Warm U.S. West, cold East: 4,000-year pattern; Global warming may bring more curvy jet streams during winter

These maps show winter temperature patterns (top) and winter precipitation patterns (bottom) associated with a curvy jet stream (not shown) that moves north from the Pacific to the Yukon and Alaska, then plunges down over the Canadian plains and into the eastern United States. A University of Utah-led study shows that starting 4,000 years ago, the jet stream tended to become curvier than it was between 8,000 and 4,000 years ago, and suggests global warming will enhance such curviness and thus frigid weather in the eastern states similar to this past winter's. The curvy jet stream brought abnormally warm temperatures (red and orange) to the West and Alaska and an abnormal deep freeze (blue) to the East this past winter, similar to what is shown in the top map, except the upper Midwest was colder than shown. The bottom map of a typical curvy jet stream precipitation pattern shows how that normally brings dry winters to reddish-orange areas and wet winters to blue regions. Precipitation patterns this winter matched the bottom map in many regions, except California was drier than expected and the upper Midwest was wetter than expected.Credit: Zhongfang Liu, Tianjin Normal University, China. Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, and suggests it may worsen as Earth's climate warms.

"If this trend continues, it could contribute to more extreme winter weather events in North America, as experienced this year with warm conditions in California and Alaska and intrusion of cold Arctic air across the eastern USA," says geochemist Gabe Bowen, senior author of the study.

The study was published online April 16 by the journal Nature Communications.

"A sinuous or curvy winter jet stream means unusual warmth in the West, drought conditions in part of the West, and abnormally cold winters in the East and Southeast," adds Bowen, an associate professor of geology and geophysics at the University of Utah. "We saw a good example of extreme wintertime climate that largely fit that pattern this past winter," although in the typical pattern California often is wetter.

It is not new for scientists to forecast that the current warming of Earth's climate due to carbon dioxide, methane and other "greenhouse" gases already has led to increased weather extremes and will continue to do so.

The new study shows the jet stream pattern that brings North American wintertime weather extremes is millennia old -- "a longstanding and persistent pattern of climate variability," Bowen says. Yet it also suggests global warming may enhance the pattern so there will be more frequent or more severe winter weather extremes or both.

"This is one more reason why we may have more winter extremes in North America, as well as something of a model for what those extremes may look like," Bowen says. Human-caused climate change is reducing equator-to-pole temperature differences; the atmosphere is warming more at the poles than at the equator. Based on what happened in past millennia, that could make a curvy jet stream even more frequent and-or intense than it is now, he says.

Bowen and his co-authors analyzed previously published data on oxygen isotope ratios in lake sediment cores and cave deposits from sites in the eastern and western United States and Canada. Those isotopes were deposited in ancient rainfall and incorporated into calcium carbonate. They reveal jet stream directions during the past 8,000 years, a geological time known as middle and late stages of the Holocene Epoch.

Next, the researchers did computer modeling or simulations of jet stream patterns -- both curvy and more direct west to east -- to show how changes in those patterns can explain changes in the isotope ratios left by rainfall in the old lake and cave deposits.

They found that the jet stream pattern -- known technically as the Pacific North American teleconnection -- shifted to a generally more "positive phase" -- meaning a curvy jet stream -- over a 500-year period starting about 4,000 years ago. In addition to this millennial-scale change in jet stream patterns, they also noted a cycle in which increases in the sun's intensity every 200 years make the jet stream flatter.

Bowen conducted the study with Zhongfang Liu of Tianjin Normal University in China, Kei Yoshimura of the University of Tokyo, Nikolaus Buenning of the University of Southern California, Camille Risi of the French National Center for Scientific Research, Jeffrey Welker of the University of Alaska at Anchorage, and Fasong Yuan of Cleveland State University.

The study was funded by the National Science Foundation, National Natural Science Foundation of China, Japan Society for the Promotion of Science and a joint program by the society and Japan's Ministry of Education, Culture, Sports, Science and Technology: the Program for Risk Information on Climate Change.

Sinuous Jet Stream Brings Winter Weather Extremes

The Pacific North American teleconnection, or PNA, "is a pattern of climate variability" with positive and negative phases, Bowen says.

"In periods of positive PNA, the jet stream is very sinuous. As it comes in from Hawaii and the Pacific, it tends to rocket up past British Columbia to the Yukon and Alaska, and then it plunges down over the Canadian plains and into the eastern United States. The main effect in terms of weather is that we tend to have cold winter weather throughout most of the eastern U.S. You have a freight car of arctic air that pushes down there."

Bowen says that when the jet stream is curvy, "the West tends to have mild, relatively warm winters, and Pacific storms tend to occur farther north. So in Northern California, the Pacific Northwest and parts of western interior, it tends to be relatively dry, but tends to be quite wet and unusually warm in northwest Canada and Alaska."

This past winter, there were times of a strongly curving jet stream, and times when the Pacific North American teleconnection was in its negative phase, which means "the jet stream is flat, mostly west-to-east oriented," and sometimes split, Bowen says. In years when the jet stream pattern is more flat than curvy, "we tend to have strong storms in Northern California and Oregon. That moisture makes it into the western interior. The eastern U.S. is not affected by arctic air, so it tends to have milder winter temperatures."

The jet stream pattern -- whether curvy or flat -- has its greatest effects in winter and less impact on summer weather, Bowen says. The curvy pattern is enhanced by another climate phenomenon, the El Nino-Southern Oscillation, which sends a pool of warm water eastward to the eastern Pacific and affects climate worldwide.

Traces of Ancient Rains Reveal Which Way the Wind Blew

Over the millennia, oxygen in ancient rain water was incorporated into calcium carbonate deposited in cave and lake sediments. The ratio of rare, heavy oxygen-18 to the common isotope oxygen-16 in the calcium carbonate tells geochemists whether clouds that carried the rain were moving generally north or south during a given time.

Previous research determined the dates and oxygen isotope ratios for sediments in the new study, allowing Bowen and colleagues to use the ratios to tell if the jet stream was curvy or flat at various times during the past 8,000 years.

Bowen says air flowing over the Pacific picks up water from the ocean. As a curvy jet stream carries clouds north toward Alaska, the air cools and some of the water falls out as rain, with greater proportions of heavier oxygen-18 falling, thus raising the oxygen-18-to-16 ratio in rain and certain sediments in western North America. Then the jet stream curves south over the middle of the continent, and the water vapor, already depleted in oxygen-18, falls in the East as rain with lower oxygen-18-to-16 ratios.

When the jet stream is flat and moving east-to-west, oxygen-18 in rain is still elevated in the West and depleted in the East, but the difference is much less than when the jet stream is curvy.

By examining oxygen isotope ratios in lake and cave sediments in the West and East, Bowen and colleagues showed that a flatter jet stream pattern prevailed from about 8,000 to 4,000 years ago in North America, but then, over only 500 years, the pattern shifted so that curvy jet streams became more frequent or severe or both. The method can't distinguish frequency from severity.

The new study is based mainly on isotope ratios at Buckeye Creek Cave, W. Va.; Lake Grinell, N.J.; Oregon Caves National Monument; and Lake Jellybean, Yukon.

Additional data supporting increasing curviness of the jet stream over recent millennia came from seven other sites: Crawford Lake, Ontario; Castor Lake, Wash.; Little Salt Spring, Fla.; Estancia Lake, N.M.; Crevice Lake, Mont.; and Dog and Felker lakes, British Columbia. Some sites provided oxygen isotope data; others showed changes in weather patterns based on tree ring growth or spring deposits.

Simulating the Jet Stream

As a test of what the cave and lake sediments revealed, Bowen's team did computer simulations of climate using software that takes isotopes into account.

Simulations of climate and oxygen isotope changes in the Middle Holocene and today resemble, respectively, today's flat and curvy jet stream patterns, supporting the switch toward increasing jet stream sinuosity 4,000 years ago.

Why did the trend start then?

"It was a when seasonality becomes weaker," Bowen says. The Northern Hemisphere was closer to the sun during the summer 8,000 years ago than it was 4,000 years ago or is now due to a 20,000-year cycle in Earth's orbit. He envisions a tipping point 4,000 years ago when weakening summer sunlight reduced the equator-to-pole temperature difference and, along with an intensifying El Nino climate pattern, pushed the jet stream toward greater curviness.

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Arctic nearly free of summer sea ice during first half of 21st century

April 12, 2013

For scientists studying summer sea ice in the Arctic, it’s not a question of “if” there will be nearly ice-free summers, but “when.” And two scientists say that “when” is sooner than many thought — before 2050 and possibly within the next decade or two.

James Overland of NOAA’s Pacific Marine Environmental Laboratory and Muyin Wang of the NOAA Joint Institute for the Study of Atmosphere and Ocean at the University of Washington, looked at three methods of predicting when the Arctic will be nearly ice free in the summer. The work was published recently online in the American Geophysical Union publication Geophysical Research Letters.

“Rapid Arctic sea ice loss is probably the most visible indicator of global climate change; it leads to shifts in ecosystems and economic access, and potentially impacts weather throughout the northern hemisphere,” said Overland. “Increased physical understanding of rapid Arctic climate shifts and improved models are needed that give a more detailed picture and timing of what to expect so we can better prepare and adapt to such changes. Early loss of Arctic sea ice gives immediacy to the issue of climate change.”   

“There is no one perfect way to predict summer sea ice loss in the Arctic,” said Wang. “So we looked at three approaches that result in widely different dates, but all three suggest nearly sea ice-free summers in the Arctic before the middle of this century.”

NOAA scientists explore the Arctic during a 2005 mission.

Download here (Credit: NOAA)

Overland and Wang emphasized that the term “nearly” ice free is important as some sea ice is expected to remain north of the Canadian Archipelago and Greenland.           

The “trendsetters” approach uses observed sea ice trends. These data show that the total amount of sea ice decreased rapidly over the previous decade. Using those trends, this approach extrapolates to a nearly sea ice-free Arctic by 2020. The “stochasters” approach is based on assuming future multiple, but random in time, large sea ice loss events such as those that occurred in 2007 and 2012. This method estimates it would take several more events to reach a nearly sea ice-free state in the summer. Using the likelihood of such events, this approach suggests a nearly sea ice-free Arctic by about 2030 but with large uncertainty in timing.
The “modelers” approach is based on using the large collection of global climate model results to predict atmosphere, ocean, land, and sea ice conditions over time. These models show the earliest possible loss of sea ice to be around 2040 as greenhouse gas concentrations increase and the Arctic warms. But the median timing of sea ice loss in these models is closer to 2060. There are several reasons to consider that this median timing of sea ice loss in these models may be too slow.

“Some people may interpret this to mean that models are not useful. Quite the opposite,” said Overland. “Models are based on chemical and physical climate processes and we need better models for the Arctic as the importance of that region continues to grow.”

Taken together, the range among the multiple approaches still suggests that it is very likely that the timing for future sea ice loss will be within the first half of the 21st century, with a possibility of major loss within a decade or two.

NOAA’s mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Join us on Facebook, Twitter and our other social media channels.

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Cruising During Hurricane Season -- to Insure or Not? (ContributorNetwork)

With Hurricane Hilary churning off the coast of Baja California and tropical storm Philippe causing chaos in the Caribbean, I caught up with Travelzoo Senior Editor Gabe Saglie to ask him about cruising during hurricane season.

Q: To your knowledge, what percentage of cruisers purchase trip insurance of some sort?

A: I don't have a good data on how many cruisers buy travel insurance. Some purchase directly from the cruise line, others through third parties. I'd safely say not all cruisers who purchase travel insurance make the investment on every cruise. I think it's a safe bet that most cruisers would rather take the gamble that nothing will go wrong with their trip

Q: What are the most likely scenarios for cruising during hurricane season? Will travel insurance cover an extra night in a hotel if my cruise is delayed, or if I miss my flight home because my ship stays at sea to avoid a hurricane? What about missed ports?

A: For the most part, travelers taking to sea even during hurricane season will see no problems. Let's face it, most days that fall on "hurricane season" -- June through September -- are void of storms. But, especially later in that season, bad storms become more likely. Cruise ships can be safe havens during tropical storms and hurricanes since these vessels can easily sail around them. This means the traveler needs to be flexible and open to skipping ports or visiting alternate ones, as well as open to the possibility some of their travel days will be rainy. Travel insurance generally will not cover wet days or changed itineraries.

The key to any insurance policy is to read the fine print, and if you're confused or unclear as to what exactly is covered, call your insurer before you travel so you don't have any lingering doubts about what is covered. That said, yes, most policies will cover expenses (not always 100 percent of your costs, though, so read the fine print) incurred by things like delayed or lengthened cruises, like hotel stays. While cruise lines will generally help passengers in cases where these altered plans are their fault, it's not always clear how much of your trip cost will be covered. Keep in mind cruise lines could be handling thousands of passengers at once, so a call to your travel insurer could resolve issues like rebooked flights or missed hotel stays much more quickly. Depending on your policy, insurance can also pay for the cost of getting you, or your mishandled luggage, to the next port, should you (or your bags) miss setting sail on day one.

Q: Sometimes people tell me, "We self-insure." Do you have anything to say to those people?

A: Self-insurance can be a safe bet for most travel scenarios; again, odds are that the vast majority of the travel we do over our lifetime will happen unaffected by the unforeseen. The potential downfall is that not enough money is set aside for unexpected mishaps. The cost of a missed hotel night or even flying yourself to the next port of call if you miss your cruise's departure time may be manageable. But on very expensive trips, or trips to exotic ports of call, the biggest concern is that not enough self-insurance was planned to offset some of those very high costs. It all comes down to your own, personal capacity and financial wherewithal for risk. For many people, investing an extra 8 to 10 percent on third-party insurance for that bucket list trip may be worth considering.

Q: What are some things that travel insurance doesn't cover? For example, if I miss an extra day of work due to a hurricane delay, will it cover lost wages?

A: Weather is often the biggest sticking point when it comes to insurance. Certainly, trip delay, trip cancellation or trip interruption insurance will come to your aid should a hurricane derail your cruise -- but keep in mind this counts only if you've bought insurance before the storm develops. But bad weather during your cruise will not be covered. Also, since cruise lines reserve the right to skip ports of call or visit alternate ones due to storms, itinerary tweaks are also generally not covered.

You can find a policy to insurance against a wide range of scenarios. I know, for example, that some policies will cover the cost of your vacation if you need to cancel last minute because you lost your job and can no longer afford to go. Lost wages may be covered by some insurers, but it must be clearly stated in your policy before you go.

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Four Tornadoes Hit Kentucky Hit During Storm System (ContributorNetwork)

The National Weather Service has now confirmed that at least four different tornadoes touched down in Louisville, Kentucky on Wednesday evening, with a fifth striking in Indiana. No injuries were reported.

One of the tornadoes struck iconic Churchill Downs, where the Kentucky Derby is held each year. Concern for the stabled horses led many to brave the weather and make sure the animals were safe. Several barns on the property sustained damage, which led to some of the horses being set free to wander the Downs, but they were eventually rounded up and no injuries to the animals were reported.

The number of tornadoes and the ensuing damage has been compared to activity normally seen in the Gulf area. Media outlets and residents were also quick to compare Wednesday's storms with the much larger tornado that hit the area in 1974.

Here are some numbers related to the Louisville tornadoes.

EF2: The strongest of Wednesday night's tornadoes is believed to only have been a medium-strength funnel according to guidelines. The wind speed of this twister is believed to have been approximately 115 miles per hour. The path of this tornado was measured at about 1 mile in length.

EF0: The tornado that hit Churchill Downs was reportedly fairly weak according to guidelines, although the National Weather Service believes it may have picked up a little strength to become an EF1 as it left the area and moved towards Papa John's Cardinal Stadium.

EF1: The strength of the other two tornadoes that touched down in Kentucky on Wednesday night. The wind speed of this tornado is thought to have reached between 95-100 miles an hour.

100: The number of stable workers that are in residence at Churchill Downs at any one time.

1,300: The number of horses that were stabled at Churchill Downs when the tornado struck.

136: The number of years Churchill Downs has been in business. Wednesday's tornado was the first to ever strike the property.

1974: The year of Louisville's largest tornado to date. An EF4 that caused massive property damage, including the destruction of 900 homes. It also downed power lines all over the city, as well as causing the deaths of 2 people and the injuries of 207 more.

25: The number of crew members that Louisville Gas and Electric has assigned to deal with all the downed power lines.

7,600: The number of people without power in Jefferson County, which includes Louisville, after Wednesday's storms.

Vanessa Evans is a musician and former freelance writer based in Michigan with a lifelong interest in politics and community issues.

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Terminology Used During the Hurricane Season (ContributorNetwork)

As the hurricane season makes its grand opening in June, all eyes turn to the Gulf of Mexico and Atlantic Ocean to see just what the is in store for coastal residents this year. The National Hurricane Center released its annual outlook for the Atlantic hurricane season, and information is the most important tool anyone can use to survive through a disaster. This terminology guide for the Hurricane Season can help make sense of the watches, warnings and advisories. The full National Hurricane Center glossary can be found here.

Advisories

The National Hurricane Center (NHC) issues advisories that include all information pertaining to tropical cyclone watches and warnings, as well as the storm's location, intensity and other pertinent information. This is different than other storm advisories which, according to NOAA's glossary, usually identify weather phenomenon that are less severe forms of weather, like flood advisories, but can still cause damage or loss of life if not treated with caution.

Tropical Storm Watch

This is a weather notice that identifies that tropical storm force winds (sustained winds 39 to 73 mph) are possible in a given area within the next 48 hours.

Tropical Storm Warning

This is a weather notice that identifies that tropical storm force winds are expected in a given area over the next 36 hours. It is important to note that the likelihood of the storm occurring in an area with a tropical storm warning is significantly higher than an area with just a tropical storm watch.

Hurricane Watch

This is a weather announcement that identifies that hurricane conditions (sustained winds above 74 mph) are possible at a given location. This notice is issued when it is expected that the tropical storm force winds will reach an area within 48 hours. In theory, a hurricane watch could be issued for an area before a hurricane has officially developed. This would happen if a storm was a tropical storm force, but conditions are right for it to gain strength and make landfall at an area within the 48 hour window.

Hurricane Warning

This is a weather announcement that hurricane conditions are expected in a given area. Again, these notices are going to be issued in advance of the tropical storm force winds reaching the area, usually when those winds are expected within the next 36 hours.

Knots

This is a speed representation of nautical miles per hour. One nautical mile, according to an international agreement detailed by the agency formerly known as the National Bureau of Standards, is equal to approximately 6,076 feet, as opposed to a statute mile which is 5,280 feet. Wind speeds in hurricanes and speed of storm movement are typically reported in knots (kt) and also converted to statute miles per hour (mph).

Tropical Disturbance

This is the beginning of a hurricane. These storms begin showing development and may, or may not, have sustained winds. Their size is usually 100 to 300 nautical miles wide, but are not organized enough to be classed as a tropical depression.

Tropical Depression

A tropical cyclone that has sustained winds of 33kt or less (38 mph or less). Depressions normally represent the first phase of a storm that shows strong development, including a central core that the storm rotates around.

Tropical Storm

A tropical cyclone that has sustained winds between 34kt and 63kt (39 mph and 73 mph). Tropical storms normally are given a name, which stays with the storm until it loses enough energy to return to tropical depression status.

Hurricane

A tropical cyclone that has sustained winds greater than 64kts (74 mph). The term hurricane is used for storms north of the equator and east of the International Date Line and west the Prime Meridian. Pacific tropical cyclones west of the International Date Line are known as typhoons.

Donald is an instructor in military command and control as well as emergency management. He has supported disaster response in a wide range of situations, including hurricanes, forest fires, volcano eruptions and aircraft accidents.

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