NWS Increases Severe Hail Threshold

If you step outside in a thunderstorm and get bonked on the head with penny size hail, don’t blame your misfortune on a severe storm. On January 5, the National Weather Service changed the criteria for severe thunderstorms by upping the minimum size hail from ¾ to 1 inch—quarter size. The wind threshold—50 knots, or 58 mph—remains the same.

Hail size penny vs. quarter
Comparison of the diameter of a penny to a quarter, and an actual quarter atop hailstones to show relative sizes.

The reason for the change, according to a statement issued by the Fire and Public Weather Services Branch of the NWS, is that research reveals “significant damage” doesn’t occur from hail smaller than an inch. Hailstones the size of quarters or larger are the ones most destructive to cars, homes, buildings, and crops.
Over the years, and particularly in the Plains states, the statement reads, “the frequency of severe thunderstorm warnings issued for penny-size and nickel-size hail might have desensitized the public to take protective action during a severe thunderstorm warning.” Too many warnings for events that were not damaging garnered complaints and made the warnings somewhat meaningless.
Experimental warnings for 1-inch hail in Kansas the last few years expanded in the central and western United States in 2009. Emergency managers and media outlets in the areas that previously made the changes noted that people seem to take warnings for severe hail more seriously now as they carry more weight.
Of course observing hailstones 1 inch or larger and forecasting hail size are two different things. But, just as research has supported increasing the severe hail threshold, scientists are making strides toward more accurately predicting hail size from radar observations of severe thunderstorms. A poster that will be presented by Matthew Kramar of the NWS office in the Washington, D.C. area, et al., on Wednesday afternoon at the Annual Meeting (January 20, 2:30-4:00 PM, Exhibit Hall B2) reveals results of correlating radar hail cores to hail size for the Mid-Atlantic region—a study that piggybacks on successes in establishing operational hail prediction in the Plains states.

Shedding New Light on Night-Shining Clouds

Photo credit: Pekka Parviainen

Scientists have been making new progress in solving the mysteries of noctilucent clouds [also known as Polar Mesospheric Clouds (PMCs)], thanks to NASA’s Aeronomy of Ice in the Mesosphere (AIM) satellite. AIM recently recorded a series of complete polar seasons of these clouds, which form in the mesosphere and are only visible on Earth when illuminated by sunlight from below the horizon. The satellite’s findings “have altered our previous understanding of why PMCs form and vary,” according AIM principal investigator James Russell III of Hampton University in Virginia.

AIM observed the PMCs in each hemisphere’s summer season at all longitudes and over a latitude range of 60°–85°; this video shows the clouds in the northern skies from late May to mid-August of 2009.

AIM’s data revealed that the clouds form and dissipate at very high speeds and may be affected by high-altitude weather systems.
“The cloud season abruptly turns on and off going from no clouds to near complete coverage in a matter of days, with the reverse pattern occurring at the season end,” Russell said.  Russell likens this seasonal on-off switch to a  “geophysical light bulb” in the presentation he will make about the new findings at the Space Weather Symposium during the AMS Annual Meeting in Atlanta (Tuesday, 8:30 AM, B303).
Noctilucent clouds are made of ice crystals that form when water vapor condenses onto dust particles at extremely cold temperatures (around -210° to -235°F). Scientists are using the new imagery as well as computer models to figure out more about what conditions trigger the clouds. So far, the new data indicate that high altitude temperature determines the onset, variability, and end of the cloud season. Satellite imagery also seems to show relationships to planetary waves as well as smaller scale gravity waves in the atmosphere.

Charting the Course of Arctic Warmth…and Oceanography

While many parts of the country have recently been experiencing conditions that residents might call “Arctic,” the Arctic region itself has been warming since at least the early 1990s, reaching warmth unprecedented in the last century. The consequences for global climate are potentially critical―particularly if fresh water from melting ice and increased atmospheric precipitation in the Arctic slow the overturning circulation of the North Atlantic. With Arctic sea ice melting dramatically in recent years, scientists  are trying to understand the influence of the warmer water that flows into the Arctic from the North Atlantic.
At the National Oceanography Centre (NOCS) in Southampton, United Kingdom, scientists using high-resolution computer models found that from 1989 to 2009, about 50% of the salty North Atlantic water entering the Arctic Ocean came through Fram Strait, a deep channel between Greenland and the Norwegian island of Spitsbergen that connects the Nordic Seas to the Arctic Ocean. The Barents Sea contributes about as much Atlantic water to the Arctic, but the Fram Strait water carried most of the heat that has been a primary cause of Arctic ice melting.
An example of the modeling in this study, published in the January 2010 issue of Journal of Marine Systems, can be seen in the image below, which shows a computer simulation of ocean temperatures at a depth of 100 meters and sea ice thickness in September 2006. The pathways of warm saline water toward the Arctic have previously been poorly understood, but here the 8-km resolution defines three distinct pathways for this water to move under the more pure Arctic water, thus pumping heat northward between 50 and 170 meters below the surface.
“Computers are now powerful enough to run multidecadal global simulations at high resolution,” said NOCS scientist Yevgeny Aksenov. “This helps to understand how the ocean is changing and to plan observational programs so as to make measurements at sea more efficient.”
Ocean-climate interactions are a primary focus of the ocean science research priorities recommended by the U.S. National Science and Technology Council’s Joint Subcommittee on Ocean Science and Technology (JSOST) in their 2007 report, “Charting the Course for Ocean Science in the United States for the Next Decade: An Ocean Research Priorities Plan and Implementation Strategy.” As our understanding continues to evolve regarding the ocean and its influence on the Earth system, the priorities outlined in this report have also evolved. A town hall meeting on “Refreshing Our Ocean Research Priorities” (Monday, 12:15–1:15 p.m., B212) at the upcoming AMS Annual Meeting will explore some of these developments and give participants a forum to discuss topics of interest with the chairs of JSOST.


This Christmas, the Gift of Salience

Midwesterners take pride in their ability to handle blizzards and ice that make walking and driving miserable and harrowing, not to mention downright dangerous. Even so, yesterday, people generally stayed off the roads, canceling long awaited Christmas Eve events. Those who ventured out often ran into trouble, according to news reports:

Betsy Graupe lost count of the number of vehicles she saw in the ditch while driving from Chicago to see her family in Minneapolis, a journey of some 350 miles (570 kilometers).
“It was very, very bad out,” said Graupe, who ended up pulling off the highway and spending Wednesday night in a hotel.
“It was poor visibility, and icy and the road was rutted… it was quite an adventure.”

Were the people who spun out beside the road lacking experience with winter? Were they unaware of the situation? Were they making a bad calculation of the risks, or just unlucky?

OK Mesonet peak gusts chart--a bad day for driving.
OK Mesonet peak gusts chart–a bad day for driving on ice.

We’ll probably never know unless some enterprising social scientist follows up. Scientists did follow up on one recent storm—the miserable icing in January 2007 that turned roads into skating rinks in the nation’s midsection during the AMS Annual Meeting in San Antonio.
If you remember, hundreds of attendees never made it to that meeting due to airport and road closures. Kim Klockow and Randy Peppler of the University of Oklahoma polled their peers about travel to that meeting. Their findings, presented at the 2008 AMS Annual Meeting (and published this summer in the NCAR newsletter, Weather and Society Watch), show that very few of their cohorts chose to stay home. Some avoided hopeless airline delays by choosing to drive despite road conditions. Some were anxious about the trip from Norman to San Antonio, some were not. Many left early, others left late, but they found ways to deal with the weather, minimizing but not eliminating travel risks. Access to information gave them enough confidence to brave the situation and make relatively bold choices.
Of course, these were weather savvy travelers—“weather salient,” in the psychological lexicon (see this BAMS paper by Alan E. Stewart for more on this). One wonders how seasoned natives navigated similar choices yesterday and today.
In Oklahoma, at least, the governor didn’t wait long to see what people would do. He closed interstates and state highways:

“I am urging all Oklahomans to take winter storm precautions and stay off the roads unless travel is absolutely necessary,” Gov. Brad Henry said earlier in the day after declaring a state of emergency. “This is a very serious winter storm, and we want Oklahomans to stay safe.”

Perhaps the governor didn’t read Klockow and Peppler’s study. Or maybe he did, and realized that the bar for weather salience this Christmas was a little too high.

Author, Sailor, Scientist, AMS President-to-Be

“I’ve been trying to keep this to the scientific side tonight, Amy,” Mike said. “But you can tell this has been more of a spiritual experience, for me.”–from Seraphim Sky, by Jonathan Malay (iUniverse, 2003)
It’s not every day that we get to quote from a novel, but then, with the

Jon Malay
Jon Malay

results from this fall’s AMS elections announced today, we’re understandably going to stray from the scientific side and get into the spirit of the moment.
Seraphim Sky is not just any book, but a novel by our newly announced AMS President-Elect Jon Malay, a one-time research oceanographer, astronaut candidate, and meteorological officer for the Navy, more recently an entrepreneur, government manager, and long-time proponent and practitioner of space-based observational programs, now at Lockheed-Martin.
Undoubtedly, we’ll have more in this blog later about his ideas for 2011, when he takes over leadership of our Society from incoming president, Margaret LeMone. Already in BAMS he’s emphasized the commitment the United States must maintain in geophysical observations and services, as well as the breadth of AMS and its impact:

We in the AMS have a collective responsibility to do whatever we can to ensure that policy decisions are based on sound science and reasoned judgment. The economic consequences of actions taken by the U.S. government (and, for that matter, governments around the world) will have enormous consequences—either for good or for very, very, bad. What stands between these two extremes is the effectiveness of the educated and technically correct voice of the AMS community.

Congratulations to Jon and to the four newly-elected AMS Councilors, Ken Carey, John Schaake, Rick Spinrad, and Ahsha Tribble. Now back to the (mostly) scientific side.

Have Your Cake and Communicate Better, Too

UPDATE, 1/16/10: Due to a last-minute change, David Schultz will not be able to attend the Annual Meeting and participate in the events discussed in this post. The AMS book launch party will be held as scheduled on Monday.
In the modern world of text messages, Tweets, and, yes, blogs, it’s easy for the craft of writing to be overlooked for the sake of immediacy, shock value, or just plain laziness. Indeed, time for eloquence increasingly seems like a luxury as technology makes communication more convenient and commonplace.
Thankfully, there are still defenders of the art; one of them, the University of Helsinki’s David Schultz, chief editor of Monthly Weather Review, has recently written a book

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Exposing Air Travel Radiation Concerns

The Space Weather Symposium at the AMS Annual Meeting once again will discuss the radiation exposure that airplane passengers get from outer space. This year the presentations in this area of space weather cover future suborbital flights as well (Tuesday, 1:30 p.m., B315).
A typical flight exposes airline passengers to minimal levels of extraterrestrial radiation; such occasional exposures are not considered harmful. The radiation concern is usually reserved for high-flying pilots who spend a lot of time in the air, especially on long polar routes, or for flights during a solar storm.
But one source of gamma rays and typical x-rays might indeed be quite problematic, though very rare, for ordinary air travelers. The radiation is not from outer space, but instead from Earth.
A research group led by Joe Dwyer, professor of physics and space sciences at Florida Institute of Technology, shows that terrestrial gamma-ray flashes (TGFs) produced by thunderclouds could expose nearby airplanes to a radiation dose of 10 rem. That’s about 400 chest X-rays, three CAT scans, or 7,500 hours of normal flight time, what the researchers describe as

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On Mars, the Dust Devil's in the Details

Discoveries about the atmospheres of other planets have been closely linked to insights about our own. When a young Carl Sagan confirmed the effect of high CO2 concentrations—a runaway greenhouse effect—on Venus in 1960, for instance, he helped intensify interest in potential anthropogenic warming on Earth.
Conversely, climate models, and now mesoscale weather models such as the WRF, developed for Earthly forecasting, are applied to modeling conditions elsewhere.  At the AMS’s first Symposium on Planetary Atmospheres in Atlanta, Scot Rafkin of the Southwest Research Institute will present, “Application of Mesoscale Atmospheric Models to Mars Missions” (Thursday, 11 a.m., B211). He’ll discuss how terrestrial weather models helped engineers anticipate landing conditions on the Red Planet as well as

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When Wars Are Hot, Crops Are Not

As if it weren’t enough to keep track of arms trafficking, political mischief, and ethnic tensions around the world, now international aid agencies and national security watchdogs are told they have to watch temperatures, too. An article last week in the Proceedings of the National Academy of Sciences links warm years in West Africa with major civil conflicts (defined to include battle deaths of at least 1,000).
The authors, led by Marshall Burke, an economist at the University of California, Berkeley,  show that temperature has a stronger relationship to internal strife than typical indicators like per capita income or type of political regime. They predict more conflict in the region as the world warms.
Other studies, noting the centrality of rain-fed agriculture in West Africa, have identified precipitation as a regional security indicator. However, the new study shows that temperature may be an even better

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Magic Numbers

The tangibility of numbers makes them an ideal tool for marketing. Telling drivers to slow down isn’t nearly as vivid as telling them that “55 saves lives,” (though we later learned that 65 m.p.h. apparently saves lives just as well). Football fans have probably seen ads for the NFL’s “Play 60” campaign that encourages children to get a daily hour of exercise, and there is a similar program for K-5 teachers and their students called “Take 10.” Numerous other examples abound.
Not surprisingly, climate change activists have discovered the allure of numbers, too. A recent worldwide demonstration highlighted

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