Large Fires in Northern Mexico

These images, taken by the Landsat-5 satellite on April 9, 2011, illustrate the challenges facing firefighters combating two large wildfires in northern Mexico’s Coahuila state. The fires are burning on steep mountain slopes that are difficult to impossible for ground crews to reach. The top image shows dense plumes of smoke blowing northeast on strong winds. The lower image, which includes both infrared and visible light, provides a view through the smoke to the freshly burned terrain.

The fires, called El Bonito and La Sabina, were caused by lightning strikes in mid-March and had burned 99,000 hectares (245,000 acres or 380 square miles) as of April 11. The fires are among the largest in Mexico’s history, according to news reports. The burned land is brick red in the lower image. Hot areas glow orange in infrared light, revealing the active fire front on the south and west sides of the burned area. (The orange horizontal stripes are satellite sensor artifacts.)

The fires are burning mostly grass and shrub land, ecosystems that are adapted to fire, says the Comisión Nacional Forestal (CONAFOR, Mexico’s National Forest Service). Lack of winter rain and frost left the plants dry and prone to fire. On top of that, the area has not burned for more than 20 years, during which time fuel built up. Thunderstorms and steady strong winds with gusts up to 70 miles per hour completed the formula for a dangerous, fast-moving wildfire.

As of April 11, the fire-prone vegetation, inaccessible terrain, and strong winds had thwarted 900 firefighters working to control the fires, said CONAFOR. On April 11, a Boeing 747 tanker and three helicopters from the United States joined nine helicopters in fighting the fires.

Once the fire is out, the grass and shrub ecosystems should return quickly. In such ecosystems, fire usually destroys the above-ground plants while sparing the roots. This means that the burned area should begin to recover in the next rainy seaso

Dust Storm in the Middle East

An intense dust storm blew over the Middle East in April 2011. Dust plumes extended from the western shore of the Persian Gulf to the eastern shore of the Caspian Sea. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image on April 13, 2011.
Dust is thickest over northern Saudi Arabia, southern Iraq, and Kuwait—the latter being completely covered by dust plumes. Dust also hides the northwestern shoreline of the Persian Gulf. On April 13, United Press International reported that the dust storm had paralyzed Kuwait, stalling air traffic and oil exports. The dust likely picked up material from the vast sand seas of Saudi Arabia.
The opaque plume covers the southwestern tip of Iran, and thinner plumes extend northeast across Iran and the Caspian Sea. The northeastern margin of the storm ap

Bezymianny Volcano

Russia’sBezymianny Volcano erupted vigorously on the morning of April 14, 2011. At the time of the eruption, the Joint Air Force & Army Weather Information Network reported ash at an altitude of 25,000 feet (7,600 meters) above the volcano. This natural-color satellite image (top) shows evidence of the size of the eruption. Dark volcanic deposits (likely a combination of pyroclastic flows and lahars) extend more than 7.3 kilometers (4.5 miles) into valleys to the southeast. A light-colored plume of ash, steam, and sulfur dioxide rises above Bezimianny’s summit and blows towards the west. Volcanic ash covers the upper slopes of the volcano, especially to the south and west. White snow, still deep in late April, blankets the surrounding landscape.
A false-color image (lower) reveals more features on the active volcano. At the summit, a red “hot spot” may indicate where fresh lava is being extruded from the lava dome. To the southeast, an active lava flow appears as a similar hot spot. In these wavelengths, bare rock and ash are gray, and snow and ice appear cyan. These images were acquired near noon on April 22, 2011, by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite.

Bottoms Up for Antarctic Ice

Upending the idea that all ice sheets grow from the accumulation of snow at the top, researchers working in Antarctica have found evidence of large-scale ice-making at the bottom of that continent's massive ice sheets. The surprise finding could change scientists’ understanding of how glaciers rise, fall, and move horizontally across the landscape.

An international research team flew multiple Twin Otter airplane passes over East Antarctica’s Gamburtsev Mountains from November 2008 through January 2009. Equipped with ice-penetrating radar, magnetometers, laser ranging systems, and gravity meters, scientists mapped the topography of the ice surface and of the buried mountain range at the bottom of the ice sheet. The project was funded by the U.S. National Science Foundation and other international institutions as part of the International Polar Year.

The image above shows a radar profile of the ice as recorded on January 1, 2009, on the south side of Dome A in the Gamburtsevs. The base of the image reveals the rugged land beneath the ice, while the upper edge shows the flat, annual layering typical of ice formation from the top. In between, there is a jumbled mess unlike anything researchers had seen before.

When the science team first examined their radar profiles in real time, they thought there was a mistake, a glitch in the instrument or data. Perhaps the science team was just too tired from the long, cold flights. But further analysis confirmed what they were seeing.

“We usually think of ice sheets like cakes—one layer at a time, added from the top,” said Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory. “This is like someone injected a layer of frosting at the bottom—a really thick layer.”

Beneath Dome A, a plateau that forms the high point of the East Antarctic ice sheet, at least 24 percent of the ice formed from the bottom up. In other places, as much as half of the ice sheet is made up of this bottom-forming ice.

Researchers believe friction between the ice and land surface, as well as natural heat radiating from the solid earth, can melt significant amounts of water on the underside of an ice sheet. Several years ago, scientists found large lakes underneath the Antarctic ice that were likely formed by such processes. The liquid water is insulated from the extreme cold of the surface air by the ice sheet; the extreme pressure from the overlying ice can also make it harder for water to freeze.

The movement of the ice sheet and the natural flow of water over the landscape can then move some of that water to areas where there is less ice above—meaning less pressure and less insulation. Sometimes the water is squeezed up valley walls. Either way, the result is a quick re-freezing that makes the unusual ice formations shown above. The creation of this bottom ice can deform the shape of the entire ice sheet above.

“Water has always been known to be important to ice sheet dynamics, but mostly as a lubricant,” Bell added. “As ice sheets change, we want to predict how they will change. Our results show that models must include water beneath.”

Earth's Magnetosphere

You've seen the pattern in science class when you laid bits of iron around a bar magnet. The invisible force field around the magnet becomes suddenly visible when the iron filings fall into line.

The iron-cored Earth is also a great magnet, and scientists have spent a century exploring its shape and structure. The visualization above shows the magnetic field around Earth—the magnetosphere—as it might look from space. This view is conceptual, but based on real science observations that have been made since the beginning of the Space Age. The orange and blue lines depict the opposite north and south polarity of Earth's field lines.

The field lines are not actually visible, but they can be detected by sensors that count atomic particles—protons and electrons moving in the space around Earth. Unlike the symmetrical pattern of the iron filings and magnet, the magnetosphere is pushed in on the side facing the Sun and stretched out in the Earth's wake. This is caused by the solar wind, a stream of high-speed particles flowing out from the Sun and carrying the signatures of its own magnetic field.

Like the ozone layer, the magnetosphere is important to life on Earth because it protects us from most of the harmful radiation and hot plasma from the Sun, deflecting it into space. The magnetic field is constantly buffeted by our nearest star's emissions, which can lead to electrical currents flowing in the space around Earth—currents that can disrupt radio transmissions and damage satellites in a phenomenon known as space weather

Sunset over Western South America

Astronauts onboard the International Space Station see, on average, 16 sunrises and sunsets during a 24-hour orbital period. Each changeover between day and night is marked by the terminator, a line on Earth's surface separating the sunlit side from the darkness.

While the terminator is often conceptualized as a hard boundary—and is frequently presented as such in graphics and visualizations—in reality the edge of light and dark is diffuse due to the scattering of light by the Earth’s atmosphere. This zone of diffuse lighting is experienced as dusk or twilight on the ground; while the Sun is no longer visible, some illumination is still present due to light scattering over the local horizon.

The terminator is visible in this panoramic view across central South America, looking towards the northeast. An astronaut shot the photo at approximately 7:37 p.m. local time. Layers of the Earth’s atmosphere, colored bright white to deep blue, are visible on the horizon (or limb). The highest cloud tops have a reddish glow due to direct light from the setting Sun, while lower clouds are in twilight.

The Salar de Coipasa, a large salt lake in Bolivia, is dimly visible on the night side of the terminator. The salar provides a geographic reference point for determining the location and viewing orientation of th