"Photo of the Month." Weatherwise, 76(5), pp. 14–15 Additional informationNotes on contributorsWalter LyonsWalter Lyons (Past President, American Meteorological Society) and Ian Loxley (www.CloudAppreciationSociety.org) both have a lifelong love of the diverse performers in the theater of the sky.Ian LoxleyWalter Lyons (Past President, American Meteorological Society) and Ian Loxley (www.CloudAppreciationSociety.org) both have a lifelong love of the diverse performers in the theater of the sky.

The World Meteorological Organization has recognized a new world record lightning discharge distance of 829 km ± 8 km (515 ± 5 mi) that extended from eastern Texas to near Kansas City MO USA within a 22 October 2017 thunderstorm complex.

High‐speed video observations of two sprites with halo features were analyzed with concurrent measurements of broadband magnetic sferics. Both events were produced by positive cloud‐to‐ground (CG) strokes. Moreover, the halo features appeared less than 0.5 ms after the return stroke, and the first sprite elements followed within 1 and 3 ms, respectively, for the two cases. The persistent charge transfer in the causative stroke from long continuing current can maintain the continuous glowing of existing sprite elements, and also may aid the vertical development and enhanced luminescence of later sprite elements. The observations with electric field (E‐field) simulations by the transmission line model provide evidence that the induction component of the lightning‐induced E‐field contributes significantly to halo formation. Our results suggest additional measurements and analysis are needed to identify the specific role of induction E‐field in addition to the well‐known quasi‐electrostatic (QE) field in the lightning‐induced impact on the mesosphere.

A momentary cloud created by artist Berndnaut Smilde floats in St. Helen’s Church on the Island of Lundy in England’s Bristol Channel. On average, at any given time, two-thirds of our planet is cov...

The existence of mesoscale lightning discharges on the order of 100 km in length has been known since the radar-based findings of Ligda in the mid-1950s. However, it took the discovery of sprites in 1989 to direct significant attention to horizontally extensive “megaflashes” within mesoscale convective systems (MCSs). More recently, 3D Lightning Mapping Arrays (LMAs) have documented sprite-initiating lightning discharges traversing several hundred kilometers. One such event in a 2007 Oklahoma MCS having an LMA-derived length of 321 km, has been certified by the WMO as the longest officially documented lightning flash. The new Geostationary Lightning Mapper (GLM) sensor on GOES-16/17 now provides an additional tool suited to investigating mesoscale lightning. On 22 October 2017, a quasi-linear convective system moved through the central United States. At 0513 UTC, the GLM indicated a lightning discharge originated in northern Texas, propagated north-northeast across Oklahoma, fortuitously traversed the Oklahoma LMA (OKLMA), and finally terminated in southeastern Kansas. This event is explored using the OKLMA, the National Lightning Detection Network (NLDN), and the GLM. The NLDN reported 17 positive cloud-to-ground flashes (+CGs), 23 negative CGs (−CGs), and 37 intracloud flashes (ICs) associated with this massive discharge, including two +CGs capable of inducing sprites, with others triggering upward lightning from tall towers. Combining all available data confirms the megaflash, which illuminated 67,845 km 2 , was at least 500 km long, greatly exceeding the current official record flash length. Yet even these values are being superseded as GLM data are further explored, revealing that such vast discharges may not be all that uncommon.

Identification and validation of atmospheric extremes are essential to monitoring climate change, to addressing engineering and safety concerns, and to promoting technological advancement. An international World Meteorological Organization evaluation committee has critically adjudicated and recommended acceptance of two lightning megaflash events (horizontal mesoscale lightning discharges of >100 km in length) as new global extremes using analysis of Geostationary Lightning Mapper data. The world's greatest extent for an individual lightning flash is a single flash that covered a horizontal distance of 709 ± 8 km (441 ± 5 mi) across parts of southern Brazil on 31 October 2018. The greatest duration for a single lightning flash is 16.730 ± 0.002 s from a flash that developed continuously over northern Argentina on 4 March 2019.

Upward lightning from tall objects can be either (1) triggered by preceding IC and/or CG flashes nearby, termed lightning-triggered upward lightning (LTUL), or (2) can be selfinitiated upward lightning (SIUL). In the latter, upward leaders originate due to locally strong electric fields but without any preceding lightning. Observations have confirmed that the conditions producing sprites in summertime mesoscale convective systems also favor LTUL development, with both sometimes resulting from the same parent +CG. Though relatively infrequent, sprite-class +CGs also occur during continental winter cyclonic storms producing heavy snow and strong winds. Monitoring of two blizzards revealed one storm was devoid of energetic (sprite-class) lightning while a second produced considerable lightning, including some capable of inducing sprites. However, upward lightning from a variety of tall, and some not so tall (~100 m), structures occurred in both storms. These upward discharges were dominated by self-initiated upward lightning. It is believed that sufficiently intense electric fields were generated by elevated, embedded convective cells. The strong winds played a key role in “stripping away” the corona discharge shielding at the tops of tall objects allowing for leader initiation, as has been observed in Japanese winter snowstorms. Keywords—lightning; self-initiated upward lightning (SIUL); thundersnow; sprites; charge moment change

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How did the tiger elve get its stripes? It's simple, really: a massive and impulsive CG emits an intense burst of EMP, detectable worldwide at ELF radio frequencies, resulting in a large glowing el...

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AbstractMore than three dozen red sprites were captured above Hurricane Matthew on the nights of 1 and 2 October 2016 as it passed to the north of Venezuela after undergoing rapid intensification. Analyses using broadband magnetic fields indicate that all of the sprites were produced by positive cloud‐to‐ground (CG) strokes located within the outer rainbands as defined by relatively cold cloud top brightness temperatures (≤194 K). Negative CG strokes with impulse charge transfers exceeding the threshold of sprite production also existed, but the timescale of the charge transfer was not sufficiently long to develop streamers. The reported observations are contrary to the finding of the Imager of Sprites/Upper Atmospheric Lightning showing that sprites are preferentially produced by negative strokes in the same geographic region. Further ground‐based observations are desired to obtain additional insights into the convective regimes associated with the dominance of negative sprites in many oceanic and coastal thunderstorms.

What is the most essential tool for a die-hard weather enthusiast? A thermometer? Or maybe a barometer? I would maintain it is a camera. The theater of the sky is an ever-changing pageant of perfor...

CHRISTOPHER SINGER/CLOUD APPRECIATION SOCIETYThere is a birthday coming up. On March 23, 2018, World Meteorological Day, asperitas will be one year old. On that date in 2017, the World Meteorologic...

On June 5, 2013, the SpriteCam network recorded a relatively weak sprite over a thunderstorm in Oklahoma. The broadband magnetic fields recorded at multiple stations consistently indicate that this event was produced by a negative cloud-to-ground (CG) event that probably contained two ground strokes separated by about 3 ms. Although neither stroke caused substantial impulse charge moment change that is sufficient to produce a negative sprite, the contributions of the two strokes are combined so that. The similar sprite-associated sferic waveform is also observed for a negative sprite recorded by ISUAL from space on August 15, 2012. In this case, the negative sprite appeared to be unusually bright due to the electric field enhancement cased by the second stroke. Therefore, the intrinsic complexity in the parent stroke is probably responsible for the observed variance in the morphology of negative sprites.

Iceland is a bucket list country—a desired destination for many who wish to experience an old, yet sophisticated, Nordic culture, wonderful food, surprisingly mild though occasionally wild weather,...