A VIEW OF THE CLOUDY EARTH

FROM:  NASA 

Decades of satellite observations and astronaut photographs show that clouds dominate space-based views of Earth. One study based on nearly a decade of satellite data estimated that about 67 percent of Earth’s surface is typically covered by clouds. This is especially the case over the oceans, where other research shows less than 10 percent of the sky is completely clear of clouds at any one time. Over land, 30 percent of skies are completely cloud free.

Earth’s cloudy nature is unmistakable in this global cloud fraction map, based on data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite. While MODIS collects enough data to make a new global map of cloudiness every day, this version of the map shows an average of all of the satellite’s cloud observations between July 2002 and April 2015. Colors range from dark blue (no clouds) to light blue (some clouds) to white (frequent clouds).

There are three broad bands where Earth’s skies are most likely to be cloudy: a narrow strip near the equator and two wider strips in the mid-latitudes. The band near the equator is a function of the large scale circulation patterns—or Hadley cells—present in the tropics. Hadley cells are defined by cool air sinking near the 30 degree latitude line north and south of the equator and warm air rising near the equator where winds from separate Hadley cells converge. (The diagram here illustrates where Hadley cells are located and how they behave.) As warm, moist air converges at lower altitudes near the equator, it rises and cools and therefore can hold less moisture. This causes water vapor to condense into cloud particles and produces a dependable band of thunderstorms in an area known as the Inter Tropical Convergence Zone (ITCZ).

Clouds also tend to form in abundance in the middle latitudes 60 degrees north and south of the equator. This is where the edges of polar and mid-latitude (or Ferrel) circulation cells collide and push air upward, fueling the formation of the large-scale frontal systems that dominate weather patterns in the mid-latitudes. While clouds tend to form where air rises as part of atmospheric circulation patterns, descending air inhibits cloud formation. Since air descends between about 15 and 30 degrees north and south of the equator, clouds are rare and deserts are common at this latitude.

Image Credit: NASA Earth Observatory image by Jesse Allen and Kevin Ward, using data provided by the MODIS Atmosphere Science Team, NASA Goddard Space Flight Center

Caption: Adam Voiland, with information from Steve Platnick and Tom Arnold

Last Updated: May 9, 2015

Editor: Sarah Loff

NASA INFO ON MT. EVEREST

FROM:  NASA   

Fourteen mountain peaks on Earth stand taller than 8,000 meters (26,247 feet). The tallest of these “eight-thousanders” is Mount Everest, the standard to which all other mountains are compared. The Nepalese name for the mountain is Sagarmatha: “mother of the universe.” Everest’s geological story began 40 million years ago when the Indian subcontinent began a slow-motion collision with Asia. The edges of two continents jammed together and pushed up the massive ridges that make up the Himalayas today. Pulitzer-winning journalist John McPhee summed up the wonder of the mountain’s history when he wrote Annals of the Former World: “The summit of Mount Everest is marine limestone. This one fact is a treatise in itself on the movements of the surface of the Earth. If by some fiat, I had to restrict all this writing to one sentence; this is the one I would choose.” In other words, when climbers reach the top of Mount Everest, they are not standing on hard igneous rock produced by volcanoes. Rather, they are perched on softer sedimentary rock formed by the skeletons of creatures that lived in a warm ocean off the northern coast of India tens of millions of years ago. Meanwhile, glaciers have chiseled Mount Everest’s summit into a huge, triangular pyramid, defined by three faces and three ridges that extend to the northeast, southeast, and northwest. The southeastern ridge is the most widely used climbing route. It is the one that Edmund Hillary and Tenzing Norgay followed in May 1953 when they became the first climbers to reach the summit and return safely. Climbers who follow this route begin by trekking past Khumbu glacier and through the Khumbu ice fall, an extremely dangerous area where ice tumbles off the mountain into a chaotic waterfall of ice towers and crevasses. Next, climbers reach a bowl-shaped valley—a cirque—called the Western Cwm (pronounced coom) and then the foot of the Lhotse Face, a 1,125-meter (3,691-foot) wall of ice.

Climbing up the Lhotse face leads to the South Col, the low point in the ridge that connects Everest to Lhotse. It is from the South Col that most expeditions launch their final assault on the summit, following a route up the southeastern ridge. Some climbers opt for the northern ridge, which is known for having harsher winds and colder temperatures. That is the path that British climbers George Mallory and Andrew Irvine used in 1924 during what may, in fact, have been the first ascent.

Whether the pair made it to the summit remains a topic of controversy, but what is known for certain is that the men were spotted pushing toward the peak just before the arrival of a storm. Mallory’s corpse was discovered near the northeast ridge at 8,160 meters (26,772 feet) by an American climber in 1999, but it still isn’t clear whether he reached the summit. Despite its reputation as an extremely dangerous mountain, commercial guiding has done much to tame Everest in the last few decades. As of March 2012, there had been 5,656 successful ascents of Everest, while 223 people had died—a fatality rate of 4 percent. > Read More Image Credit: NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team, archived on the USGS Earth Explorer. Caption: Adam Voiland.

THE LARGEST VOLCANO ON EARTH

FROM:  NATIONAL SCIENCE FOUNDATION 
Scientists confirm existence of largest single volcano on Earth

The summer blockbuster movie Pacific Rim told a fanciful tale of giant monsters rising from the deep in the middle of the Pacific Ocean.

Now, scientists have confirmed that the northwest Pacific is home to a real-life giant of a different type: the largest single volcano yet documented on Earth.

Covering an area roughly equivalent to the British Isles or the State of New Mexico, Tamu Massif is nearly as big as the giant volcanoes of Mars, placing it among the largest in the solar system.

"This is an amazing discovery, and overturns previous conclusions that Earth cannot support the development of such giant volcanoes because it lacks a thick and rigid planetary lithosphere," says Jamie Allan, program director in the National Science Foundation's Division of Ocean Sciences, which funded the research.

"Much remains to be discovered about our planet," says Allan, "with scientific drilling offering a means of observation and discovery into otherwise inaccessible parts of the Earth."

Located about 1,000 miles east of Japan, Tamu Massif is the largest feature of Shatsky Rise, an underwater mountain range formed 145-130 million years ago by the eruption of several underwater volcanoes.

Until now, it was unclear whether Tamu Massif was a single volcano, or a composite of many eruption points.

By integrating several sources of evidence, including core samples and data collected on board the JOIDES Resolution, scientists have confirmed that the mass of basalt that constitutes Tamu Massif did indeed erupt from a single source near the center.

The results appear today in a paper in the journal Nature Geoscience.

"Tamu Massif is the biggest single shield volcano ever discovered on Earth," says lead paper author Will Sager of the University of Houston.

"There may be larger volcanoes, because there are bigger igneous features out there such as the Ontong Java Plateau. But we don't know if these features are one volcano or complexes of volcanoes."

Tamu Massif stands out among underwater volcanoes not just for its size, but also its shape.

It is low and broad, meaning that the erupted lava flows must have traveled long distances compared to most other volcanoes on Earth.

The seafloor is dotted with thousands of underwater volcanoes, or seamounts, most of which are small and steep compared to the low, broad expanse of Tamu Massif.

"It's not high, but very wide, so the flank slopes are very gradual," Sager explains.

"In fact, if you were standing on its flank, you would have trouble telling which way is downhill.

"We know that it is a single immense volcano constructed from massive lava flows that emanated from the center of the volcano to form a broad, shield-like shape. Before now, we didn't know this because oceanic plateaus are huge features hidden beneath the sea. They have found a good place to hide."

Tamu Massif covers an area of about 120,000 square miles.

By comparison, Hawaii's Mauna Loa--the largest active volcano on Earth--is a mere 2,000 square miles, or less than 2 percent the size of Tamu Massif.

To find a worthy comparison, one must look skyward to the planet Mars, home to Olympus Mons. That giant volcano, which is visible on a clear night with a good backyard telescope, is only about 25 percent larger by volume than Tamu Massif.

The study relies on two distinct yet complementary sources of evidence: core samples collected on Integrated Ocean Drilling Program Expedition 324, which tested plume and plate models of ocean plateau formation at Shatsky Rise in the northwest Pacific Ocean in 2009, and seismic reflection data gathered on two separate expeditions of the research vessel Marcus G. Langseth in 2010 and 2012.

The core samples, drilled from several locations on Tamu Massif, showed that thick lava flows up to 75 feet thick characterize this volcano.

Seismic data from the Langseth cruises revealed the structure of the volcano, confirming that the lava flows emanated from its summit and flowed hundreds of miles downhill into the adjacent basins.

"This finding gives us new insights about oceanic volcanism, the way in which oceanic plateaus form, and the operation of the mantle-crust system," Sager explains.

"Volcanologists debate about the eruptive centers of what are called large igneous provinces. I think most would tell you that they probably come from multiple, distributed fissure eruptions.

"But apparently not at Tamu Massif."

-NSF-