Transient currents in the global electric circuit due to cloud-to-ground and intracloud lightning (original) (raw)
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Electric fields and current densities under small Florida thunderstorms
Journal of Geophysical Research, 1991
The surface electric field E and Maxwell current density JM have been measured simultaneously under and near small Florida thunderstorms. These records show that the amplitude of JM is of the order of 1 nA/m 2 or less in the absence of precipitation and that there are regular time variations in JM during the intervals between lightning discharges that tend to have the same shapes after different discharges in different storms. Negative cloud-to-ground (CG) lightning produces an abrupt negative change in E and a corresponding negative (or bipolar) transient in JM that is followed by a positive overshoot. Under a storm, this overshoot peaks about 1 nA/m2 above background and then decays in a quasi-exponential or linear fashion until the next discharge occurs. Nearby cloud discharges produce a lightning transient and then either a small change in JM or a negative change that subsequently relaxes back to the predischarge level in 5 to 20 s. CG flashes at a range of about 20 km produce a fast transient in JM and then a positive overshoot that subsequently relaxes back to the predischarge level in 5 to 20 s. Distant cloud discharges produce overshoots and subsequent decays that are very similar to CG flashes but of opposite (i.e., negative) polarity. We believe that the major causes of the aforementioned time variations in JM between lightning discharges are currents that flow in the finitely conducting atmosphere in response to the field changes rather than rapid time variations in the strength of the cloud current sources. The displacement current densities that are computed from the E records dominate JM except when there is precipitation, when E is large and steady, or when E is unusually noisy. 1. INTRODUCTION Until recently, most observations of the electrical environment Ufider and near thunderstorms have focused on the cloud electric fields or the field changes that are caused by lightning.. Such data can be used to infer the cloud charge distrlbutiofi and the chafiges tn this distribution that are caused by lightning. These results, in turn, provide information about the electrification processes and how the cloud electrical structure evolves throughout the storm fLatham,
A modeling study of the time-averaged electric currents in the vicinity of isolated thunderstorms
Journal of Geophysical Research, 1992
A thorough examination of the results of a time-dependent computer model of a dipole thunderstorm revealed that there are numerous similarities between the time-averaged electrical properties and the steady state properties of an active thunderstorm. Thus, the electrical behavior of the atmosphere in the vicinity of a thunderstorm be can be determined with a formulation similar to what was first described by Holzer and Saxon in 1952. From the Maxwell continuity equation of electric current, a simple analytical equation was derived that expresses a thunderstorm's average current contribution to the global electric circuit in terms of the generator current within the thundercloud, the intracloud lightning current, the cloud-to-ground lightning current, the altitudes of the charge centers, and the conductivity profile of the atmosphere. This equation was found to be nearly as accurate as the more computationally expensive numerical model, even when it is applied to a thunderstorm with a reduced conductivity thundercloud, a time-varying generator current, a varying flash rate, and a changing lightning mix.
Journal of The Atmospheric Sciences, 2010
The long-standing mainstay of support for C. T. R. Wilson's global circuit hypothesis is the similarity between the diurnal variation of thunderstorm days in universal time and the Carnegie curve of electrical potential gradient. This rough agreement has sustained the widespread view that thunderstorms are the ''batteries'' for the global electrical circuit. This study utilizes 10 years of Tropical Rainfall Measuring Mission (TRMM) observations to quantify the global occurrence of thunderstorms with much better accuracy and to validate the comparison by F. J. W. Whipple 80 years ago. The results support Wilson's original ideas that both thunderstorms and electrified shower clouds contribute to the DC global circuit by virtue of negative charge carried downward by precipitation. First, the precipitation features (PFs) are defined by grouping the pixels with rain using 10 years of TRMM observations. Thunderstorms are identified from these PFs with lightning flashes observed by the Lightning Imaging Sensor. PFs without lightning flashes but with a 30-dBZ radar echotop temperature lower than 2108C over land and 2178C over ocean are selected as possibly electrified shower clouds. The universal diurnal variation of rainfall, the raining area from the thunderstorms, and possibly electrified shower clouds in different seasons are derived and compared with the diurnal variations of the electric field observed at Vostok, Antarctica. The result shows a substantially better match from the updated diurnal variations of the thunderstorm area to the Carnegie curve than Whipple showed. However, to fully understand and quantify the amount of negative charge carried downward by precipitation in electrified storms, more observations of precipitation current in different types of electrified shower clouds are required.
Modeling the electric structures of two thunderstorms and their contributions to the global circuit
Atmospheric Research, 2009
This study examines the electricity in two thunderstorms, typical for their respective locales (the Great Plains and the New Mexico mountains), by modeling them as a set of steady-state horizontal layers of external currents. The model electric sources, corresponding to the charge separation processes in the thundercloud, are embedded in an exponential conducting atmosphere. The source parameters are determined by fitting the model electric field to measured profiles. The resulting currents to the ionosphere (i.e., the Wilson current) from the two storms are 0.53 A and 0.16 A, while the calculated electrical energies of the storms are 2.3 × 10 10 J and 2.8 × 10 9 J, respectively. The more vigorous storm is estimated to transfer 16 000 C in the global circuit during 8.5 h of its lifetime, while the weaker mountain storm transferred about 1200 C in its entire 2-h lifetime. Removal of the screening charge layer from above the updraft region in one modeled storm leads to only a small increase in the net Wilson current of less than 3%, while it provides a substantial local disturbance of the electric field. Overall, the model findings indicate that differences in the Wilson currents and electrical energies of the two storms result from differences in their internal dynamical and electrical structures as well as their geographical locations.
Maxwell currents under thunderstorms
Journal of Geophysical Research, 1982
We point out that recent observations of the time variations in thunderstorm electric fields, both aloft and at the ground, can be interpreted in terms of a total Maxwell current density that varies slowly with time in the intervals between lightning discharges. We utilize this quasi-static behavior to estimate and map the Maxwell current densities under a small Florida thunderstorm using data provided by a large field mill network. An area integral of these current densities gives a total Maxwell current just above the ground of about 0.5 A, a value which is a reasonable lower limit for the total Maxwell current produced by the cloud, and an upper limit for the rate of charge transport to ground between lightning flashes. Using the quasi-static behavior of the Maxwell current density, we derive an expression for the field-dependent current density under a thunderstorm during the field recovery following a lightning discharge, and we infer values of air conductivity under the small storm which range from 2 to 6 x 10-• 3 mho/m. Finally, we present data that indicate that the area-average Maxwell current is not usually affected by lightning, but instead varies slowly throughout the evolution of the storm. Therefore, we suggest that cloud electrification processes probably do not depend on the cloud electric field, which exhibits large and rapid time variations, as much as they do on more slowly varying quantities, such as the meteorological structure of the storm and/or the storm dynamics. 1. INTRODUCTION Recent tethered-balloon measurements by Winn and Byerley [-1975], Standlet and Winn [-1979], and Winn et al. [1980] show that, under thunderstorms, the electric field at an altitude of a few hundred meters tends to increase linearly with time between lightning discharges, whereas the field at the ground is not linear due to the space charge produced by corona processes. Standler [1980] has applied these results and has shown that, when the field at the ground is steady, then the spatially averaged corona current density at this time can be estimated from the slope of the electric field recovery following a lightning discharge at an earlier time when the field at the ground was not steady but was crossing zero. In this note we point out that the experimental and theoretical results of Winn, Standler, and associates can be interpreted simply in terms of a total Maxwell current density which varies slowly with time between lightning discharges. We show that measurements of the displacement current density when the field is close to zero can be used to estimate values of the Maxwell current density; and we compute and map Maxwell current densities under a small Florida storm, using data provided by a large field mill network. We show that, if the Maxwell current is quasi-static and if convection currents are steady, then the local field-dependent current density, which includes the corona current, can be derived from changes in the displacement current during a lightning field recovery. We apply this method and find reasonable values for the fielddependent current densities and atmospheric conductivities under the small storm. Finally, we present evidence that shows that the average Maxwell current density is usually not affected by lightning discharges and varies slowly throughout the evolution of the storm. Since the Maxwell current is steady at times when the field, both at the ground and aloft, undergoes large
Journal of Geophysical Research, 1996
A least squares method for analyzing multiple, ground-based measurements of electric field changes produced by lightning has been applied to seven small thunderstorms that occurred on July 19 and August 9, 1991, during the Convection and Precipitation Electrification (CAPE) experiment. Two of the storms produced little or no cloud-toground (CG) lightning, and a third produced CG lightning only during its early stages. A total of 79 flashes were analyzed on July 19 and 315 on August 9. About 58% of these discharges could be fitted to either a point charge (Q) or a point dipole (P) model, and in this sample, the spatial pattern of the Q and P solutions was consistent with a tripole or double dipole charge pattern in the cloud. In cases where there was little or no CG lightning, the inferred region of upper positive charge was quite close to the inferred negative region. Comparisons of the locations of upper P solutions with measurements of radar reflectivity at S band show that the P solutions tended to cluster at altitudes where the reflectivity was between 25 and 35 dBZ. Comparisons of Q (and P) model solutions with the locations of CG flash strike points, determined using a network of wideband direction finders, showed an average horizontal displacement of 3.9 km with a standard deviation of 3.3 km. This displacement is consistent with the expected random development of a stepped-leader channel from the altitude of the negative Q region to the ground. of the storms that will be described below. Jacobson and Krider [1976], Maier and Krider [1986], and Koshak and Krider [1989] have previously analyzed multiplestation measurements of electric field changes at the KSC/ ESMC. Maier and Krider [1986] found that a large fraction of the cloud-to-ground flashes could be fitted to a point charge
Insights into high peak current in‐cloud lightning events during thunderstorms
Geophysical Research Letters, 2015
We investigated National Lightning Detection Network reports and lightning radio waveforms in a 44 day observation period to analyze the in-cloud (IC) events producing currents above 200 kA. The results show that there are two distinct classes of IC lightning events with very high peak currents: the well-known narrow bipolar events, and a previously unreported type that we call energetic in-cloud pulses (EIPs). Their temporal and spatial context shows that EIPs are generated from existing negative polarity leaders that are propagating usually upward but sometimes downward. The nearly identical characteristics of EIPs and some previously reported terrestrial gamma ray flashes (TGFs) indicate a likely connection between the two, which further suggests the possibility of downward directed TGFs. These very high peak current IC events also suggest the association of EIPs with ionospheric perturbations and optical emissions known as elves.
Remote Measurements of Currents in Cloud Lightning Discharges
IEEE Transactions on Electromagnetic Compatibility, 2000
Using measured wideband electric field waveforms and the Hertzian dipole (HD) approximation, we estimated peak currents for 48 located compact intracloud lightning discharges (CIDs) in Florida. The HD approximation was used because 1) CID channel lengths are expected to range from about 100 to 1000 m, and in many cases can be considered electrically short and 2) it allows one to considerably simplify the inverse source problem. Horizontal distances to the sources were reported by the U.S. National Lightning Detection Network (NLDN), and source heights were estimated from the horizontal distance and the ratio of electric and magnetic fields. The resultant CID peak currents ranged from 33 to 259 kA with a geometric mean of 74 kA. The majority of NLDN-reported peak currents for the same 48 CIDs are considerably smaller than those predicted by the HD approximation. The discrepancy is primarily because NLDN-reported peak currents are assumed to be proportional to peak fields, while for the HD approximation, the peak current is proportional to the peak of the integral of the electric radiation field. An additional factor is the limited (400 kHz) upper frequency response of the NLDN.
Journal of Geophysical Research: Atmospheres
This study compared the detection capabilities of the Geostationary Lightning Mapper (GLM) and ground-based Earth Networks Total Lightning Network (ENL) over the contiguous United States (CONUS) from 25 April 2017 to 5 May 2018. GLM detection efficiency (DE) relative to ENL varied spatially with greater DE in the southeastern United States and lower DE in the Northern Plains. Regions with greater DE were often regions where most intracloud flashes had normal positive polarity, while lower DE regions frequently had inverted negative intracloud. According to the tripolar noninductive charging model, inverted intracloud flashes are lower altitude than normal intracloud flashes. This lower altitude flash may result in greater cloud scattering of the optical lightning signal, which at cloud top is less than the GLM detection limits. DE was generally also greater for greater absolute peak current flashes, which serves as a proxy for optical energy. Additionally, GLM observed flashes to be generally greater in area and duration in the eastern relative to the western CONUS, which may result in the greater DE. GLM DE was also varied with the solar zenith angle as greatest DE occurred at night. ENL DE relative to GLM was varied spatially over CONUS with greater DE over eastern CONUS. ENL DE was greater for flashes of greater GLM flash radiant energy, area, and duration. 1.1. Lightning and Electrical Charging Proper evaluation of GLM and its detection necessitates understanding the cause of lightning and lightning characteristics. Noninductive charging (NIC), resulting from collisions of ice hydrometeors in the presence of supercooled water, likely represents the primary mechanism for electrical charging and the production of lightning in storms (Saunders et al., 2006). Charging of hydrometeors can be either positive or negative, with differences in charge partially neutralized by lightning discharges after sedimentation of charged hydrometeors. Stronger updrafts in the mixed-phase region (0°C to approximately −40°C) generally produce more charging and more frequent lightning flashes that are smaller and weaker (Bruning & MacGorman, 2013; Mecikalski et al., 2015). At warmer temperatures (e.g., 0°C to −10°C), graupel hydrometeors are positively charged during riming collisions, while ice particles are negatively charged. At cooler temperatures (e.g., −20°C to −40°C), graupel charges negatively, while ice hydrometeors charge positively. Since graupel is heavier relative to ice, a lowest positive-charged layer will generally form, while negatively charged ice particles are lofted to near negatively charged graupel, forming a negatively charged layer above the lowest positively charged layer. The positively charged ice is lifted upward to form an upper layer of positive charge. This forms the typical tripolar model of charging and lightning formation (see Figure 1 of Williams (1989) for further illustration). Examination of electric field data from balloons released into 33 thunderstorms indicates that the tripolar structure is generally observed in the updraft core (Stolzenburg et al., 1998).
Journal of Computational Engineering, 2014
This paper presents for the first time a case for the importance of ground to cloud (upward leader) lightning flash parameters for safety testing of direct aircraft-lightning interaction and protection of wind turbines, as well as the importance of radiated electric fields for indirect lightning-aircraft interaction and generation of electric discharges called sprites and halos in the ionosphere. By using an electric circuit model of the transverse magnetic waves along the return stroke channel, electric currents at ground level as well as cloud level are determined for both the cloud to ground lightning flash and the ground to cloud lightning flash. We show that when an aircraft triggers lightning, the electric currents will be much more severe in current magnitude, rate of rise of currents, and frequency spectrum than otherwise and are more severe than the parameters observed for the usual and well monitored (and measured) cloud to ground (downward leader) flashes. The rate of ris...