VHF Source Research Articles

Imaging Step Formation in In‐Cloud Lightning Initial Development With VHF Interferometry

AbstractWe investigate sequential processes underlying the initial development of in‐cloud lightning flashes in the form of initial breakdown pulses (IBPs) between 7.4 and 9.0 km altitudes, using a 30–250 MHz VHF interferometer. When resolved, IBPs exhibit typical stepped leader features but are notably extensive (>500 m) and infrequent (∼1 millisecond intervals). Particularly, we observed four distinct phases within an IBP stepping cycle: the emergence of VHF sources forming edge structures at previous streamer zone edges (interpreted as space stem/leader development), the fast propagation of VHF along the edge structure (interpreted as the main leader connecting the space leader), the fast extension of VHF beyond the edge structure (interpreted as fast breakdown), and a decaying corona fan. These measurements illustrate clearly the processes involved in the initial development of in‐cloud lightning flashes, evidence the conducting main leader forming, and provide insights into other processes known to occur simultaneously, such as terrestrial gamma ray flashes.

Six years of electrified convection over the island of Corsica monitored by SAETTA: General trends and anomalously electrified thunderstorms during African dust south flow events

By means of the SAETTA 3D lightning mapping array, the total lightning activity has been detected in a 240 km × 240 km square domain centred on the island of Corsica located in the West Mediterranean basin, and characterized by a maritime and mountainous environment, with a complex and relatively high relief. The study period covers the months from April to December of the 6 years from 2014 to 2019. Observations are reported with a horizontal resolution of 1 km and a vertical resolution of 0.1 km in terms of density of VHF sources emitted by lightning, and of number of lightning day, in plane- and vertical- projections. Vertical distributions of VHF sources are also provided monthly for the whole period and over the full domain. These 3D long term observations show that the number of lightning days is more important on the main relief of the island. The density of VHF sources exhibits a sharp maximum over the confluence area of the 3 main valleys in the center of the northern part of the island, characterized by a recurrent and vertically well developed lightning activity. The period from 11:00 UTC to 14:00 UTC in July, and in a lesser extent in June and August, is at the origin of this density maximum. This behavior is thus due to a diurnal convection. The whole lightning activity is characterized by 2 maxima in June and September. The first one is linked with the diurnal convection in phase with the maximum elevation of the Sun. The second one must be due to usual large-scale organized thunderstorm events of the fall season. The vertical distribution of VHF sources exhibits an increase in the number of VHF sources from April to August at all altitudes, as well as an increase in the altitude of the main upper peak (from 5.8 km to 10 km) and of the secondary lower peak (from 4.2 km to 6.7 km) of this distribution. From August to December, the opposite evolution appears, except that October is characterized by a strong anomaly with a single intense lower peak at 5.5 km, apparently due to 2 strong events corresponding to anomalously electrified thunderstorms. Several of these anomalously electrified thunderstorms (negative dipoles) are reported. They are all characterized by the movement of cloud cells spatially small and relatively undeveloped vertically propagating from southwest to northeast and associated with a strong transport of desert dust from the African continent. The analysis of the meteorological environment of some of the studied events allows concluding that in each of the studied cases elevated convection was triggered, above the relatively dry atmospheric boundary layer characterized by a strong convective inhibition. The low cloud liquid water content which is a key parameter of the non-inductive charging process is probably a good candidate to explain the anomalous electrification of these events.

Experimental Investigation of Nonlinear Standing Waves in DC/VHF Hybrid Capacitive Discharges

It is recognized that in very-high-frequency capacitively coupled plasma (VHF CCP) reactors, the standing wave effects can be enhanced by the presence of nonlinear higher harmonics self-excited by the plasma series resonance (PSR). In this work, we investigated the influence of the dc bias on the excitation of the nonlinear standing waves in a parallel-plate capacitively coupled dc/VHF (60 MHz) hybrid discharge sustained in argon, with both the dc source and the VHF source applied to the top electrode. A hairpin probe was employed to determine the axial/radial distribution of the electron density, while a high-frequency B-dot probe was used to measure the radial distributions of the harmonic magnetic field and the harmonic current density. With no dc bias applied, the nonlinear standing wave excitation was observed to be predominant; the high-order harmonic current density exhibited a main peak at the electrode center and one or more minor peaks between the electrode center and the edge, leading to a center-high electron density profile. With the addition of the dc source, the harmonic excitations and the corresponding nonlinear standing wave effect tend to be suppressed with the increase of dc bias, resulting in improved plasma uniformities. Underlying mechanisms of the suppression effect of the dc bias on the nonlinear standing wave excitation were analyzed.

Polarimetric and Electrical Structure of the 19 May 2013 Edmond–Carney, Oklahoma, Tornadic Supercell

AbstractWe demonstrate the utility of transient polarimetric signatures (ZDR and KDP columns, a proxy for surges in a thunderstorm updraft) to explain variability in lightning flash rates in a tornadic supercell. Observational data from a WSR-88D and the Oklahoma lightning mapping array are used to map the temporal variance of polarimetric signatures and VHF sources from lightning channels. It is shown, via three-dimensional and cross-sectional analyses, that the storm was of inverted polarity resulting from anomalous electrification. Statistical analysis confirms that mean flash area in the ZDR column region was 10 times smaller than elsewhere in the storm. On an average, 5 times more flash initiations occurred within ZDR column regions, thereby supporting existing theory of an inverse relationship between flash initiation rates and lightning channel extent. Segmentation and object identification algorithms are applied to gridded radar data to calculate metrics such as height, width, and volume of ZDR and KDP columns. Variability in lightning flash rates is best explained by the fluctuations in ZDR column volume with a Spearman’s rank correlation coefficient value of 0.72. The highest flash rates occur in conjunction with the deepest ZDR columns (up to 5 km above environmental melting level) and largest volumes of ZDR columns extending up to the −20°C level (3 km above the melting level). Reduced flash rates toward the end of the analysis are indicative of weaker updrafts manifested as low ZDR column volumes at and above the −10°C level. These findings are consistent with recent studies linking lightning to the interplay between storm dynamics, kinematics, thermodynamics, and precipitation microphysics.

On the conditions for winter lightning at the Eagle Nest Tower (2537 m asl) during the Cerdanya-2017 field experiment

In this paper, we analyze meteorological conditions, thundercloud structure, lightning activity and characteristics of the flashes that strike two towers separated by 1.3 km on Tosa d'Alp (2537 m asl) for two days (March 24 and 31) of the Cerdanya-2017 field campaign. Remote sensing products (cloud top temperature, lightning flash location, volumetric radar scans) and a set of sensors installed at Cerdanya station (electric field mill, microwave radiometer, vertically-pointing K-band Doppler radar, atmospheric soundings) provide the data for the analysis. A total of 20 flashes (72 strokes) have been detected on these towers with a large majority on March 24 (18 flashes and 66 strokes), despite of a lower convective activity in the study region. All these flashes are negative and most of them exhibit the features of upward flashes: large multiplicity (3.67 in average on March 24), strokes with low peak current (−10.6 kA in average on March 24), and short inter-stroke time interval (40 ms in average on March 24). Some flashes are supposed to be self-triggered on the towers because of the absence (the low number) of VHF sources before (after) the strokes. Compared to the instrumented “Eagle Nest Tower”, the “Cerdanya Tardia Antenna” collects a greater number of flashes (strokes) during the most prolific day with 14 out of 18 (57 out of 66). During this day, all flashes that radiate in VHF at less than 5 km from the towers strike them. We observe also that the cloud region around −15 °C favorable for charging process is located at lower altitude (1000 m above tower altitude) and produce strong radar reflectivity values on that day. Furthermore, the wind at the altitude of Tosa d'Alp stronger on March 24 could facilitate the inception from the towers by evacuating the corona ions.

Needles and Lightning Leader Dynamics Imaged with 100–200 MHz Broadband VHF Interferometry

AbstractA new short‐baseline VHF interferometer with 200 MHz bandwidth images lightning with significantly higher spatial resolution than our previous system with a 60 MHz maximum frequency. Needles (Hare et al., 2019, https://doi.org/10.1038/s41586‐019‐1086‐6), needle‐associated negative leaders, a nearby bidirectional leader, and their interactions were imaged during an intracloud lightning flash. Six recoil leaders traversing the positive leader channel definitively determined the leader path and verified that needles originate from positive channels. Two negative leaders initiated from the positive channel, either from or close to needles, when another active positive leader passed ~1 km away. While the needles develop continuously with a VHF source density decreasing from the front end to the back end, a bidirectional leader initiated nearby and had strong influence on subsequent needle dynamics. These rarely observed yet perhaps common lightning processes are analyzed comprehensively to give new insight into the origin and impact of needles on positive lightning leaders.

Initiation locations of lightning flashes relative to radar reflectivity in four small Florida thunderstorms

AbstractThis study examines initiation locations of intracloud (IC) and cloud‐to‐ground (CG) lightning near Kennedy Space Center, Florida, on 1 day. One unicellular and two multicellular thunderstorms occurred over land, and one multicellular storm was 30 km offshore. The storm over ocean was visible on radar 47–51 min before its first flash (of 17 total); first echoes in the storms over land were 23, 12, and 16 min prior to the first flashes (of 34, 16, and 9 total). Initiation points of 66 flashes were identified using the first initial breakdown (IB) pulse location from electric field change measurements or a VHF source coincident with the first IB pulse; 10 ICs occurred without enough data to similarly locate the initiation. All but 2 of 35 flashes that initiated as negative CGs began below 6.8 km altitude; two higher CG initiations (7.1–7.5 km) were the first CGs in two storms. Initiations of 21 normal ICs occurred above 7.9 km, 6 late stage ICs initiated at 5.5–7.5 km, and 4 hybrid IC‐CG flashes initiated as ICs at 6.6–8.1 km. Initiation locations were tightly clustered in small regions of each cell. Over land, early and mature stage flashes initiated within 2 × 2 km in each cell, or about 10–25% of the midlevel reflectivity coverage. One cell over ocean had initiations within 6 × 5 km, less than 30% of its reflectivity area. The IC initiations generally occurred above reflectivity cores, in 15–35 dBZ, and CG initiations were in 30–45 dBZ beside or atop cores.

Luminosity with intracloud‐type lightning initial breakdown pulses and terrestrial gamma‐ray flash candidates

AbstractHigh‐speed video data for four hybrid lightning flashes show luminosity bursts at visible wavelengths that are time‐correlated with large, intracloud flash (IC) initial breakdown (IB) pulses in electric field change (E‐change) data. The candidate IC‐type IB pulses are large in range‐normalized E‐change amplitude and peak current (2.2‐3.4 V/m at 100 km, 2.9‐11.1 kA) and have slow (0.3‐2.2 ms duration) field changes corresponding to charge moment changes of 0.5‐15 C km. Such large amplitude IB pulses have been associated with production of terrestrial gamma‐ray flashes in prior work. No gamma‐ray observations were available for these events. In each flash, a luminosity increase was evident in the video data at the time of the largest IC‐type IB pulses, when VHF sources and E‐change data indicate the IC initial leader was at 6.1 ‐ 9.4 km altitude and rapidly developing upward. Luminosity starts increasing within ‐10 µs to +20 µs of the main IC‐type IB pulse peak, i.e., within the same 20‐µs video frame as that in which the E‐change peak occurs. Delay time between the beginning of the E‐change pulse and beginning of the luminosity increase is 40‐110 µs. Video intensities increase sharply for 80‐220 µs to maximum value, then decrease over a longer period, with entire burst durations of 300‐800 µs. The time lag between IB pulse peak and maximum luminosity is consistent with these IC‐type IB pulses starting a large current that peaks and becomes bright at the time of the main pulse peak, and lasts for several hundred microseconds.

Lightning channel length and flash energy determined from moments of the flash area distribution

AbstractA widely used approach in observational and modeling studies of NOx produced by lightning is to relate NOx production to the number of flashes, without regard for the distribution of lightning flash sizes. Recent studies have begun to consider channel length and flash size, which is now observable with VHF Lightning Mapping Array data. This study uses a capacitor model for flash energy based on the flash coverage area, which defines a size scale. This flash area is then filled with channel using a fractal method and compared to other methods that estimate length directly from the VHF source locations. In the presence of instrument measurement errors, area‐ and fractal‐based estimates are shown to be more stable estimators of flash length than connect‐the‐dots approaches and therefore are better suited for comparison to NOx production. A geometric interpretation of using vertical profiles of VHF source density to weight the altitude distribution of total channel length is developed. An example of the time series of moments of the lightning flash size distribution is shown for an example case, and some meteorological interpretation is given.

Electromagnetic activity before initial breakdown pulses of lightning

AbstractLightning flash initiation is studied using electric field change (E‐change) measurements made in Florida. An initial E‐change (IEC) was found immediately before the first initial breakdown (IB) pulse in both cloud‐to‐ground (CG) and intracloud (IC) flashes if the E‐change sensor was within 80% of the reversal distance of the IEC. For 18 CG flashes, the IECs had an average point dipole moment of 23 C m and an average duration of 0.18 ms; these parameters for 18 IC flashes were −170 C m and 1.53 ms. The IECs of CG flashes began with a change in the slope of the E‐change (with respect to time) from zero slope to a positive slope, consistent with downward motion of negative charge and/or upward motion of positive charge. For IECs of IC flashes, the beginning slope change was from zero to negative slope, consistent with upward motion of negative charge and/or downward motion of positive charge. During an IEC, the E‐change monotonically increased for CG flashes and monotonically decreased for IC flashes. In 14 of 36 cases, the IEC beginning was coincident with a discrete, impulsive source of VHF radiation; another 13 cases had at least one VHF source during the IEC or the first IB pulse. Before the IECs, there were no preliminary variations detected in the 36 flashes. It is hypothesized that lightning initiation begins with an ionizing event that causes the IEC and that the IEC enhances the ambient electric field to produce the first IB pulse.

On the relationship between continuing current and positive leader growth

AbstractIt has long been speculated that the source of continuing current (CC) for a negative cloud‐to‐ground flash is provided by the growth of its positive leader into negative charge regions. In this study, data from the Langmuir Electric Field Array (LEFA) and Lightning Mapping Array (LMA) are used to investigate these speculations. LEFA and LMA data provide a way to estimate the occurrence and duration of CC and channel growth throughout a flash, respectively. By connecting LMA VHF sources onto contiguous channels, the growth of the positive leader associated with each return stroke is inferred. A linear correlation between positive‐channel growth and CC duration is found, providing evidence that the positive leader grows with a constant velocity, but no obvious correlation of this velocity with CC occurrence is found. Each return stroke is then sorted by its channel growth rate and further identified by its CC type. This analysis also provides no identifiable correlation linking the positive‐channel growth rate to CC occurrence or duration. Finally, the positive‐channel growth rate for the whole flash is calculated in 10 ms windows so that any trends occurring before, during, or after the CC can be observed. This analysis too shows no correlation, which implies that positive‐channel growth is not the primary mechanism that determines CC occurrence and duration.

Initial results of LF sensor network for lightning observation and characteristics of lightning emission in LF band

AbstractWe have been developing an LF sensor network called Broadband Observation network for Lightning and Thunderstorm (BOLT), to image the structure of lightning discharges in 3D using time of arrival (TOA) technique. This paper documents initial results and characteristics of BOLT source locations for further understanding of LF radiation associated with lightning. Theoretical reduced Chi‐square distribution fitted to BOLT observation data indicates a root mean square (rms) timing error of about 200 ns for each sensor. Monte Carlo simulations of BOLT indicate that at an altitude of 5000 m the standard deviations for horizontal differences between a known source and a location that the BOLT algorithm produces are less than 200 m, and vertical differences are less than 400 m in most of the network. Furthermore, comparison of BOLT and VHF source locations arriving at the same site within 5 µs indicates that the average difference for elevation direction is 0.73° with a standard deviation of 3.64°, and that for the azimuth direction is 0.58° with a standard deviation of 1.98°. Lightning flash processes of intracloud (IC) and cloud‐to‐ground (CG) flashes, including preliminary breakdown pulses, negative leaders, breakdown in the negative charge region (NCR), and an attempted leader, are well imaged by BOLT. Normalized amplitudes in E‐field change waveform of BOLT sources associated with negative leaders and breakdown occurred in the NCR do not have significant difference, implying that most BOLT sources in the NCR might be associated with negative recoil leaders.

Registration of X‐rays at 2500 m altitude in association with lightning flashes and thunderstorms

AbstractElectric fields and high‐energy radiation of natural lightning measured at close range from a mountaintop tower are discussed. In none of the 12 negative cloud‐to‐ground upward flashes were X‐rays observed. Also no energetic radiation was found in one negative upward leader at close range (20 m). In the first of two consecutive negative cloud‐to‐ground flashes, X‐rays were detected during the last ~1.75 ms of the leader. During the time of energetic radiation in the flash an intense burst of intracloud VHF sources was located by the interferometers. The X‐ray production is attributed to the high electric field runaway electron mechanism during leader stepping. Even though the second flash struck closer than the previous one, no X‐rays were detected. The absence of energetic radiation is attributed to being outside of the beam of X‐ray photons from the leader tip or to the stepping process not allowing sufficiently intense electric fields ahead of the leader tip. High‐speed video of downward negative leaders at the time when X‐rays are commonly detected on the ground revealed the increase of speed and luminosity of the leader. Both phenomena allow higher electric fields at the leader front favoring energetic radiation. Background radiation was also measured during thunderstorms. The count rate of a particular day is presented and discussed. The increases in the radiation count rate are more coincident with radar reflectivity levels above ~30 dBZ than with the total lightning activity close to the site. The increases of dose are attributed to radon daughter‐ion precipitation.

Development of VLF/LF Bands Interferometer and Its Initial Observations

SummaryWe have been developing an EM source location system using the VLF/LF bands based on broadband digital interferometry to monitor lightning activity in a wide area. Since EM waves in VLF/LF radiated by lightning discharges propagate a long distance, the VLF/LF interferometer locates lightning discharges a few hundred kilometers away from the VLF/LF interferometer. We conducted a lightning observation campaign using a prototype of a VLF/LF band digital interferometer and VHF band digital interferometers in Darwin, Australia. The VLF/LF radiation sources were located near those of the VHF source. We succeeded in locating the VLF/LF radiation sources associated with return strokes near the ground. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(4): 9–17, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22300

Characteristics of lightning radiation source distribution and charge structure of squall line

Lightning information indicates the intensity and the development of severe convection. The characteristics of lightning activity and charge structure of a squall line over Beijing on 13 June 2010 are analyzed by using the SAFIR3000 lightning detection data, Doppler weather radar and precipitation data. Results show that the lightning radiation sources are the major part in the convective leading region with a high reflectivity in front of the squall line, and the number of lightning radiation sources gradually increases in the back of stratiform region only at the dissipating stage. The correlation coefficient between the total lightning and convective precipitation is found to be 0.82, and that of intra-cloud lightning and convective precipitation is 0.76. It is inferred that the lightning is closely related to dynamical and microphysical processes of the squall line. According to the lightning radiation distribution, the charge structure of squall line is also discussed. At the mature stage of the squall line, the lightning radiation sources have two layers with the upper level centered at 11 km and the lower level at 6 km. Based on the bidirectional leader of lightning propagation and by assuming VHF source density maxima being most likely associated with the positive charge region, it is concluded that the squall line is characterized by a tripole charge structure with a middle charge region between the levels of 8 km and 10 km, and the two positive charge regions at the levels of 10 to 12 km and 4 to 7 km above the ground, respectively.

Geometrical and electrical characteristics of the initial stage in Florida triggered lightning

We characterize the geometrical and electrical characteristics of the initial stages of nine Florida triggered lightning discharges using a Lightning Mapping Array (LMA) and measured channel‐base currents. We determine initial channel and subsequent branch lengths, average initial channel and branch propagation speeds, and channel‐base current at the time of each branch initiation. The channel‐base current is found to not change significantly when branching occurs, an unexpected result. The initial stage of Florida triggered lightning typically transitions from vertical to horizontal propagation at altitudes of 3–6 km, near the typical freezing level of 4 km and several kilometers below the expected center of the negative cloud‐charge region at 7–8 km. The data presented potentially provide information on thunderstorm electrical and hydrometeor structure and discharge propagation physics. LMA source locations were obtained from VHF sources of positive impulsive currents as small as 10 A, in contrast to expectations found in the literature.

用于大面积薄膜沉积的线形等离子体源研究进展

本文系统介绍了几种线形等离子体源的特点及其应用，根据激励源的不同分别称为直流、射频、甚高频、微波、双频线形等离子体源，有磁场辅助的称为磁场增强线形等离子体源。与传统的大面积等离子体源不同，线形等离子体源仅需在一维方向实现均匀、稳定的等离子体，采用多个线形结构并排，或者与被镀样品在水平/垂直方向以适当速度运动，即可获得大面积均匀的薄膜沉积。近年来，研究人员采用磁场约束技术，减少带电粒子在器壁的复合损失，进一步提高等离子体的密度、均匀度和稳定性。线形等离子体及磁场增强线形等离子体密度 > 1011 cm−3，不均匀度 1 m)，被广泛用于Si3N4、SiO2、光伏电池硅本征层、纳米金刚石等薄膜的大面积沉积，具有很重要的应用价值和科学意义。 The characteristics and application of several kinds of linear plasma sources are introduced. According to the power sources for plasma systems, there are DC, RF, VHF, microwave and dual frequency linear plasma sources, which with a magnet system are called magnetic field enhanced linear plasma sources. Compared with the conventional large scale plasma sources, linear plasma sources take the advantage that they just need to obtain uniform and stable plasma in one dimension. Through the linear plasma array or moving the substrate in horizontal and vertical direction, large scale uniform thin film can be deposited. Recent years, researchers tried to use the magnetic field to confine plasma so as to reduce the recombination loss in plasma and improve the density, uniformity and stability of plasma. The linear plasma sources with the density above1011 cm−3, dis-uniformity below ±5% (L >1 m), have been applied to fabricate large scale Si3N4, SiO2, intrinsic Si and nano-diamond thin film.

Lightning initiation from a tall structure in the Basque Country

Lightning detection in the Spanish Basque Country is performed using the LF TOA, VHF interferometer and the VLF lightning detection technologies in which two independent networks are based, providing a better detection quality due to the combination of these different techniques. Total lightning activity related to the tall structure of the weather radar operated by the Basque Meteorology Agency (Euskalmet) is presented. The tall structure is a 50m tower located on the top of Kapildui Mountain (at about 1169.48m ASL). Remarkable electrical activity associated to this place has been witnessed in the last two years. Two particular flashes during November 30th 2009 caused damage to the weather radar. Two different lightning detection networks detected five and six cloud-to-ground strokes, respectively. Only nine VHF sources were detected in the first flash without any VLF detection classified as intracloud. But for the second flash non VHF source was detected and two detections were reported by the VLF system. In both cases some intracloud detections were reported before cloud-to-ground strokes and some others during the flash. This paper presents the study of a winter episode with a special impact in the tower, the research carried out for characterizing the lightning events and the measures taken in order to achieve a better protection mechanism for the radar site.

Lightning Activity in a Hail-Producing Storm Observed with Phased-Array Radar

Abstract This study examined lightning activity relative to the rapidly evolving kinematics of a hail-producing storm on 15 August 2006. Data were provided by the National Weather Radar Testbed Phased-Array Radar, the Oklahoma Lightning Mapping Array, and the National Lightning Detection Network. This analysis is the first to compare the electrical characteristics of a hail-producing storm with the reflectivity and radial velocity structure at temporal resolutions of less than 1 min. Total flash rates increased to approximately 220 min−1 as the storm’s updraft first intensified, leveled off during its first mature stage, and then decreased for 2–3 min despite the simultaneous development of another updraft surge. This reduction in flash rate occurred as wet hail formed in the new updraft and was likely related to the wet growth; wet growth is not conducive to hydrometeor charging and probably contributed to the formation of a “lightning hole” without a mesocyclone. Total flash rates subsequently increased to approximately 450 min−1 as storm volume and inferred graupel volume increased, and then decreased as the storm dissipated. The vertical charge structure in the storm initially formed a positive tripole (midlevel negative charge between upper and lower positive charges). The charge structure in the second updraft surge consisted of a negative charge above a deep midlevel positive charge, a reversal consistent with the effects of large liquid water contents on hydrometeor charge polarity in laboratory experiments. Prior to the second updraft surge, the storm produced two cloud-to-ground flashes, both lowering the usual negative charge to ground. Shortly before hail likely reached ground, the storm produced four cloud-to-ground flashes, all lowering the positive charge. Episodes of high singlet VHF sources were observed at approximately 13–15 km during the initial formation and later intensification of the storm’s updraft.

Spatial structure of plasma potential oscillation and ion saturation current in VHF multi-tile electrode plasma source

Increasing RF frequency in the VHF range in the PECVD of Silicon for photovoltaic applications enables a higher rate of deposition while maintaining film quality. However, plasma uniformity on large substrates is compromised as wavelength effects are encountered at high frequencies. Using a segmented electrode consisting an array of individual tiles each 180° out of phase with adjacent tiles, a scalable VHF source that is not affected by wavelength effects is achieved. Due to the 180° phase shift between tiles, a spatial structure is imposed on the plasma. In this paper the spatial structure of the plasma potential oscillation and the ion saturation current density are examined. A capacitive probe measures the oscillation of the plasma potential. Spatial profiles of the plasma potential oscillation exhibit peaks on tile centers at odd harmonics (1F and 3F). The measured even harmonic (2F) is small in amplitude, as expected for the differential power feed, and peaks at tile boundaries. Spatial profiles of ion saturation current show peaks in plasma density over the tile-to-tile boundaries, with non-uniformity increasing with RF power. A discussion of the measured profiles at a variety of powers and pressures is presented.