BAMS Paper

Observations without Fear: NOAA’s Drones for Hurricane Hunting

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Nowhere is it more dangerous to fly in a hurricane than right near the roiling surface of the ocean. These days, hurricane hunting aircraft wisely steer clear of this boundary layer, but as a result observations at the bottom of the atmosphere where we experience storms are scarce. Enter the one kind of plane that’s fearless about filling this observation gap: the drone.

NOAA’s hurricane hunter aircraft in recent storms has been experimenting with launching small unmanned aircraft systems (sUAS) into raging storms–and these devices show promise for informing advisories as well as improving numerical modeling.

Lead author Joe Cione of NOAA's hurricane research division holds a Coyote sUAS. The drones are being launched into hurricanes from the P-3 hurricane hunter aircraft in the background.
Lead author of a new paper in BAMS, Joe Cione of NOAA’s Hurricane Research Division, holds a Coyote sUAS. The drones are being launched into hurricanes from the WP-3D Orion hurricane hunter aircraft in the background.

 

The observations were made by a new type of sUAS, described in a recently published paper in BAMS, called the Coyote that flew below 1 km in hurricanes. Sampling winds, temperature, and humidity in this so-called planetary boundary layer (PBL), the expendable Coyotes flew as low as 136 m in wind speeds as high as 87 m s-1 (196 mph) and for as long as 40 minutes before crashing (as intended) into the ocean.

In the BAMS article, Joe Cione at al. describe the value of and uses for the low-level hurricane observations:

Such high-resolution measurements of winds and thermodynamic properties in strong hurricanes are rare below 2-km altitude and can provide insight into processes that influence hurricane intensity and intensity change. For example, these observations—collected in real time—can be used to quantify air-sea fluxes of latent and sensible heat, and momentum, which have uncertain values but are a key to hurricane maximum intensity and intensification rate.

Highs-lows

Coyote was first deployed successfully in Hurricane Edouard (2014) from NOAA’s WP-3 Orion hurricane hunter aircraft. Recent Coyote sUAS deployments in Hurricanes Maria (2017) and Michael (2018) include the first direct measurements of turbulence properties at low levels (below 150 m) in a hurricane eyewall. In some instances the data, relayed in near real-time, were noted in National Hurricane Center advisories.

Turbulence processes in the PBL are also important for hurricane structure and intensification. Data collected by the Coyote can be used to evaluate hurricane forecasting tools, such as NOAA’s Hurricane Weather Research and Forecasting (HWRF) system. sUAS platforms offer a unique opportunity to collect additional measurements within hurricanes that are needed to improve physical PBL parameterization.

Coyote launch sequence: (a) Release in a sonobuoy canister from a NOAA P-3. (b) A parachute slows descent. (c) The canister falls away and the Coyote wings and stabilizers deploy. The main wings and vertical stabilizers have no control surfaces; rather, elevons (i.e., combined elevator and aileron) are on the rear wings, controlled by the GPS-guided Piccolo autopilot system with internal accelerometers and gyros. (d) After the Coyote is in an operational configuration, the parachute releases. (e) The Coyote levels out after starting the electric pusher motor, which leaves minimally disturbed air for sampling at the nose. The cruising airspeed is 28 m s-1. (f) The Coyote attains level flight and begins operations. When deployed, the Coyote’s wingspan is 1.5 m and its length is 0.9 m. The 6-kg sUAS can carry up to 1.8 kg. Images were captured from a video courtesy of Raytheon Corporation.
Coyote launch sequence: (a) Release in a sonobuoy canister from a NOAA P-3. (b) A parachute slows descent. (c) The canister falls away and the Coyote wings and stabilizers deploy. The main wings and vertical stabilizers have no control surfaces; rather, elevons (i.e., combined elevator and aileron) are on the rear wings, controlled by the GPS-guided Piccolo autopilot system with internal accelerometers and gyros. (d) After the Coyote is in an operational configuration, the parachute releases. (e) The Coyote levels out after starting the electric pusher motor, which leaves minimally disturbed air for sampling at the nose. The cruising airspeed is 28 m s-1. (f) The Coyote attains level flight and begins operations. When deployed, the Coyote’s wingspan is 1.5 m and its length is 0.9 m. The 6-kg sUAS can carry up to 1.8 kg.
Images were captured from a video courtesy of Raytheon Corporation.

 

The authors write that during some flights instrument challenges occurred. For example:

thermodynamic data were unusable for roughly half of the missions. Because the aircraft are not recovered following each flight, the causes of these issues are unknown. New, improved instrument packages will include a multi-hole turbulence probe, improved thermodynamic and infrared sensors, and a laser or radar altimeter system to provide information on ocean waves and to more accurately measure the aircraft altitude.

Future uses of the sUAS could include targeting hurricane regions for observations where direct measurements are rare and models produce large uncertainty. Meanwhile, the article concludes, efforts are underway to increase sUAS payload capacity, battery life, and transmission range so that the NOAA P-3 need not loiter nearby.

The Perils of Rime Mushrooms

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Mountain climber Dmitry Golovchenko captured tremendous video of the February 27 collapse of a “rime mushroom” atop Patagonia’s Cerro Torre. These are bulbs of massively accumulated rime—built up in the freezing of moisture in winds pounding at the peak over time. The mushrooms increase the difficulty of this infamous climb of more than 3,000 meters, but never more so than when their precariousness increases in summer—just when conditions might otherwise seem calm enough for climbing. Here is the video via an Instagram from patagoniavertical, the site of Rolando Garibotti, who co-authored a BAMS article on these infamous mushroom features:

 


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CERRO TORRE – Escarcha escrachadora / Crushing rime. . Esto sucedió el 27 de febrero a las 11:25am. Si hubiese habido cordadas en la Via dei Ragni, las consecuencias hubiesen sido gravísimas. El video y las fotos las tomó @golovchenko.dmitry, el conocido alpinista ruso. . Los factores que influencian la rotura de los hongos de escarcha son desconocidos, pero parece probable que se comporten como un manto de nieve, y que la combinación de gravedad, calor y humedad, puedan llevar a este tipo de ocurrencias. Esta temporada hay mucha escarcha, que con el calor veraniego, y lluvia en altura, pueden haber sido el disparador. No sabiendo cuales son los factores que afectan las capas profundas de los hongos, es difícil hipotetizar un protocolo, pero parece razonable evitar periodos con la isoterma zero por encima del pie de vía (2300m), o periodos posteriores a lluvia en altura. . Del link en nuestro perfil se puede bajar un artículo sobre la formación de la escarcha en la montaña, publicado en el boletín del American Meteorological Society, escrito por Dave Whiteman, con ayuda de quien escribe. . . . This happened on February 27th, at 11:25am. Had there been any parties on the Ragni Route, the consequences would have been serious. The video and images were shot by @golovchenko.dmitry, the well-known Russian alpinist. . The factors that influence rime mushrooms to result in break off are not known, but it seems plausible that they behave in part like a snowpack, and that the combination of gravity, heat and moisture can result in events like this one. This summer there is ample rime, which combined with heat, and rain at higher altitudes could have lead to this. Not knowing what factors affect the deeper layers of rime mushrooms, it is difficult to hypothesize a protocol to minimize exposure, but avoiding periods with the freezing-line above the base of the route (2300m) would be a wise first step. . Link in our profile to an article about rime formation in the mountains published in the Bulletin of the American Meteorological Society, written by Dave Whiteman, with help from yours truly. . #rime #cerrotorre #patagonia #chalten

A post shared by Patagonia Vertical – guidebook (@patagoniavertical) on


In their BAMS article, David Whiteman and Garibotti introduced rime mushrooms, well known to alpinists, but not previously to many meteorologists:

Rime mushrooms, commonly called ice mushrooms, build up on the upwind side of mountain summits and ridges and on windward rock faces. These large, persistent, rounded or bulbous accretions of hard rime range from pronounced mounds to towering projections with overhanging sides….[They] form when clouds and strong winds engulf the terrain. Supercooled cloud droplets are blown onto subfreezing surfaces and freeze rapidly, making an opaque “hard” rime with air trapped between granular deposits. The mushrooms are most frequent and best developed on isolated summits and exposed ridges in stormy coastal areas.

They showed the distribution of these mountain features around the world.

mushroomsThanks to Dr. Whiteman’s Univ. of Utah colleague Jim Steenburgh for bringing the video to our attention via social media. Jim’s own newly published BAMS article features the often well-rimed sea-effect snows of Japan and their similarities to lake-effect snows in the United States. The article explains how the heavy snowy accumulations of crunchy graupel (loose, rimed, large icy particles) in lowlands of the Japanese coast can be quite avalanche prone, too.

Scratch that Cat: Revising the Saffir-Simpson Scale

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British adult orange cat and little kittenIn recent years minimum sea level pressure (MSLP) measured in a hurricane’s eye has become “a much better predictor of hurricane damage” than the maximum sustained wind speed (Vmax) upon which the revered Saffir-Simpson hurricane wind scale is based.

New research by seasonal hurricane forecaster Phil Klotzbach et al. finds that MSLP is also more accurately measurable than Vmax, “making it an ideal quantity for evaluating a hurricane’s potential damage.”

Given that the Saffir-Simpson scale was developed to characterize the risk of hurricanes to the public, we propose classifying hurricanes in the future using MSLP as opposed to Vmax. While no scale will ever perfectly account for the totality of storm risk to life and property (e.g., inland flooding), any improvements to better explain and warn the potential hurricane impacts to an increasingly vulnerable coastal and inland population is, in our view, a worthwhile endeavor.

Klotzbach et al. argue that Vmax is “nearly impossible to measure directly” as the maximum wind mentioned in advisories issued by the National Hurricane Center is the highest 1 minute sustained surface wind occurring “in an unobstructed exposure; (i.e., not blocked by buildings or trees),” which is essentially at sea, not over land. Even with today’s technology, the sparsely observed maximum wind speed is often just an estimate–even land observations are limited by anemometer failure at speeds over 50 kt.

In contrast, MSLP is easy to locate at the storm’s center and is routinely measured by the hurricane hunters in every aircraft reconnaissance mission.

Earlier versions of the Saffir-Simpson scale, created in the early 1970s by engineer Herb Saffir and meteorologist and Hurricane Center director Bob Simpson, incorporated MSLP as a proxy for wind, and they also included ranges by category of storm surge height. But these led to public confusion when actual storm surges and low pressure readings didn’t match up with the categorized winds, and they were removed in 2012.

 Vmax …provides less information on the overall storm risk to life and property than does MSLP. MSLP, on the other hand, is a useful metric in that it is strongly correlated with both Vmax and storm size, which is directly related to storm surge as well as a larger wind and rain footprint. The risk to human life is also more directly correlated to MSLP than to Vmax, given the better relationship of MSLP with storm size. MSLP was a more skillful predictor of fatalities caused by CONUS landfalling hurricanes from 1988-2018 than was Vmax. Consequently, we recommend that more emphasis be placed on MSLP when assessing the potential risks from future landfalling hurricanes.

Saffir-Simpson Hurricane Scale with current Vmax criteria, proposed MSLP criteria and original MSLP criteria from Simpson (1974). Also provided in parentheses are the percentage of Atlantic storms from 1979-2018 whose lifetime maximum intensity exceeded the weakest intensity criteria for each category threshold.
Saffir-Simpson Hurricane Scale with current Vmax criteria, proposed MSLP criteria and original MSLP criteria from Simpson (1974). Also provided in parentheses are the percentage of Atlantic storms from 1979-2018 whose lifetime maximum intensity exceeded the weakest intensity criteria for each category threshold.

 

The difference between using MSLP and Vmax when predicting damage potential has become more noticeable in recent years. This is “likely due to larger-sized hurricanes such as Ike (2008) and Sandy (2012) which did much more damage than would be typically associated with hurricanes making landfall at Category 2 and Category 1 intensity, respectively.” Both storms had much larger storm surges than their category rankings suggested, as did Hurricane Katrina, which was Category 3 at landfall based on Vmax, but had a MSLP equivalent to a Category 5. Its storm surge was measured at a record 28 feet and the resulting damage was catastrophic, consistent with a Cat 5 hurricane.

Using MSLP to re-categorize some historic hurricanes at landfall, the study finds the following:

  • Hurricane Katrina (2005) would go from a Cat 3 to Cat 5;
  • Superstorm Sandy, which was post-tropical but considered “just” a Cat 1 when it made landfall in 2012, would rank as a Cat 4.
  • Hurricane Ike (2008) would be elevated from a Cat 2 to a Cat 3.
  • Hurricane Michael (2018) would have been Cat 5 at landfall rather than a high-end Cat 4 stated in advisories.

The new BAMS paper is available as an Early Online Release. It will be adapted for print and published in the February issue.

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

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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.

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.

 
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.

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

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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.

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.

 

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.

What a Launch!…and More GEMS to Follow

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Nothing quite like watching lift-off…here’s the video sequence from Arianespace showing the flight of the rocket carrying South Korea’s GEMS satellite instrument into space earlier this week.

GEMS–the Geostationary Environment Monitoring Spectrometer–is a centerpiece of the Asian contribution to a triad of geostationary satellite missions watching air quality in some of the most pollution-prone urban centers of the world. The other similar missions to be launched are Sentinel-4 over Europe and TEMPO over North America.

GEMScoverage

The image above superimposes the field of view for each of the satellites over an image of nitrogen dioxide concentrations averaged over the 10 years 2005-2014 from the Ozone Mapping Instrument aboard NASA’s Aura satellite. Aura is part of the “afternoon-train” or A-train of international satellites focused on anthropogenic aerosols. But these satellites pass over any given spot on Earth the same time each day.

With GEMS, such information is now going to be 24/7 for Asia. As a geostationary eye on air quality, the new South Korean satellite watches meteorology and atmospheric chemistry continuously. In addition to GEMS, which uses spectrometers to track ozone, nitrogen dioxide, sulfur dioxide, aerosols, ultraviolet index, and other health-related factors in the atmosphere, the satellite includes meteorological and ocean color sensors. This gives a synergy to Earth observing at faster sampling rates and higher resolution over the region, advancing investigations of air pollution for a large portion of the world’s population.

The push for geostationary satellite monitoring of air quality that led to the launch of GEMS has been long in the making. In an article 8 years ago in BAMS, W.A. Lahoz explained that geostationary satellites give

an improved likelihood of cloud-free observations …with continuous observations of a particular location during at least part of the day. This “stare” capability …makes it very effective for the retrieval of the lowermost troposphere information for capturing the diurnal cycle in pollutants and emissions, and the import/export of pollutants or proxies for pollutants.

You can read more about the new capabilities in the BAMS article on GEMS by Jhoon Kim (Yonsei Univ.) and colleagues. The article, appropriately, posted online within an hour of the launch of the satellite.

BAMS cover outline 2This is actually a twin launch: The GEMS article is among the first of the new-look BAMS in AMS Journals Online. You’ll find highly readable typefaces with a simple layout easier for scrolling on screen. You’ll also note that we’re starting to publish articles as soon as they’re ready for launch, rather than waiting for them to collect into issues in print.

Also about to launch into the mail is a whole new approach BAMS is taking to print as well. The magazine is much more dense with important and exciting new information. The printed features (mirrored as well in the digital edition for AMS members) are short, highly accessible versions of the peer-reviewed research articles. We’re expanding our focus on new and important articles to relay the authors’ thoughts—in their own words—about their work and the challenges they’re solving in their next articles as well. This blog and AMS social media will reflect such thought-provoking new BAMS content in all sorts of ways—for reading, listening, and watching.

So GEMS is our partner in launch: a new era of air quality monitoring for Asia is paired with a new era of communications for AMS. As they say in the media..stay tuned, more to follow!