Fort Collins, CO, United States
Fort Collins, CO, United States

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Warner T.A.,ZTResearch | Lang T.J.,NASA | Lyons W.A.,FMA Research Inc.
Journal of Geophysical Research: Atmospheres | Year: 2014

A major central U.S. winter cyclone on 1-2 February 2011 produced a band of high winds, up to 75 cm of snow, and numerous reports of thundersnow from Oklahoma into Ontario over a 26 h period. The National Lightning Detection Network (NLDN) recorded 282 flashes comprised of 1153 events which were >96% negative polarity. Hopes of imaging winter sprites associated with energetic positive cloud-to-ground events that sometimes accompany such winter storms did not materialize. However, the lack of lightning over the Great Lakes waters, plus media reports of numerous thundersnow events in downtown Chicago, prompted a detailed analysis of the NLDN data. This revealed that >93% of all lightning in the snow band was likely or possibly associated with self-initiated upward lightning (SIUL) events from a variety of tall, and some not so tall, structures. In addition to 43 events from two Chicago skyscrapers, many shorter structures were involved, including wind turbines (13.1% of the total) and transmission line towers (6.7%). Wind speeds for all events exceeded the 8 m s-1 minimum threshold associated with SIULs in Japanese winter lightning storms. Radar reflectivities at the event locations had a mean of 28 dBZ and were almost always <35 dBZ. While conventional radar displays suggested stratiform precipitation in the thundersnow region, detailed analysis of 3-D-gridded NMQ (National Mosaic and Multi-Sensor Quantitative Precipitation Estimation) radar reflectivity data confirmed elevated embedded cellular convection spanning the -10°C region associated with isentropic lifting above a frontal surface, evidence of noninductive charge generation sufficient to allow upward leader initiation from tall objects. ©2014. American Geophysical Union. All Rights Reserved.

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).

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.

Lang T.J.,NASA | Lyons W.A.,FMA Research Inc. | Cummer S.A.,Duke University | Fuchs B.R.,Colorado State University | And 6 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2016

Two sprite-producing thunderstorms were observed on 8 and 25 June 2012 in northeastern Colorado by a combination of low-light cameras, a lightning mapping array, polarimetric and Doppler radars, the National Lightning Detection Network, and charge moment change measurements. The 8 June event evolved from a tornadic hailstorm to a larger multicellular system that produced 21 observed positive sprites in 2 h. The majority of sprites occurred during a lull in convective strength, as measured by total flash rate, flash energy, and radar echo volume. Mean flash area spiked multiple times during this period; however, total flash rates still exceeded 60 min−1, and portions of the storm featured a complex anomalous charge structure, with midlevel positive charge near −20°C. The storm produced predominantly positive cloud-to-ground lightning. All sprite-parent flashes occurred on the northeastern flank of the storm, where strong westerly upper level flow was consistent with advection of charged precipitation away from convection, providing a pathway for stratiform lightning. The 25 June event was another multicellular hailstorm with an anomalous charge structure that produced 26 positive sprites in less than 1 h. The sprites again occurred during a convective lull, with relatively weaker reflectivity and lower total flash rate but relatively larger mean flash area. However, all sprite parents occurred in or near convection and tapped charge layers in adjacent anvil cloud. The results demonstrate the sprite production by convective ground strokes in anomalously charged storms and also indicate that sprite production and convective vigor are inversely related in mature storms. ©2016. American Geophysical Union. All Rights Reserved.

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.

Lang T.J.,Colorado State University | Lyons W.A.,FMA Research Inc. | Rutledge S.A.,Colorado State University | Meyer J.D.,FMA Research Inc. | And 3 more authors.
Journal of Geophysical Research: Space Physics | Year: 2010

Two warm-season mesoscale convective systems (MCSs) were analyzed with respect to their production of transient luminous events (TLEs), mainly sprites. The 20 June 2007 symmetric MCS produced 282 observed TLEs over a 4 h period, during which the storms intense convection weakened and its stratiform region strengthened. TLE production corresponded well to convective intensity. The convective elements of the MCS contained normal-polarity tripole charge structures with upper-level positive charge (-40°C), midlevel negative charge (-20°C), and low-level positive charge near the melting level. In contrast to previous sprite studies, the stratiform charge layer involved in TLE production by parent positive cloud-to-ground (+CG) lightning resided at upper levels. This layer was physically connected to upper-level convective positive charge via a downward sloping pathway. The average altitude discharged by TLE-parent flashes during TLE activity was 8.2 km above mean sea level (MSL; -25°C). The 9 May 2007 asymmetric MCS produced 25 observed TLEs over a 2 h period, during which the storms convection rapidly weakened before recovering later. Unlike 20 June, TLE production was approximately anticorrelated with convective intensity. The 9 May storm, which also had a normal tripole in its convection, best fit the conventional model of low-altitude positive charge playing the dominant role in sprite production; however, the average altitude discharged during the TLE phase of flashes still was higher than the melting level: 6.1 km MSL (-15°C). Based on these results, it is inferred that sprite production and sprite-parent positive charge altitude depend on MCS morphology. Copyright 2010 by the American Geophysical Union.

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.

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.

Lang T.J.,Colorado State University | Lang T.J.,NASA | Cummer S.A.,Duke University | Rutledge S.A.,Colorado State University | Lyons W.A.,FMA Research Inc.
Journal of Geophysical Research: Atmospheres | Year: 2013

This study examined the meteorological characteristics of precipitation systems that produced 38 "sprite-class" negative cloud-to-ground (CG) strokes (i.e., peak currents in excess of 100 kA and charge moment changes in excess of 800 C km) as well as those that produced three confirmed negative sprites on 23 different days during 2009-2011. Within 15 km of the negative sprite-parent/class stroke, the median characteristics for these systems were to produce negative CGs as 69.2% of all CGs, and for the 30 dBZ radar reflectivity contour to reach on average 14.2 km above mean sea level (MSL), during a 25 min period encompassing the occurrence of the stroke. The median contiguous area of 30 dBZ composite radar echo (i.e., maximum value in the vertical column) for these systems was 6.73 × 103 km2. All but three of the discharges occurred in intense multicellular convection, with 30 dBZ exceeding 10 km MSL in altitude, while the others occurred in the stratiform regions of mesoscale convective systems. All but six of the systems produced greater than 50% negative CG lightning, though flash rates tended to be low near the stroke (1-2 min-1 on average). The results suggest that negative sprite-parent/class lightning typically occurs in precipitation systems of similar size and intensity as those that produce positive sprites, but not necessarily the same systems, and the negative lightning normally strikes ground in the convection rather than the stratiform precipitation. However, upper-level positive charge in the convection may play an important role in sprite-class/parent lightning of either polarity. Key Points Negative sprite lightning mainly occurred near intense, deep convection The systems producing these discharges were frequently large Systems producing these discharges mainly produced negative CG lightning ©2013. American Geophysical Union. All Rights Reserved.

Beavis N.K.,Colorado State University | Lang T.J.,NASA | Rutledge S.A.,Colorado State University | Lyons W.A.,FMA Research Inc. | Cummer S.A.,Duke University
Monthly Weather Review | Year: 2014

The use of both total chargemoment change (CMC) and impulse chargemoment change (iCMC) magnitudes to assess the potential of a cloud-to-ground (CG) lightning stroke to induce a mesospheric sprite has been well described in the literature, particularly on a case study basis. In this climatological study, large iCMC discharges for thresholds of>100 and >300C km in both positive and negative polarities are analyzed on a seasonal basis. Also presented are local solar time diurnal distributions in eight different regions covering the lower 48 states as well as the adjacent Atlantic Ocean, including the Gulf Stream. The seasonal maps show the predisposition of large positive iCMCs to dominate across the northern Great Plains, with large negative iCMCs favored in the southeastern United States year-round. During summer, the highest frequency of large positive iCMCs across the upper Midwest aligns closely with the preferred tracks of nocturnalmesoscale convective systems (MCSs).As iCMCvalues increase above 300Ckm, themaximumshifts eastward of the 100Ckm maximum in the central plains. Diurnal distributions in the eight regions support these conclusions, with a nocturnal peak in large iCMC discharges in the northern Great Plains and Great Lakes, an early to midafternoon peak in the Intermountain West and the southeasternUnited States, and amorning peak in large iCMCdischarge activity over theAtlantic Ocean. Large negative iCMCs peak earlier in time than large positive iCMCs, which may be attributed to the growth of large stratiform charge reservoirs following initial convective development. © 2014 American Meteorological Society.

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