vector, which represents the vertical motion associated with synoptic-scale waves, is dominant within the near-jet environment. The QG vertical motion diagnosed from the across-isotherm component of the Q vector, which represents the vertical motion associated with frontal circulations in the vicinity of the jet, is subordinate within the near-jet environment, but is relatively more important during eastern subtropical dominant events compared to polar dominant and western subtropical dominant events.

Autumn Arctic Pacific Sea Ice Dipole as a Source of Predictability for Subsequent Spring Barents Sea Ice Condition

AbstractThis study uses observational and reanalysis datasets in 1980–2016 to show a close connection between a boreal autumn sea ice dipole in the Arctic Pacific sector and sea ice anomalies in the Barents Sea (BS) during the following spring. The September–October Arctic Pacific sea ice dipole variations are highly correlated with the subsequent April–May BS sea ice variations (r = 0.71). The strong connection between the regional sea ice variabilities across the Arctic uncovers a new source of predictability for spring BS sea ice prediction at 7-month lead time. A cross-validated linear regression prediction model using the Arctic Pacific sea ice dipole with 7-month lead time is demonstrated to have significant prediction skills with 0.54–0.85 anomaly correlation coefficients. The autumn sea ice dipole, manifested as sea ice retreat in the Beaufort and Chukchi Seas and expansion in the East Siberian and Laptev Seas, is primarily forced by preceding atmospheric shortwave anomalies from late spring to early autumn. The spring BS sea ice increases are mostly driven by an ocean-to-sea ice heat flux reduction in preceding months, associated with reduced horizontal ocean heat transport into the BS. The dynamical linkage between the two regional sea ice anomalies is suggested to involve positive stratospheric polar cap anomalies during autumn and winter, with its center slowly moving toward Greenland. The migration of the stratospheric anomalies is followed in midwinter by a negative North Atlantic Oscillation–like pattern in the troposphere, leading to reduced ocean heat transport into the BS and sea ice extent increase.

Temperature dependence of the spontaneous polarization, acoustic and strain anomalies in strontium barium niobate crystals of different chemical compositions probed by the second harmonic generation technique

In SrxBa1−xNb2O6 crystals (x = 0.33, 0.5, 0.61, and 0.75), temperature dependences of spontaneous polarization, strain, elastic modules, and second harmonic generation (SHG) signal are compared. It is revealed that SHG describes the temperature dependences of dipole moments in polar nanoregions in paraelectric phase. In the vicinity of the phase transition in paraelectric phase, SHG reflects the temperature behavior of relatively large and long-lived polar asymmetric regions as indicated by the presence of the intermediate temperature range on the temperature dependence of this nonlinear response.