Archives for category: Earth Science

Image mosaic by Daily Mail.

Image mosaic by Daily Mail.

A few years ago, while working on a story about wildfires, a V appeared to me in a satellite image of a smoke plume over Canada. That image made me wonder: could I track down all 26 letters of the English alphabet using only NASA satellite imagery and astronaut photography?

With the help of readers and colleagues, I started to collect images of ephemeral features like clouds, phytoplankton blooms, and dust clouds that formed shapes reminiscent of letters. Some letters, like O and C, were easy to find. Others—A, B, and R—were maddeningly difficult.

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NASA Earth Observatory, December 2015


A Monster Slide

A Monster Slide

A Monster Slide

One of the world’s largest recorded landslides occurred on April 9, 2000, when more than 100 million cubic meters (3.5 billion cubic feet) of loose rock, ice, and other debris tumbled down a steep, narrow gorge in eastern Tibet.

Within ten minutes, the slurry of debris—which included granite and marble boulders, snow, and sediment—moved nearly 10 kilometers (6 miles) and dropped from an elevation of 5,520 meters (18,110 feet) to the valley floor 2,190 meters above sea level. The debris, lubricated by recent rainfall and meltwater from glaciers on the surrounding mountain peaks, slid through a gully carved by Zhamu Creek at velocities up to 14 meters per second (31 miles per hour).

By the time the mass of material stopped, it had buried the Yigong River, creating a debris dam that blocked the flow of the river. The dam occupied 2.5 square kilometers (1 square mile) and was 90 meters (295 feet) high at its tallest edge. River water began to back up immediately, creating a large lake behind the dam. As time passed, increasing volumes of water began to seep through the bottom of the dam, muddying the river water downstream. Meanwhile, the area and volume of the lake continued to grow.

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Earth Observatory, June 2012

In March 2012, a magnitude 9.0 earthquake—the fourth largest recorded since 1900—triggered a powerful tsunami that pummeled the northeastern coast of Japan. The earthquake occurred offshore, about 130 kilometers (80 miles) east of Sendai at 2:46 p.m. on March 11. Within 20 minutes, massive swells of water started to inundate the mainland.

The tallest waves and most devastating flooding from the 2011 T?hoku-oki tsunami occurred along the jagged coast of northern Honshu, a landscape dimpled with bays and coves known as ria coast. The steep, narrow bays of ria coasts trap and focus incoming tsunami waves, creating destructive swells and currents that can push huge volumes of water far inland, particularly along river channels.

That’s exactly what happened in the days before the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), an instrument on NASA’s Terra satellite, captured the middle image above (on March 14, 2011). It shows severe flooding along the Kitakami River three days after the earthquake struck.

Earth Observatory, March 2012

Ships churning across the Pacific Ocean left this cluster of bright cloud trails lingering in the atmosphere late last month. The narrow clouds, known as ship tracks, form when water vapor condenses around tiny particles of pollution that ships either emit directly as exhaust or that form as a result of gases within the exhaust.

The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite captured this natural-color image on February 21, 2012. The criss-crossing clouds off the coast of California stretch many hundreds of kilometers from end to end. The narrow ends of the clouds are youngest, while the broader, wavier ends are older.

Some of the pollution particles generated by ships (especially sulfates) are soluble in water and can serve as the seeds around which cloud droplets form. Clouds infused with ship exhaust have more and smaller droplets than unpolluted clouds. As a result, light hitting the ship tracks scatters in many directions, making them appear brighter than other types of marine clouds, which are usually seeded by larger, naturally occurring particles such as sea salt. (In this image, the ship tracks don’t appear particularly bright because the surrounding clouds are also fairly bright. But in this March 2009 image and this July 2010 image the brightening effect of the pollution is quite clear.)

The enhanced reflectivity of ship tracks means they shade Earth’s surface from incoming sunlight, which produces a local cooling effect. However, determining whether ship emissions have a broader climate effect is complex because ships also emit pollutants that have a warming influence, such as carbon dioxide and black carbon. Research is ongoing, but one recent satellite study found that ship emissions do not cause changes on a large enough scale to affect climate significantly.

At the same time, researchers have shown that the ship emissions pose a clear hazard to human health. Seventy percent of all ship tracks occur within 500 kilometers of the coast, which means shipping exposes large numbers of people in coastal cites to high levels of health-sapping particulates. One study concluded, for example, that shipping-related particulate matter is responsible for 60,000 premature deaths each year, about 5 percent of the total premature deaths associated with particulate air pollution each year.

Earth Observatory, March 2012

A new NASA study underscores the fact that greenhouse gases generated by human activity — not changes in solar activity — are the primary force driving global warming.

The study offers an updated calculation of the Earth’s energy imbalance, the difference between the amount of solar energy absorbed by Earth’s surface and the amount returned to space as heat. The researchers’ calculations show that, despite unusually low solar activity between 2005 and 2010, the planet continued to absorb more energy than it returned to space.

James Hansen, director of NASA’s Goddard Institute for Space Studies (GISS) in New York City, led the research. Atmospheric Chemistry and Physics published the study last December.

Total solar irradiance, the amount of energy produced by the sun that reaches the top of each square meter of the Earth’s atmosphere, typically declines by about a tenth of a percent during cyclical lulls in solar activity caused by shifts in the sun’s magnetic field. Usually solar minimums occur about every eleven years and last a year or so, but the most recent minimum persisted more than two years longer….

NASA, January 2012

A Less Hardy Hardiness Map

The USDA has unveiled a new version of its plant hardiness map, which gardeners use to gauge which plants will survive in which climate zone. (Check your nearest seed packet.)  In the newest iteration, many zones have shifted northward because winters aren’t as cold as they were 22 years ago when the agency last updated the map — good news if you’re trying to grow, say, figs in Boston. On the new map, most parts of the United States are a half-zone warmer — about 5 degrees Fahrenheit (2.7 Celsius). Global warming surely underlies much of the change, but theUSDA points out that more sophisticated mapping techniques, plus the inclusion of data from additional weather stations, has also affected the distribution of the zones.

Why the Arctic Ocean Isn’t Freshening
Rapid freshening on the North American side of the Arctic Ocean in recent decades has prompted speculation that rapid melting of sea ice might be causing a slowing of the “conveyor belt” that keeps water circulating through the world’s oceans. New research led by scientists at the University of Washington helps allay such fears. The researchers conclude that freshwater from the Eurasian part of the Arctic Ocean, which comes originally from rivers in Russia, has simply found a new route that brings more of it toward Canada. The cause for the new freshwater route: changes in winds associated with a weather patternknown as the Arctic Oscillation. In fact, the analysis of satellite and oceanographic data shows that overall salinity in the Arctic Ocean remained constant between 2005 and 2008; as the Canadian portion became fresher, the Eurasian portion grew saltier. The shifting path of the fresh water is shown in red in the animation below.

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Temperature Ranking-palooza
There’s always a flurry of media activity in January when scientists at NASANOAA, and the UK Met Office tally up the year’s temperature measurements and rank how warm the past year was. This January was no exception. In NASA’s analysis, 2011 came in as the 9th warmest year on the modern meteorological record. However, the longer-term trends are what really matter. Look at the whole record – and here are a fewinteractive charts that are useful for doing that – and it’s clear that the last decade has been the hottest on record. Another remarkable stat: 9 of the 10 hottest years have occurred since 2000. For more details, the science team that manages NASA’s analysis has published a thorough temperature update here.

Earth Observatory, January 2012