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“Megaflashes”: How Long Can a Lightning Discharge Be?

February 24, 2020

New research by Walt Lyons and colleagues, published in BAMS, reports such a perspective-altering observation of long lightning flashes. To appreciate the observation, consider first the “ordinary” lightning flash. The charge center of the cloud itself is typically 6–10 km above ground. And from there the lightning doesn’t necessarily go straight down: it may extend horizontally, even 100 km or more. Typical lightning might be best measured in kilometers or a few tens of kilometers.

A world record flash in 2007 meandered across Oklahoma for “approximately 300 km.” But that may be a mere cross-counties commute compared to newly discovered interstate “megaflashes” that are almost twice as long. One such megaflash, as the BAMS paper names them, sparked across the sky for ~550 km from northeast Texas across Oklahoma to southeast Kansas in October 2017. And this megaflash, too, may not be the longest ̶ it just happened to occur within the Oklahoma lightning mapping array (OK LMA), allowing for its full study.

Time integrated GLM radiances over 7.18s beginning at 0513:27.433 UTC on 22 October 2017. Two distinct electrical regimes are evident. The first is the cluster of smaller flashes in the leading line of convective cells stretching from eastern Oklahoma and then southwest into north Texas. The second regime is an extensive horizontal flash propagating from near the Red River in Texas across central Oklahoma into southeastern Kansas. — Time-integrated satellite (GLM) radiances over 7.18s beginning at 0513:27.433 UTC on 22 October 2017. Two distinct electrical regimes are evident. The first is the cluster of smaller flashes in the leading line of convective cells stretching southwest from eastern Oklahoma into north Texas. The second is the horizontal megaflash propagating from near the Red River in Texas across central Oklahoma into southeastern Kansas.

The new Geostationary Lightning Mapper sensor on the GOES-16/17 satellite has become the latest tool suited to investigating long-path lightning. The BAMS paper says the sensor is showing that a megaflash “appears able to propagate almost indefinitely as long as adequate contiguous charge reservoirs exist” in the clouds. Such conditions seem to be present in mesoscale convective systems—large conglomerates of thunderstorms that extend rainy stratiform clouds across many hundreds of km. The paper adds,

Megaflashes also pose a safety hazard, as they can be thought of as the stratiform region’s version of the ‘bolt-from-the blue,’ sometimes occurring long after the local lightning threat appears to have ended. But some key questions remain – what is the population of megaflashes and how long can they actually become?

The authors conclude:

Is it possible that a future megaflash can attain a length of 1000 km? We would not bet against that. Let the search begin.

"Megaflashes": How Long Can a Lightning Discharge Be?

February 24, 2020

Even though Earth’s atmosphere is laced by more than a billion brilliant discharges of electricity every year, lightning itself never seems ordinary. But there’s a broad range of lightning, and sometimes, at the extreme, it’s possible to recognize a difference between the ordinary and amazing, even among lightning flashes. The challenge is finding and observing such extremes.
New research by Walt Lyons and colleagues, published in BAMS, reports such a perspective-altering observation of long lightning flashes. To appreciate the observation, consider first the “ordinary” lightning flash. The charge center of the cloud itself is typically 6–10 km above ground. And from there the lightning doesn’t necessarily go straight down: it may extend horizontally, even 100 km or more. Typical lightning might be best measured in kilometers or a few tens of kilometers.
A world record flash in 2007 meandered across Oklahoma for “approximately 300 km.” But that may be a mere cross-counties commute compared to newly discovered interstate “megaflashes” that are almost twice as long. One such megaflash, as the BAMS paper names them, sparked across the sky for ~550 km from northeast Texas across Oklahoma to southeast Kansas in October 2017. And this megaflash, too, may not be the longest ̶ it just happened to occur within the Oklahoma lightning mapping array (OK LMA), allowing for its full study.

Also, just like the official record flash, which produced 13 cloud-to-ground (CG) lightning strikes, including two triggering sprites that shot high into the atmosphere, this horizontal megaflash also triggered a plethora of CG bolts, in-cloud discharges, and upward illuminations during its 7.18 second lifespan.
The new Geostationary Lightning Mapper sensor on the GOES-16/17 satellite has become the latest tool suited to investigating long-path lightning. The BAMS paper says the sensor is showing that a megaflash “appears able to propagate almost indefinitely as long as adequate contiguous charge reservoirs exist” in the clouds. Such conditions seem to be present in mesoscale convective systems—large conglomerates of thunderstorms that extend rainy stratiform clouds across many hundreds of km. The paper adds,

Megaflashes also pose a safety hazard, as they can be thought of as the stratiform region’s version of the ‘bolt-from-the blue,’ sometimes occurring long after the local lightning threat appears to have ended. But some key questions remain – what is the population of megaflashes and how long can they actually become?

The authors conclude:

Is it possible that a future megaflash can attain a length of 1000 km? We would not bet against that. Let the search begin.

Flying the Fastest Skies

February 20, 2019

How fast can an airliner go? Monday night a Virgin Atlantic Boeing 787-9 reached 801 m.p.h. en route from Los Angeles to London. Matthew Cappucci of the Washington Post reported the jet reached this amazing speed—a record for the Boeing 787-9 and probably the highest speed for a non-supersonic commercial flight—while cruising at 35,000 feet over the central Pennsylvania.
Clearly the plane was hurled along by an intense jet streak; Cappucci showed a sounding at 250 mb—a level nearly as high as the plane—that night over Long Island: the jet stream was moving at 231 m.p.h. This is what pushed the aircraft more than 200 m.p.h. beyond its top airspeed. (The plane’s record speed was relative to the ground, not the swiftly moving air around it.) The Post article states that the sounding “sets the record for the fastest 250-millibar wind speed ever recorded over New York and, probably, the country.”
This raises the other question of speed: just how fast can a jet stream go? It turns out the question is not so easy to answer. To find out, we e-mailed an experienced weather records sleuth, Arizona State University’s Randy Cerveny, who is the World Meteorological Organization’s rapporteur of weather and climate extremes. Cerveny replied,

I had set up a WMO committee this past summer to look into that very question—the strongest tropospheric winds (and so the strongest winds recorded on the planet). As we started to look at the data, we found that by far the strongest tropospheric winds are found east of Japan in the Pacific and normally occur right at this time of the year. They are associated with the normal area when polar and subtropical jets merge. The second area of max tropospheric winds are over New Hampshire and has the same thing happen—polar and subtropical jets merge. BUT unfortunately we ran into serious problems with the quality of extreme tropospheric wind measurements. My experts say that right now the quality of the data for those upper air extreme winds is not good enough to support an investigation for global fastest tropospheric winds. So we are not investigating that record until (and if) NCEI and other groups can establish a viable record for an extreme. We have seen data (again, not good to accept) that has winds in excess of 133 m/s or 297 miles per hour. It is likely that some of those values ARE good but we are still quality-controlling the radiosonde extreme dataset.

With that in mind, we dug into the AMS journals archive and found a February 1955 Journal of Meteorology article by Herbert Riehl, F. A. Berry, and H. Maynard detailing research flights into the jet stream over the Mid-Atlantic states. They record one case of a 240-knot jet stream (276 m.p.h.) and another of 210 knots (241 m.p.h.), each representing averages over 28 miles of flight path.
These can’t be counted as definitive—Riehl et al. emphasized the difficulties of their measurement process. And Cerveny emphasizes that, “No measurement that we have seen at extreme values has been judged of sufficient quality to warrant a full evaluation at this time.”
So for now, just sit back and enjoy the flight.

2015: The Hottest Hiatus

January 20, 2016

It was predicted early and often—and now, finally, it’s official. Throughout 2015, climate-watchers at NOAA and NASA were giving indications that the world’s surface temperature was going to top every annual mean measured since records began in 1880. Today, the two agencies with independent analyses jointly confirmed that global surface temperatures in 2015 blew away the record set in 2014.
The mean global temperature in the analysis by NASA’s Goddard Institute for Space Studies was 0.13°C above the 2014 record, and NOAA’s National Centers for Environmental Information had it as 0.16°C above. In all, according to NCEI, 2015 was 0.90°C above the 20th-century average.
The temperature record was no surprise, even though 2015 set a new record by the largest margin ever recorded. In the horse race of annual temperatures, 2015 jumped out of the gate ahead of the pack and never looked back at previous record holders like 1997, 2005, and 2014 (see the NOAA graphic below). It was a wire-to-wire victory in which 10 of 12 months were the hottest ever on record for their respective periods. Indeed, going into the homestretch, NCEI pointed out that December 2015 would have to stumble to more than 0.81°C below average to avoid setting a record. Instead, December extended the year’s lead by registering 1.11°C above the 1880-2015 century average—in other words, it was the hottest month in the century-plus of measurement history.

Inevitably, the question arises: does this record conflict with the notion of a “hiatus,” which the IPCC addressed in its Fifth Assessment Report in 2013? Trend aside, 15 of the 16 hottest years on record have occurred in this still-young 21st century, according to NASA; NOAA says four different years in that brief period have now reset the global surface temperature record.
Not surprisingly, a decade or so is a mere blip in climatology terms, and the short-term trend of global warming depends on where you mark the start and end point of your analysis. The warming has been relatively fast since 1970—about 0.16 or 0.17°C per decade, depending on your dataset. If you just look at only 1998-2012, as IPCC did, during sustained warmth near record levels, the upward trend is half what it is over the longer period. Of course, starting with 1998 means starting out very warm—hence a trend with major handicapping.
As a result, there’s been scientific backlash against use of the term “hiatus.” As Stephan Lewandowsky, James Risbey, and Naomi Oreskes point out in a newly released article in BAMS, the word doesn’t fit:

The meaning of the terms “pause” and “hiatus” implies that the normal fluctuations in warming rate have been surpassed such that warming has stopped.

They show that warming looks slower or faster depending on the start date of any given 15-year period, but that none of the slowest-warming periods, including the last 15 years, is any slower than one might expect in a warming climate post-1970 (or indeed less remarkable with longer periods one might choose). They conclude,

The “pause” is not unusual or extraordinary relative to other fluctuations and it does not stand out in any meaningful statistical sense.

Lewandowsky and colleagues go on to show that, objectively, “hiatus” doesn’t pass the eye test. When tested by looking at a curve resembling the global temperature curve, experts and nonexperts alike perceived a long-term, uninterrupted upward trend. The authors conclude that misuse of the word “hiatus” distorts how the data look, and thus impedes not only public perception of global warming but also scientific work.
One benefit of the “hiatus” talk is that scientists have been motivated to ask more questions about the normal short-term fluctuations of climate. One purpose of the Community Earth System Model’s Large Ensemble Project, for example, is to produce large numbers of climate model simulations to help “disentangle” model error from internal climate variability—that is, the fluctuations caused by climate irrespective of anthropogenic forcing.
In an article in the August issue of BAMS, the ensemble project’s investigators show a sample experiment in which the slower warming of the last 15 years has actually been a pace well within normal variability, with or without greenhouse gas forcing (see figure below).
As the world continues to warm, this year’s record is prone to fall. Meanwhile, the ensemble also shows that the odds of a 10- or 20-year fluctuation stopping the warming—let alone a brief cooling—keeps getting tinier and tinier.

World Record Temperature Overturned by Climatologists

September 13, 2012

“I think he read on the wrong side of the [thermometer] scale, and so was off by five degrees of Celsius. If you adjust for that, there was no 136-degree Fahrenheit temperature at El Azizia, Libya, in September 1922. Based on some really involved detective work, [a committee of experts] decided that this reading simply is not valid. It’s not the world’s hottest temperature.”
–Randall Cerveny, Arizona State University, one of the co-authors of the BAMS article published on-line today, speaking in this video available on Vimeo.

In Case You Didn't Notice, July Was REALLY Hot

August 12, 2012

This past July was the hottest month on record in U.S. history, according to NOAA’s National Climatic Data Center. The average temperature throughout the contiguous 48 states was 77.6°F, surpassing the previous mark of 77.4°F set in 1936. The first seven months of 2012 were also the hottest on record in the United States, as was the 12-month period of August 2011-July 2012. (Records go back to 1895.)
Interestingly, only one state–Virginia–experienced its hottest July on record, which goes to show how widespread the heat wave was across the country. Thirty-two states had one of their top-10 hottest Julys of all time this year, with seven states recording their second-hottest ever. July temperatures were 3.3°F warmer than the U.S. twentieth-century average for the month, with particularly intense heat in the Plains, the Midwest, and along the Eastern Seaboard.
The five hottest individual months in U.S. history have all been Julys: 2012, 1936, 2006, 2011, and 1934.
In addition to the historic heat, the U.S. Climate Extremes Index, which NOAA uses to calculate temperature anomalies, severe drought, downpours, tropical storms, and hurricanes, was a record-high 37% in July; the previous maximum occurred last July. And the index for the first seven months of the year was 46%, breaking a 78-year-old record. The average index is 20%.
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Mt. Washington's World Record Wind Toppled

January 26, 2010

It stood for 62 years and helped earn New Hampshire’s 6,288-foot Mt. Washington the distinction of having the World’s Worst Weather. Yet, more than a decade ago, a little known tropical cyclone in the South Indian Ocean blew away Mt. Washington’s famous gust of 234 mph — the previous fastest wind ever measured on Earth outside of a tornado. According to the World Meteorological Organization (WMO), the record now belongs to Barrow Island, Australia, a spot of land 31 miles off that continent’s northwest coast that was blasted by Tropical Cyclone Olivia on April 10, 1996. Olivia delivered a record gust of 253 mph (408 kph).

Tropical Cyclone Olivia intensifies as it bears down on northwest Australia in April 1996. (Satellite image from the Japan Meteorological Agency, courtesy of Australia's Bureau of Meteorology.)

A panel of scientists charged with determining global weather and climate extremes as part of the WMO’s Commission for Climatology (CCl) recently reviewed numerous exceptional wind gusts recorded on Barrow Island during Olivia. They concluded that five peak gusts, ranging from 186 mph to the peak of 253 mph were indeed accurate. The other gusts measured 229 mph, 233 mph, and 215 mph, lending credibility to the record wind. The scientists concluded that a mesovortex in Olivia’s well-defined eyewall was likely the cause of the extreme winds.
But the record wind went unnoticed for a decade before the panel happened upon the observations from Barrow Island. Already stunned by losing the record wind gust distinction, Mt. Washington Observatory Executive Director Scot Henley told the Associated Press he was shocked the record remained hidden so long.
“Somehow it fell through the cracks and the Australians didn’t think it was a big deal,” he stated. “We hear that, and it kinds of blows our minds.”
Well, it might not have been quite as simple as that, as Jeff Masters of Weather Underground reports in his blog. He writes that Australia’s Bureau of Meteorology (BOM) was notified about the gusts, but considered them suspect since they were extraordinarily high for a 145 mph tropical cyclone, and because the accuracy of the equipment used to measure the gusts was unknown. Even after a paper on the extreme wind was written in 1999, the data remained in wait another 10 years until someone with the BOM resurrected it and brought it to the attention of the CCl. Read more about why it took 14 years for the record wind to be recognized.
The CCl panel determined the instrument that measured the record wind was a “heavy duty three-cup Synchrotac anemometer,” its report states. It was located near the center of Barrow Island and positioned 33 feet (10 m) above ground level and 210 feet (64 m) above sea level in relatively open terrain. Guy wires stabilized the cyclone-rated Hills telescoping mounting tower, and the anemometer was found to be regularly inspected and calibrated.
According to Wikipedia, Barrow Island, which is slightly larger than Brooklyn, New York, was uninhabited until the 20th century. Oil was discovered there in commercial quantities in 1964 and subsequent drilling resulted in Barrow Island becoming Australia’s leading producer of petroleum and natural gas. The anemometer that measured the world’s new fastest surface wind is owned and maintained by Chevron.
A report of the record wind is posted on the Arizona State University Web site. It contains additional details of Olivia’s record event and names the report’s panel of experts within CCl.

Harsh Cold Wave Slowly Retreating

January 11, 2010

Well, the big winter cold snap that has been gripping much of the United States since December is nearing its end. Temperatures in most places from the Plains to the East Coast have started to rebound and no renewed surges of Arctic air are on the horizon after a final weak front moves through the East Tuesday. But the damage is done in places from the Dakotas and Montana to Florida: burst pipes, roads that drifted shut, and wind chills lower than -50 in the North, and car crashes on icy roads, power outages, and record cold that has chilled the South.

Last Thursday, the wind chill in Bowbells, North Dakota hit 52° F below zero. That degree of cold “freezes your nostrils, your eyes water, and your chest burns from breathing — and that’s just going from the house to your vehicle,” said Jane Tetrault of Burke County. Her vehicle started, but the tires were frozen. “It was bump, bump, bump all the way to work with the flat spots on my tires,” she said, adding, “It was a pretty rough ride.”
Snow and icy winds whipped southward from the Midwest into Tennessee, Georgia, and Alabama late in the week, making travel a disaster in Memphis and Atlanta. Video of cars sliding off roads or into each other played every half hour on The Weather Channel into the weekend.
Even the Sunshine State had wintry precipitation with this unusual cold surge—something not seen in more than 30 years. The weekend into Monday was especially brutal by Florida standards. With temperatures in the 30s and low 40s, light rain enveloped the peninsula Friday night through Saturday. Sleet fell in spots from Jacksonville and Ocala southward through Orlando, Tampa, and Melbourne into Palm Beach. A few wet snowflakes mixed in here and there with snow reported by trained spotters as far south as Kendall, a southern suburb of Miami. In some places north of Tampa, enough sleet accumulated on cars and outdoor furniture to build little “sleet” men, complete with tiny hats and tree-twig arms, their photos rivaling those taken of snowmen built in Tampa on January 17, 1977. (View a photo of Florida sleet from a snow and ice slideshow on Tampa’s baynews9.com.)
Clearing led to record morning lows both Sunday and Monday that threatened harm to Florida’s $3 billion citrus industry. Temperatures bottomed out at 25° in Tampa, 29° in Orlando, and 31° in Ft. Myers. On Sunday, the temperature in Miami tied the 1970 record for the date with 35°, and a 36° low Monday morning broke the previous record for the date of 37° set in 1927. Despite the records, it has been the duration of the cold, especially in the South, that makes this cold snap memorable. Morning after morning since the previous weekend, photos of Florida strawberries encased in ice showed up on newscasts. Such protective measures against the frigid temperatures are expected for several more mornings in central Florida, even as the chill slowly moderates.
The cold was even long-lasting in the Midwest and Plains, as noted in TWC meteorologist Tim Ballisty’s article “It’s Cold But So What?” last week. He points out that Chicago hasn’t been above freezing since Christmas Day, at the time 11 straight days and counting. Cleveland had 10 consecutive days of snow, and that count continued right into the weekend.
Unlike the extensive heat waves of recent summers, this long and harsh cold snap resulted in relatively few new temperature records. At the Annual Meeting in Atlanta, Gerry Meehl of NCAR will explore the rising ratio of record high temperatures to record low temperatures, which is expected to markedly increase by the middle of the century with current projections of climate warming.

An Inconvenient Snow

December 6, 2009

Next week on Friday (11 December), 7 p.m. Central Time, the University of Texas-Austin will present a live Webcast of “Global Warming—Lone Star Impacts,” a lecture by Gerald North ofTexas A&M.
It should be an interesting occasion, not just because North is an experienced scientist and climate change is a hot topic, but also because of the timing. The lecture was supposed to be delivered this past Friday, yet an unseasonable snowstorm got in the way. Ah, the inconvenient truths of climate: day-to-day weather can be uncooperative.
As SciGuy blogger Eric Berger for the Houston Chronicle observes: “What does snow falling in Houston have to do with global warming? Nothing. Nada. Zip.” For emphasis, Berger also posted a great photo from a record Houston snowfall in 1895, not to be missed by history buffs.
Friday’s storm across the Gulf Coast delivered the earliest snow on record for Houston–but just five years ago the region had a Christmas snowfall with depths of up to 13 inches.
Fortunately this week’s snow was lighter, but if you’re interested in a detailed perspective about how Gulf coast snow mechanisms can be surprisingly prolific and yet quite “ordinary”, check out the poster by Ronald Morales presented at the 2007 AMS Conference on Mesoscale Processes. It’s full of vivid satellite and radar imagery from the 2004 storm, as well as this overview of the snowfall.

24-25 December 2004 Texas Gulf Coast snowfall analysis, from Morales 2007.