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Lu G.,Duke University | Lu G.,CAS Institute of Atmospheric Physics | Cummer S.A.,Duke University | Li J.,Duke University | And 16 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

The temporal and spatial development of sprite-producing lightning flashes is examined with coordinated observations over an asymmetric mesoscale convective system (MCS) on 29 June 2011 near the Oklahoma Lightning Mapping Array (LMA). Sprites produced by a total of 26 lightning flashes were observed simultaneously on video from Bennett, Colorado and Hawley, Texas, enabling a triangulation of sprites in comparison with temporal development of parent lightning (in particular, negatively charged stepped leaders) in three-dimensional space. In general, prompt sprites produced within 20 ms after the causative stroke are less horizontally displaced (typically <30 km) from the ground stroke than delayed sprites, which usually occur over 40 ms after the stroke with significant lateral offsets (>30 km). However, both prompt and delayed sprites are usually centered within 30 km of the geometric center of relevant LMA sources (with affinity to negative stepped leaders) during the prior 100 ms interval. Multiple sprites appearing as dancing/jumping events associated with a single lightning flash could be produced either by distinct strokes of the flash, by a single stroke through a series of current surges superposed on an intense continuing current, or by both. Our observations imply that sprites elongated in one direction are sometimes linked to in-cloud leader structure with the same elongation, and sprites that were more symmetric were produced above the progression of multiple negative leaders. This suggests that the large-scale structure of sprites could be affected by the in-cloud geometry of positive charge removal. Based on an expanded dataset of 39 sprite-parent flashes by including more sprites recorded by one single camera over the same MCS, the altitude (above mean sea level, MSL) of positively charged cloud region tapped by sprite-producing strokes declined gradually from ~10 km MSL (-35°C) to around 6 km MSL (-10°C) as the MCS evolved through the mature stage. On average, the positive charge removal by causative strokes of sprites observed on 29 June is centered at 3.6 km above the freezing level or at 7.9 km above ground level. Key Points Triangulated sprites with lightning structure shown by the LMA. Spatial correlation between sprite, parent stroke, and in-cloud negative leader. Significant variation of positive charge reservoir for sprite production. © 2013. American Geophysical Union. All Rights Reserved. Source

Lang T.J.,George rshall Space Flight Center | Cummer S.A.,Duke University | Petersen D.,University of Oklahoma | Flores-Rivera L.,University of Puerto Rico at Mayaguez | And 3 more authors.
Journal of Geophysical Research D: Atmospheres | Year: 2015

On 31 May 2013, a line of severe tornadic thunderstorms (the El Reno event) developed during the local afternoon in central Oklahoma, USA. Within range of the Oklahoma Lightning Mapping Array, the evolution of the event can be separated into three distinct periods: an Early period (before 02:00 UTC on 1 June) when the storm consisted of discrete supercells, a Middle period (02:00-05:00 UTC) when the convection began merging into a linear feature and stratiform precipitation developed, and a Late period (after 05:00 UTC) featuring a mature mesoscale convective system (MCS). Each of these periods demonstrated distinct patterns in the large (>100 C km) charge moment change (CMC) lightning that was produced. During the Early period, large-CMC positive cloud-to-ground (+CG) lightning was produced in the convective cores of supercells. These flashes were small in area (typically <500 km2) and were commonly associated with a sloping midlevel positive charge region in the echo overhang on the storm's forward flank. The Middle period featured a population of larger +CMCs (>500 km2, >300 C km) in the developing stratiform, similar to typical sprite-parent lightning in MCSs. During the Late period, convective large CMC +CGs ceased and instead large-CMC negative CGs were produced in and near the MCS convection. These flashes neutralized charge both in convection as well as in adjacent stratiform and anvil precipitation. The results suggest that the CMC metric has potential applications for studying tropospheric weather. © 2015. American Geophysical Union. All Rights Reserved. Source

Yue J.,High Altitude Observatory | Nakamura T.,Japan National Institute of Polar Research | She C.-Y.,Colorado State University | Weber M.,Colorado State University | And 2 more authors.
Annales Geophysicae | Year: 2010

Ripples as seen in airglow imagers are small wavy structures with short horizontal wavelengths (<15 km). Ripples are thought to form as the result of local instabilities, which are believed to occur when the amplitude of gravity waves becomes large enough. We have investigated ripple formation based on years of airglow imager observations located at Fort Collins, Colorado (41° N, 105° W) and Misato Observatory, Japan (34° N, 135° E)/Shigaraki MU Observatory (35° N, 136° E). Na temperature-wind lidar observations are employed to detect convective and dynamic instabilities in the mesosphere and lower thermosphere (MLT) region over Fort Collins, Colorado. Seasonal variation of the ripple occurrence in Colorado is compared to that of the lidar-measured instability. The occurrence frequency of ripples varies semiannually, with maxima occurring during solstices and minima during equinoxes in both Colorado and Japan. However, the probability of convective and dynamic instabilities varies annually with a peak in Colorado winter. The seasonal variation of the occurrence frequency of ripples correlates with that of the gravity wave variances in the MLT. Ripple occurrence over Colorado also shows strong local time dependence, but it bears little resemblance to the local time dependence of instability probability. © 2010 Author(s). Source

Lang T.J.,Colorado State University | Li J.,Duke University | Lyons W.A.,FMA Research Inc. | Cummer S.A.,Duke University | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

Charge moment change (ΔMQ) data were examined for 41 positive cloud-to-ground (+CG) lightning discharges that were parents of transient luminous events (TLEs; mainly sprites) over two different storms: 9 May (20 parents) and 20 June 2007 (21). Data were broken down by contributions from the impulse ΔMQ (iΔMQ), within the first 2 ms of the return stroke, and the ΔMQ from the continuing current (CC), which can last tens of ms afterward. Three-dimensional lightning mapping data provided positions for the in-cloud components of the parent +CGs. Charge and charge density neutralized by the strokes were estimated. The 20 June parents were more impulsive than 9 May, with increased iΔMQ and CC amplitude but reduced CC duration. Total MQ values between the two storms were very similar, averaging ∼1800 C km. Estimated charge density on 20 June was nearly twice that on 9 May, consistent with the 20 June storm being more intense with a stronger electrical generator. Lightning metrics were analyzed for 9 high- iΔMQ (>300 C km) +CGs that did not produce an observable TLE on 20 June, and compared to that day's TLE parents. Non-TLE +CGs had reduced CC magnitudes and duration, with less total ΔMQ. Photogrammetric estimates of TLE azimuthal swaths were positively correlated with similar metrics of the in-cloud portions of the parent +CGs, as well with total ΔMQ. The implications of all these results for the ΔMQ theory of sprite initiation, and for the relationship between sprite development and in-cloud discharging, are discussed. Copyright © 2011 by the American Geophysical Union. Source

Meyer T.C.,Colorado State University | Meyer T.C.,National Weather Service - NWS | Lang T.J.,Colorado State University | Lang T.J.,NASA | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

An analysis of thunderstorm environment, structure, and evolution associated with six gigantic jets (five negative polarity, one positive) was conducted. Three of these gigantic jets were observed within detection range of very high frequency lightning mapping networks. All six were within range of operational radars and two-dimensional lightning network coverage: five within the National Lightning Detection Network and one within the Global Lightning Detection (GLD360) network. Most of the storms producing the jets formed in moist tropical or tropical-like environments (precipitable water ranged from 37 to 62 kg m-2, and 0-6 km shear from 3.5 to 24.8 m s-1), featuring high convective available potential energy (1200-3500 J kg -1) and low lifted indices (-2.8 to -6.4). The storms had maximum radar reflectivity factors of 54 to 62 dBZ, and 10 dBZ echo contours reached 14-17 km. Storms covered by three-dimensional lightning mappers were near peak altitude of lightning activity (modes of the vertical distributions of radio sources were at altitudes colder than -50°C) and vertical reflectivity intensity, with overshooting echo tops around the times of their jets. Two of the other three jet-producing storms produced their jet around the time of a convective surge as indicated by radar data and likely featured overshooting tops. The observations suggest a link between convective surges, overshooting tops, and the occurrence of gigantic jets, similar to prior modeling studies. © 2013. American Geophysical Union. All Rights Reserved. Source

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