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September-October 2010

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Observing Weather at the Bottom of the World: The South Pole

Weather. In Antarctica, it can make or break a scientific expedition. It can mean life or death for explorers. At the bottom of the world, weather is not small talk; it is the foundation of many conversations. In a word, weather means everything.

Science research at Amundsen-Scott South Pole Station and elsewhere on the continent can only take place when many dedicated meteorologists and observers are watching the Antarctic sky. There are few who brave the weather there; there are even fewer whose jobs are to observe it.

Antarctic Weather: A Primer

As the world's highest, driest, coldest, and windiest continent, Antarctica is no stranger to extreme weather. A number of features contribute to this. Perhaps the most influential is the lack of a diurnal (day-to-night) cycle. Rather than setting every evening, the sun simply circles the sky each day. The South Pole lies at 90 degrees South latitude, and therefore receives one sunrise per year in September and one sunset per year in March, leading to six months of sunlight during austral (Southern Hemisphere) summer and six months of darkness during austral winter.

Unlike the Arctic, which consists of open ocean surrounded by continents, Antarctica is a landmass surrounded by ocean and covered by ice.

“Antarctica is basically a big ice cube, and it's snow-covered,” said Matthew Lazzara, assistant researcher and meteorologist at the Antarctic Meteorological Research Center at University of Wisconsin-Madison, who oversees the Antarctic Automatic Weather Stations program.

Antarctica is affectionately known as “the ice” to scientists and staff of the National Science Foundation's United States Antarctic Program (USAP). USAP manages U.S. science activities on the continent, including three permanent U.S. science stations: South Pole Station in the interior; Palmer Station on the Antarctic peninsula; and McMurdo Station, the largest of the three and the hub of U.S. operations on the ice, on the Ross Sea. The nickname “the ice” is fitting: 98 percent of the continent is covered with ice, and 70 percent of Earth's freshwater is locked within that ice. Sea ice—frozen seawater floating on the ocean's surface—extends beyond the continent. During every austral winter, a dramatic increase in the area of sea ice surrounding the continent effectively doubles Antarctica's size—one of the largest seasonal changes on Earth.

The Antarctic ice sheet is simply a massive glacier moving slowly over the continent toward the Southern Ocean. In terms of elevation, Lazzara describes it as a giant bowl turned upside down, with the coast near sea level and the elevation of the interior anywhere from 6,500 to 13,100 feet (2,000 to 4,000 meters). Because of year-round below-freezing temperatures in the interior, snow never melts there. Rather, it accumulates layer upon layer, eventually compressing into solid ice beneath the weight of fresher snow above it.

The Transantarctic Mountains provide slopes for the continent's katabatic winds to gain speed as they move cold air from higher to lower elevations. On a larger scale, circumpolar westerly winds, deemed the Antarctic Vortex, occur year-round, and are largely responsible for cyclonic formation over the Antarctic seas and coast. Coastal storms do not survive long once they move over the cold, high interior (though storms do form over the interior, these contain much less moisture). The Vortex is strongest in winter because of the dramatic temperature gradient between extremely cold temperatures over the ice sheet and relatively warmer temperatures in the surrounding waters. “This part of the world gets almost cut off from the rest of the world during austral winter,” said Lazzara.

The South Pole: Not Your Everyday Atmosphere

Life in the Antarctic isn't for everyone. The weather and locale can be intimidating. But for some, like meteorologist Tim Markle, it is home away from home. Markle decided he needed a change about three years after he graduated from college. He had been chief meteorologist and weather observer at the Mount Washington Observatory in New Hampshire for three years, and he knew he loved extreme winter weather. But few places besides Mount Washington offer this challenge.

Then came an opportunity that would change his career—and his life—forever: a 13-month position as meteorology manager at the geographic South Pole in Antarctica. He would work for Raytheon Polar Services Company, USAP's main contractor. With an average annual temperature of −56.9°F (−49.4°C), six months of complete darkness, and eight months of isolation with about 250 colleagues to keep him company in summer and only 50 during the winter, this was exactly the setting he had been searching for. Three years later, Antarctica has not disappointed.

Caption: The ski-equipped LC-130 “Hercules” plane, operated by the New York Air National Guard, carries supplies and staff to South Pole Station.

“I love my job,” said Markle, who has worked three summer seasons and is in the midst of his second winter at the Pole. Compared to Mount Washington, he doesn't think of South Pole weather as “bad.” For one, it's much drier. Relative humidity at the Pole is in the single digits year-round, even inside the station. Polies (those who work at the Pole) hang out in the station's greenhouse to get some relief from dry lips and cracked skin.

Antarctica is a true desert — in fact, it's the largest desert in the world. The Pole receives just over 10 inches of snow accumulation per year, but only about one inch of this comes from precipitation. The rest is blown in by storm winds, though it is a challenge for meteorologists to determine exactly how much comes from either source.

As opposed to the more variable weather conditions along the Antarctic coast, the South Pole is consistently extreme: either very cold, calm, and clear or relatively windy, foggy, and warmer. There's either daylight or no light at all. Because the sun rotates around the sky during austral summer rather than setting, the Pole does not experience diurnal temperature changes like the mid-latitudes; high and low temperatures can occur at any time of the day. The Pole experiences a dramatic temperature drop after the sun sets in late March, after which average high and low temperatures remain relatively constant until sunrise in September — a pattern known as a “coreless” winter.

Temperatures at McMurdo and Palmer Stations regularly jump above freezing in midsummer. The highest recorded temperature at the Pole, on the other hand, is only 7.5°F (the lowest is −117°F or −83°C).

Because the Pole lies on an ice plateau at an elevation of 9,300 feet (which, atmospherically, is more akin to upwards of 10,000 feet due to the thin air), a temperature inversion is typical. “When it's really cold and calm, the colder air is at the surface, and that's really accentuated in the winter months. In July and August, it's not uncommon to have a temperature of −94°F (−70°C) at the surface and −22°F (−30°C) about 1,000 feet up,” said Markle.

Snow and ice have a high albedo, or reflectivity. More than 80 percent of incoming solar radiation is reflected back from the Antarctic ice sheet, making the surface colder than the air aloft. During winter, the ice sheet constantly loses infrared radiation, and air near the surface cools further as it interacts with the ice. The wintertime inversion can be so strong in the interior of the continent that the air at an observer's feet may be 10 to 15 degrees colder than the temperature at his head as he stands outside.

“Because of the nearly constant temperature inversion at the Pole,” Markle explained, “pressure changes are counterintuitive to most other locations on the planet.” In fact, they're completely reversed. Instead of warm air rising from the surface with increasing air pressure, as is typical in most other places on Earth, warm air sinks into colder air, forming low clouds and overall stormy conditions. With decreasing pressure, cold air rises up against warmer air and clouds dissipate. As one might expect, convection is extremely rare. One should not expect thunderstorms when visiting the Pole.

Medications and oxygen tanks are on hand for scientists and staff who suffer from altitude sickness during their first few days on site. The Pole's average barometric pressure—681.2 millibars—means fewer air molecules and 25 percent less oxygen than at sea level. The average pressure at sea level is 1013.25 millibars, compared to 882 millibars in the center of Hurricane Wilma in October 2005, and approximately 330 millibars on the peak of Mount Everest.

Wind speeds don't measure up to Markle's former office, Mount Washington, where the second highest surface wind speed on Earth was recorded, or even the katabatic winds that cruise down the Transantarctic Mountains toward the coast of Antarctica at nearly 200 miles per hour. As is typical for the interior, South Pole winds are low, averaging about 13 miles per hour (11.1 knots). However, these speeds are no laughing matter at the coldest place on Earth: a wintertime temperature of −100°F and a five mile-per-hour wind result in a wind chill temperature of −143°F.

Lazzara experienced the Pole's bone-chilling temperatures during austral summer: “The one time I went to South Pole it was November. It was cold, and a contrail formed on the ground in back of the plane.”

Polies can view many unique optical effects during the summer, including fogbows, sun dogs, halos, and “diamond dust”—clouds of small ice crystals that hover close to the surface on clear days and “glitter” as they reflect sunlight. Those who winter over are treated to an unparalleled view of the night sky, including brilliant displays of the aurora australis, or Southern Lights.

Lazzara appreciates all types of weather in Antarctica, but the most memorable is a calm, clear, windless day. “There's no biology, no people, nothing around for miles but ice. It's one of the few places in the world where you can experience true silence,” he said.

Observing the Weather: A Lost Art

Once a common profession throughout the United States the job of weather observer is now only found in locations where the human eye is needed, such as airfields, military zones, and remote weather observatories—anywhere clouds and visibility are concerned. Most manned observation stations in the National Weather Service network in the United States have been replaced by automated stations.

But in Antarctica, weather observation is a way of life. Amundsen-Scott South Pole Station was established during the International Geophysical Year 1957–1958, an international effort to expand earth science research and observations, with an emphasis on polar regions. Important science research in atmospheric monitoring, earth science, cosmology, space physics, and other disciplines continues to this day. For more than 50 years, meteorologists there have been observing and recording basic atmospheric conditions such as temperature, air pressure, precipitation, and wind speed and direction.

Caption: A Doppler radar sits above the United States Antarctic Program's McMurdo Station in Antarctica.

The purpose is twofold: to ensure safe conditions for USAP activities and to record weather data for research purposes.

“What we're doing is observing and coding this to help support the flight operations that go on, not only here at South Pole, but all around the continent as well,” said Markle. “We are also looking at the climatology of the South Pole and Antarctica as a whole.”

All staff and supplies for the South Pole are transported on ski-equipped jets operated by the New York Air National Guard between mid-October and mid-February. If bad weather is forecasted or appears before a planned flight, observers may have to take observations as often as every 10 minutes for several hours and relay that on-the-ground information to forecasters.

Forecasts for Antarctica are made using manual and automated weather observations and satellite composite images by staff at the Space and Naval Warfare Systems (SPAWAR) Command center in Charleston, South Carolina, and at McMurdo Station. Though forecasting technology has dramatically improved over the years, with only a few images from polar orbiting satellites per day and relatively few observations given the size of the continent and seas, forecasters depend on observers to fill in the gaps. As one forecaster put it, “Forecasting for Antarctica is like being on the East Coast [of the United States] and having to forecast [for flight operations] in the entire United States, including California and Alaska.” Without 24-hour Internet connection at most of the stations and field camps, meteorologists must also rely on forecasters for the bigger picture.

“[T]he tricky thing is the timing of storms,” said Lazzara. That's where observers come in.

Every year, Michael Carmody, who manages South Pole meteorological operations from the Raytheon headquarters outside of Denver, Colorado, hires a meteorology manager and three meteorologists for the summer season at the South Pole. The manager and one meterologist stay on through the winter. They use instruments to measure basic conditions, but their most important tool is their vision—having the skills to decipher conditions that automated stations cannot, most importantly cloud type, cloud ceiling height, visibility, blowing snow, and generally severe conditions. These data must be recorded and coded into a METAR report—a coded weather report used by pilots and forecasters—every hour.

Weather observations are taken both manually and electronically throughout the continent. Automated stations are useful for climatology in remote places because they constantly record basic data in short time intervals and can operate without humans.

However, all of USAP's permanent stations and temporary field camps on the ice have meteorologists or certified observers to support flight operations. “There's a safety issue. There's some comfort in knowing that a person is forecasting,” said Lazzara.

Observations consist of hourly METAR reports and taking synoptic observations every six hours. The crew launches two radiosondes per day in summer to support flight operations and one per day in winter (about 500 to 530 per year). Once per week, these balloons carry ozone monitoring sensors to collect data for th (NOAAs) Atmospheric Research Observatory, which is housed in a separate building outside the main station. Observers must heat the balloons in an oven for 12 minutes before launching them so they do not become deformed or break from the cold conditions. Before heading outside to launch balloons, fix instruments, and measure snow stakes, observers don pounds of weatherproof clothing to avoid frostbite and hypothermia, especially during winter.

Having manned observations works well for day-to-day flight operations to transport staff and essential cargo, but it is also important during extreme situations. In 2001, the physician wintering over at the Pole fell ill with a serious condition and needed to be evacuated in April during the dark of winter, during which flight operations do not take place. Forecasters determined a five-day window for a rescue plane to fly in, while observers worked on the ground to ensure the flight was successful. The crew set out a series of lights along the landing strip to guide the plane in, and the doctor was evacuated safely to South America.

Winter brings other challenges as well. The moon can only be seen on two-week cycles. On the off weeks, it is very dark outside, and human eyes take a while to adjust. “It is hard to observe in the dark here because there are no lights and no landmarks. You have to take into account the clarity of the sky and precipitation to determine visibility and missing patches of stars to figure out where the clouds are,” said Markle. NOAA recently installed LIDAR (Light Detection And Ranging) at the Pole to more accurately determine cloud heights.

All crew members who winter over are also required to pass rigorous medical and psychological testing before beginning the season. Workers must be able to tolerate the physical effects of life at the bottom of the world and endure the psychological effects of being in isolation with the same people for eight months straight, all while performing their “day” jobs.

Markle has made the best of his two winters at the Pole: “This place is beautiful in the summer with the constant daylight, ice crystals, and halos. In the winter you have an infinite number of stars in the sky, dazzling auroras, and hopefully the ability to say that you've stood outside in temperatures below −100°F.” Tim's wish was granted this year, when he experienced these temperatures in April, an unusually early time of year for that type of extreme.

Antarctic Automatic Weather Stations: Filling in the Gaps

The NWS runs more than 800 automated weather observing stations across the U.S., not including those owned by other agencies and research institutions. Antarctica is nearly twice the surface area of the United States, but it has only about 120 automated stations operated by several of the countries that perform research on the continent. Sixty-three of these are managed by Lazzara and his team at the University of Wisconsn-Madison.

While manual observations are most helpful in the short term, automated observations are most useful in the long term. Forecasters depend on both, as do scientists who must consider a site's weather history before choosing it for their field study.

There are a number of benefits to automated stations, the first being that they record baseline data in remote, uninhabited places. They are also more reliable and consistent than observers in taking certain measurements, and they record data more often. They can operate independently for two to five years before requiring maintenance or replacement.

Automated stations can record basic conditions during severe weather, but cannot observe the visual information, such as visibility and cloud ceiling, that manned observations provide. “Those require optical sensors that are just not practical in Antarctica,” said Lazzara. Some stations are one-time installations that only measure temperature and pressure. Others include high wind speed sensors.

“One of the main challenges is keeping the stations powered,” said Lazzara. They are equipped with batteries that recharge from the stations' solar panels, but only during austral summer. Keeping them free of ice, snow drifts, hoar frost, and high winds is also a struggle, as is corrosion from salty air at coastal sites.

The Bigger Picture

While observations help forecasters and researchers in the short term, the long-term benefit is the detailed record they provide for the coldest, windiest, and iciest place on Earth.

“The Antarctic acts as the thermostat for the planet, in some sense,” said Lazzara. The temperature gradient between tropic and polar latitudes is the main force that drives Earth's climate. This heat is balanced by weather in the short term and climate in the long term. “If we want to understand the climate and how it is changing now, we'll have a hard time predicting it for the future [without data from Antarctica].”

But there are still many questions to answer: How have weather patterns shaped the ice sheet, and how might they do so in the future? What is the relationship between Antarctica, the global climate system, and regional climate variability? How can data from Antarctica improve weather and climate models? What effect does Antarctic weather have on midlatitude weather and vice versa? There is much work to be done.

In the meantime, South Pole meteorologists try to make themselves at home while working at the bottom of the world. This year, Markle's fiancée, whom he met at the Pole two years ago, has also returned to the station for a winter position. Though he hopes to come back for another winter, they also have their sights set on a normal life: cooking meals together, going for walks, decorating their new house.

“Soon sunlight will appear on the horizon and we will have a light at the end of the tunnel,” he said.

ANN POSEGATE is outreach coordinator for Earth Gauge, the Weather & Environment program of the National Environmental Education Foundation. She also writes for Capital Weather Gang, the local weather blog on www.washingtonpost.com. In January 2010, she accompanied the National Science Foundation on a media expedition to report on the science of Antarctica. For more information and to see other materials from the trip, visit www.earthgauge.net/antarctica. Special thanks to Matthew Lazzara, Tim Markle, and Michael Carmody for their contributions to this article.

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