How Saharan dust regulates hurricane rainfall

Giant plumes of Sahara Desert dust that gust across the Atlantic can suppress hurricane formation over the ocean and affect weather in North America.

But thick dust plumes can also lead to heavier rainfall -- and potentially more destruction -- from landfalling storms, according to a July 24 study in Science Advances. The research shows a previously unknown relationship between hurricane rainfall and Saharan dust plumes.

"Surprisingly, the leading factor controlling hurricane precipitation is not, as traditionally thought, sea surface temperature or humidity in the atmosphere. Instead, it's Sahara dust," said the corresponding author Yuan Wang, an assistant professor of Earth system science at the Stanford Doerr School of Sustainability.

Previous studies have found that Saharan dust transport may decline dramatically in the coming decades and hurricane rainfall will likely increase due to human-caused climate change.

However, uncertainty remains around the questions of how climate change will affect outflows of dust from the Sahara and how much more rainfall we should expect from future hurricanes. Additional questions surround the complex relationships among Saharan dust, ocean temperatures, and hurricane formation, intensity, and precipitation. Filling in the gaps will be critical to anticipating and mitigating the impacts of climate change.

"Hurricanes are among the most destructive weather phenomena on Earth," said Wang. Even relatively weak hurricanes can produce heavy rains and flooding hundreds of miles inland. "For conventional weather predictions, especially hurricane predictions, I don't think dust has received sufficient attention to this point."

Competing effects

Dust can have competing effects on tropical cyclones, which are classified as hurricanes in the North Atlantic, central North Pacific, and eastern North Pacific when maximum sustained wind speeds reach 74 miles per hour or higher.

"A dust particle can make ice clouds form more efficiently in the core of the hurricane, which can produce more precipitation," Wang explained, referring to this effect as microphysical enhancement. Dust can also block solar radiation and cool sea surface temperatures around a storm's core, which weakens the tropical cyclone.

Wang and colleagues set out to first develop a machine learning model capable of predicting hurricane rainfall, and then identify the underlying mathematical and physical relationships.

The researchers used 19 years of meteorological data and hourly satellite precipitation observations to predict rainfall from individual hurricanes.

The results show a key predictor of rainfall is dust optical depth, a measure of how much light filters through a dusty plume. They revealed a boomerang-shaped relationship in which rainfall increases with dust optical depths between 0.03 and 0.06, and sharply decreases thereafter. In other words, at high concentrations, dust shifts from boosting to suppressing rainfall.

"Normally, when dust loading is low, the microphysical enhancement effect is more pronounced. If dust loading is high, it can more efficiently shield [the ocean] surface from sunlight, and what we call the 'radiative suppression effect' will be dominant," Wang said.

Read more at Science Daily

In a warming world, climate scientists consider category 6 hurricanes

For more than 50 years, the National Hurricane Center has used the Saffir-Simpson Windscale to communicate the risk of property damage; it labels a hurricane on a scale from Category 1 (wind speeds between 74 -- 95 mph) to Category 5 (wind speeds of 158 mph or greater).

But as increasing ocean temperatures contribute to ever more intense and destructive hurricanes, climate scientists Michael Wehner of Lawrence Berkeley National Laboratory (Berkeley Lab) and James Kossin of the First Street Foundation wondered whether the open-ended Category 5 is sufficient to communicate the risk of hurricane damage in a warming climate.

So they investigated and detailed their extensive research in a new article published in the Proceedings of the National Academy of Sciences (PNAS), where they also introduce a hypothetical Category 6 to the Saffir-Simpson Wind Scale, which would encompass storms with wind speeds greater than 192 mph.

"Our motivation is to reconsider how the open-endedness of the Saffir-Simpson Scale can lead to underestimation of risk, and, in particular, how this underestimation becomes increasingly problematic in a warming world," said Wehner, who has spent his career studying the behavior of extreme weather events in a changing climate and to what extent human influence has contributed to individual events.

According to Wehner, anthropogenic global warming has significantly increased surface ocean and tropospheric air temperatures in regions where hurricanes, tropical cyclones, and typhoons form and propagate, providing additional heat energy for storm intensification.

When the team performed a historical data analysis of hurricanes from 1980 to 2021, they found five storms that would have been classified as Category 6, and all of them occurred in the last nine years of record.

They determined a hypothetical upper bound for Category 5 hurricanes by looking at the expanding range of wind speeds between the lower-category storms.

Hurricanes, tropical storms, and typhoons are essentially the same weather phenomenon; their name difference is purely geographical: storms in the North Atlantic and Northeast Pacific Oceans are called hurricanes, events in the Northwest Pacific Ocean are called typhoons, and occurrences in the South Pacific and Indian Oceans are called tropical cyclones.

In addition to studying the past, the researchers analyzed simulations to explore how warming climates would impact hurricane intensification.

Their models showed that with two degrees Celsius of global warming above pre-industrial levels, the risk of Category 6 storms increases by up to 50% near the Philippines and doubles in the Gulf of Mexico and that the highest risk of these storms is in Southeast Asia, the Philippines, and the Gulf of Mexico.

"Even under the relatively low global warming targets of the Paris Agreement, which seeks to limit global warming to just 1.5°C above preindustrial temperatures by the end of this century, the increased chances of Category 6 storms are substantial in these simulations," said Wehner.

Read more at Science Daily

Scientists find two ways that hurricanes rapidly intensify

Hurricanes that rapidly intensify for mysterious reasons pose a particularly frightening threat to those in harm's way. Forecasters have struggled for many years to understand why a seemingly commonplace tropical depression or tropical storm sometimes blows up into a major hurricane, packing catastrophic winds and driving a potentially deadly surge of water toward shore.

Now scientists have shed some light on why this forecasting challenge has been so difficult to overcome: there's more than one mechanism that causes rapid intensification. New research by scientists at the U.S. National Science Foundation (NSF) National Center for Atmospheric Research (NCAR) uses the latest computer modeling techniques to identify two entirely different modes of rapid intensification. The findings may lead to better understanding and prediction of these dangerous events.

"Trying to find the holy grail behind rapid intensification is the wrong approach because there isn't just one holy grail," said NCAR scientist Falko Judt, lead author of the new study. "There are at least two different modes or flavors of rapid intensification, and each one has a different set of conditions that must be met in order for the storm to strengthen so quickly."

One of the modes discussed by Judt and his co-authors occurs when a hurricane intensifies symmetrically, fueled by favorable environmental conditions such as warm surface waters and low wind shear. This type of abrupt strengthening is associated with some of the most destructive storms in history, such as Hurricanes Andrew, Katrina, and Maria. Meteorologists were stunned this week when the winds of Hurricane Otis defied predictions and exploded by 110 miles per hour in just 24 hours, plowing into the west coast of Mexico at category 5 strength.

Judt and his co-authors also identified a second mode of rapid intensification that had previously been overlooked because it doesn't lead to peak winds reaching such destructive levels. In the case of this mode, the strengthening can be linked to major bursts of thunderstorms far from the storm's center. These bursts trigger a reconfiguration of the cyclone's circulation, enabling it to intensify rapidly, reaching category 1 or 2 intensity within a matter of hours.

This second mode is more unexpected because it typically occurs in the face of unfavorable conditions, such as countervailing upper-level winds that shear the storm by blowing the top in a different direction than the bottom.

"Those storms are not as memorable and they're not as significant," Judt said. "But forecasters need to be aware that even a storm that's strongly sheared and asymmetric can undergo a mode of rapid intensification."

The new study appeared in the Monthly Weather Review, a journal of the American Meteorological Society. It was funded by the U.S. Navy Office of Naval Research and by the U.S. National Science Foundation, which is NCAR's sponsor. It was co-authored by NCAR scientists Rosimar Rios-Berrios and George Bryan.

A serendipitous finding

Rapid intensification occurs when the winds of a tropical cyclone increase by 30 knots (about 35 miles per hour) in a 24-hour period. Judt came across the two modes of rapid intensification when working on an unrelated project.

The discovery emerged after Judt produced a very high-resolution, 40-day computer simulation of the global atmosphere, using the NCAR-based Model for Prediction Across Scales (MPAS). That simulation, run at the NCAR-Wyoming Supercomputing Center, was designed for an international project comparing the output of leading atmospheric models, which have achieved unprecedented detail because of increasingly powerful supercomputers.

Once Judt produced the model, he was curious to examine storms in the simulation that rapidly intensified. By looking at a number of cases across the world's ocean basins, he noticed that rapid intensification occurred in two distinct ways. This had not previously been apparent in models, partly because previous simulations captured only individual regions instead of allowing scientists to track a spectrum of hurricanes and typhoons across the world's oceans.

Judt and his co-authors then combed through actual observations of tropical cyclones and found a number of real-world instances of both modes of rapid intensification.

"It was kind of a serendipitous finding," Judt said. "Just by looking at the storms in the simulation and making plots, I realized that storms that rapidly intensify fall into two different camps. One is the canonical mode in which there's a tropical storm when you go to bed and when you wake up it's a category 4. But then there's another mode that goes from a tropical storm to a category 1 or 2, and it fits the definition of rapid intensification. Since nobody has those storms on their radar, that mode of rapid intensification went undetected until I went through the simulation."

Meteorologists have long known that favorable environmental conditions, including very warm surface waters and minimal wind shear, can generate rapid intensification and bring a cyclone to category 4 or 5 strength with sustained winds of 130 mph or higher. In their new paper, Judt and his co-authors referred to that mode of rapid intensification as a marathon because the storm keeps intensifying symmetrically at a moderate pace while the primary vortex steadily amplifies.

Judt described Hurricane Otis as a fast marathon because it intensified symmetrically but at an unusually rapid pace, marked by an 80 mph increase in wind speed during a 12-hour period.

The study team labeled the other mode of rapid intensification as a sprint because the intensification is extremely quick but generally doesn't last as long, with storms peaking at category 1 or 2 strength and sustained winds of 110 mph or less. In such cases, explosive bursts of thunderstorms lead to a rearrangement of the cyclone and the emergence of a new center, enabling the storm to become more powerful -- even in the face of adverse environmental conditions.

The paper concludes that the two modes may represent opposite ends of a spectrum, with many cases of rapid intensification falling somewhere in between. For instance, rapid intensification may begin with a chain of discrete events such as a burst of thunderstorms that are characteristic of the sprint mode, but then transition into a more symmetrical mode of intensification that is characteristic of the marathon mode.

A question for future research is why bursts of thunderstorms can cause about 10% of storms in an unconducive environment to rapidly intensify, even though the other 90% do not, Judt said.

Read more at Science Daily

Climate change brings earlier arrival of intense hurricanes

Intense tropical cyclones are one of the most devastating natural disasters in the world due to torrential rains, flooding, destructive winds, and coastal storm surges. New research co-authored by a University of Hawai'i at Manoa atmospheric scientist revealed that since the 1980s, Category 4 and 5 hurricanes (maximum wind speed greater than 131 miles per hour) have been arriving three to four days earlier with each passing decade of climate change. Their findings were published recently in Nature.

"When intense tropical cyclones occur earlier than usual, they cause unexpected problems for communities," said Pao-Shin Chu, atmospheric sciences professor in the UH Manoa School of Ocean and Earth Science and Technology and Hawai'i State Climatologist. "Moreover, the earlier advance of these storms will overlap with other weather systems, for example local thunderstorms or seasonal monsoon rainfall, and can produce compounding extreme events and strain the emergency response."

Changes in many characteristics of intense hurricanes under a warming climate, for example, the number, intensity, and lifespan, are fairly well-studied. However, little is known about changes in the seasonal cycle of these intense events.

Using satellite data, historical tropical cyclone tracks, NOAA rainfall records, and various statistical methods, Chu and co-authors found that there has been a significant shift of these intense tropical cyclones from autumn to summer months since the 1980s in most tropical oceans. The effect was particularly observed in the eastern North Pacific off the coast of Mexico, where most hurricanes near Hawai'i come from; the western North Pacific; the South Pacific; the Gulf of Mexico; and the Atlantic coast of Florida and the Caribbean.

"It was surprising to consistently see earlier arrivals when we independently assessed satellite data and conventional ground-based observations of intense tropical cyclones," said Chu.

In August 2017, for example, Hurricane Harvey, a Category 4 hurricane, made landfall on Texas and Louisiana and inflicted catastrophic flooding and more than 100 deaths.

Using simulations from multiple global climate models (e.g., high-resolution CMIP6 models), the team detected warmer oceanic conditions developed earlier, which favored the earlier onset of intense tropical cyclones. Further, they found that the warming was primarily driven by greenhouse gas forcing.

"In a future with high carbon dioxide emissions, the earlier shifting trend is projected to be amplified," said Chu.

In South China and the Gulf of Mexico, the earlier onset of intense tropical cyclones contributes significantly to an earlier onset of extreme rainfall.

Read more at Science Daily

A butterfly flaps its wings and scientists make jewelry

The further out in time, the more unreliable a weather forecast. That's because small variations in initial weather conditions can completely change the entire system, making it unpredictable. Put another way, in the "butterfly effect," an insect can flap its wings and create a microscopic change in initial conditions that leads to a hurricane halfway around the world.

This chaos is seen everywhere, from weather to labor markets to brain dynamics. And now, in the journal Chaos, by AIP Publishing, researchers from the University of Calabria explored how to turn the twisting, fractal structures behind the science into jewelry with 3D printing.

The jewelry shapes are based on the Chua circuit, a simple electronic system that was the first physical, mathematical, and experimental proof of chaos. Instead of an ordinary circuit, which produces an oscillating current, Chua's circuit results in oscillations that never repeat.

"These chaotic configurations, called strange attractors, are complex structures that had never been observed before," said author Eleonora Bilotta. "The depictions of such structures are strikingly beautiful, continually shifting when the point of view is changing. Jewelry seemed to be the best way to interpret the beauty of chaotic shapes."

At first, the team tried to employ goldsmiths to create prototypes of the twisting, arcing patterns. But the chaotic forms proved too difficult to manufacture with traditional methods. In contrast, additive printing allows for the necessary detail and structure. By 3D-printing the jewelry, the team created a counter-mold for a goldsmith to use as a cast.

"Seeing the chaotic shapes transformed into real, polished, shiny, physical jewelry was a great pleasure for the whole team. Touching and wearing them was also extremely exciting," said Bilotta. "We think it is the same joy that a scientist feels when her theory takes form, or when an artist finishes a painting."

The jewelry can also be used as an educational tool, providing students the ability to develop their scientific knowledge and artistic creativity. By building Chua's circuit, they can manipulate chaos and discover the extreme sensitivity to initial conditions. While designing the jewelry before sending it to be printed, they can tweak the parameters to generate different shapes according to personal taste.

Read more at Science Daily

Hurricanes and other tropical cyclones linked to rise in U.S. deaths from several major causes

Over recent decades, hurricanes and other tropical cyclones in the U.S. were associated with up to 33.4 percent higher death rates from several major causes in subsequent months.

This is the finding of research from Columbia University Mailman School of Public Health, Colorado State University, Imperial College London, and Harvard T. H. Chan School of Public Health, published in the journal JAMA.

The study exemplifies how far-reaching and varied the hidden costs to life could be from climate-related disasters and climate change.

Until now, there had been a critical knowledge gap about cause-specific tropical cyclone mortality risks from a large-scale study covering the entire U.S. across multiple decades.

After collecting 33.6 million U.S. death records from 1988 to 2018, the researchers used a statistical model to calculate how death rates changed after tropical cyclones and hurricanes (a subset of the strongest tropical cyclones) when compared to equivalent periods in other years.

The researchers found the largest overall increase in the month of hurricanes for injuries (33.4 percent),with increases in death rates in the month after tropical cyclones for injuries (3.7 percent), infectious and parasitic diseases (1.8 percent), respiratory diseases (1.3 percent), cardiovascular diseases (1.2 percent), and neuropsychiatric conditions (1.2 percent).

Residents of 1206 counties, covering half of the entire U.S. population, experienced at least one tropical cyclone during the study period. Tropical cyclones were most frequent in eastern and south-eastern coastal counties.

"Recent tropical cyclone seasons -- which have yielded stronger, more active, andlonger-lasting tropical cyclones than previously recorded -- indicate that tropical cyclones will remain an important public health concern," said Robbie Parks, PhD, post-doctoral research scientist at Columbia University Mailman School of Public Health, and first author. "Our results show that tropical cyclones in the U.S. were associated with increases in deaths for several major causes of death, speaking to the 'hidden burden' of climate-related exposures and climate change.

An outsized proportion of low-income and historically-disadvantaged communities in the United States reside in tropical cyclone-affected areas; understanding the public health consequences of climate-related disasters such as hurricanes and other tropical cyclones is an essential component of environmental justice."

Female injury death rate increases (46.5 percent) were higher than males (27.6 percent) in the month of hurricanes. Death rate increases were higher for those aged 65 years or older in the month after tropical cyclones (6.4 percent) when compared with younger ages (2.7 percent).

"In the U.S., tropical cyclones, such as hurricanes and tropical storms, have a devastating effect on society, yet a comprehensive assessment of their continuing health impacts had been lacking,"said Marianthi-Anna Kioumourtzoglou, ScD, assistant professor of Environmental Health Sciences at Columbia Mailman School of Public Health, and senior author. "Our study is a first major step in better understanding how cyclones may affect deaths, which provides an essential foundation for improving resilience to climate-related disasters across the days, weeks, months, and years after they wreak destruction."

Read more at Science Daily

Climate modeling confirms historical records showing rise in hurricane activity

When forecasting how storms may change in the future, it helps to know something about their past. Judging from historical records dating back to the 1850s, hurricanes in the North Atlantic have become more frequent over the last 150 years.

However, scientists have questioned whether this upward trend is a reflection of reality, or simply an artifact of lopsided record-keeping. If 19th-century storm trackers had access to 21st-century technology, would they have recorded more storms? This inherent uncertainty has kept scientists from relying on storm records, and the patterns within them, for clues to how climate influences storms.

A new MIT study published today in Nature Communications has used climate modeling, rather than storm records, to reconstruct the history of hurricanes and tropical cyclones around the world. The study finds that North Atlantic hurricanes have indeed increased in frequency over the last 150 years, similar to what historical records have shown.

In particular, major hurricanes, and hurricanes in general, are more frequent today than in the past. And those that make landfall appear have grown more powerful, carrying more destructive potential.

Curiously, while the North Atlantic has seen an overall increase in storm activity, the same trend was not observed in the rest of the world. The study found that the frequency of tropical cyclones globally has not changed significantly in the last 150 years.

"The evidence does point, as the original historical record did, to long-term increases in North Atlantic hurricane activity, but no significant changes in global hurricane activity," says study author Kerry Emanuel, the Cecil and Ida Green Professor of Atmospheric Science in MIT's Department of Earth, Atmospheric, and Planetary Sciences. "It certainly will change the interpretation of climate's effects on hurricanes -- that it's really the regionality of the climate, and that something happened to the North Atlantic that's different from the rest of the globe. It may have been caused by global warming, which is not necessarily globally uniform."

Chance encounters

The most comprehensive record of tropical cyclones is compiled in a database known as the International Best Track Archive for Climate Stewardship (IBTrACS). This historical record includes modern measurements from satellites and aircraft that date back to the 1940s. The database's older records are based on reports from ships and islands that happened to be in a storm's path. These earlier records date back to 1851, and overall the database shows an increase in North Atlantic storm activity over the last 150 years.

"Nobody disagrees that that's what the historical record shows," Emanuel says. "On the other hand, most sensible people don't really trust the historical record that far back in time."

Recently, scientists have used a statistical approach to identify storms that the historical record may have missed. To do so, they consulted all the digitally reconstructed shipping routes in the Atlantic over the last 150 years and mapped these routes over modern-day hurricane tracks. They then estimated the chance that a ship would encounter or entirely miss a hurricane's presence. This analysis found a significant number of early storms were likely missed in the historical record. Accounting for these missed storms, they concluded that there was a chance that storm activity had not changed over the last 150 years.

But Emanuel points out that hurricane paths in the 19th century may have looked different from today's tracks. What's more, the scientists may have missed key shipping routes in their analysis, as older routes have not yet been digitized.

"All we know is, if there had been a change (in storm activity), it would not have been detectable, using digitized ship records," Emanuel says "So I thought, there's an opportunity to do better, by not using historical data at all."

Seeding storms

Instead, he estimated past hurricane activity using dynamical downscaling -- a technique that his group developed and has applied over the last 15 years to study climate's effect on hurricanes. The technique starts with a coarse global climate simulation and embeds within this model a finer-resolution model that simulates features as small as hurricanes. The combined models are then fed with real-world measurements of atmospheric and ocean conditions. Emanuel then scatters the realistic simulation with hurricane "seeds" and runs the simulation forward in time to see which seeds bloom into full-blown storms.

For the new study, Emanuel embedded a hurricane model into a climate "reanalysis" -- a type of climate model that combines observations from the past with climate simulations to generate accurate reconstructions of past weather patterns and climate conditions. He used a particular subset of climate reanalyses that only accounts for observations collected from the surface -- for instance from ships, which have recorded weather conditions and sea surface temperatures consistently since the 1850s, as opposed to from satellites, which only began systematic monitoring in the 1970s.

"We chose to use this approach to avoid any artificial trends brought about by the introduction of progressively different observations," Emanuel explains.

He ran an embedded hurricane model on three different climate reanalyses, simulating tropical cyclones around the world over the past 150 years. Across all three models, he observed "unequivocal increases" in North Atlantic hurricane activity.

"There's been this quite large increase in activity in the Atlantic since the mid-19th century, which I didn't expect to see," Emanuel says.

Within this overall rise in storm activity, he also observed a "hurricane drought" -- a period during the 1970s and 80s when the number of yearly hurricanes momentarily dropped. This pause in storm activity can also be seen in historical records, and Emanuel's group proposes a cause: sulfate aerosols, which were byproducts of fossil fuel combustion, likely set off a cascade of climate effects that cooled the North Atlantic and temporarily suppressed hurricane formation.

Read more at Science Daily

Hurricanes expected to linger over Northeast cities, causing greater damage

By the late 21st century, northeastern U.S. cities will see worsening hurricane outcomes, with storms arriving more quickly but slowing down once they've made landfall. As storms linger longer over the East Coast, they will cause greater damage along the heavily populated corridor, according to a new study.

In the new study, climate scientist Andra Garner at Rowan University analyzed more than 35,000 computer-simulated storms. To assess likely storm outcomes in the future, Garner and her collaborators compared where storms formed, how fast they moved and where they ended from the pre-industrial period through the end of the 21st century.

The researchers found that future East Coast hurricanes will likely cause greater damage than storms of the past. The research predicted that a greater number of future hurricanes will form near the East Coast, and those storms will reach the Northeast corridor more quickly. The simulated storms slow to a crawl as they approach the East Coast, allowing them to produce more wind, rain, floods, and related damage in the Northeast region. The longest-lived tropical storms are predicted to be twice as long as storms today.

The study was published in Earth's Future, which publishes interdisciplinary research on the past, present and future of our planet and its inhabitants.

The changes in storm speed will be driven by changes in atmospheric patterns over the Atlantic, prompted by warmer air temperatures. While Garner and her colleagues note that more research remains to be done to fully understand the relationship between a warming climate and changing storm tracks, they noted that potential northward shifts in the region where Northern and Southern Hemisphere trade winds meet or slowing environmental wind speeds could be to blame.

"When you think of a hurricane moving along the East Coast, there are larger scale wind patterns that generally help push them back out to sea," Garner said. "We see those winds slowing down over time." Without those winds, the hurricanes can overstay their welcome on the coast.

Garner, whose previous work focused on the devastating East Coast effects of storms like Hurricane Sandy, particularly in the Mid-Atlantic, said the concern raised by the new study is that more storms capable of producing damage levels similar to Sandy are likely.

And the longer storms linger, the worse they can be, she said.

"Think of Hurricane Harvey in 2017 sitting over Texas, and Hurricane Dorian in 2019 over the Bahamas," she said. "That prolonged exposure can worsen the impacts."

From 2010 to 2020, U.S. coastlines were hit by 19 tropical cyclones that qualified as billion-dollar disasters, generating approximately $480 billion in damages, adjusted for inflation. If storms sit over coasts for longer stretches, that economic damage is likely to increase as well. For the authors, that provides clear economic motivation to stem rising greenhouse gas emissions.

"The work produced yet more evidence of a dire need to cut emissions of greenhouse gases now to stop the climate warming," Garner said.

Read more at Science Daily

Hurricane resembling those in lower atmosphere observed over Earth's polar ionosphere

 The first observations of a space hurricane have been revealed in Earth's upper atmosphere, confirming their existence and shedding new light on the relationship between planets and space.

Hurricanes in the Earth's low atmosphere are known, but they had never before been detected in the upper atmosphere.

An international team of scientists led by Shandong University in China analysed observations made by satellites in 2014 to reveal a long-lasting hurricane, resembling those in the lower atmosphere, in the polar ionosphere and magnetosphere with surprisingly large energy and momentum deposition despite otherwise extremely quiet geomagnetic conditions.

The analysis allowed a 3D image to be created of the 1,000km-wide swirling mass of plasma several hundred kilometres above the North Pole, raining electrons instead of water.

Professor Qing-He Zhang, lead author of the research at Shandong University, said: "These features also indicate that the space hurricane leads to large and rapid deposition of energy and flux into the polar ionosphere during an otherwise extremely quiet geomagnetic condition, suggesting that current geomagnetic activity indicators do not properly represent the dramatic activity within space hurricanes, which are located further poleward than geomagnetic index observatories."

Professor Mike Lockwood, space scientist at the University of Reading, said: "Until now, it was uncertain that space plasma hurricanes even existed, so to prove this with such a striking observation is incredible."

"Tropical storms are associated with huge amounts of energy, and these space hurricanes must be created by unusually large and rapid transfer of solar wind energy and charged particles into the Earth's upper atmosphere.

"Plasma and magnetic fields in the atmosphere of planets exist throughout the universe, so the findings suggest space hurricanes should be a widespread phenomena."

Hurricanes often cause loss of life and property through high winds and flooding resulting from the coastal storm surge of the ocean and the torrential rains. They are characterised by a low-pressure centre (hurricane eye), strong winds and flow shears, and a spiral arrangement of towering clouds with heavy rains.

In space, astronomers have spotted hurricanes on Mars, and Saturn, and Jupiter, which are similar to terrestrial hurricanes in the low atmosphere. There are also solar gases swirling in monstrous formations deep within the sun's atmosphere, called solar tornadoes. However, hurricanes had not been reported in the upper atmosphere of the planets in our heliosphere.

The space hurricane analysed by the team in Earth's ionosphere was spinning in an anticlockwise direction, had multiple spiral arms, and lasted almost eight hours before gradually breaking down.

The team of scientists from China, the USA, Norway and the UK used observations made by four DMSP (Defense Meteorological Satellite Program) satellites and a 3D magnetosphere modelling to produce the image. Their findings were published in Nature Communications.

Professor Zhang added: "This study suggests that there are still existing local intense geomagnetic disturbance and energy depositions which is comparable to that during super storms. This will update our understanding of the solar wind-magnetosphere-ionosphere coupling process under extremely quiet geomagnetic conditions.

Read more at Science Daily

Long-term data show hurricanes are getting stronger

Illustration of hurricane seen from space

In almost every region of the world where hurricanes form, their maximum sustained winds are getting stronger. That is according to a new study by scientists at the National Oceanic and Atmospheric Administration National Center for Environmental Information and University of Wisconsin-Madison Cooperative Institute for Meteorological Satellite Studies, who analyzed nearly 40 years of hurricane satellite imagery.

A warming planet may be fueling the increase.

"Through modeling and our understanding of atmospheric physics, the study agrees with what we would expect to see in a warming climate like ours," says James Kossin, a NOAA scientist based at UW-Madison and lead author of the paper, which is published today (May 18, 2020) in the Proceedings of the National Academy of Sciences.

The research builds on Kossin's previous work, published in 2013, which identified trends in hurricane intensification across a 28-year data set. However, says Kossin, that timespan was less conclusive and required more hurricane case studies to demonstrate statistically significant results.

To increase confidence in the results, the researchers extended the study to include global hurricane data from 1979-2017. Using analytical techniques, including the CIMSS Advanced Dvorak Technique that relies on infrared temperature measurements from geostationary satellites to estimate hurricane intensity, Kossin and his colleagues were able to create a more uniform data set with which to identify trends.

"The main hurdle we have for finding trends is that the data are collected using the best technology at the time," says Kossin. "Every year the data are a bit different than last year, each new satellite has new tools and captures data in different ways, so in the end we have a patchwork quilt of all the satellite data that have been woven together."

Kossin's previous research has shown other changes in hurricane behavior over the decades, such as where they travel and how fast they move. In 2014, he identified poleward migrations of hurricanes, where tropical cyclones are travelling farther north and south, exposing previously less-affected coastal populations to greater risk.

In 2018, he demonstrated that hurricanes are moving more slowly across land due to changes in Earth's climate. This has resulted in greater flood risks as storms hover over cities and other areas, often for extended periods of time.

"Our results show that these storms have become stronger on global and regional levels, which is consistent with expectations of how hurricanes respond to a warming world," says Kossin. "It's a good step forward and increases our confidence that global warming has made hurricanes stronger, but our results don't tell us precisely how much of the trends are caused by human activities and how much may be just natural variability."

Read more at Science Daily

Hurricanes are slowing down, and that's bad news

Flooded Las Olas Blvd and Palm trees blowing in the winds, catastrophic hurricane Irma.

Some hurricanes are moving more slowly, spending increased time over land and leading to catastrophic local rainfall and flooding, according to a new study published Wednesday (June 6) in the journal Nature.

While hurricanes batter coastal regions with destructive wind speeds, study author James Kossin says the speed at which hurricanes track along their paths -- their translational speed -- can also play a role in the damage and devastation they cause. Their movement influences how much rain falls in a given area.

This is especially true as global temperatures increase.

"Just a 10 percent slowdown in hurricane translational speed can double the increase in rainfall totals caused by 1 degree Celsius of global warming," says Kossin, a researcher at the National Oceanic and Atmospheric Administration's (NOAA) Center for Weather and Climate. He is based at the University of Wisconsin-Madison.

The study compared 68 years (1949-2016) of worldwide hurricane track and intensity data, known as best-track data, from NOAA to identify changes in translational speeds. It found that, worldwide, hurricane translational speeds have averaged a 10 percent slowdown in that time.

One recent storm highlights the potential consequences of this slowing trend. In 2017, Hurricane Harvey stalled over eastern Texas rather than dissipating over land, as hurricanes tend to do. It drenched Houston and nearby areas with as much as 50 inches of rain over several days, shattering historic records and leaving some areas under several feet of water.

How much hurricanes have slowed depends on where they occur, Kossin found. "There is regional variation in the slowdown rates when looking at the 10 percent global average across the same time frame," he says.

The most significant slowdown, 20 percent, occurred in the Western North Pacific Region, an area that includes Southeast Asia. Nearby, in the Australian Region, Kossin identified a reduction of 15 percent. In the North Atlantic Region, which includes the U.S., Kossin found a 6 percent slowdown in the speeds at which hurricanes move.

When further isolating the analysis to hurricane speeds over land, where their impact is greatest, Kossin found that slowdown rates can be even greater. Hurricanes over land in the North Atlantic have slowed by as much as 20 percent, and those in the Western North Pacific as much as 30 percent.

Kossin attributes this, in part, to the effects of climate change, amplified by human activity. Hurricanes move from place to place based on the strength of environmental steering winds that push them along. But as the Earth's atmosphere warms, these winds may weaken, particularly in places like the tropics, where hurricanes frequently occur, leading to slower-moving storms.

Additionally, a warmer atmosphere can hold more water vapor, potentially increasing the amount of rain a hurricane can deliver to an area.

The study complements others that demonstrate climate change is affecting hurricane behavior.

For instance, in 2014, Kossin showed that hurricanes are reaching their maximum intensities further from the tropics, shifting toward the poles in both the Northern and Southern Hemispheres. These shifts can deliver hurricanes to areas -- including some heavily populated coastal regions -- that have not historically dealt with direct hits from storms and the devastating losses of life and property that can result.

Another study, published in April by researchers at the National Center for Atmospheric Research, used a modeling approach to look at what would happen to hurricanes under future climate projections. Using real hurricane data from 2000-2013, the researchers found future hurricanes will experience a 9 percent slowdown, higher wind speeds, and produce 24 percent more rainfall.

Read more at Science Daily

12,000 years ago, Florida hurricanes heated up despite chilly seas

Figure 3 from the paper: Simulated changes in climatic controls on hurricane activity between the Younger Dryas (YD, 12.0-12.5 ka) and early Holocene (EH, 10.2-10.8 ka). A: Spatial difference in storm season surface temperature (Tsfc). B: Spatial difference in genesis potential index (GPI), averaged for each Transient Climate Evolution Experiment (TraCE) interval (see text). C: Filtered (20 yr) time series of maximum potential intensity (PI) near the Dry Tortugas (red) and Barbados (gray) from 13,850 yr ago through the EH. CAT - category; TS - tropical storm.

Category 5 hurricanes may have slammed Florida repeatedly during the chilly Younger Dryas, 12,000 years ago. The cause? Hurricane-suppressing effects of cooler sea surface were out-weighed by side effects of slowed ocean circulation. That's the finding of USGS researcher Michael Toomey and colleagues in their Geology article published online today.

As the last ice age waned, undersea landslide deposits called turbidites captured the fury of Florida's stormy days. Previously, Toomey linked turbidites in the Bahamas with modern hurricanes. For this study, the group examined turbidites in cores spanning the shift from the Younger Dryas into the warmer early Holocene, collected offshore the Dry Tortugas, Florida. The turbidites, complete with smashed up shells and jumbled sediments, reveal that in Younger Dryas days Florida was surprisingly hurricane-prone, at a time when cooler sea surface temperatures may have put the brakes on such intense storms elsewhere in the Atlantic.

To explore why, Toomey and colleagues analyzed computer models that simulated ocean and atmospheric conditions near Florida during that period. In modern times, the Atlantic Meridional Overturning Circulation (AMOC) brings cool water south and warm water north. But during the Younger Dryas the AMOC is thought to have weakened considerably, slowing circulation and reshaping environmental conditions across much of the Northern Hemisphere.

Modeling results indicated that lower sea surface temperatures in the tropical Atlantic, near Barbados, for example, corresponded with a drop in storm potential intensity. Near Florida, sea surfaces cooled as well. However, the change there was not as dramatic as further south or to the north. The relative warmth of waters offshore the southeastern U.S. compared to the regional Atlantic, explains Toomey, seems to have set the stage for intense hurricanes near Florida. "The modeling work suggests other factors, such as wind shear and humidity at mid-latitudes, outweighed changes in sea surface temperature at our core site," he says. Models and geologic records both show that by the early Holocene, as the AMOC regained strength, Florida's hurricanes subsided.

Read more at Science Daily