Past studies have identified weekly cycles in a variety of weather phenomena, including rainfall, lightning, and storm heights. It’s called the weekend effect, and it’s thought to be be linked to the industrial air pollution associated with the five-day work week, though there has been a lot of discussion about the mechanics of that connection. These aren’t global analyses—many of these studies have focused on the southeastern United States during the summer months, though similar trends have been identified in other regions, as well. There’s a good reason for this. It seems that warm, moist conditions are a pre-requisite for the effect to manifest.

A new study published recently in the Journal of Geophysical Research adds to the list, finding strong evidence for weekly cycles in tornadoes and hail storms, and discusses the most likely mechanism behind them.

The researchers looked at the eastern half of the US (east of 100° W longitude) during the months of June to August. There’s a pretty sharp divide in average dewpoint temperature right along that longitude in the summer, with much higher dewpoints across most of the eastern United States. Data on the weekly pattern of atmospheric particulate matter (or aerosols) comes from EPA air quality monitoring. Summer aerosol concentrations seem to peak on Tuesdays (about 4-8 percent above the weekly average, depending on the particle size), and are lowest over the weekend (4-10 percent below average).

The group did some heavy-duty statistics to ensure a robust analysis, adjusting for things like long-term trends and seasonal patterns. In order to avoid the reporting bias that comes with improvements in weather-observing technology, the tornado and hail storm data only go back to 1995. In the end, they found a strong correlation between aerosol concentrations and the number of tornadoes and hail storms. The number of tornadoes was about 20 percent above average mid-week, and nearly 20 percent below average on the weekend. The hail storm pattern was nearly identical.

They repeated the analysis separately for each month and region of the eastern US to show that correlation is indeed strongest over the summer months in the southeast, and that no other significant correlation shows up anywhere. They also confirm that there is little difference in the correlation from year to year, and that no significant correlation exists for the western United States.

Aerosols and hail

So what is behind this apparent linkage between air pollution and violent weather events? Unlike the fabled inverse relationship between pirate population and global warming, there’s a good physical basis for the connection: it comes down to heat transport.

Aerosol particles are perfect condensation nuclei. More particles means more cloud droplets, but they’re competing for a limited pool of water vapor. Consequently, more cloud droplets also means smaller cloud droplets. The smaller the droplets, the less rain develops at low altitudes as warm air along a front rises and cools. Instead, the moisture is carried higher into the cloud before condensing.

Water vapor condensing into a liquid releases a lot of energy to the surrounding environment. By causing this energy release to occur higher in the cloud, aerosols strengthen the upward transport of heat that drives storm clouds—they push storm clouds closer to their maximum potential for severity.

Aerosols can stimulate hail formation by carrying cloud droplets above the freezing line. (Freezing a liquid, of course, releases even more energy.) Strong updrafts and plentiful hail stones are a potent mix for lightning. Those updrafts can also juggle hail back up above the freezing line repeatedly, building larger and larger hail stones. Even if the cloud is not cold enough or vigorous enough to produce hail, some cloud droplets will form small ice crystals, which are the very best seeds for raindrops. Paradoxically, by starting out with smaller cloud droplets (that reach greater heights) we end up with larger raindrops.

Giving tornadoes a push

All this has been indicated by extensive modeling as well as observations of weather systems affected by volcanic aerosols, but tornadoes are a bit different. Tornadoes require supercell-like conditions, where the storm cloud tilts like the Tower of Pisa, allowing cooler downdrafts to sink without interfering with rising warm air. Larger pools of cool air can bump into the rising column of warm air, disrupting the supercell state.

It should be clear that storm clouds are wild places for H2O, with freezing, melting, and evaporation accompanying large gusts of air that shift them from one place to another. As rain falls through the lower portion of the cloud, some of it evaporates. Since evaporation uses energy, this acts to cool that air—the mirror opposite of the effect of condensing cloud droplets at higher altitudes.

This evaporative cooling feeds the pool of cool air at the base of the cloud. Larger rain drops (aerosols help create these, too) provide less evaporative cooling than smaller rain drops. I’m guessing that’s essentially a surface area relationship—for the same amount of water falling as rain, smaller drops make for a much larger total surface area. Several modeling studies have shown that, for a storm cloud with the potential for producing tornadoes, simply increasing the rain drop size can push it over the edge.

Altogether, there seems to be a solid basis to conclude that anthropogenic aerosol emissions modulate certain types of weather events in areas where the atmospheric conditions are amenable.

You might want to keep an eye on severe weather in the states that recently passed legislation weakening labor unions. If storms have become accustomed to relaxing on the weekend, they may protest.

Journal of Geophysical Research, 2011. DOI: 10.1029/2011JD016214 (About DOIs).

Fuente: Ars Technica

Fragmentos del segundo capítulo de la novena temporada (nº 161, 2011) de Los cazadores de mitos (Mythbusters), en el que se examina la veracidad de la formación del llamado “hielo azul”; es decir, de proyectiles de hielo generados en los fuselajes de los aviones a consecuencia de pérdidas de agua en los lavabos. Estrenado en EE.UU. el 13 de abril de 2011. © Discovery Channel.

Los resultados indican que es perfectamente posible la formación de proyectiles si la pérdida de líquido es gradual (no si es abrupta), pero para ello deben fallar hasta tres distintos mecanismos que en condiciones normales impiden la salida del agua del lavabo al exterior.

El equipo de Alexander Michaud, de la Universidad Estatal de Montana en Bozeman, y Brent Christner, de la Universidad Estatal de Luisiana, analizó los granizos de más de 5 centímetros de diámetro recolectados en el campus universitario tras una tormenta en Junio del 2010. Los granizos fueron separados en 4 capas y se dejaron fundir para analizar el agua de cada capa. El número de bacterias cultivables resultó ser bien alto en los núcleos internos de condensación de los granizos.

Para que se produzca una precipitación, debe haber partículas que actúen como núcleos de condensación, para así permitir la agregación de las moléculas de agua. Hay evidencias cada vez más abundantes de que estos núcleos también pueden ser bacterias u otras partículas biológicas.

El estudio de Michaud sigue una línea de investigación de actividad creciente, centrada en la bioprecipitación, un nuevo concepto según el cual las bacterias pueden iniciar la lluvia y otras formas de precipitación como nevadas y granizadas. La formación de hielo en las nubes, proceso que es necesario para producir los copos de nieve y originar casi todos los casos de lluvia, requiere de estas partículas nucleantes, también llamadas núcleos de condensación o de congelación, que son partículas alrededor de las cuales puedan crecer los cristales de hielo.

Los aerosoles ejercen un importante papel en los procesos que en las nubes llevan a la precipitación. Ese papel deriva de la capacidad de los aerosoles para servir como núcleos para el crecimiento del hielo. A temperaturas más cálidas que 40 grados centígrados bajo cero, la formación de hielo no es espontánea y requiere de núcleos de condensación.

Hay una gama diversa de partículas capaces de servir como núcleos de condensación, pero las más activas que existen de manera natural tienen un origen biológico, y son capaces de catalizar la formación de hielo a temperaturas tan altas como 2 grados centígrados bajo cero.

En estos momentos, el núcleo de condensación mejor estudiado es el patógeno Pseudomonas syringae, una bacteria conocida por las muchas especies vegetales a las que infecta.

Ciertas cepas de P. syringae poseen un gen que codifica una proteína en su membrana externa, permitiendo así que se adhiera a moléculas de agua en una configuración específica, proporcionando una plantilla de condensación muy eficaz que mejora la formación de cristales de hielo.

Todo parece apuntar a que las altas concentraciones de núcleos biológicos de hielo pueden influir en la concentración y tamaño promedio de los cristales de hielo en las nubes, la cantidad de precipitación que llega al suelo, e incluso el grado de aislamiento de la Tierra frente a la radiación solar.

Fuente: Noticias de la Ciencia y la Tecnología

Vídeo de RTVE (La 2 Noticias, 26/01/2010) al cumplirse los diez años de las primeras caídas registradas en España.

Ice meteors have always posed dangers for all flying aircraft, because they are difficult to analyze and because they either melt as they fall from the sky or melt thereafter on reaching the ground. For centuries people from all over the globe have reported large chunks of ice falling from a clear blue sky. The size and weight of the mystery ice has varied greatly, from a chunk described as being as large as an elephant that fell in India in 1800, down to the size of a grapefruit. Although some of the older reports predate the invention of the airplane, whenever a ice-falls occur, in modern times they are attributed to airplanes passing overhead. However, in most instances, ice-falls occur when there is no aircraft visible in the sky at all. Granted there are minority reports of small pieces of ice attributed to ice that builds up on the outer parts of flying aircraft; most ice-falls, however, have origins that go beyond our high flying aircraft, and are as treacherous as they are insidious. In this book, Mr. Tambini offers great details into the history of each reported ice meteor. His inventory is simply staggering.

Format: Kindle Edition
File Size: 1141 KB
Publisher: Branden Books; 1st edition (April 6, 2011)
Sold by: Amazon Digital Services
Language: English
ASIN: B004VNQ43Y

Contents
Introduction
I- Historical Reports of Ice Falls
II- The Mystery of Cold Meteorites
- Hot Meteorites
- Cold Meteorites
III- Theories of Origins
- Upper Atmosphere
- Aircraft
- Space
IV- Analysis of Falls
V- Chemical Composition of Fallen Ice
VI- Conclusion
VII- Recommendations for Future Falls
VIII- Appendix
- Jet Stream Charts
- Ice Fall Spread Sheet
- Photographs
IX- References
X- Index
XI- Recommended Reading

En Amazon: Ice Meteors Unknown Dangers Overhead

WHITTIER – Chicken Little she’s not. But when a huge chunk of ice deplaned from a passing jumbo jet on Sunday, it deposited itself right on the hood of Grace Caiazza’s 1999 Ford Escort in the 8300 block of Vicki Drive.

Now she faces an estimated $2,000 in damages and is looking for the responsible airline.

Caiazza, 71, was home at 5 p.m. that afternoon when she and her daughter, Anna Caiazza, 39, heard what sounded like a car crash in front of their house.

The mother and daughter rushed out to discover large pieces of shattered ice strewn across the front lawn and on top of the Ford Escort.

Grace Caiazza discovered a massive dent on the hood of her vehicle with numerous spider cracks in the windshield.

Pico Rivera Sheriff’s deputies were called to the scene and Caiazza was issued a supplementary loss report.

Next, the disabled great-grandmother, breast cancer survivor and former reverend contacted the Federal Aviation Administration and filed a complaint.

“We have assigned this incident to an inspector from the FAA’s Flight Standards District Office. The inspector will review radar data to see if an aircraft flew over the house around the time the event occurred,” said Ian Gregor, communications manager for the FAA’s Western-Pacific Region.

Caiazza said the FAA was very helpful and concerned with her situation.

This was not the first time she had experienced this rare event. In 1984, she and her

husband were living in the same house when they heard something fall in the back yard.

They saw a large piece of shattered ice spread along their back lawn.

There were no damages and the incident went unreported.

“I thought this was a once-in-a-blue-moon incident,” Caiazza said.

In 2008, a block of ice weighing 80 to 100 pounds fell 9,000 to 10,000 feet smashing the roof of Lupe Murillo’s house on Myron Street in Pico Rivera, snapping rafters in half and making a 3-foot hole in the ceiling.

Whittier lies in an aircraft flight path on approach to Los Angeles International Airport.

“It’s rare, but not unheard of, for ice to fall from a plane. I can recall a couple of cases here in the L.A. area during the past five years. I have never heard of anyone being injured or killed by falling ice,” Gregor said.

“When these events occur, it’s not a matter of a plane lacking de-icing equipment. Ice builds up on an aircraft’s exterior when there is a small leak in a lavatory or galley. As the plane descends, the air warms up and the ice melts and falls,” he said.

Caiazza said she visited Eckles Auto Body in Whittier and said mechanics were astonished at the vehicle’s damage, which they estimated at $2,000.

Her insurance company, MetLife, will pay to fix the vehicle, but Caiazza said she will be stuck with a $500 deductible.

“I’m hoping to find out which airline dropped this piece of ice onto my vehicle and have them refund my monetary losses,” she said.

Caiazza is worried because the 8300 block of Vicki Drive is primarily made up of senior citizens and families.

“Now I’m more concerned with planes flying over my house because this is the second time this has happened in 27 years. I feel uneasy because next time it could seriously injure a human,” she said.

venusse.navid@sgvn.com

562-698-0955, ext. 3000
Read more: Huge ice block falls from the sky onto Whittier woman’s Escort – Whittier Daily News http://www.whittierdailynews.com/news/ci_17141418#ixzz1BgbTCbaZ

Fuente: Whittier Daily News

http://www.meteored.com/ram/11964/11964/

19 de noviembre 2010

Praga – Un trozo de hielo, posiblemente de un avión que pasaba, se estrelló contra el techo de una casa en el este de la República Checa, aterrizando a pocos centímetros de la cama de un niño, dijo un funcionario el viernes.

Nadie resultó herido por la caída del bloque, que se rompió por el impacto y se cree que cayó desde un avión, de acuerdo con Petr Dvorak, un portavoz del Instituto Meteorológico checo.

“No podría provenir de un retrete de avión. Esos está sellados herméticamente”, dijo Dvorak a la agencia de prensa alemana DPA.

Un experto examinó la evidencia, un pedazo que los dueños de la casa habían guardado en un congelador.

http://www.monstersandcritics.com/news/europe/news/article_1600232.php/Narrow-escape-for-Czech-child-as-ice-crashes-through-roof

Fuente: Marcianitos verdes

Bill Snyder of Neffsville holds a piece of ice that sheared through a tree in his yard under cloudless skies on Sunday.

By AD CRABLE, Staff Writer
What was that football-size chunk of ice that dropped out of the clear blue sky Sunday afternoon and tore through Bill Snyder’s pear tree, startling several neighbors?

Frozen lavatory waste leaking from a passing airplane?

A state-record hailstone?

An unusual atmospheric ice formation from conditions caused by global warming?

Something from a flying saucer?

A sign from God?

All of the above have been suggested as answers to the strange worldwide phenomenon of unusually large pieces of ice falling from clear skies.

Snyder, 52, who lives in the Cobblestone Court development near Neffsville, doesn’t know what to think.

Around noon Sunday, the behavioral health therapist was sitting in the family’s kitchen, working on a computer, when he heard a “thump” outside, he said.

His dog stood up. A neighbor’s dog started to bark.

Snyder went to the window and looked outside. There, on the ground about 60 feet away, was a round block of ice next to the pear tree. Leaves were still fluttering downward.

Silly teens must have thrown it into the yard as they drove by, he thought, and he went back to work.

But an hour later, when he went outside to take the dog for a walk, he approached the melting ice.

This time, he noticed that the milky ice had plummeted through the tree like a missile, breaking branches on its way. The largest chunk landed about 10 feet from the base of the tree; a couple of baseball-size pieces lay nearby.

It occurred to him that something strange had happened.

He brought his oldest daughter outside and called over his neighbors. “I wanted to show people so they didn’t think I was crazy,” Snyder said.

He thought he’d preserve the ice in a freezer, even though, by that time, it had been melting for an hour and had been chewed on by the dog.

Still, he estimated its weight at 10 pounds and its diameter at 8 inches — big enough to have hurt someone or damaged nearby homes and cars.

“It scares me a little, because it would easily have come through a roof,” he said.

A mysterious piece of ice falling from the sky is not a new occurrence — not even in Lancaster County.

In November 2002, a Lititz man working in his yard heard a whoosh, looked up and watched in stunned amazement as a 2-foot-long chunk of ice embedded itself in his lawn.

In an incident that made national headlines in October 2008, a 6-pound piece of ice crashed through the roof of a house in York. It shattered into pieces in a woman’s bedroom. A small piece hit the woman, giving her a bump on the forehead.

The first suspects in such cases are usually airplanes.

Lavatory holding tanks sometimes spring leaks, said Jim Peters, a spokesman for the Federal Aviation Administration. The waste seeps along the plane’s fuselage and freezes in the high-altitude air. At some point, pieces might break off and hurtle to earth.

There’s even a phrase coined for such an incident: blue ice, taken from the blue sanitizing chemical used in toilets. However, not all lavatories use the chemical and a leaking water supply could result in ice that is white.

In 2005, however, FAA put out a fact sheet that listed a number of what it called popular “myths” about material attributed to planes.

In the case of blue ice, the fact sheet says: “If any of this blue ice were to fall from an aircraft, it would melt long before it hit the ground, dissipating into minuscule droplets that are nearly invisible.”

Still, Peters contacted Snyder on Tuesday, and the FAA’s Harrisburg office was to call Snyder about examining the ice chunk he saved.

“We’d just like to know about these things,” Peters said.

Could the chunk be hail?

The ice that Snyder found fell from a clear sky, and hailstorms are formed during thunderstorms.

Debris from a meteor or a comet?

Unlikely, said Peter Allen, a visiting assistant professor of astronomy at Franklin & Marshall College.

These space objects could send rocks to Earth as they burn up entering the Earth’s atmosphere, but it would have to be a huge ice object to survive the incredible heat from slamming through Earth’s atmosphere, he said.

Besides, lab tests on some of the large ice balls have shown them to have the makeup of terrestrial hailstones.

“It does not appear to be extraterrestrial,” Allen said.

Eric Horst, Millersville University meteorologist, said, “If it came from a clear sky, it was from an airplane.”

After a 2000 incident in which ice chunks up to 6.6 pounds pelted Spain and Italy on cloudless days for 10 days, a Spanish planetary geologist coined a new phrase and theory. Jesus Martinez-Frias called the phenomenon megacryometeors and said it happens under unusual atmospheric conditions.

A website devoted to ice-falling events is www.megacryometeors.com. Disciples of the megacryometeors theory say that there have been recorded instances of large chunks of ice falling to Earth since the 1800s, well before the creation of the modern airplane.

acrable@lnpnews.com

Fuente: Lancaster online

(CNN) — A South Dakota ranch worker who found a record-setting hailstone says the chunks of ice falling from the sky sounded like “big bricks” being thrown at his house.

Leslie “Les” Scott found the record-breaker, which is almost the size of a soccer ball, last week. It’s been been officially declared the largest ever recorded in the United States, in terms of both diameter and weight. The hailstone measured 8.0 inches in diameter, had a circumference of 18.62 inches, and weighed one pound, 15 ounces, according to the NOAA National Climate Extremes Committee.

Scott says larger hailstones fell around the tiny town of Vivian, South Dakota last week. As severe thunderstorms swept through the area on July 23, Scott says he and a few friends gathered on a hilltop to watch the weather system. He abandoned his position when he saw twisters taking shape in the clouds, but continued watching the storm from his home. He told CNN that he saw hailstones that were as large or larger than the one he actually kept. In fact, Scott said the smallest hailstone he found was about the size of a tennis ball.

Damage around the town is also evidence of the unusual large size of the hailstones that fell, according to Scott. He said there are patches on every home in Vivian. Hailstones punched through many roofs and ended up in attics and even bedrooms.

As for the record-breaking hailstone itself, Scott said it’s unusual shape was what caught his attention initially. He told CNN that, as he watched the storm pass, he saw this particular stone falling from the sky and thought it looked “spidery.” On closer inspection, he found it covered in “fingers” of ice that were four or five inches long

Scott immediately took steps to preserve his unique specimen. But the after-effects of the storm interfered. He put it in the freezer but a power outage lasting 5 or 6 hours caused some melting. Scott said many of the ice “fingers” that first attracted his attention disappeared and the entire hailstone shrank a bit. He believes it was up to eleven inches in diameter when he picked it up the first time.

With the focus in Vivian firmly on cleaning up and repairing homes, Scott seems bemused by the new-found notoriety that has come along with breaking a U.S. record. He wasn’t even the one who notified weather officials about the hailstone. News about its unusual size actually spread by word-of-mouth. Scott says he was surprised when he started getting calls from the media.

It was the weather office in Aberdeen, South Dakota that notified regional weather authorities about the discovery. They asked the National Climate Extremes Committee to evaluate the stone. Official measurements were submitted to the committee of three, who then certified that the hailstone was a record-breaker.

Scott says the weather in his area has been “way out of whack” all summer. It’s been much wetter than normal, and says he can keep track because he has to cut the grass about twice as often as he normally does.

Even Scott’s mother has been talking about how strange the weather has been during the summer of 2010. She’s celebrating her 86th birthday Friday, and Scott says she’s never seen anything like this before in her life.

Scott’s hailstone actually broke two previous records. The previous record in the weight category came from a hailstone that fell in Coffeyville, Kansas. It weighed 1.67 pounds. The previous record-holding hailstone in the diameter category fell in Aurora, Nebraska. It measured 7 inches across. This stone — at 18.75 inches — still holds the hailstone record for circumference.

Fuente: CNN