Strong Anomalies Research Articles

Midwinter breakdown of ENSO climate impacts in East Asia

The El Niño-Southern Oscillation (ENSO) influence on the East Asian winter monsoon (EAWM) exhibits remarkable non-stationarity on subseasonal timescales, severely limiting climate predictability. Here, based on observational and reanalysis datasets, we identify a robust subseasonal variability in the EAWM response to ENSO, with a notable synchronous break in mid-January lasting about 10 days. We suggest that this breakdown is largely caused by interference from the abrupt phase reversal of the ENSO-driven North Atlantic Oscillation (NAO), which occurs about a week earlier in early January. During El Niño years, the NAO phase transition from positive to negative triggers a rapid change in the mid-latitude atmospheric circulation via the quasi-stationary Rossby wave adjustment. This results in the strengthening of the Siberian high, which produces strong northerly wind anomalies over East Asia, while the anomalous western North Pacific anticyclone weakens and shrinks to the south, eventually leading to the collapse of the teleconnection.

Magmatic arc construction within the Kedougou-Kenieba inlier, eastern Senegal: Petrographic, lithogeochemical and radiogenic isotope constraints

New petrographic, lithogeochemical and radiogenic isotope results from magmatic intrusions of the southeastern part of the Kedougou-Kenieba Inlier, Senegal document that these intrusions display evidence of a magmatic continuum of medium to high-K composition. A low-K intrusion group consists of andesitic, dioritic and tonalitic compostitions, with moderate (La/Yb)N and low (Dy/Yb)N ratios ranging, respectively, from 7.3 to 21.4 (with an average of 17.3) and 1.0 to 1.5. These intrusions have no obvious Eu anomalies (Eu/Eu* = 0.90–1.17), an average SiO2 concentration of 60.5 wt%, and are enriched in MgO, with an average concentration of 4.1 wt%. Their εNd values are high and range from +5.16 to +8.88, whereas they have low 87Sr/86Sri ratios of 0.701380–0.702552. This geochemical signature is characteristic of a depleted mantle source, which is supported by high Ni concentrations up to 211 ppm and high Mg# up to 85.35. The high-K leucogranite is characterized by high (La/Yb)N and higher (Dy/Yb)N ratios of, respectively, 10.6–48.3 (with an average of 30.5) and 2.0 to 2.4. It displays strong negative Eu anomalies (Eu/Eu* = 0.33–0.52), and has a higher average SiO2 concentration of 74 wt%, lower MgO concentration with an average of 0.21 wt%, as well as lower εNd values below −1.95. This geochemical signature suggests a continental crustal source for the magmas. Between these two end-members, there is an intermediate group of medium to high-K intrusions including quartz diorite, tonalite, granodiorite and monzogranite. These rocks are characterized by a wide variation of geochemical compositions and are most likely the result of a mixing of different magmatic sources and extreme fractional crystallization processes. Furthermore, we demonstrate that these magmatic intrusions were formed in a volcanic arc. These new data are evidence for a diversity of the intrusions within the southeastern part of the Kedougou-Kenieba Inlier.

Dynamical Phonons Following Electron Relaxation Stages in Photoexcited Graphene.

Ultrafast electron-phonon relaxation dynamics in graphene hides many distinct phenomena, such as hot phonon generation, dynamical Kohn anomalies, and phonon decoupling, yet it still remains largely unexplored. Here, we unravel intricate mechanisms governing the vibrational relaxation and phonon dressing in graphene at a highly nonequilibrium state by means of first-principles techniques. We calculate dynamical phonon spectral functions and momentum-resolved line widths for various stages of electron relaxation and find photoinduced phonon hardening, overall increase of relaxation rate and nonadiabaticity, as well as phonon gain. Namely, the initial stage of photoexcitation is found to be governed by strong phonon anomalies of finite-momentum optical modes along with incoherent phonon production. The population inversion state, on the other hand, allows the production of coherent and strongly coupled phonon modes. Our research provides vital insights into the electron-phonon coupling phenomena in graphene and serves as a foundation for exploring nonequilibrium phonon dressing in materials where ordered states and phase transitions can be induced by photoexcitation.

Strong geochemical anomalies following active submarine eruption offshore Mayotte

Submarine volcanic activity releases large amounts of gases and metals in the water column, affecting biogeochemical cycles and ecosystems at a regional and local scale. In 2018, Fani Maoré submarine volcano erupted 50 km offshore Mayotte Island (Comoros Archipelago, Indian Ocean). Active eruptive plumes were observed in May 2019 at and around the summit with acoustic plumes rising 2 km into the water column coupled to strong geochemical anomalies. Between May 2019 and October 2020, three research cruises monitored the eruptive activity. Here, we report spatial and temporal variability of water column chemistry above the volcano, focusing on dissolved gases, trace metal concentrations, and physico-chemical parameters. In May 2019, concentrations above 800 nM in CH4 and H2 were measured throughout the water column, with Total Dissolvable Mn and Total Dissolvable Fe concentrations above 500 nM, and CO2 values of 265 μM. Strong water column acidification was measured (0.6 pH unit) compared to the regional background. From May 2019 to October 2020, we observed a general decrease in gas concentrations, and an evolution of the TDMn/TDFe ratios similar to previously reported values in other submarine volcanic contexts, and consistent with a decrease of the eruptive activity at the volcano. In October 2020, a rebound of high H2 concentrations resulted from new lava flows, which were identified by seafloor observation using deep-towed camera, 5 km further than the volcano summit. During 2 years timespan of our observations (2019–2020), He, CO2 and CH4 concentrations correlate highlighting a magmatic origin of dissolved gases. δ13C-CH4 values of −34‰ vs. vPDB might suggest magma/sediments interaction during the magma ascent, and potential thermal cracking of organic matter, although abiotic methane generation cannot be ruled out given the volcanic context. Weak correlations between H2 and excess of 3He suggest complex processes of H2 from magmatic degassing, lava/seawater interaction, and oxidation processes in the water column. Strong and correlated Fe, Mn and Si water column anomalies are also consistent with fluid-rock reactions induced by acidic fluids rich in magmatic volatiles. Water column acidification appears to be associated with the release of CO2-rich fluids. A year after the main eruptive event, the system seems to be back to steady-state highlighting the buffer capacity and resilience of the seawater column environment.

On the Decadal Changes of the Interannual Relationship Between ENSO and Tropical South Atlantic SST in Boreal Summer

AbstractThis study aims to investigate the underlying mechanisms driving changes in the contemporaneous relationship between El Niño–Southern Oscillation (ENSO) and tropical South Atlantic (TSA) sea surface temperatures (SST) during boreal summer over the past century. Our findings indicate that the negative TSA–ENSO relationship is primarily attributed to persistent ENSO years rather than ENSO transition or development years. This is because of the distinct anomalies observed in both spring ENSO and the tropical North Atlantic (TNA) during ENSO persistent years, whose impacts on summer TSA are of the same sign. Thus, their combined effects lead to a strong TSA anomaly that is opposite to that of ENSO. On a decadal timescale, the frequency of persistent ENSO occurrence can explain the fluctuation of the ENSO–TSA relationship over the past century. These findings enhance our comprehension of the relationship between summer ENSO and the tropical Atlantic SST.

Studying inner core and lower mantle structure with a combination of PKP and converted SKP and PKS waves

SUMMARYStructure of the inner core is often measured through traveltime differences between waves that enter the inner core (PKPdf) and waves that travel through the outer core only (PKPab and PKPbc). Here we extend the method to converted waves PKSdf and SKPdf and compare results to PKP wave measurements. PKSdf and SKPdf have a very similar path to PKPdf and if velocity variations are present in the inner core, all three wave types should experience them equally. Since traveltime deviations can be due to velocity changes (either isotropic or anisotropy) as well as wave path deviations born from heterogeneity, we simultaneously investigate wave path directions and traveltimes of PKP, SKP and PKS waves for several source-array combinations. One of the path geometries is the anomalous polar corridor from South Sandwich to Alaska, which has strong traveltimes anomalies for PKPdf relative to more normal equatorial path geometries. Here we use array methods and determine slowness, traveltime and backazimuth deviations and compare them to synthetic data. We find that path deviations from theoretical values are present in all wave types and paths, but also that large scatter exists. Although some of the path deviations can be explained by mislocation vectors and crustal variations, our measurements argue that mantle structure has to be considered when investigating inner core anisotropy. Our polar path data show similar traveltime residuals as previously published, but we also find slowness residuals for this path. Interestingly, SKPdf and PKSdf for the South Sandwich to Alaska path show traveltime residuals that are partly opposite to those for PKPdf, possibly due to an interaction with a localized ultra-low velocity zone where waves enter the core.

Determination of Grid-Wise Monsoon Onset and Its Spatial Analysis for India (1901–2019)

Monsoon onset in India has always been a topic of interest for the research fraternity and various stakeholders. This study aimed to determine the monsoon onset date at the grid point scale, to obtain the trend of monsoon onset, and to unravel the spatial distribution of monsoon onset during the period 1901–2019 (especially in different climate modes). Based on observed cumulative rainfall, the piecewise linear regression model (PLRM), which employs least-squares principles, finds changepoints that signify the beginning of the monsoon season with the onset of monsoon. In this study, monsoon onset is examined with respect to several climate modes to evaluate their impact on monsoon onset. Monsoon onset is delayed in El Niño and drought years due to strong negative anomalies that are revealed by a spatial examination of monsoon onset. However, because of local atmospheric circulation impacts, there are outliers. The study also reveals areas with notable monotonic tendencies in monsoon onset, suggesting future changes in onset dates. These areas need more sophisticated frameworks for developing mitigation strategies since they should be viewed as susceptible. The comparison of the PLRM outcomes with objective methods reveals a strong correlation, confirming the accuracy of the PLRM method. Overall, the PLRM has been shown to be a useful tool for predicting the start of the monsoon on fine spatial scales and may be used in conjunction with regional climate models to anticipate the start of the monsoon in various regions of India. The results of this study could have a significant impact on regional planning and policy initiatives for sustainable development.

PREM-like velocity structure in the outermost core from global SKS and ScS waveform modeling

Seismic structure in the Earth's outermost core is important for our understanding of thermochemical stratification in the outer core, and is yet heavily debated. Here we study the compressional velocity structure in the Earth's outermost core based on waveform modeling of a unique untapped SKS and ScS dataset near bifurcation distances, collected from global seismic arrays for earthquakes occurring from 2000 to 2020. Using the SKS-ScS array dataset minimizes the effects of many uncertainties associated with earthquake source parameters and seismic heterogeneities in the mantle, and affords an opportunity to study and assess the seismic structure in the outermost core. We study outer core structure by testing two end-member models: 1) the D″ model that attributes any anomalous seismic observations to the effects of the lowermost mantle structure and is paired with a PREM (the Preliminary Reference Earth's Model) structure in the outermost core and 2) the outer core model that is paired with either a PREM or a tomographic structure in the lowermost mantle and attributes other unexplained seismic signals to an outer core structure. The results of the outer core models present unreasonable large lateral variations of >3.1% in the outermost core, while the inferred D″ models exhibit large-scale seismic anomalies that are consistent with the tomographic models and small-scale anomalies that are confirmed by further analysis of the seismic array data. Our analyses suggest a PREM-like seismic velocity structure and a lack of strong thermochemical anomalies in the topmost ∼200 km of the outer core, placing bounds on possible thermal and compositional conditions in the region of the Earth's outermost core. Our study also identifies the existence of small-scale seismic anomalies and sharp velocity variations in the lowermost mantle beneath the south coast of Alaska, northwestern Atlantic and the middle of Central America.

Statistical characteristics and mechanism of the South Atlantic Ocean Dipole

AbstractThe statistical characteristics and mechanism of the South Atlantic Ocean Dipole (SAOD) from 1980 to 2021 are analysed using observational datasets. The spatial pattern of the sea surface temperature anomaly (SSTA) during SAOD is a dipole pattern oriented in the northeast‐southwest direction, and the intensity of the SSTA in the northeast pole (NEP) is stronger than that in the southwest pole (SWP). SAOD has a decadal variability of about 12 years during 1980–2007, along with obvious seasonal phase‐locking, with the anomaly pattern developing in boreal spring (March–May), peaking in summer (June–August) and decaying in autumn (September–November). For a positive SAOD event (positive SSTA in the NEP, negative in the SWP), positive SSTA in the NEP grows due to a decrease in wind speed and thus in latent heat flux loss in boreal spring, as well as an increase in shortwave radiation flux from boreal spring to summer. However, southwesterly wind anomalies drive cold water from high latitudes to the SWP in boreal spring and summer, coupled with strong wind speed anomalies enhancing the loss of latent heat flux, which contributes to a negative SSTA in the SWP. In addition, the intensity of the SSTA in the SWP is weaker than that in the NEP because of the contribution of smaller shortwave radiation flux, sensible heat flux and larger mixed layer depth in the SWP in summer. For a negative SAOD mode (negative SSTA in the NEP, positive in the SWP), the wind, shortwave radiation flux, sensible heat flux and mixed layer depth anomalies are the opposite of those under a positive SAOD event.

Physiological responses of scallops and mussels to environmental variability: Implications for future shellfish aquaculture

Puget Sound (Washington, USA) is a large estuary, known for its profitable shellfish aquaculture industry. However, in the past decade, scientists have observed strong acidification, hypoxia, and temperature anomalies in Puget Sound. These co-occurring environmental stressors are a threat to marine ecosystems and shellfish aquaculture. Our research assesses how environmental variability in Puget Sound impacts two ecologically and economically important bivalves, the purple-hinge rock scallop (Crassodoma gigantea) and Mediterranean mussel (Mytilus galloprovincialis). Our study examines the effect of depth and seasonality on the physiology of these two important bivalves to gain insight into ideal grow-out conditions in an aquaculture setting, improving the yield and quality of this sustainable protein source. To do this, we used Hood Canal (located in Puget Sound) as a natural multiple-stressor laboratory, which allowed us to study acclimatization capacity of shellfish in their natural habitat and provide the aquaculture industry information about differences in growth rate, shell strength, and nutritional sources across depths and seasons. Bivalves were outplanted at two depths (5 and 30 m) and collected after 3.5 and 7.5 months. To maximize mussel and scallop growth potential in an aquaculture setting, our results suggest outplanting at 5 m depth, with more favorable oxygen and pH levels. Mussel shell integrity can be improved by placing out at 5 m, regardless of season, however, there were no notable differences in shell strength between depths in scallops. For both species, δ13C values were lowest at 5 m in the winter and δ15N was highest at 30 m regardless of season. Puget Sound's combination of naturally and anthropogenically acidified conditions is already proving to be a challenge for shellfish farmers. Our study provides crucial information to farmers to optimize aquaculture grow-out as we begin to navigate the impacts of climate change.

Linking ENSO to Synoptic Weather Systems in Eastern Australia

AbstractEl Niño‐Southern Oscillation (ENSO) is the main driver of interannual east Australian rainfall variability, but its link with rain‐producing synoptic weather systems is unclear. By tracking low pressure systems in ERA5 over 1979 to 2021, we find that springtime cyclones are linked to variations in the large‐scale atmospheric circulation during ENSO events. On spring days with a cyclone during La Niña, a pressure dipole occurs with a strong anticyclonic anomaly southeast of Australia and a cyclonic anomaly over eastern Australia. The northeasterly circulation directs tropical moisture toward eastern Australia, and coupled with induced ascent, promotes rainfall in this region. Both dynamical and thermodynamical changes are important for the rainfall response. An almost opposite circulation response occurs on cyclone days during El Niño events: high‐pressure over the Australian continent reduces rainfall in eastern Australia. These synoptic setups resemble the seasonal‐mean Rossby wave teleconnections, indicating a link between weather systems and ENSO.

Temporal and spatial evolution of the 2021 eruption in the Tajogaite volcano (Cumbre Vieja rift zone, La Palma, Canary Islands) from geophysical and geodetic parameter analyses

The eruption of the Tajogaite volcano in 2021, in the Cumbre Vieja rift zone (La Palma, Canary Islands), is the most recent but also the most damaging and longest-lasting eruption on the island since historical records began. We analyzed geophysical parameters (seismicity, surface deformation, thermal anomalies, and volcanic activity) with the aim of reconstructing the temporal development of the magma plumbing system. The seismic sequence (> 9000 events, mbLg ≤ 5.0) can be grouped into nine distinct phases, which correspond to well-separated spatial clusters and distinct earthquake regimes. A strong premonitory thermal anomaly was calculated on July 2021 in the South of La Palma. The source of the magma was within the upper mantle (40–20 km depth). A second magma budget (< 15 km depth) indicated a short-term stagnation of alkaline magma within the lower crust, near the Moho. The outline of these earthquakes delineates the magma pathway. Just before and immediately after the eruption (phases 2 and 3), the high-frequency seismicity in the mantle disappeared completely, reappearing ten days after the eruption started. The pattern of deformation began before the eruption with a breakpoint around September 11, after which, deformation accelerated sharply, followed by stabilization in phase 3 and a decrease in the following phases. The level of deformation suggested that a shallow magma intrusion was established. Based on the historical eruptive pattern, it is possible to infer two possible hazard-forecast scenarios: (a) the volcano could enter a prolonged phase of tranquility for more than one century or, (b) a new eruption could occur between ca. 2045 and 2065, with a slightly shorter duration than this recent one. Therefore, if the more pessimistic scenario is assumed, appropriate territorial planning is required.

Two Small Volcanoes, One Inside the Other: Geophysical and Drilling Investigation of Bažina Maar in Western Eger Rift

AbstractMaar‐diatreme volcanoes are small volcanic structures with a funnel‐shaped crater surrounded by a tephra‐ring. They are usually formed by the explosive phreatomagmatic eruptions when groundwater comes into the contact with magma. We focus on such a structure in the geodynamically active western Eger Rift (Czech Republic) and present results from multidisciplinary geophysical investigation calibrated by drilling in the newly discovered Pleistocene Bažina maar. We evaluated morphological (LiDAR‐based DEM) data and confirmed the existence of a maar‐diatreme structure by combined geophysical methods. In the map view, they revealed circular negative gravity anomaly, funnel‐shape low‐resistivity anomaly, and strong magnetic anomaly. These results allowed for the optimal location of two boreholes in the maar crater, which evinced its contact with country rocks and lithologies of the maar‐diatreme filling. The drilling revealed coherent volcanic rocks and volcaniclastic deposits, moreover, it revealed a presence of a pyroclastic cone with the olivine nephelinite feeding conduit. Further investigations disclosed maar structure and subsequent pyroclastic cone(s) with several generations of eruptions and systematic decrease of water influence on the eruption style. Different eruption styles suggest a unique evolution of two volcanoes, one inside the other. The age of the Bažina maar eruption, estimated from the reverse polarity of the detected magnetic anomaly, implies that the effusion and solidification of the lava during the eruption must be older than 0.78 Ma (Pleistocene). This points to an active volcanism in the western Eger Rift in a span of ∼0.5 Ma, where Bažina represents the oldest (maybe opening) phase.

Marble trace element and C-O isotope geochemistry of the Paleoproterozoic Jingshan Group, North China: Insights into BIF formation during the Lomagundi-Jatuli Event

The North China Craton, one of the oldest continental blocks in the world, comprises Paleoproterozoic metamorphic sedimentary formations that record the effects of multiple major events in early Earth history, including the Great Oxidation Event (GOE) and its consequent Lomagundi-Jatuli carbon isotope event (LJE). The lack of focused research on the geological record of LJE-equivalent rocks of the Jiaodong Peninsula, Shandong Province, eastern China, has hindered our understanding of the Precambrian atmospheric oxygen evolution recorded by rocks of the North China Craton. This paper considers carbon and oxygen isotope and trace element geochemical data recovered from marble deposits of the Paleoproterozoic Jingshan Group (2.20–1.90 Ga) of the Jiaolai Basin. The investigated strata display a pronounced positive δ13CV-PDB excursion greater than 4.2 ‰. δ13CV-PDB and δ18OV-SMOW values range from −3.7 ‰ to 5.4 ‰ and 4.5 ‰ to 18.7 ‰, respectively. Positive co-variance of carbon and oxygen isotope values of the analyzed Jingshan Group samples is interpreted to reflect the effects of metamorphism and water–rock reactions. Marble deposits of the Jingshan Group experienced recrystallization, metamorphism, and silicification resulting in strong decarbonation. High amphibolite facies metamorphism may have reduced δ13CV-PDB by 3 ‰ to 5 ‰. Thus, estimated original sedimentary δ13CV-PDB values of as great as +8.4 ‰ suggest the existence of a strong positive anomaly that may reflect the global Lomagundi-Jatuli event. Rare earth and other trace element geochemical results of the present study suggest that banded iron formation (BIF) deposits associated with the Jingshan Group marble formed in a redox stratified ocean in the Jiaolai Basin dominated by ferruginous conditions. Moreover, our results suggest that positive carbon isotope anomaly associated with the LJE is largely constrained to sediment deposited in shallow and coastal marine environments.

Moisture Source Analysis of Two Case Studies of Major Extreme Precipitation Events in Summer in the Iberian Peninsula

Extreme summer precipitation events commonly affect the Iberian Peninsula (IP), and studying the moisture sources that generate intense precipitation is extremely important. Therefore, this study analyzed the moisture sources of two major extreme precipitation events in summer in the IP. The events occurred on 18 September 1999 and 7 September 1989, and the anomalies of the associated meteorological variables are shown with respect to a 30-year reference period (1985–2014). A Lagrangian approach is used for determining the moisture source pattern using only the precipitating particles that reach the target region. In this research a dynamic downscaling methodology is applied using the WRF-ARW model forced using the ERA5 reanalysis and then the WRF-ARW outputs used to force the Lagrangian dispersion model FLEXPART-WRF. Specifically, the first event was associated with an atmospheric river favoring strong moisture transport from remote sources and the second event was caused by local convergence of moisture under the influence of a cut-off low system. For the 18 September 1999 case study, the major contribution to moisture reaching the target region was associated with the central and eastern North Atlantic, with values of up to approximately 32%. In addition, the moisture source pattern exhibited a strong anomaly in the climatological pattern. However, the origin of the moisture sources associated with the case of 7 September 1989 was mainly the western Mediterranean Sea, with a contribution of up to 40% or higher. Finally, Northwest Africa and precipitation recycling processes over the IP contributed approximately 16% to the moisture supply for this event.

Extreme events in the multi-proxy South Pacific drought atlas

Droughts are a natural occurrence in many small Pacific Islands and can have severe impacts on local populations and environments. The El Niño-Southern Oscillation (ENSO) is a well-known driver of drought in the South Pacific, but our understanding of extreme ENSO events and their influence on island hydroclimate is limited by the short instrumental record and the infrequency of ENSO extremes. To address this gap, we developed the South Pacific Drought Atlas (SPaDA), a multi-proxy, spatially resolved reconstruction of the November–April Standardised Precipitation Evapotranspiration Index for the southwest Pacific islands. The reconstruction covers the period from 1640 to 1998 CE and is based on nested principal components regression. It replicates historical droughts linked to ENSO events with global influence, compares well to previously published ENSO reconstructions, and is independently verified against fossil coral records from the Pacific. To identify anomalous hydroclimatic states in the SPaDA that may indicate the occurrence of an extreme event, we used an Isolation Forest, an unsupervised machine learning algorithm. Extreme El Niño events characterised by very strong southwest Pacific drought anomalies and a zonal SPCZ orientation are shown to have occurred throughout the reconstruction interval, providing a valuable baseline to compare to climate model projections. By identifying the spatial patterns of drought resulting from extreme events, we can better understand the impacts these events may have on individual Pacific Islands in the future.

Unique electric and dielectric features of dipole-pair substituted barium titanate ferroelectric ceramics (I): electrical characterization

A comparison study of pure barium titanate BaTiO3, dipole-pair [Ga3+, Ta5+] substituted barium titanate Ba(Ga3+, Ta5+)0.005Ti0.99O3 ([Ga3+, Ta5+]: BaTiO3), single ion [Ga3+] substituted barium titanate Ba(Ga3+)0.01Ti0.99O3 ([Ga3+]: BaTiO3), and single ion [Ta5+] substituted barium titanate Ba(Ta5+)0.01Ti0.99O3 ([Ta5+]: BaTiO3) ferroelectric ceramics have been conducted in order to discern the unique electric and dielectric properties derived from dipole-pair substitution. The band gap, DC resistivity, relative permittivity, dissipation factor, and complex impedance have been measured and analyzed. The dipole-pair substituted material is demonstrated to be an excellent dielectric, which possesses high electrical resistivity, high activation energy, significant dielectric diffuseness, high relative permittivity and low dissipation factor, due to charge compensation and creation of dipole-pairs in barium titanate solid solution ceramic matrix. The single substituted (acceptor and donor, respectively) samples behave more like traditional semiconductors, which have lower electrical resistivity, lower activation energy, and exhibit strong dielectric anomaly and large dissipation factor due to charge imbalance (electrons and holes) in part compensated for through additional defect creation. The relaxor-like behavior of the dipole-pair substituted sample is distinguishable from the classic relaxor through electric properties and structural phase diagram and is anticipated to spark more attention and further exploration. The unique features of electric resistivity and dielectric diffuseness of the dipolar-pair engineered BaTiO3 affords opportunity for designing properties of novel relaxor-like ferroelectrics.

Sensitive characteristics of contributed region and detectability analysis for semi-airborne frequency-domain electromagnetic system

There is restricted research on the sensitive characteristic and detection ability analysis of semi-airborne frequency domain electromagnetic system at present. However, it is critical to the optimal design of the observation scheme, and it may be beneficial for the optimal selection of the record region and increasing the resolution of apparent resistivity imaging. So it is necessary to analyze the sensitive characteristic of the semi-airborne frequency domain system. In this paper, the primary electric field based on the closed-form expression of the electromagnetic field in the underground excited by a horizontal electric dipole is calculated, each element of the underground will be regarded as a current source, and the secondary magnetic field can be obtained based on tensor Green's function. The sensitivity is defined by the contribution of each element to the total secondary magnetic field at the receiving point, and the sensitivity distribution characteristic of the related region is analyzed. Numerical experiments reveal that the region with high sensitivity can produce a strong relative anomaly, and the contribution of the region with sensitivity near zero is almost negligible. To verify the analysis for sensitive characteristics and detectability, we have conducted a field test, after the design of the observation scheme, the data obtained reflects the underground fault zone well. Thus, the relationship between detectability and sensitivity is worth studying.

Impacts of the Surface Potential Vorticity Circulation over the Tibetan Plateau on the East Asian Monsoon in July

Based on the definition of potential vorticity substance (W) and its equation, an index “iPV” representing the leading mode of the surface potential vorticity circulation (PVC) over the Tibetan Plateau is defined to characterize the orographic potential vorticity (PV) forcing on the atmospheric general circulation. The relationships between the iPV index and the East Asian monsoon in July, as well as the Silk Road pattern in Eurasia, are investigated on an interannual time scale. Results show that the iPV in July is closely related to the interannual variability of the East Asian monsoon. Corresponding to the positive phase of iPV with negative (positive) PVC over the north (south) of the plateau, strong positive PV anomalies and westerly flows develop in the troposphere over the plateau. Consequently, in the downstream region, the zonal PV advection increases with height just above the Jianghuai Meiyu front, which is conducive to the generation of upward movement. Over the East Asian area, the upper troposphere is controlled by the eastward shifted South Asian High. In the lower troposphere, the southwesterly flow anomaly on the northwestern side of the strengthened western Pacific subtropical high transports abundant water vapor to the north, forming a convergence in the Jianghuai area, leading to the formation of large-scale precipitation along the Meiyu front. Results from partial correlation analysis also demonstrate that the link between the variability of the East Asian monsoon in July and the plateau PV forcing is affected very little by the Silk Road pattern, whereas the plateau PV forcing plays a key “bridging” role in the influence of the Silk Road pattern on the East Asian monsoon.

Pacific Meridional Mode Does Not Induce Strong Positive SST Anomalies in the Central Equatorial Pacific

Abstract The positive phase of the Pacific meridional mode (PMM) is closely related to the onset of El Niño. Previous studies have indicated that positive sea surface temperature anomalies (SSTAs) in the central equatorial Pacific (CEP) during the spring and summer of positive PMM years primarily originate from the northeastern tropical Pacific (NETP) via positive wind–evaporation–SST feedback. We review the evolution of PMM and find weak evidence to support such a linkage. Coupled model experiments show that the positive PMM-regressed SSTAs in the NETP only account for ∼24% of those in the CEP from winter to spring, illustrating the principle that correlation does not necessarily mean causality. The strongest positive PMM SSTAs in the NETP and CEP increase El Niño intensity by 1.07°C, whereas that in the NETP alone increase El Niño intensity by 0.69°C. When the composite SSTAs in the NETP during positive PMM years are used, however, the El Niño intensity is increased merely by 0.17°C. The change in the subsurface temperature in the equatorial Pacific is curtailed for the NETP SSTAs to trigger El Niño, while the wind–evaporation–SST feedback plays a less important role. Our results indicate that the impact of PMM on El Niño might be overestimated by ∼55%. Moreover, a comprehensive understanding about the role of the tropical North Pacific on El Niño can be obtained only when the impact from the western North Pacific is considered.