Polarization Anomalies Research Articles

Types and genesis of induced polarization anomalies in the water-rich structures of the Taian karst area

From December 2010 to April 2011, agricultural production in North China and Huang-Huai basin experienced difficulties because of severe drought. Based on samples from the development of deep karst groundwater resources, a set of laws has been established to reflect the types and genesis of induced polarization (IP) anomalies in a range of water-rich karst structures in Taian area. The curves of IP anomalies in the water-rich structures can be classified into ramps, slow downs, low-resistance platforms and low-resistance V patterns. IP anomalies observed in apparent resistivities contours can be classified as low-resistance steps, low-resistance gradients and low-resistance U patterns. In water-rich areas hosted mainly in caves, IP anomalies include low-apparent resistivity, low-visible polarization, low half decay time, low attenuation and low multi-parameter synchroneity. These water-rich areas mainly consist of fault structures, where the IP anomalies have a low-apparent resistivity and low-vision polarization, and exhibit relatively long half decay time, maximum attenuation value exceptions, apparent resistivities and multi-parameter “reverse phase” anomalies.

GCM simulations of Titan’s middle and lower atmosphere and comparison to observations

Simulation results are presented from a new general circulation model (GCM) of Titan, the Titan Atmospheric Model (TAM), which couples the Flexible Modeling System (FMS) spectral dynamical core to a suite of external/sub-grid-scale physics. These include a new non-gray radiative transfer module that takes advantage of recent data from Cassini–Huygens, large-scale condensation and quasi-equilibrium moist convection schemes, a surface model with “bucket” hydrology, and boundary layer turbulent diffusion. The model produces a realistic temperature structure from the surface to the lower mesosphere, including a stratopause, as well as satisfactory superrotation. The latter is shown to depend on the dynamical core’s ability to build up angular momentum from surface torques. Simulated latitudinal temperature contrasts are adequate, compared to observations, and polar temperature anomalies agree with observations. In the lower atmosphere, the insolation distribution is shown to strongly impact turbulent fluxes, and surface heating is maximum at mid-latitudes. Surface liquids are unstable at mid- and low-latitudes, and quickly migrate poleward. The simulated humidity profile and distribution of surface temperatures, compared to observations, corroborate the prevalence of dry conditions at low latitudes. Polar cloud activity is well represented, though the observed mid-latitude clouds remain somewhat puzzling, and some formation alternatives are suggested.

Intraseasonal and Interdecadal Jet Shifts in the Northern Hemisphere: The Role of Warm Pool Tropical Convection and Sea Ice

Abstract This study uses cluster analysis to investigate the interdecadal poleward shift of the subtropical and eddy-driven jets and its relationship to intraseasonal teleconnections. For this purpose, self-organizing map (SOM) analysis is applied to the ECMWF Interim Re-Analysis (ERA-Interim) zonal-mean zonal wind. The resulting SOM patterns have time scales of 4.8–5.7 days and undergo notable interdecadal trends in their frequency of occurrence. The sum of these trends closely resembles the observed interdecadal trend of the subtropical and eddy-driven jets, indicating that much of the interdecadal climate forcing is manifested through changes in the frequency of intraseasonal teleconnection patterns. Two classes of jet cluster patterns are identified. The first class of SOM pattern is preceded by anomalies in convection over the warm pool followed by changes in the poleward wave activity flux. The second class of patterns is preceded by sea ice and stratospheric polar vortex anomalies; when the Arctic sea ice area is reduced, the subsequent planetary wave anomalies destructively interfere with the climatological stationary waves. This is followed by a decrease in the vertical wave activity flux and a strengthening of the stratospheric polar vortex. An increase in sea ice area leads to the opposite chain of events. Analysis suggests that the positive trend in the Arctic Oscillation (AO) up until the early 1990s might be attributed to increased warm pool tropical convection, while the subsequent reversal in its trend may be due to the influence of tropical convection being overshadowed by the accelerated loss of Arctic sea ice.

An Approximation to the General Galerkin Method of Computing Coupled-Mode Synthetic Seismograms

Research Article| February 25, 2014 An Approximation to the General Galerkin Method of Computing Coupled‐Mode Synthetic Seismograms Duayne M. Rieger; Duayne M. Rieger Department of Geology and Geophysics, Yale University, Kline Geology Lab, 210 Whitney Avenue, New Haven, Connecticut 06511 Search for other works by this author on: GSW Google Scholar Jeffrey J. Park Jeffrey J. Park Department of Geology and Geophysics, Yale University, Kline Geology Lab, 210 Whitney Avenue, New Haven, Connecticut 06511 Search for other works by this author on: GSW Google Scholar Author and Article Information Duayne M. Rieger Department of Geology and Geophysics, Yale University, Kline Geology Lab, 210 Whitney Avenue, New Haven, Connecticut 06511 Jeffrey J. Park Department of Geology and Geophysics, Yale University, Kline Geology Lab, 210 Whitney Avenue, New Haven, Connecticut 06511 Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1943-3573 Print ISSN: 0037-1106 Bulletin of the Seismological Society of America (2014) 104 (2): 962–971. https://doi.org/10.1785/0120130114 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Duayne M. Rieger, Jeffrey J. Park; An Approximation to the General Galerkin Method of Computing Coupled‐Mode Synthetic Seismograms. Bulletin of the Seismological Society of America 2014;; 104 (2): 962–971. doi: https://doi.org/10.1785/0120130114 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract Quasi‐Love (QL) scattered surface waves are the result of lateral gradients of seismic anisotropy in Earth’s upper mantle. These polarization anomalies can be forward modeled in the context of normal‐mode coupling. However, methods for computing coupled‐mode synthetic seismograms, such as the general Galerkin method, are computationally intensive, especially in the case of 3D structure. In this report, we present an approximation of the general Galerkin method of computing coupled‐mode synthetic seismograms. The approximation replaces the formal eigenvector decomposition of the elastic potential energy coupling matrix V in the general Galerkin method with a piecewise approach. The approximation uses the closed‐form eigenvectors of 2×2 coupling matrices V(kj), which represent the interactions between two individual singlets sk and sj, to form the eigenvectors of V. The approximation is benchmarked against the exact general Galerkin method using zonally symmetric anisotropic structure. We find the approximation successfully reproduces the QL waveforms with a slight underestimate of the amplitude. By limiting the east–west extent of the zonally symmetric structure, we extend the approximation to a 3D structure. We find that the sharp lateral gradients in anisotropy created by the north–south running boundaries of the 3D structure contribute to the observed scattering until they are outside the sensitivity zone as defined by Ritzwoller et al. (2002). This demonstrates the sensitivity of QL surface‐wave scattering to off‐path structure. We also explicitly confirm the path‐integral asymptotics that in the limit of smooth off‐path structure, QL surface‐wave scattering can be represented via the path integral along the source–receiver great circle path rather than the volume integral over Earth. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The boreal spring stratospheric final warming and its interannual and interdecadal variability

Based on the daily NCEP/DOE reanalysis II data, dates of the boreal spring Stratospheric Final Warming (SFW) events during 1979–2010 are defined as the time when the zonal-mean zonal wind at the central latitudes (65°-75°N) of the westerly polar jet drops below zero and never recovers until the subsequent autumn. It is found that the SFW events occur successively from the mid to the lower stratosphere and averagely from the mid to late April with a temporal lag of about 13 days from 10 to 50 hPa. Over the past 32 years, the earliest SFW occurs in mid March whereas the latest SFW happens in late May, showing a clear interannual variability of the time of SFW. Accompanying the SFW onset, the stratospheric circulation transits from a winter dynamical regime to a summertime state, and the maximum negative tendency of zonal wind and the strongest convergence of planetary-wave are observed. Composite results show that the early/late SFW events in boreal spring correspond to a quicker/ slower transition of the stratospheric circulation, with the zonal-mean zonal wind reducing about 20/5 m s−1 at 30 hPa within 10 days around the onset date. Meanwhile, the planetary wave activities are relatively strong/weak associating with an out-of-/in-phase circumpolar circulation anomaly before and after the SFW events in the stratosphere. All these results indicate that, the earlier breakdown of the stratospheric polar vortex (SPV), as for the winter stratospheric sudden warming (SSW) events is driven mainly by wave forcing; and in contrast, the later breakdown of the SPV exhibits more characteristics of its seasonal evolution. Nevertheless, after the breakdown of SPV, the polar temperature anomalies always exhibit an out-of-phase relationship between the stratosphere and the troposphere for both the early and late SFW events, which implies an intimate stratosphere-troposphere dynamical coupling in spring. In addition, there exists a remarkable interdecadal change of the onset time of SFW in the mid 1990s. On average, the SFW onset time before the mid 1990s is 11 days earlier than that afterwards, corresponding to the increased/decreased planetary wave activities in late winter-early spring before/after the 1990s.

The extremely cold 2009–2010 winter and its relationship with the Arctic oscillation

The Northern-Hemisphere high-latitude continents experienced extremely cold weathers in winter 2009–2010. In the present paper, we show that the cold winter was associated with the activity of the Arctic oscillation (AO), which demonstrated the strongest negative polarity over the past six decades and persisted from December, 2009 to March, 2010. It is found that variations of the surface AO was closely linked to stratospheric polar vortex anomalies, and that the surface AO phases followed downward propagation of stratospheric Northern-Hemisphere Annular mode (NAM) anomalies during the winter. The case of 2009–2010 winter provides us with a typical example that anomalous stratospheric signals can be used to improve skills of long-range weather forecast and intra-seasonal climate prediction in winter time. We also show that the El Nino event, which started developing from May 2009, might contribute the formation of exceptionally negative and persistent AO and stratospheric NAM, particularly over North Pacific and North America.

Influences of ENSO on Stratospheric Variability, and the Descent of Stratospheric Perturbations into the Lower Troposphere

Abstract The linkage between El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) through the stratospheric pathway is examined using a global coupled climate model [GFDL Climate Model version 3 (CM3)], with increased vertical resolution and extent in the stratosphere as compared to an earlier model [GFDL Climate Model version 2 (CM2)]. It is demonstrated that the relationship between ENSO and NAO is stronger in CM3 than in CM2. It is found that ENSO plays an important role in modulating the frequency of occurrence of the stratospheric polar vortex anomalies through enhancement/attenuation of the amplitudes of zonal wavenumbers 1 and 2, especially in late winter. A higher frequency of weak (strong) stratospheric vortex events is simulated in CM3 during El Niño (La Niña) episodes. The weak vortex events during El Niño winters are preceded by enhancement of the zonal wave-1 pattern and weakening of zonal wave-2 pattern. These modified tropospheric planetary waves propagate upward and then weaken the stratospheric polar vortex through eddy–mean flow interaction. The zonal-mean geopotential response in the stratosphere propagates downward and weakens the polar vortex throughout the troposphere. The effects of planetary wave refraction in the upper troposphere on the zonally averaged circulation cells in the tropospheric meridional plane, and the linkage between the lower branches of these cells and the near-surface wind patterns, play an important role in the flow pattern over the region corresponding to the southern lobe of the NAO. Specifically, a negative annular mode and NAO response is discernible in weak stratospheric vortex events during El Niño. Conversely, the positive annular mode and NAO is evident in strong vortex events during La Niña.

Simultaneous EM and IP inversion using relaxation time constraints

S. Garina, S. Ivanov, E. Kudryavceva, P. Legeydo, P. Veeken and V. Vladimirov, discuss geochemical alteration zones above hydrocarbon accumulations, identified by differentially normalized electromagnetic surveying, and how they may give rise to induced polarization (IP) anomalies.

Inversion for weak triclinic anisotropy from acoustic axes

Acoustic axes are directions in anisotropic elastic media, in which phase velocities of two or three plane waves (P, S1 or S2 waves) coincide. Acoustic axes are important, because they can cause singularities in the field of polarization vectors and anomalies in the shape of the slowness surface. The maximum number of acoustic axes in triclinic anisotropy is 16, and their directions depend on anisotropy parameters in a complicate way. Under weak anisotropy approximation this dependence simplifies and the directions of acoustic axes can be used for the inversion for anisotropy parameters. The maximum acoustic axes under weak anisotropy is 16, the minimum number of acoustic axes is zero. In the inversion, we can retrieve 13 combinations of anisotropy parameters provided we use directions of 7 acoustic axes at least. Under weak anisotropy approximation, the directions of acoustic axes are insensitive to strength of anisotropy; hence we cannot invert for absolute values of weak anisotropy parameters, but only for their relative values. Numerical tests have shown that the inversion is applicable only to very weak anisotropy with strength of less than 5%, provided that the acoustic axes used in the inversion are determined with an accuracy of 0.1∘ or better. In this case the inversion yields an average error for elastic parameters of less than 10%. In order to invert for the total set of 21 anisotropy parameters it is necessary to combine the measurements of the directions of the acoustic axes with measurements of other attributes of elastic waves in anisotropic media.

First-principles study on the differences of possible ferroelectric behavior and magnetic exchange interaction between Bi2NiMnO6 and La2NiMnO6

The differences of possible ferroelectric behavior and magnetic exchange interaction between Bi2NiMnO6 and La2NiMnO6 have been investigated by first-principles calculation. Paying attention to the electronic structures, bonding interaction, and Born effective charges of the two compounds, the calculations reveal that ferroelectric distortion occurs only in Bi2NiMnO6 rather than La2NiMnO6. The calculation also indicates that the Ni-Mn ferromagnetic exchange interaction is weakened in Bi2NiMnO6 compared with that in La2NiMnO6. Thus the present work explains why Bi2NiMnO6 has a lower Curie temperature compared with La2NiMnO6. The mechanism why Bi2NiMnO6 has weaker Ni-Mn ferromagnetic exchange interaction than La2NiMnO6 is explored by considering the Kugel-Khomskii model. Finally, the electric polarizations of Bi2NiMnO6 with ferromagnetic and ferrimagnetic order are estimated to be 18.05 and 19.01 μC/cm2, respectively, indicating the anomaly of electric polarization near the Curie temperature of Bi2NiMnO6.

Anomalies of heat capacity and spontaneous polarization of nonstoichiometric KTiOPO4 crystals in the low-temperature region

The data of experiments that characterize the dependences of the unit cell volume, heat capacity, and spontaneous polarization of a nonstoichiometric KTiOPO4 sample are presented for the low-temperature region. It is shown that the influence of the electric field leads to variation in the sample nonstoichiometry, which is characterized by the appearance of anomalous behavior of spontaneous polarization in the region below 30 K. This experimental fact is associated with the appearance of the donor-acceptor pairs possessing the dipole moment. As the temperature increases, they gradually dissociate with the subsequent appearance of the cationic component of conduction.

Propagation of planetary-scale zonal mean wind anomalies and polar oscillations

Global atmospheric variables can be physically decomposed into four components: (1) the zonal time averaged climate symmetric component, (2) the time averaged climate asymmetric, (3) the zonal-mean transient symmetric anomaly, and (4) the transient asymmetric anomaly. This study analyzes the relationships between the intra-seasonal and inter-annual variability of planetary scale decomposed zonal and meridional winds in the tropopause, and oscillations such as those from the El Nino-Southern Oscillation (ENSO), the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO). The tropical inter-annual zonal mean wind anomalies in the tropopause are linked with the ENSO cycle and can propagate into the subtropics, mid-latitudes, and polar front regions via abnormal meridional vertical cells. Similarly, tropical intra-seasonal (40–60-d) zonal wind anomalies can reach the subtropics and mid-latitudes. The polar intra-seasonal zonal wind anomalies in the tropopause can propagate toward high-latitude areas. Thus, the AO and the AAO are the result of the interaction and propagation of these planetary scale zonal wind anomalies.

Essential role of ubiquitin C‐terminal hydrolases UCHL1 and UCHL3 in mammalian oocyte maturation

Ubiquitin C-terminal hydrolases (UCHs) comprise a family of deubiquitinating enzymes that play a role in the removal of multi-ubiquitin chains from proteins that are posttranslationally modified by ubiquitination to be targeted for proteolysis by the 26S proteasome. The UCH-enzymes also generate free monomeric ubiquitin from precursor multi-ubiquitin chains and, in some instances, may rescue ubiquitinated proteins from degradation. This study examined the roles of two oocyte-expressed UCHs, UCHL1, and UCHL3 in murine and rhesus monkey oocyte maturation. The Uchl1 and Uchl3 mRNAs were highly expressed in GV and MII oocytes, and were associated with the oocyte cortex (UCHL1) and meiotic spindle (UCHL3). Microinjection of the UCH-family enzyme inhibitor, ubiquitin-aldehyde (UBAL) to GV oocytes prevented oocyte meiotic progression beyond metaphase I in a majority of treated oocytes and caused spindle and first polar body anomalies. Injection of antibodies against UCHL3 disrupted oocyte maturation and caused meiotic anomalies, including abnormally long meiotic spindles. A selective, cell permeant inhibitor of UCHL3, 4, 5, 6, 7-tetrachloroidan-1, 3-dione also caused meiotic defects and chromosome misalignment. Cortical granule localization in the oocyte cortex was disrupted by UBAL injected after oocyte maturation. We conclude that the activity of oocyte UCHs contributes to oocyte maturation by regulating the oocyte cortex and meiotic spindle.

CASTING LIGHT ON THE GHOST

The infrared sector of QCD contains all the necessary ingredients, once laid onto a time-dependent, curved background, to cater for the much needed cosmological vacuum energy. This is achieved through the fields that describe the impact of the long-range interactions of QCD, the Veneziano ghost and its dipolar partner. Although technically extremely challenging, the physics is well understood and the estimated dark energy density is of the correct order of magnitude. In this brief review I will retrace the steps leading to two new cosmological applications of this model, namely the possibility of the generation of cosmic magnetic fields, and the unification of several observed polarization anomalies under the same roof.

Polarization anomalies of microwave radiation and additional electromagnetic waves in deformable ice covers

Polarization measurements are performed for the intensity of microwave radiation at frequencies 13–14 GHz passing through fresh-water ice cover parallel to the interface between the media. The reasons for the emergence of additional electromagnetic waves are investigated. In experiments, the formation of two types of additional electromagnetic waves determined by the plane-layer geometry of the medium (coherent waves) and by the fluidity of ice under the action of mechanical stresses (incoherent waves) is observed.

Observational evidence of the delayed response of stratospheric polar vortex variability to ENSO SST anomalies

The temporal and spatial relationship between ENSO and the extratropical stratospheric variability in the Northern Hemisphere is examined. In general, there exists a negative correlation between ENSO and the strength of the polar vortex, but the maximum correlation is found in the next winter season after the mature phase of ENSO event, rather than in the concurrent winter. Specifically, the stratospheric polar vortex tends to be anomalously warmer and weaker in both the concurrent and the next winter season following a warm ENSO event, and vice versa. However, the polar anomalies in the next winter are much stronger and with a deeper vertical structure than that in the concurrent winter. Our analysis also shows that, the delayed stratospheric response to ENSO is characterized with poleward and downward propagation of temperature anomalies, suggesting an ENSO-induced interannual variability of the global mass circulation in the stratosphere. Particularly, in response to the growing of a warm ENSO event, there exist warm temperature and positive isentropic mass anomalies in the midlatitude stratosphere since the preceding summer. The presence of an anomalous wavenumber-1 in the concurrent winter, associated with an anomalous Aleutian high, results in a poleward extension of warm anomalies into the polar region, and thus a weaker stratospheric polar vortex. However, the midlatitude warm temperature and positive isentropic mass anomalies persist throughout the concurrent winter till the end of the next summer. In comparison with the concurrent winter, the strengthening of poleward heat transport by an anomalous wavenumber-2 in the next winter results in a much warmer and weaker polar vortex accompanied with a colder midlatitude stratosphere.

Troposphere and stratosphere influence on tropopause in the polar regions during winter and spring

Arctic and Antarctic tropopause is formed under unique climate conditions, both in the troposphere and stratosphere. Individual patterns of polar tropopause anomalies are formed under dominance or competition of the tropospheric and stratospheric sources. We analyse the thermal tropopause climatology in the polar regions using National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP–NCAR) Reanalysis-1 data between 1979 and 2008. The role of the troposphere and stratosphere in tropopause anomaly distribution is examined using corresponding temperature and geopotential height fields. By location, the tropopause anomalies in the Arctic and Antarctic are closer to patterns of cold anomalies in the troposphere and stratosphere respectively. Results indicate that the 30-year climatological tropopause anomalies in polar winter and spring could have different relationships to troposphere and stratosphere influences, even in neighbouring parts of the polar atmosphere.

Marking the Fifth Anniversary of the Discovery of Enceladus's Plumes

Enceladus as an Active Moon; Bern, Switzerland, 14–18 June 2010; In commemoration of the fifth anniversary of the discovery of Enceladus's plumes, a group of about 2 dozen specialists gathered at the International Space Science Institute (ISSI) in Switzerland (http://www.issibern.ch/teams/ActiveEnceladus) with the goal of advancing understanding of the nature of Enceladus and its unusual phenomena. Speakers at the meeting noted that Enceladus is much more exciting than even their wildest expectations for it more than 20 years ago when the Cassini‐Huygens mission to Saturn was conceived, in the 1980s, several years after the Voyager flybys. Cassini revealed the surprising activity of the icy moon Enceladus, which is ejecting plumes of water vapor and ice grains from its anomalously warm south polar region. During the flyby of Enceladus on 17 February 2005, the Cassini magnetometer observed magnetic effects caused by Enceladus's plumes. Alerted by these stunning measurements, the Cassini investigators focused in on Enceladus during subsequent flybys and obtained the presently known facts about the plumes and the large south polar thermal anomaly.

Limits of Enceladus's ice shell thickness from tidally driven tiger stripe shear failure

[1] Enceladus's south polar thermal anomaly and water-rich plumes suggest the existence of a subsurface ocean, which is overlain by an ice shell of uncertain thickness. Our objective is to constrain Enceladus's ice shell thickness, through assessment of tidally driven Coulomb failure of Enceladus's tiger stripe faults. We find that thin to moderate ice shell thicknesses (<40 km) support shear failure along the tiger stripes, assuming low ice coefficients of friction (0.1–0.3) and shallow fault depths (<3 km). These results are marginally consistent with the minimum ice shell thickness which can permit convection within Enceladus's ice shell. A plausible scenario is one in which the heat loss and tectonic style of Enceladus has changed through time, with convection initiating in a thick ice shell, and tiger stripe activity commencing as the ice shell thinned.

Observed and simulated precursors of stratospheric polar vortex anomalies in the Northern Hemisphere

The Northern Hemisphere stratospheric polar vortex is linked to surface weather. After Stratospheric Sudden Warmings in winter, the tropospheric circulation is often nudged towards the negative phase of the Northern Annular Mode (NAM) and the North Atlantic Oscillation (NAO). A strong stratospheric vortex is often associated with subsequent positive NAM/NAO conditions. For stratosphere–troposphere associations to be useful for forecasting purposes it is crucial that changes to the stratospheric vortex can be understood and predicted. Recent studies have proposed that there exist tropospheric precursors to anomalous vortex events in the stratosphere and that these precursors may be understood by considering the relationship between stationary wave patterns and regional variability. Another important factor is the extent to which the inherent variability of the stratosphere in an atmospheric model influences its ability to simulate stratosphere–troposphere links. Here we examine the lower stratosphere variability in 300-year pre-industrial control integrations from 13 coupled climate models. We show that robust precursors to stratospheric polar vortex anomalies are evident across the multi-model ensemble. The most significant tropospheric component of these precursors consists of a height anomaly dipole across northern Eurasia and large anomalies in upward stationary wave fluxes in the lower stratosphere over the continent. The strength of the stratospheric variability in the models was found to depend on the variability of the upward stationary wave fluxes and the amplitude of the stationary waves.