Surface Electric Field Measurements Research Articles

Consistent dust electrification from Arabian Gulf sea breezes

The Arabian Gulf region experiences regular thermally driven sea breeze circulations which occur all year round, penetrating hundreds of kilometres inland. As a sea breeze front moves inland, substantial electric fields are generated by separation of charged desert dust. In the first surface electric field measurements made in the United Arab Emirates (UAE), consistent and repeatable substantial electric field changes with magnitudes up to 7 kV m−1 have been detected at Al Ain (170 km from the western coast), during 80 separate sea breeze events in 2018. Every sea breeze frontal passage shows the same characteristic signature of a transient maximum peak in electric field lasting tens of minutes. Electric field changes during these events were always negative (i.e. enhancing the existing negative ‘fair weather’ electric field), in contrast to many other reported observations in dust storms in which conditions were less repeatable. The regular and substantial dust electrification found demonstrates that accurate representation of dust in climate and weather models requires electrical effects to be addressed, both in the generation process, and by considering aggregates in radiative transfer calculations as electrically aligned rather than randomly ordered. Furthermore, satellite aerosol retrievals are affected by the changed attenuation of electromagnetic radiation when dust particles are charged, for which corrections may be needed.

Finite-element analysis of top-casing electric source method for imaging hydraulically active fracture zones

Imaging hydraulically active fracture zones (HAFZ) is of paramount importance to subsurface resource extraction, geologic storage, and hazardous waste disposal. We have developed advanced 3D finite-element (FE) electrical imaging algorithms for HAFZ in the presence of a steel-cased well. The algorithms use tetrahedral FE meshes in the simulation domain and coarse rectangular finite-difference meshes in the imaging domain. This heterogeneous dual-mesh approach is well suited to modeling the multiscale earth model due to steel-cased wells. We find that the algorithms accurately and efficiently simulate surface electric field measurements over a 3D HAFZ at depth when one end point of a surface electric source is connected to a wellhead. For brevity, this configuration is called the top-casing electric source method. By replacing a hollow cased well with a solid prism, we improve our computational efficiency without affecting the solution accuracy. The sensitivity of the top-casing source method to HAFZ highly depends on the continuity of a steel-cased well because it makes currents preferentially flow to HAFZ. The sensitivity also depends on conductivity structures around the well because they control current leaking from the steel-cased well. We find that the method can image a localized HAFZ and detect changes in its width and height. The imaging results are improved when a volume of the imaging domain is constrained from geomechanical perspectives. A primary advantage of the method is the fact that the sources and receivers are placed on the surface, thus not interrupting the well operation.

Study of Atmospheric Discharges by Near Surface Electric Field Measurements

Background:In this work the disturbances of the near surface electric field are investigated, which are attributed to different types of atmospheric discharges: intracloud or cloud-to-ground.Method:The patterns of the lightning occurrences are discussed as measured by the network of the electric field mills located at the stations of Cosmic Ray Division of Yerevan Physics Institute. Discharges make changes in the near surface electric field, which can be separated into two groups. The differences of those two groups and shapes of the recovery curves are discussed using the data from electric field mills network for a stormy day on May 23, 2015.Conclusion:The results presented in this work show that magnitudes of field changes from one of the groups are larger and have shorter duration compared to another one. Recovery curves of the near surface electric field produced by lightning flashes also have a power-law or a linear dependence besides exponential shape.

Electrical characteristics of thunderstorms in the Eastern part of India

Measurements of surface electric field made during the Pilot experiment to STORM at Kharagpur, India have been analyzed. During period of observations, i.e., from April 15 to May 31 2006, 14, thunderstorms were observed. Some electrical characteristic features of lighting associated with these thunderstorms are presented here. The electric field pattern shows that large number of negative electric field changes occur during mature stage of thunderstorm indicating removal of negative charge from overhead. Based on the polarity of electric field changes induced by lightning and shape of recovery curves, it is concluded that the most of thunderstorms in this region have positive-dipole type charge structure. These thunderstorms generally exhibit End-Of-Storm-Oscillation (EOSO).

Evolution of lightning in an isolated hailstorm of moderate size in the tropics

Evolution of lightning activity in a tropical hailstorm of moderate size that developed in the premonsoon season at Pune (18°32′N, 73°51′E, 559 m above sea level) is studied from the measurements of surface electric field, the Maxwell current and thunder. Total flash rate is counted from the electric field record, and the cloud‐to‐ground (CG) flash rate is estimated from the visual observations. Precise timings of their occurrence were confirmed from the observations of overshoot in the Maxwell current records. The storm exhibited an almost constant rate of one CG flash every 1 to 2 min over the whole life time of the storm. The ratio of intracloud (IC) to CG flashes (IC/CG) increased with the increase in total flash rate. In the convective stage of the storm, field changes from consecutive flashes were generally found to alternate in polarity. Moreover, in this stage, field changes occur in pairs, the first field change of each pair being of negative polarity and the second one of positive polarity. The two field changes in a pair occur with an average time difference of 14.3 ± 8.4 s while two consecutive pairs appear after 29.3 ± 9.1 s. In between the convective and mature stages, our observations suggest the occurrence of the phenomenon of rain gush and the field excursion associated with falling precipitation. Development of the mature stage was marked with rapid transitions in the surface electric field and the Maxwell current polarities from negative to positive. Further, total flash rate and IC/CG ratio sharply increase, and the lightning‐induced electric field changes become almost exclusively of negative polarity. Observations suggest possibly a lifting up of the charging region in mature stage of the storm. The dissipating stage of the storm witnessed hail and rain showers, sharp transition of electric field and the Maxwell current from positive to negative polarity and occurrence of a few positive CG discharges. Our observations are consistent with the general belief that that some lightning flashes, by neutralizing and depositing charge in the region of opposite polarity, change the charge distribution so as to trigger another discharge in the storm.

Microwave transmission through metallic hole arrays: Surface electric field measurements

The authors investigate the enhanced microwave transmission through a metal plate perforated by a square lattice of subwavelength holes, predicted to occur as a structure factor resonance phenomenon [F. J. Gracía de Abajo and J. J. Sáenz, Phys. Rev. Lett. 95, 233901 (2005)]. By probing the surface electric field on the metallic plate at the peak transmission frequency, they establish the similarities and differences between the structure factor resonance and surface plasmon.

Measurement of surface electric fields by an excited-state atomic beam technique

Electric fields due to adsorbates on a metal surface are studied experimentally with highly excited atoms as probes. A beam containing Li Rydberg atoms, with principal quantum numbers in the range 20 ≲ n ≲ 80, is detected after passing through a metal mesh having 6 micro m square openings. Adsorbates at 10 −2 monolayer can produce 400 V/cm electric fields 0.6 micro m from the surface. Fields of this magnitude can ionize Rydberg atoms in the atomic beam, reducing the flux through the mesh. Measurements of the excited-state atomic beam flux can thus yield information about the presence of adsorbates, including sticking probability, orientation and magnitude of electric dipole moment, and desorption energy. In the analysis of the experimental calibration, a relationship is obtained for the mesh transmission as a function of the adsorbate dipole-moment density. The measured desorption energies are compared with values reported in the literature.

Measurement of surface electric fields by an excited-state atomic beam technique

Measurement of surface electric fields by an excited-state atomic beam technique

Dependence of photoreflectance on space charge electric fields in Ge

Simultaneous photoreflectance (PR) and surface electric field measurements are taken on intrinsic Ge under controlled surface conditions at the Ge-aqueous electrolyte interface. PR spectra are observed to vanish at zero surface field, which provides conclusive evidence that PR is due solely to electroreflectance (ER) at moderate light levels. The measured PR spectra are in agreement with the predictions of the inhomogeneous perturbation theory of ER.

A Recording Generating Voltmeter for the Study of Atmospheric Electricity

A generating voltmeter type automatic electric field recorder designed for continuous measurement of surface electric fields in thunderstorms is described. The performance of the instrument in the field under thunderstorm conditions is discussed. The application of this instrument to the study of the normal potential gradient of the earth is suggested.