Derecho Downs Trees from Indiana Eastward

On June 29, 2012, a long-lived, fast-moving windstorm blew over the eastern United States. The storm started in northwestern Indiana and, over the next 10 hours, traveled roughly 600 miles (1,000 kilometers) toward the East Coast. Wind speeds matched those of an EF-1 tornado in places. The storm uprooted trees, damaged homes, smashed cars, downed power lines, and left more than a million residents of the Washington, D.C. area without electricity.

This photo shows an unusual cloud formation on the leading edge of the June 29 windstorm. Image courtesy Kevin Gould and NOAA.

Meteorologists classified the storm as a derecho—a windstorm associated with fast-moving thunderstorms. A derecho is not a new phenomenon; the term was coined in the late nineteenth century. These storms can rival tornadoes in terms of the damage they cause but, unlike tornadoes, derecho winds generally cause damage in one direction.

The derecho that struck on June 29, 2012, occurred along the boundary of a stable, dry air mass to the north, and a moist, unstable air mass to the south. Areas affected by the southern air mass were suffering a severe heat wave, including record-breaking temperatures in multiple locations. The high heat and humidity provided energy to the strong winds. The thunderstorms sucked up warm, moist air and subsequently returned it in downdrafts. Hitting the ground at tremendous speed, the downdrafts fanned out over the surface, sometimes picking up speed.

The U.S. National Oceanic and Atmospheric Administration (NOAA) provides a primer on derechos, and an overview of the June 29 event. The Capital Weather Gang also provides a summary of the event.

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National Research Council Video Series Summarizes the State of Climate Science Research

A  new video series from the National Research Council  summarizes what scientists have learned about global warming and climate change.  It’s difficult to pack decades of complex research into short video snippets, but the makers of these videos have done an excellent job. As you watch, keep an eye out for mentions of the key role that remote sensing has played in advancing climate science. Also, look for the numerous data visualizations produced by the Scientific Visualization Studio at Goddard Space Flight Center that made the cut.

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Silent Spring Turns 50

On June 16, 1962, The New Yorker began publishing a serialized version of Silent Spring by Rachel Carson. Spring would eventually turn silent, Carson warned, because widespread pesticide use was killing so many birds that there might be none left to sing. The book provoked a strong reaction from the pesticide industry, but also led to tighter restrictions on pesticide use in the United States and other nations.

Born in 1907, Rachel Carson studied at The Johns Hopkins University and the Marine Biological Laboratory. She was the second woman hired by the U.S. Bureau of Fisheries for a non-secretarial position. In her spare time, she wrote newspaper and magazine articles. Between 1941 and 1955, she published three books about the ocean, leaving the fisheries bureau in 1952 to become a full-time writer. A decade later, she completed the book that made her beloved by some and despised by others.

Rachel Carson in 1944. Image courtesy of the National Conservation Training Archives.

When Carson wrote Silent Spring, dichlorodiphenyltrichloroethane (better known as DDT) was frequently used as an insecticide in domestic and agricultural applications. At the same time, multiple bird species were showing signs of decline. Carson connected the dots between pesticide use, wildlife decline, and human health.

One common misconception about Rachel Carson’s work is that she opposed all use of DDT, even when it could prevent the spread of malaria. Although she described dire scenarios of how pesticides might affect nature and people, she didn’t argue for an end to all DDT use. Instead, she argued for more cautious, targeted uses. A Nature article commemorating the anniversary of her book reported that the pesticide restrictions eventually implemented probably left DDT more effective in fighting malaria because pests had fewer opportunities to adapt and evolve.

Carson faced a firestorm of criticism for her book, but helped spur environmentalism in the United States and abroad. She did not live to see many of the consequences of her work as she had breast cancer when Silent Spring was published and died from it in 1964. As she wrote her book, iconic birds such as the American bald eagle were in decline; but by 2007, the bald eagle was removed from the U.S. Endangered Species list.

To learn more about Rachel Carson, please see the Earth Observatory feature article by guest author Brian Payton.

Reference: Dunn, R. (2012) In retrospect: Silent Spring. Nature, 485, 578–579

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Tornado Tracks

Tornadoes plague the central and eastern sections of the contiguous United States far more than the western portion. That much is obvious from this map showing 56 years of tornado tracks, from 1950 through 2006.

Image courtesy John Nelson, IDV Solutions.

This map breaks down tornadoes by strength based on the Fujita scale. Stronger tornadoes appear as brighter lines. (An enhanced Fujita scale was implemented in 2007, but these tornado tracks were classified according to the earlier version.)

One prerequisite for tornado formation is humidity, which is much greater in the east than in the west. But topography also plays a role; few tornadoes form over mountainous West Virginia, for instance.

This map was created by John Nelson of IDV Solutions. He obtained the data through Data.gov, which was set up to “increase public access to high value, machine readable datasets” generated by the U.S. government. A high-resolution version of this image is available here.

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Who Says Climate Models Aren’t Worth Talking About?

Here at the Earth Observatory we know as well as anybody that explaining the nuance and complexity of climate modeling isn’t easy.

In May, Nature Climate Change published a study pointing out that the number of news articles that mention climate change has been declining since 2007. There was a slight increase in mentions following the “Climategate” scandal in 2009, but the number has fallen rapidly since then (see the dashed line below).

Climate models are especially unpopular. Just a tiny fraction of the articles about climate science mention models (see the solid black line in the graph above). And, among the influential newspapers, that number is declining (see graph below).

When climate models do appear in the news, they’re often flagged as inaccurate, and political opinion outlets — rather than news outlets — account for a surprisingly large percentage of the mentions. Twice as many of the media outlets that mentioned climate models did so in a negative rather than a positive light, the study found. Political commentary outlets — The Rush Limbaugh Show, The Nation and The National Review — had the highest frequency of negative content about climate models, but a variety of other news outlets had ample negative content about models as well.

That’s surprising given the central role that modeling has played in revealing key aspects of climate science and in how the Earth works at a basic level. If you attend a scientific meeting these days, you’ll find there are few Earth science topics that don’t involve some sort of modeling. Want to know, for example, whether the plume from the huge fire burning in New Mexico is going to blow into Albuquerque? You need a model. Whether that hurricane brewing in the Gulf of Mexico will be coming to your city? You need a model. Whether there’s enough groundwater for your soybean crop to thrive? Again, you might well get your answer from a model. See the video below to see how researchers are predicting the severity of the Amazon fire season months in advance with the help of models.

Most earth science models, it’s worth noting, base their output on huge amounts of real observations; scientific modelers are not just pulling numbers from thin air. One model based at Goddard called the Modern Era Retrospective-analysis for Research and Applications (MERRA), for example, has ingested more than 50 billion satellite observations made since NASA launched the Terra satellite — and a new era of Earth observations — in 1999. Another model called GEOS-5, one of the highest-resolution models, also ingests huge amounts of data from the real world. GEOS-5 simulated the massive winter storm that struck the eastern United States in 2010 with remarkable accuracy.

Models are not just for earth science. The same sort of complex, numerical models are used all over the sciences. Alfio Quarteroni, a professor of mathematics at a university in Switzerland, laid out a few of them in an article in Notices of the Mathematical Society in 2009.

Credit: Notices of the AMS/Alfio Quarteroni

Aerospace engineers, he points out, use numerical models of fluid dynamics to make wingtips and fuselages more aerodynamic. Likewise, cardiovascular researchers take advantage of similar models to calculate how quickly blood flows through key arteries and how much stress the flow puts on artery walls as they narrow. Quarteroni has even used fluid dynamics models to try to figure out the best way to sail in different wind conditions.

Credit: Notices of the AMS/Alfio Quarteroni

Atmospheric scientists would be the first to point out that climate models aren’t always perfect. But as NASA modeler Gavin Schmidt pointed out in this Physics World article (which is worth the read if you want to understand what climate models can and can’t do), that lack of perfection doesn’t mean they’re not useful.

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The Big Picture around a Little Swamp

The Earth Observatory image of the day for June 5 shows flooding in Botswana’s Savuti River and Savuti Swamp. The abundant water turns out to be a very small part of a much bigger picture.

The Savuti Swamp sits within the Kalahari Desert, which stretches across Namibia, Angola, Zambia, South Africa, and most of Botswana. More of a sandy savannah than an actual desert, the Kalahari has wet and dry seasons that cause significant differences in vegetation. When the region is plunged into drought, an inland river delta, the Okavango, provides life-sustaining water for the wildlife. Since 2009, that water supply has been more abundant than usual, and the water has overflowed into other waterways in the region.

In 2009, the Okavango started experiencing record floods. “We first saw good flooding in Lake Ngami a few years back,” said Frank Eckardt of the University of Cape Town. “We have seen the Boteti River in flood since 2009 and also water in Lake Xau, southeast of the Okavango Delta.”

The satellite images below were acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite on April 28, 2012. The first image uses a combination of visible and infrared light to better distinguish between water and land. Water is navy blue, vegetation is bright green, and bare ground is earth-toned. The imagery shows not only abundant but early water: flows have arrived in the Okavango Detla well ahead of schedule (usually July) and the delta is overflowing.

The area outlined in white above is shown in this next close-up view of the Savuti channel and swamp that was featured as our image of the day. Impressive when well-watered, the swamp is in fact just a small part of a large network of rivers and basins.

“We had in concurrence the highest flood on record in the Cuando River and the flood in the Okavango River pushing through the Selinda Channel, the first time I have seen that documented,” said Guido van Langenhove of Hydrological Services Namibia. “The combined waters then reactivated the Linyanti River, which had been drying out since 1982, to reach the overflows/backwater of the Zambezi River through the Chobe River (Lake Liambezi).” Wetter conditions were apparent in the Bukalo Channel in 2011.

Van Langenhove explains that water has also started flowing through the Savuti Channel to the Mababe Depression, a 50-by-90-kilometer (30-by-60-mile) heart-shaped basin that normally receives little water.

The skinny strip of land jutting out from Namibia eastward is known as the Caprivi Strip. The Zambezi floodplain sits at the easternmost extent of this strip, and flooding occurred in that region before 2009.

References

Burrough, S.L., Thomas, D.S.G. (2008) Late Quaternary lake-level fluctuations in the Mababe Depression: Middle Kalahari palaeolakes and the role of Zambezi inflows. Quaternary Research, 69(3), 388-403.

Okavango-Delta.net. Okavango Delta Information. Accessed June 4, 2012.

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Mollusks, corals, carbon, and volcanoes

Paleozoic, Mesozoic, and Cenozoic. These are the major eras in the history of life on Earth, and the transition from one period to another has been marked by a major turnover in fossils — one assemblage of organisms going extinct and being replaced by another.

Today paleontologists agree that the biggest extinction in the fossil record occurred at the transition between the Paleozoic and Mesozoic, about 250 million years ago. During this Permo-Triassic extinction, perhaps as much as 70 percent of the plant, reptilian, amphibian, and insect species died on land. In the ocean, the consequences were even more devastating; up to 96 percent of Earth’s marine species went extinct.

The cause of such a catastrophic loss of life has been the subject of ongoing study. One proposed explanation is an asteroid strike like the one blamed for dinosaur extinction 65 million years ago. Another explanation involves the oxygen level in the ocean. Marine organisms need oxygen just as terrestrial organisms do, and some scientists have speculated that oxygen-poor water welled up from the ocean depths and suffocated marine life. Another hypothesis is large-scale volcanism. Studies published in November 2011 and May 2012 argue that volcanism does the best job of explaining all the evidence in the geologic record. And it not only explains the ancient mass extinction, but also hints at future threats to ocean life.

Although weathered by 250 million years of erosion, the Siberian Traps remain unmistakable today. Photo by Jon Ranson, NASA.

The volcanic hypothesis centers around the Siberian Traps, flat-topped volcanic mountains in Russia. The massive eruption that produced these mountains occurred 250 million years ago, about the same time as the Permo-Triassic extinction. The eruption was one of the biggest volcanic events in the last 500 million years, and it matches up with not only the timing of the extinction, but with the kinds of animals that were hit hardest.

Volcanoes release carbon dioxide, and the Siberian Traps eruptions would have emitted huge quantities of it, while also producing it indirectly. The basalts released by the eruptions flowed over sedimentary rock rich in organic material. Geologic studies of the Siberian Traps have revealed gas explosion structures along the margins of the flood basalts, which geologists have interpreted as evidence of sudden, violent carbon releases from sedimentary rocks under pressure by lava.

Besides raising atmospheric temperatures with heat-trapping gas, the newly released carbon dioxide would also have affected the ocean. Carbon dioxide dissolves in seawater to create carbonic acid, increasing ocean acidity. The carbonic acid reacts with carbonate ions, leaving less carbonate for marine life to use for shells or skeletons. Animals with such shells or skeletons suffer, but they don’t all suffer equally. Mollusks and marine arthropods have what biologists refer to as “buffered physiology,” which means they have closed circulation systems and/or gas-exchanging features (such as gills) to buffer their internal tissues from changes in ocean chemistry. Other animals such as sponges, corals, sea urchins, and sea lilies do not; their tissues are directly exposed to seawater. What the Permo-Triassic extinction studies found was that the poorly buffered organisms experienced greater rates of extinction and took longer to rebound.

Likely to be among the biggest losers in ocean chemistry changes, corals have few mechanisms to protect their internal tissues from increasing acidity. Image courtesy NOAA Ocean Explorer.

Carbon dioxide alone did not cause the catastrophic extinction 250 million years ago. Other factors, including higher temperatures and lower oxygen levels in the water, also pressured marine life. But carbon dioxide likely played an outsized role.

No one can predict when volcanic activity as widespread and destructive and the Siberian Traps eruptions might occur again. But we do know that rising carbon dioxide levels in the atmosphere pose a threat to marine life today. While volcanoes currently release 130 to 380 million metric tons of carbon dioxide each year, human burning of fossil fuels releases about 30 billion tons of it. That’s anywhere from 100 to 300 times as much greenhouse gas that can increase ocean acidity.

Today’s ocean contains a sizable reservoir of fine-grained calcium carbonate sediment that acts as a counterweight to rising ocean acidity. Geologists surmise that such a reservoir probably didn’t exist in the Permo-Triassic ocean. Moreover, today’s marine organisms descended from the survivors of high acidity episodes over the last 250 million years, so they may be better able to withstand ocean chemistry changes. Nevertheless, rising ocean acidity could spell trouble for marine organisms such as corals. A 2011 study of volcanic carbon dioxide seeps in Papua New Guinea found that ocean acidification and temperature stress reduced coral diversity and abundance. As before, poorly buffered marine life could suffer.

For more information on carbon dioxide and ocean acidification, please see the Earth Observatory features The Carbon Cycle and The Ocean’s Carbon Balance.

References

Clapham, M.E., Payne, J.L. (2011) Acidification, anoxia, and extinction: A multiple logistic regression analysis of extinction selectivity during the Middle and Late Permian. Geology. 39(11), 1059-1062.

Fabricius, K. E., Langdon, C., Uthicke, S. Humphrey, C. Noonan, S., De’ath, G. Okazaki, R. Muehllehner, N. Glas, M.S., Lough, J.M. (2011) Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations. Nature Climate Change. 1, 165-169.

Kerr, R.A. (1997) Life’s winners keep their poise in tough times. Science. 278(5342), 1403.

Mitchell, A. (2012, April 30) Life in the sea found its fate in a paroxysm of extinction. The New York Times.

Payne, J.L., Clapham, M.E. (2012) End-Permian mass extinction in the oceans: an ancient analog for the twenty-first century? Earth and Planetary Sciences. 40, 89-111.

PBS Evolution. (2001) Permian-Triassic extinction.

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Make a Movie, See a Launch

In case you missed it, NASA is sponsoring a video contest starring your home planet. The winner will receive behind-the-scenes access to the launch of NASA’s next major Earth-observing satellite — the Landsat Data Continuity Mission (LDCM) — from Vandenberg Air Force Base in January 2013.

Most of the public tends to focus on NASA’s role in planetary science, astrophysics, solar science, astronomy, and space flight. But as Earth Observatory readers know, we also have huge role in studying the one planet that is most important to us all. This contest is a chance to show how and why we should study our planet from space, and what that view means to you. The theme of your video should be: “The Home Frontier.”

We would love to see some entries from EO readers. If you dig around in our archives, you will find more than 11,000 Earth photos, maps, animations, and data visualizations to work with. Just about all of them are in the public domain and free to use in your creations.

For all of the rules and guidelines, visit this page. The contest ends on May 31, 2012. As we all know, nothing motivates quite like a quick deadline…

P.S. — For some inspiration, here is the video that won last year’s contest:

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Question from Facebook: What Controls the Thickness of a Storm’s Dust?

We recently posted an image of a dust storm in the Middle East (see below) that prompted one of our Facebook followers to ask why the dust is thicker near the left part of the image than the right. He wondered if the layer of dust is usually thickest near the origin of dust storms.

I contacted Ralph Kahn, an atmospheric scientist at NASA Goddard who specializes in studying dust and other types of aerosols for an answer. Kahn quickly emailed back with a detailed explanation. At the end of his note, he even managed to toss in a reference to dust storms on Mars. Kahn’s full note (in italics and with imagery added) is below.

“The thickness of dust in the atmosphere depends on several factors. In simple situations, there are discrete sources, and a wind that blows steadily in one direction. In this case, you get a relatively thick plume near-source that eventually thins and dissipates downwind, as the plume broadens, and as some of the dust settles out of the atmosphere. An example of this on the Earth Observatory is here (see the image below).

It is slightly more complex when the source is an extended area, and the wind still blows steadily in one direction. In this case, you can get a relatively thick plume near-source that again thins and dissipates downwind, but not so uniformly. Examples of this on the Earth Observatory are here, here, and here (see the three images below).

Here there is structure in the plumes, as there are multiple sources within the source regions whose plumes tend to merge, and some are more productive than others, which could be due to differences in the surface and/or in the near-surface wind. Moving downwind, there is some structure in the wind as well, most likely due to wind shear (different wind speeds at different elevations).

Dust storm in New Mexico. Image from the Crew Earth Observations Office. Click on it for more details.

Dust storm in the Saharan Desert. Image acquired by MODIS. Click on it for more details.

Combining multiple sources, changes in the near-surface wind speed and direction at some sources over time, differences in the speed or direction of the wind carrying the dust after it is lifted (which can occur at different *elevations* as well as different horizontal locations) and different rates of settling, any number of patterns can arise. (Note: Kahn gave us five examples, but I only included these two.  You can view the other three here, here, and here.)

Dust storm in Afghanistan. Image acquired by MODIS. Click on it for more details.

And sometimes dust heats up in the atmosphere, and actually convects, creating cumulus-like plumes. This is common on Mars, but can also occur on Earth.

Dust storm in Kazakhstan. Image from the International Space Station. Click on it for more details.

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Checking in and checking out of spring break

The past few weeks have been rough on Earth-observing satellites. (The past decade hasn’t been great either.) But there was some good news and some engineering prowess to go along with the troubles.

On April 8, 2012, the European Space Agency’s Envisat suffered a permanent loss of communications for reasons that engineers have been unable to figure out so far. The failure came just a few weeks after the satellite celebrated its 10th anniversary.

The Thematic Mapper — the primary natural-color imager on America’s venerable Landsat 5 satellite — officially ended regular operations on May 8, following several months of operator attempts to revive it. TM collected images for 27 years, and several hundred of them are part of our Earth Observatory archives. Landsat controllers are happy, however, to be collecting data once again from the Multispectral Scanner (MSS) on Landsat 5, an instrument that had not worked for nearly a decade. The next generation of Landsat is scheduled for launch in 2013.

NASA’s Earth Observer 1 (EO-1) satellite also broke off regular operations and went into a “safe mode” in April. But in that case, there is happier news.

EO-1 halted operations after experiencing a low battery charge. Like almost all satellites in earth orbit, EO-1 uses solar panels to generate electricity for its systems and to charge its batteries for orbits on the night side of Earth. Think of it like a mobile telephone that runs until the battery is low and then needs to be recharged. Except EO-1 gets drained and recharged and drained 14 times a day. Every day for the past decade.

The satellite also gets bombarded by space radiation, particularly while passing through the South Atlantic Anomaly, where electrically charged particles trapped by the Earth’s magnetic field graze deeper into the atmosphere than in other spots. The satellite also endures cycles of heating in direct sunlight and freezing in the shade…over and over again.

Low-Earth orbiting satellites like EO-1 are built to endure these cycles of charge and discharge, hot and cold, light and dark, radiation bombardment and calm vacuums. But it’s always a little amazing to think about how many variables those satellites are designed to survive.

After a few weeks of sleepless nights and long days, the NASA team was able to coax EO-1 back into operations by resetting everything on the satellite and reloading all of the flight and operations software. Think of it like reseting your computer by unplugging it and turning it back on. Granted, it’s a lot more complicated, and mission engineers had to be very sure they understood why the problem happened so it didn’t happen again right after the reset.

EO-1 has been back in operations for several weeks since its two week spring break. The “first/return to light” image above shows Christchurch, New Zealand, as viewed by the Advanced Land Imager (which was actually designed to test technologies for the next generation of Landsats). The satellite appears to be back in good health, but you can read more about the anomaly on the EO-1 satellite page. (Look for the document “EO-1 Safehold Anomaly 2012:097:23:59 2012:111:23:59″ near the bottom of the page. If that seems cryptic, it’s an indication of the time of the anomaly: just shy of midnight on day 97 of 2012 (April 6) to day 111 (April 20)).

Tags: ALI, EO-1, satellite operations
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