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Xing Hongyan - One of the best experts on this subject based on the ideXlab platform.

  • Electromagnetic Fields Associated With the M‐Component Mode of Charge Transfer
    'American Geophysical Union (AGU)', 2019
    Co-Authors: He Lixia, Rachidi Farhad, Azadifar Mohammad, Rubinstein Marcos, Rakov, Vladimir A., Cooray Vernon, Pavanello Davide, Xing Hongyan
    Abstract:

    In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M-Component or leader/return-stroke like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created channel connected to the ICC-carrying channel at relatively short distance from the tower top, resulting in the so-called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M-Component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Säntis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with the M-Component charge transfer mode (including classical M-Component pulses and M-Component-type pulses superimposed on the initial continuous current) is analyzed, and compared with its effect on the fields associated with the return-stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2D FDTD (2-Dimentional Finite-Difference Time-Domain) method, in which the M-Component is modeled by the superposition of a downward current Wave and an upward current Wave resulting from the reflection at the bottom of the lightning channel (Rakov et al. 1995 model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Säntis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for ‘classical’ M-Component and M-Component-type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of the M-Component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster travelling Wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M-Component Wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static Component which mainly depends on the overall transferred charge. The contribution of the radiation Component to the M-Component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation Component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch-to-channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E-field and 1.9 for the H-field. For a junction height greater than 6 km, the E-field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li et al. (2016b) in which an electric field propagation factor of 1.8 was inferred for return strokes and mixed mode pulses, considering that junction points lower than 1 km or so would result in a mixed-mode of charge transfer, in which a downward leader/return-stroke like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 s or so) for which the tendency reverses. Finally, model-predicted fields associated with different charge transfer modes, namely return stroke, mixed mode, classical M-Component, and M-Component-type ICC pulse are compared with experimental observations at the Säntis tower. It is found that the vertical electric field Waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field Waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed mode models (1.0 km for the return stroke and 0.8 km for the mixed-mode pulse) are lower than the value of 2.0 km typically used in the literature

  • Electromagnetic fields associated with the M‐Component mode of charge transfer
    'American Geophysical Union (AGU)', 2019
    Co-Authors: He Lixia, Rachidi Farhad, Azadifar Mohammad, Rubinstein Marcos, Rakov, Vladimir A., Cooray Vernon, Pavanello Davide, Xing Hongyan
    Abstract:

    In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M-Component or leader/return‐stroke‐like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created channel connected to the ICC‐carrying channel at relatively short distance from the tower top, resulting in the so‐called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M‐Component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Säntis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with theM‐Component charge transfer mode (including classical M‐Component pulses and M‐Component‐type pulses superimposed on the initial continuous current) is analyzed and compared with its effect on the fields associated with the return stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2‐Dimentional Finite‐Difference Time Domain method, in which the M‐Component is modeled by the superposition of a downward current Wave and an upward current Wave resulting from the reflection at the bottom of the lightning channel (Rakov et al., 1995, https://doi.org/10.1029/95JD01924 model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Säntis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for classical M‐Component and M‐Component‐type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of theM‐Component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster traveling Wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M‐Component Wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static Component, which mainly depends on the overall transferred charge. The contribution of the radiation Component to the M‐Component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation Component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch‐to‐channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E‐field and 1.9 for the H‐field. For a junction height greater than 6 km, the E‐field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li, Azadifar, Rachidi, Rubinstein, Paolone, et al. (2016, https://doi.org/10.1109/TEMC.2015.2483018) in which an electric field propagation factor of 1.8 was inferred for return strokes and mixed‐mode pulses, considering that junction points lower than 1 km or so would result in a mixed mode of charge transfer, in which a downward leader/return‐stroke‐like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 μs or so) for which the tendency reverses. Finally, model‐predicted fields associated with different charge transfer modes, namely, return stroke, mixed‐mode, classical M‐Component, and M‐Component‐type ICC pulse are compared with experimental observations at the Säntis Tower. It is found that the vertical electric field Waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field Waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed‐mode models (1.0 km for the return stroke and 0.8 km for the mixed‐mode pulse) are lower than the value of 2.0 km typically used in the literature

Venaille Antoine - One of the best experts on this subject based on the ideXlab platform.

  • Manifestation of Berry curvature in geophysical ray tracing
    2021
    Co-Authors: Perez Nicolas, Delplace Pierre, Venaille Antoine
    Abstract:

    Geometrical phases, such as the Berry phase, have proven to be powerful concepts to understand numerous physical phenomena, from the precession of the Foucault pendulum to the quantum Hall effect and the existence of topological insulators. The Berry phase is generated by a quantity named Berry curvature, describing the local geometry of Wave polarization relations and known to appear in the equations of motion of multi-Component Wave packets. Such a geometrical contribution in ray propagation of vectorial fields has been observed in condensed matter, optics and cold atoms physics. Here, we use a variational method with a vectorial Wentzel-Kramers-Brillouin (WKB) ansatz to derive ray tracing equations in geophysical Waves and reveal the contribution of Berry curvature. We detail the case of shallow water Wave packets and propose a new interpretation to the equatorial oscillation and the bending of rays in mid-latitude area. Our result shows a mismatch with the textbook scalar approach for ray tracing, by predicting a larger eastward velocity for Poincar\'e Wave packets. This work enlightens the role of Wave polarization's geometry in various geophysical and astrophysical fluid Waves, beyond the shallow water model.Comment: 20 pages, 4 figure

  • Manifestation of Berry curvature in geophysical ray tracing
    HAL CCSD, 2020
    Co-Authors: Perez Nicolas, Delplace Pierre, Venaille Antoine
    Abstract:

    22 pages, 5 figuresGeometrical phases, such as the Berry phase, have proven to be powerful concepts to understand numerous physical phenomena, from the precession of the Foucault pendulum to the quantum Hall effect and the existence of topological insulators. The Berry phase is generated by a quantity named Berry curvature, describing the local geometry of Wave polarization relations and known to appear in the equations of motion of multi-Component Wave packets. Such a geometrical contribution in ray propagation of vectorial fields has been observed in condensed matter, optics and cold atoms physics. Here, we use a variational method with a vectorial Wentzel-Kramers-Brillouin (WKB) ansatz to derive ray tracing equations in geophysical Waves and reveal the contribution of Berry curvature. We detail the case of shallow water Wave packets and propose a new interpretation to the equatorial oscillation and the bending of rays in mid-latitude area. Our result shows a mismatch with the textbook scalar approach for ray tracing, by predicting a larger eastward velocity for Poincar\'e Wave packets. This work enlightens the role of Wave polarization's geometry in various geophysical and astrophysical fluid Waves, beyond the shallow water model

Jerzy Leszczynski - One of the best experts on this subject based on the ideXlab platform.

  • Recovering four-Component solutions by the inverse transformation of the infinite-order two-Component Wave functions.
    The Journal of chemical physics, 2009
    Co-Authors: Maria Barysz, Ł. M. Mentel, Jerzy Leszczynski
    Abstract:

    The two-Component Hamiltonian of the infinite-order two-Component (IOTC) theory is obtained by a unitary block-diagonalizing transformation of the Dirac–Hamiltonian. Once the IOTC spin orbitals are calculated, they can be back transformed into four-Component solutions. The transformed four Component solutions are then used to evaluate different moments of the electron density distribution. This formally exact method may, however, suffer from certain approximations involved in its numerical implementation. As shown by the present study, with sufficiently large basis set of Gaussian functions, the Dirac values of these moments are fully recovered in spite of using the approximate identity resolution into eigenvectors of the p2 operator.

Anthony W Gummer - One of the best experts on this subject based on the ideXlab platform.

  • comparison of time domain source separation techniques for short pulse distortion product otoacoustic emissions
    Journal of the Acoustical Society of America, 2017
    Co-Authors: Dennis Zelle, Ernst Dalhoff, Anthony W Gummer
    Abstract:

    Distortion-product otoacoustic emissions (DPOAEs) are presumed to consist mainly of two Components, a nonlinear-distortion Component and a coherent-reflection Component. Wave interference between these two Components reduces the accuracy of DPOAEs when used to evaluate cochlear function. Here, short tone pulses are utilized to record DPOAE signals in normal-hearing subjects. DPOAE Components are extracted from recordings at discrete frequencies using two different techniques in the time domain. The extracted DPOAE Components are compared to recordings obtained with conventional, continuous primary tones.

  • input output functions of the nonlinear distortion Component of distortion product otoacoustic emissions in normal and hearing impaired human ears
    Journal of the Acoustical Society of America, 2017
    Co-Authors: Dennis Zelle, John Thiericke, Anthony W Gummer, Lisa Lorenz, Ernst Dalhoff
    Abstract:

    Distortion-product otoacoustic emissions (DPOAEs) arise in the cochlea in response to two tones with frequencies f1 and f2 and mainly consist of two Components, a nonlinear-distortion and a coherent-reflection Component. Wave interference between these Components limits the accuracy of DPOAEs when evaluating the function of the cochlea with conventional continuous stimulus tones. Here, DPOAE Components are separated in the time domain from DPOAE signals elicited with short stimulus pulses. The extracted nonlinear-distortion Components are used to derive estimated distortion-product thresholds (EDPTs) from semi-logarithmic input-output (I/O) functions for 20 normal-hearing and 21 hearing-impaired subjects. I/O functions were measured with frequency-specific stimulus levels at eight frequencies f2 = 1,…, 8 kHz (f2/f1 = 1.2). For comparison, DPOAEs were also elicited with continuous primary tones. Both acquisition paradigms yielded EDPTs, which significantly correlated with behavioral thresholds (p < 0.001) ...

Ernst Dalhoff - One of the best experts on this subject based on the ideXlab platform.

  • comparison of time domain source separation techniques for short pulse distortion product otoacoustic emissions
    Journal of the Acoustical Society of America, 2017
    Co-Authors: Dennis Zelle, Ernst Dalhoff, Anthony W Gummer
    Abstract:

    Distortion-product otoacoustic emissions (DPOAEs) are presumed to consist mainly of two Components, a nonlinear-distortion Component and a coherent-reflection Component. Wave interference between these two Components reduces the accuracy of DPOAEs when used to evaluate cochlear function. Here, short tone pulses are utilized to record DPOAE signals in normal-hearing subjects. DPOAE Components are extracted from recordings at discrete frequencies using two different techniques in the time domain. The extracted DPOAE Components are compared to recordings obtained with conventional, continuous primary tones.

  • input output functions of the nonlinear distortion Component of distortion product otoacoustic emissions in normal and hearing impaired human ears
    Journal of the Acoustical Society of America, 2017
    Co-Authors: Dennis Zelle, John Thiericke, Anthony W Gummer, Lisa Lorenz, Ernst Dalhoff
    Abstract:

    Distortion-product otoacoustic emissions (DPOAEs) arise in the cochlea in response to two tones with frequencies f1 and f2 and mainly consist of two Components, a nonlinear-distortion and a coherent-reflection Component. Wave interference between these Components limits the accuracy of DPOAEs when evaluating the function of the cochlea with conventional continuous stimulus tones. Here, DPOAE Components are separated in the time domain from DPOAE signals elicited with short stimulus pulses. The extracted nonlinear-distortion Components are used to derive estimated distortion-product thresholds (EDPTs) from semi-logarithmic input-output (I/O) functions for 20 normal-hearing and 21 hearing-impaired subjects. I/O functions were measured with frequency-specific stimulus levels at eight frequencies f2 = 1,…, 8 kHz (f2/f1 = 1.2). For comparison, DPOAEs were also elicited with continuous primary tones. Both acquisition paradigms yielded EDPTs, which significantly correlated with behavioral thresholds (p < 0.001) ...