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February 11, 2019

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Did you know that storms can carry atmospheric rivers? They can and now scientsits have developed a new scale for measuring these weather conditions. I had no idea.

Learn about this and more interesting stories from the scientific community in today's issue.

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*-- New scale to grade the strength of storm-carrying atmospheric rivers --*

Scientists have unveiled a new weather scale designed to characterize the size and strength of atmospheric rivers, long bands of water vapor carried by fast high-altitude winds.

For the Western United States, the atmospheric rivers that flow across the Pacific are a blessing and a curse. In California, the succession of winter rain storms delivered by atmospheric rivers help keep reservoirs filled, but they can also trigger devastating floods.

In California's Central Valley, some 80 percent of levee breachers are caused by atmospheric rivers.

To help local communities, first responders, policy makers and other decision makers better prepare for their impacts, a team of scientists led by researchers at the Scripps Institution of Oceanography at the University of California San Diego developed an intensity scale to describe the strength of atmospheric rivers.

"This scale enables improved awareness of the potential benefit versus hazard of a forecast AR," researcher Michael Anderson of the California Department of Water Resources said in a news release. "It can serve as a focal point for discussion between water managers, emergency response personnel and the research community as these key water supply and flood inducing storms continue to evolve in a changing climate."

Like the scale used to grade hurricanes, the new scale uses numbers 1 through 5 to characterize the river's strength. The scale also uses corresponding categories: weak, moderate, strong, extreme and exceptional.

Two main factors determine an atmospheric river's grade: the amount of water vapor it's carrying and the amount of time it takes for a river to move across a specific area.

Rivers that take less than 24 hours to cross an area are downgraded a single category. If a river stalls, taking more than 48 hours to pass through an area, it's upgraded.

The scale's emphasis on speed sets it apart from the scale used to categorize hurricanes, which has been criticized for failing to communicate the risks posed by relatively weak but slow-moving hurricanes.

According to the new scale, category one and two atmospheric rivers are beneficial. Their replenishing rains are much needed across much of the West. But as the rivers move up the scale, the risks begin to outweigh the benefits. Category three rivers can refill reservoirs but also cause river heights to near flood levels.

According to the scale, category four rivers, or extreme rivers, are "mostly hazardous," while category five rivers, or exceptional rivers, are "primarily hazardous."

"The scale recognizes that weak ARs are often mostly beneficial because they can enhance water supply and snow pack, while stronger ARs can become mostly hazardous, for example if they strike an area with conditions that enhance vulnerability, such as burn scars, or already wet conditions," said F. Martin Ralph, director of the Center for Western Water and Weather Extremes at Scripps. "Extended durations can enhance impacts."

Ralph, the scale's primary creator, and his colleagues published the new scale this week in the Bulletin of the American Meteorological Society.

"The concept of ARs has directly benefited NWS operations in the West through better scientific understanding, more accurate precipitation forecasts, and a better vehicle for communicating impacts to our partners," said Jon Rutz, a meteorologist at the National Weather Service who assisted in the scale's creation. "The AR scale is a significant step forward, providing forecasters with a tool to distinguish between primarily beneficial and primarily hazardous storms. I anticipate that this scale will be adopted and highly used."

*-- NOAA releases early update for World Magnetic Model --*

Winter2018Scientists at NOAA's National Centers for Environmental Information have released an early update for the World Magnetic Model that powers a variety of global navigational systems.

Over the last few years, Earth's magnetic field has been shifting rapidly. Most recently, the planet's north magnetic pole began lurching toward Siberia. The sudden and dramatic changes weren't anticipated by WMM's previous update.

Every five years, scientists with NOAA and the British Geological Survey update WMM using the latest measurements of Earth's magnetic field. The model uses the latest data to predict how the magnetic field and two magnetic poles will move in the years in-between updates.

"The model is an extrapolation," Arnaud Chulliat, a geophysicist at NCEI, told UPI. "The quality of the model is reflective of the quality of the data."

Magnetic field variation is normal, if not easily predicted, but changes typically don't throw off navigation systems enough to warrant more frequent updates to the model.

Though scientists only update the model every five years, they regularly check its accuracy. Comparing it's predictions to real time measurements on the shifting magnetic field. Too big of a discrepancy can cause navigational errors.

"We've updated the model on a five-year cycle, because in the past, that's the average amount time it takes for the errors to become too large," Chulliat said.

Early last year, scientists realized the errors were getting too big too fast, especially in the Arctic. NOAA and the British Geological Survey decided a more immediate update was necessary. The early update was initially scheduled to be released at the beginning of the January, but the government shutdown forced a delay.

"This out-of-cycle update before next year's official release of WMM 2020 will ensure safe navigation for military applications, commercial airlines, search and rescue operations, and others operating around the North Pole," officials at NCEI wrote in an update.

For decades, magnetic north was steadily inching away from the geographic North Pole, but for the last few years the north magnetic pole has been moving closer to the North Pole. Since the 1990s, magnetic north has been moving considerably faster.

These sporadic changes in direction and speed make it difficult for scientists and the WMM to predict what exactly Earth's magnetic field will look like in five years.

Scientists know the Earth's magnetic field is largely controlled by the movement of iron and nickel inside the planet's outer core, but the precise nature of the mechanism remains a mystery.

"What were are trying to understand is why we had this acceleration in the 1990s," Chulliat said. "They were caused by processes in the core that we don't yet understand."