The island of Hawaii rarely takes a direct hit from a hurricane. In August 2016, two Pacific storms almost changed that.
The Suomi NPP satel ite observed Hurricanes Madeline and Lester stirring up the central Pacific Ocean as category 3 and 4 storms while moving northwest toward the Hawai an Islands. The tight, deep eye of category 3 Hurricane Madeline (right) appears almost three-dimensional even in a two-dimensional satel ite view. Lester (next page) showed off an equal y menacing eye. The bright streaks across the ocean surface are areas of sunglint, where sunlight reflected directly back at the image.
Ultimately, the storms blew just south and north of the islands without making landfal . In fact, no hurricane has made landfall on the Big Island since recordkeeping started in 1949. Only 15 hurricanes have passed within 200 nautical miles of the island in that time.
E
HERPSOMTA
THRAE
20
E
HERPSOMTA
THRAE
22
Making Tracks
Pacific Ocean
Ships steaming across the Pacific Ocean left this cluster of bright cloud trails lingering in the atmosphere in February 2012. The narrow clouds, known as ship tracks, form when water vapor condenses around tiny particles of pol ution from ship exhaust. The crisscrossing clouds off the coast of California stretched for 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 pol ution particles generated by ships (especial y sulfates) are soluble in water and can serve as the seeds around which cloud droplets form. Clouds infused with ship exhaust have more and smal er droplets than unpol uted clouds. As a result, light hitting the ship tracks scatters in many directions, often making them appear brighter than other types of marine clouds, which are usual y seeded by larger, natural y occurring particles like sea salt.
E
HERPSOMTA
THRAE
24
Tracing the Coast
China
The ocean does not heat up as much throughout a day as landmasses do. For this reason, cool, moist marine air commonly gives rise to dense clouds over the ocean.
In this example from the coast of China, an onshore wind carries the clouds from the ocean toward the land. But the land is warmer, drier, and unfavorable for cloud growth. As a result, the marine clouds that move onshore tend to evaporate, leaving a cloud layer that traces the coastline.
E
HERPSOMTA
THRAE
26
Four Mountains Stand Out
Pacific Ocean
They are cal ed the Islands of the Four Mountains. Part of the Aleutian Island chain, these peaks are actual y the upper slopes of volcanoes rising from the seafloor: Carlisle, Cleveland, Herbert, and Tana. Standing in one of the most remote reaches of the world, these volcanoes have scarcely been studied. Satel ite sensing makes that easier, as this Landsat 8 image from June 2013 shows.
Herbert Island (right) is dominated by a symmetrical stratovolcano that stands in its center. The remote island has scarcely been studied, and there are no records of eruptions there. The 2-kilometer-wide summit caldera include a lake of meltwater, remnants of the snow that covers the peak for most of the year. The straight-down (nadir) satel ite view can make it difficult to determine which part of the landscape stands tal er than the other, a phenomenon known as relief inversion.
On the next page, you can see how a layer of low clouds and fog obscures the lower elevations of the islands and the sea surface.
But these clouds also hint at the complicated airflow patterns around and through the islands.
E
HERPSOMTA
THRAE
28
E
HERPSOMTA
THRAE
30
Framing an Iceberg
South Atlantic Ocean
In June 2016, the Suomi NPP satel ite captured this image of various cloud formations in the South Atlantic Ocean. Note how low stratus clouds framed a hole over iceberg A-56 as it drifted across the sea.
The exact reason for the hole in the clouds is somewhat of a mystery. It could have formed by chance, although imagery from the days before and after this date suggest something else was at work. It could be that the relatively unobstructed path of the clouds over the ocean surface was interrupted by thermal instability created by the iceberg. In other words, if an obstacle is big enough, it can divert the low-level atmospheric flow of air around it, a phenomenon often caused by islands.
E
HERPSOMTA
THRAE
32
Valley Fog
Canada
Fog is essential y a cloud lying on the ground. Like all clouds, it forms when the air reaches its dew point—the temperature at which an air mass is cool enough for its water vapor to condense into liquid droplets.
This false-color image shows val ey fog, which is common in the Pacific Northwest of North America. On clear winter nights, the ground and overlying air cool off rapidly, especial y at high elevations. Cold air is denser than warm air, and it sinks down into the val eys. The moist air in the val eys gets chil ed to its dew point, and fog forms. If undisturbed by winds, such fog may persist for days. The Terra satel ite captured this image of foggy val eys northeast of Vancouver in February 2010.
E
HERPSOMTA
THRAE
34
Holuhraun Lava Field
Iceland
As an island in the moist, turbulent North Atlantic, Iceland is often shrouded in clouds and difficult to observe from space. In 2014, the island started making some of its own cloud cover, as the Earth split open between the Bárðarbunga and Askja volcanoes and spewed lava and hot gas.
Landsat 8 captured this view of the eruption in September 2014. The false-color image combines shortwave infrared, near-infrared, and green light. Ice and the plume of steam and sulfur dioxide appear cyan and bright blue, while liquid water is navy blue. Bare or rocky ground around the Holuhraun lava field appears in shades of green or brown, and fresh lava is bright orange. Offshore clouds appear in bright cyan.
Infrared imagery can help scientists estimate the rate at which lava is pouring out of Earth, as well as the sulfur dioxide content of the plume. It also helps them pinpoint lava flows and model how the eruption evolved.
E
HERPSOMTA
THRAE
36
Lofted Over Land
Madagascar
Along the muddy Mania River, midday clouds form over the forested land but not the water. In the tropical rainforests of Madagascar, there is ample moisture for cloud formation. Sunlight heats the land all day, warming that moist air and causing it to rise high into the atmosphere until it cools and condenses into water droplets. Clouds general y form where air is ascending (over land in this case), but not where it is descending (over the river). Landsat 8 acquired this image in January 2015.
E
HERPSOMTA
THRAE
38
We shall not cease from exploration, and
the end of all our exploring will be to arrive
where we started and know the place for
the first time.
—T.S. Eliot
“Little Gidding”
re
atW
THRAE
40
water
Channel Country
Australia
Australia’s Channel Country is full of hundreds of channels, as the Georgina, Burke, and Hamilton rivers merge into the very broad floodplain of Eyre Creek. The land is flat and the drainage is poor, which encourages semi-permanent wetlands to form at the meeting points of the rivers.
These wide floodplains in Queensland are unique on the planet. Scientists think they are caused by the extreme variation in water and sediment discharges from the rivers. In many years there is no rai
nfall at al , and the rivers are effectively non-existent. In years of modest rainfal , the main channels will carry some water, sometimes spil ing over into narrow water holes known as bil abongs.
Every few decades, the floodplain carries extremely high discharges of water. For instance, tropical storms to the north can lead to great water flows that inundate the entire width of the floodplain. On such occasions, the floodplain appears as series of brown and green water surfaces with only tree tops indicating the location of the islands. Such is the case in this image taken from the International Space Station in September 2016.
re
atW
42
Tea-Colored Rupert Bay
Canada
Remote Rupert Bay is a place where the majesty and dynamism of fluid dynamics is regularly on display. With several rivers pouring into this nook of James Bay, the col ision of river and sea water combines with the churn of tides and the motion of currents to make swirls of colorful fluid.
As they wind through the boreal forests and wetlands of northern Quebec, the rivers that flow into Rupert Bay carry water stained brown with natural chemical substances found in plants. Tannins and lignins from roots, leaves, seeds, bark, and soil can leach into the water and give it a yel ow, brown, or even black color. (The same process gives tea its dark color.) Note that the colored plumes and intricate vortices around the islands are pointing inland—an indicator that the tide was likely coming in, or that northwesterly winds were affecting the flow of the water.
re
atW
44
re
atW
THtHRrAaEe
46
Coral Cocos
Indian Ocean
Coral atol s—which are largely composed of huge colonies of tiny animals such as cnidaria—form around islands. After the islands sink, the coral remains, general y forming complete or partial rings. The South Keeling Islands, part of the Cocos Islands in the Indian Ocean, are such a place.
Only some parts of the South Keeling Islands still stand above the water surface. In the north, the ocean overtops the coral.
Along the southern rim of this atol , shal ow water appears aquamarine. Water darkens to navy blue as it deepens toward the central lagoon. Above the water line, coconut palms and other plants form a thick carpet of vegetation. Hard and soft corals thrive throughout the reef.
re
atW
48
Bay of Whales
Russia
The area around Russia’s Ulbanskiy Bay is mostly uninhabited by humans, but it does support sizable numbers of whales. In summertime, this bay is a feeding ground for bowheads, belugas, and orcas that come to Ulbanskiy for the seafood buffet. They hunt by driving fish like herring and smelt toward the coast and into freshwater inlets.
Onshore, freshwater streams meander into marshlands and gently sloped mud flats. The marshes around the bay are dotted with small bodies of water. These are likely thermokarst lakes—pools of water that fill in depressions in the land surface as permafrost melts. Farther inland, the incline becomes steeper and the landscape darker with the greens of pine-covered slopes. A lighter green band (left side) indicates deciduous (leaf-shedding) trees that have begun to turn color.
re
atW
50
Storms Stir Up Sediment
Bermuda
In October 2014, the eye of Hurricane Gonzalo passed right over Bermuda. In the process, the potent storm stirred up the sediments in the shal ow bays and lagoons around the island, spreading a huge mass of sediment across the North Atlantic Ocean. This Landsat 8 image shows the area after Gonzalo passed through.
The suspended sediments were likely a combination of beach sand and carbonate sediments from around the shal ows and reefs.
Coral reefs can produce large amounts of calcium carbonate, which stays on the reef flats (where there are coral ine algae that also produce carbonate) and builds up over time to form islands.
Storm-induced export of carbonates into the deep ocean—where they mostly dissolve—is one of the ways that the oceans natural y balance the addition of atmospheric carbon dioxide to ocean waters.
re
atW
52
The Meeting of the Waters
Brazil
The Encontro das Águas, or the “Meeting of the Waters,” is one of those places that simply wow people.
As Robert Meade of the U.S. Geological Survey once described: “Six Mississippi Rivers’ worth of cafe-au-lait-colored water are converging here with two Mississippis’ worth of black-tea-colored water to produce the greatest hydrologic spectacle on the planet.”
The coffee-colored Rio Solimões, rich with sediment, runs down from the Andes Mountains. The black-tea-tinted Rio Negro that flows from the Colombian hil s and jungles is nearly sediment-free and colored by decayed leaf and plant matter. Where the rivers meet, east of Manaus, Brazil, they flow side by side within the same channel for several kilometers. The cooler, denser, and faster waters of the Solimões and the warmer, slower waters of the Negro form a boundary that is visible from space. Turbulent eddies eventual y mix the two and become the Lower Amazon River.
re
atW
54
A Lava Lamp Look at the Atlantic
Atlantic Ocean
Stretching from tropical Florida to the doorstep of Europe, the Gulf Stream carries a lot of heat, salt, and history. This river of water is an important part of the global ocean conveyor belt, moving water and heat from the Equator toward the far North Atlantic. It is one of the strongest currents on Earth and one of the most studied. Its discovery is often attributed to Benjamin Franklin, though sailors likely knew about the current long before they had a name for it.
This image shows a small portion of the Gulf Stream off of South Carolina as it appeared in infrared data col ected by the Landsat 8
satel ite in April 2013. Colors represent the energy—heat—being emitted by the water, with cooler temperatures in purple and the warmest water being nearly white. Note how the Gulf Stream is not a uniform band but instead has finer streams and pockets of warmer and colder water.
re
atW
56
Teeming Life in the Strait of Georgia
Canada
In August 2016, the waters off of British Columbia turned bright green. The Strait of Georgia and nearby inlets were teeming with coccolithophores—a harmless type of floating plant-like organisms called phytoplankton. Coccolithophores have chalky, scale-like shel s made of calcium carbonate. The milky-white color of those shel s can brighten and discolor otherwise blue waters when the plankton explode in such massive blooms.
While coccolithophore blooms occasional y occur off the west coast of Vancouver Island, few scientists could recall seeing a bloom like this in the strait. Research suggests that coccolithophore numbers have been increasing in recent decades even as the water has been growing more acidic.
re
atW
58
Ephemeral Lake Frome
Australia
The interior of Australia is full of ephemeral lakes. These basins pass most of their time as salt pans, but occasional heavy rains can fill them with water.
The Earth Observing-1 satel ite captured this image in April 2010 after water had flowed into Lake Frome, which stands at the southern end of an arc of salt pans. When it fil s, the waters usual y come from precipitation in the hil s and other salt pans upstream.
The land to the east has a slightly higher elevation and consists of a network of dry river channels. Inside the salt pan, the land surface is uneven. Areas shaped like sloppy teardrops rise above the surrounding plain. Water on the surface appears in shades of dull green. And throughout much of Lake Frome, water makes its presence known not through standing water but through mud or wet salts. Darker surfaces show where water has seeped through typical y dry sediments.
re
atW
>
60
Dueling Blooms
Barents Sea
As the seasons pass on Earth, different species tend to dominate the landscape at different times. Such was the case in July 2014 in the surface waters of the Barents Sea, north of Norway and Russia. The Aqua satel ite captured a transitional moment between one form of microscopic, plant-like organisms (phytoplankton) and another.
Several currents merge in this area, and intersecting waters combine with stiff winds to promote mixing of waters and nutrients from the deep. Note the green swirls on the center and left, as well as the milky, blue-white swirls on the upper right. (The fluffy white area is cloud cover.) It is likely that the green plankton were diatoms and the white ones were coccolithophores. Research has suggested that diatoms start to bloom in the wel -mixed, cooler waters of spring and dominate the early summer. As the water warms and becomes more stratified or layered, coccolithophores bloom more abundantly.
re
atW
62
A Bay Sculpted by Ice
Canada
The land around Liverpool Bay in Canada’s Northwest Territories owes its otherworldly appearance to ice past and present.
Thousands of years ago, this area was buried under a massive ice sheet that sprawled over much of North America. During that time, glacial activity carved out paral el lakes separated by strips of land that look like giant, skeletal fingers. After the glaciers retreated, pockets of ice lingered underground. As those pockets have melted and the frozen ground has thawed, lakes have formed.
Geologists have offered different explanations for the formation of the finger-shaped ridges: they may be moraines created by the movement of ice, or they might be sediment ridges that formed between channels of subglacial meltwater. Smal er thermokarst lakes in this scene are formed by both the long- and short-term melting of ice and permafrost.
earth Page 2