Today’s post is a reprint of recent story by Carol Rasmussen of NASA’s Earth Science News Team.
NASA has produced the first three-dimensional numerical model of melting snowflakes in the atmosphere. Developed by scientist Jussi Leinonen of NASA’s Jet Propulsion Laboratory, the model provides a better understanding of how snow melts. This can help scientists recognize the signature (in radar signals) of heavier, wetter snow — the kind that snaps power lines and tree limbs — and could be a step toward improving predictions of this hazard.
Leinonen’s model reproduces key features of melting snowflakes that have been observed in nature. First, meltwater gathers in any concave regions of the snowflake’s surface. These liquid-water regions then merge to form a shell of liquid around an ice core, and finally develop into a water drop. The modeled snowflake shown in the video is less than half an inch (one centimeter) long and composed of many individual ice crystals whose arms became entangled when they collided in midair.
Leinonen said he got interested in modeling melting snow because of the way it affects observations with remote sensing instruments. A radar “profile” of the atmosphere from top to bottom shows a very bright, prominent layer at the altitude where falling snow and hail melt — much brighter than atmospheric layers above and below it. “The reasons for this layer are still not particularly clear, and there has been a bit of debate in the community,” Leinonen said. Simpler models can reproduce the bright melt layer, but a more detailed model like this one can help scientists to understand it better, particularly how the layer is related to both the type of melting snow and the radar wavelengths used to observe it.
Atmospheric rivers stretched from Asia to North America in October 2017. Learn more.
If you live on the West Coast of North America, you have probably heard meteorologists talk about “atmospheric rivers” — the narrow, low-level plumes of moisture that often accompany extratropical storms and transport large volumes of water vapor across long distances. When atmospheric rivers encounter land, they can drop tremendous amounts of rain and snow. That can be good for replenishing reservoirs and for quenching droughts, but these remarkable meteorological features can also trigger destructive floods, landslides, and wind storms.
During the past decade, atmospheric rivers have fueled a flood of another type: scientific research papers. Prior to 2004, fewer than 10 studies mentioned atmospheric rivers in any given year; in 2015, about 200 studies were published on the matter. The availability of increasingly sophisticated satellite and aircraft data has fueled the trend, according to a recent article in the Bulletin of the American Meteorological Society. Here’s a sampling of what scientists have learned about these rivers in the sky.
They Can Bring Rains, Winds, And Lots of Damage
In a study led by Duane Waliser of NASA’s Jet Propulsion Laboratory and published in Nature Geoscience, researchers showed that atmospheric rivers are among the most damaging storm types in the middle latitudes. Of the wettest and windiest storms (those ranked in the top 2 percent), atmospheric rivers were associated with nearly half of them. Waliser and colleagues found that atmospheric rivers were associated with a doubling of wind speed compared to all storm conditions.
They Shift With The Seasons
During the winter, atmospheric rivers in the Pacific generally shift northward and westward, Bryan Mundhenk of Colorado State University and colleagues concluded in a study. They also found that the El Niño/Southern Oscillation (ENSO) cycle can affect the frequency of atmospheric river events and shift where they occur. The research was based on data processed by MERRA, a NASA reanalysis of meteorological data from satellites.
They Aren’t Just a West Coast Thing
Atmospheric rivers are a global phenomenon and responsible for about 22 percent of all water runoff. One recent study from a University of Georgia team underscored that the U.S. Southeast sees a steady stream of atmospheric rivers. “They are more common than we thought in the Southeast, and it is important to properly understand their contributions to rainfall given our dependence on agriculture and the hazards excessive rainfall can pose,” said Marshall Shepherd of the University of Georgia. Other studies note that atmospheric rivers have contributed to anomalous snow accumulation in East Antarctica and extreme rainfall in the Bay of Bengal.
Climate Change Could Alter Them
A recent study led by Christine Shields of the National Center for Atmospheric Research suggests that climate change could push atmospheric rivers in the Pacific toward the equator and bring more intense rains to southern California. The modeling calls for smaller increases in rain rates in the Pacific Northwest. Another ensemble of models shows a 35 percent increase in the number of days with landfalling atmospheric rivers in western North America.
Satellites Are Key to Studying Their Precipitation
While there are few ground-based weather stations in the open ocean to tally how much rain falls, satellites such as those included in the Global Precipitation Measurement (GPM) mission can estimate precipitation rates from above. “Satellites have proven valuable over both the ocean and land, though uncertainties are often larger over land because of complicating factors like the terrain and the presence of snow on the surface,” said Ali Behrangi, the author of a study that assessed the skill of different satellite-derived measurements of precipitation rates.
A June snowstorm just topped off the already thick layer of white stuff atop the Sierra Nevadas. California’s snow water equivalent rose to a heaping 170 percent of normal. But not so long ago, the state was in the midst of a deep drought; its mountains were bare and brown, and water levels plummeted in reservoirs.
Throughout, satellites were watching. Check out the California drought and its aftermath in a video from NASA Earth Observatory:
Editor’s note: Here’s a roundup of the latest eye-catching earth science videos from NASA and beyond. In March, snow emerged as a theme.
Where there is snow, there is water. Scientists trudged through thick white powder in Grand Mesa and the Senator Beck Basin to measure the depth of snow — and its water content — for the SnowEx campaign.
“Photon Jump” tells the story of an exuberant photon. Follow this miniature light particle as s/he is spat out of a satellite sensor in Earth’s orbit. A team of students at Georgia’s Savannah College of Art and Design (SCAD) created the film for the upcoming ICESat-2 mission, which will measure snow and ice on Earth.
In Hawaii, land of palm trees, pineapples, and year-round surfing, a full-blown blizzard hit last week. The early March storm brought more than 8 inches (20 centimeters) to the top of Mauna Kea volcano, leading authorities to shut the road to the peak.
The snow was all the more surprising given how little has fallen in more traditionally snowy locales. Hawaii received more snow that day than Denver has accumulated over the past seven weeks. The Colorado city got 1.6 inches (4 centimeters) in the past 51 days, according to local news.
The island archipelago also got more white stuff than Chicago. That city, famed for its bitter winters, is currently in the midst of a snow drought, with a mere 0.6 inches (1.5 centimeters) falling in 2017. That’s the least on record since the late 1800s. To put that into perspective: Chicago averages 37 inches (94 cm) of yearly snowfall. By contrast, Hawaii gets a yearly average of 3.7 inches (9 cm).
Thanks to their height, the peaks of Mauna Kea and Mauna Loa volcanoes do receive a dusting now and again. But that snow rarely sticks around for more than a few days, according to Ken Rubin, an assistant professor of geology and geophysics at the University of Hawaii.
Mauna Kea in December 2016. Image: NASA Earth Observatory/Jesse Allen, using Landsat data from the U.S. Geological Survey.
Credit: NASA Earth Observatory/VIIRS/Jesse Allen. More details about the image here.
In the past two months, weather reports in California, Oregon, and Washington have been filled with news of “atmospheric rivers” bringing copious amounts of rain and snow to the western United States. Atmospheric rivers are long, thin fingers of moisture that develop in the tropics and flow into higher latitudes. If one of them makes landfall, huge of amounts of rain and snow can fall in a short period.
Much of this moisture, of course, eventually finds its way back to the sea through rivers. When waterways are swollen and flowing rapidly, they also become rivers of suspended sediment, full of clay, mud, sand, and other debris. Though the flooding from atmospheric river events can be devastating, the enormous amount of sediment they send rushing into the sea can also be surprisingly beautiful.
For instance, on February 11, 2017, the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP acquired this remarkable view of rivers and streams spewing sediment into the Pacific Ocean. Close to the outlets of streams and rivers, sediment-rich waters appear brown. As the sediment dissipates and mixes into the ocean, the water appears teal.
Duane Waliser, a scientist at NASA’s Jet Propulsion Laboratory, recently tallied just how damaging atmospheric rivers can be for coastal areas. In a study published in Nature Geoscience, Waliser and a colleague showed that atmospheric rivers are among the most damaging storm types in the middle latitudes. Of the very wettest and windiest storms (those ranked in the top 2 percent), atmospheric rivers were associated with nearly half of them. Waliser and colleagues also found that atmospheric rivers were associated with a doubling of the typical wind speed compared to all storm conditions.
Eighty five years ago today, Wilson Alwyn Bentley died of pneumonia. It was December 23, 1931, and outside his home in Jericho, Vermont, the sky was ripe for snow. His final diary entry read: “Cold north wind afternoon. Snow Flying.” It was the sort of weather he had lived for.
Bentley began to observe snow at 15 years old, when his mother bought him a microscope. It consumed his days, he later recalled:
When the other boys of my age were playing with popguns and sling-shots, I was absorbed in studying things under this microscope: drops of water, tiny fragments of stone, a feather dropped from a bird’s wing, a delicately veined petal from some flower. But always, from the very beginning, it was snowflakes that fascinated me most. The farm folks, up in this north country, dread the winter; but I was supremely happy.
Over the subsequent decades, Bentley photographed more than 5,000 snowflakes, and created the first photomicrograph of an ice crystal, combining a microscope and an accordion-shaped bellows camera. A professor of natural history who became known as “the snowflake man,” he demonstrated what is now a common adage: no two snowflakes are alike.
Photos: Snowflakes circa 1902 by Wilson Bentley. Courtesy of Wikimedia Commons.
The snow Bentley observed at a microscopic scale, satellites now see at the size of whole continents. The subject matter that fascinated him still provides fodder for heaps of scientific papers today.
December 2016 has brought a flurry of Bentley-esuqe weather to the U.S. East Coast, including snow and biting winds. But long before winter kicked into full gear in cities like Washington and New York, it painted landscapes around the world white. From Japan to Kazakhstan, NASA satellites observed snow from space. So if you’re dreaming of a white Christmas or waiting for the gingerbread cookies to bake, here are several images—some we previously published, and others that are quite fresh.
Image: NASA Earth Observatory/Joshua Stevens, using Landsat data from the U.S. Geological Survey.
Snow fell in the town of Ain Sefra for the first time in nearly four decades this December. Satellites show a thin, white veil covering the orange sand dunes of the northern Sahara. The Enhanced Thematic Mapper Plus (ETM+) on the Landsat 7 satellite captured this natural-color image of snow on December 19, 2016. On the ground, Photographer Karim Bouchetata captured the snow before it melted.
Image: NASA Earth Observatory/Joshua Stevens using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership.
An Arctic air mass brought more snow to communities around the Great Lakes on December 14, 2016. The lake-effect snow comes on the heels of an earlier accumulation that piled up to several feet of snow in some areas, according to reports. Officials issued weather warnings and advisories from northeast Ohio to upstate New York.
Image: NASA Earth Observatory/Jeff Schmaltz, using MODIS data from LANCE/EOSDIS Rapid Response.
A plume of volcanic ash hangs over the Gulf of Alaska in this natural-color image. The plume is not the product of an active volcano; it contains re-suspended ash from the 1912 eruption of Novarupta, according to the Alaska Volcano Observatory.
Photograph: Astronaut photography from the Expedition 48 crew.
The white hills sprawling in every direction look like mounds built by snow plows, or massive hills of sugar. In fact, they’re the world’s largest gypsum dune field: the White Sands National Monument, located in southern New Mexico.
During the last Ice Age, melting snow and ice from the San Andres Mountains (west of the dunes) and the Sacramento Mountains (to the east) eroded minerals from the hillsides and carried them downhill to the basin below. As the climate warmed and the water evaporated, the basin remained full of selenite (the crystalline form of gypsum) and created the Alkali Flats. Over time, winds broke the crystals into sand grains, which built up into the dunes.
Image: NASA Earth Observatory/Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response.
Image: NASA Earth Observatory/Pola Lem, using MODIS data from LANCE/EOSDIS Rapid Response.
November 20: White hills appear amid green in England
Snow arrived in parts of northern England before a satellite took this image on November 20. According to reports, the same storm brought high winds and lashing rain farther south, in Kent and Sussex.
Image: NASA Earth Observatory/Pola Lem, using MODIS data from LANCE/EOSDIS Rapid Response.
November 17: White Kazakhstan
Broad swaths of Kazakhstan turned white before this Visible Infrared Imaging Radiometer Suite (VIIRS) image was taken on November 17, 2016. Parts of the country saw temperatures dipping well below freezing, with extreme wind chills. That’s not a surprise for locals; the country’s capital, Astana, often experiences frigid days in winter months.
Image: NASA Earth Observatory/Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 team.
More than a year after the latest eruption at Iceland’s Holuhraun lava field, the newly-formed lava may still be toasty underneath. Although the basaltic rock formed a hard crust, according to volcanologists, the flow is probably still hot enough to prevent snow from building up atop it.
“You’re not going to freeze the lava flow,” said Erik Klemetti, a volcanologist at Denison University and author of the Eruptions blog at Wired magazine. “You need to wait for the soil to freeze to get snow to accumulate in temperate latitudes.”
Snow dusted parts of Nebraska on October 6, 2016. This natural-color image, acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, shows a white blanket covering about 40 square miles (more than 100 square kilometers). Photos taken by highway cameras showed snow falling along parts of U.S. Route 83 on the afternoon of October 6.
In recent weeks, we had a good shot of activity at Kilauea, but we skipped it since it only had Halema’uma’u activity — which is much like previous images and not the new ocean entry point, which we’ve yet to glimpse in cloud-free satellite imagery. We received an excellent ALI scene of the submarine El Hierro volcano (which we published) and then the next day we received an image of the same volcano from Landsat 7 (which effectively got scooped by ALI).
Another of the moderately recent and interesting images of volcanoes we didn’t use is a very nice ALI shot of the Cerro Hudson volcano in Chile.
We do have a good reason for not using the image. Notice the volcanic activity? Yeah, we didn’t see anything either. What makes this image interesting (to me anyway) is that just two weeks earlier, it looked like this:
We did publish that one. There’s actually not much in the way of activity in that one either, but in the published image, you can see a lot of ash that’s fallen on the ground from activity in October at the volcano.
Just two weeks later, with no new activity, almost all the ashfall seems to have “disappeared.” Fresh snow fell and covered much of it. Also, we got a much better shot with ALI of the volcano, getting a very nice view of the entire caldera, the glacier draining it out of the northeast, and forests in the alpine valleys. The ashfall was nowhere near as extensive and damaging as the Puyehue eruption, which at one point spewed out ash that circled the globe.