UCAR > Communications > Quarterly > Winter 1998 Search

Winter 1998

A field project sampler

by Carol Rasmussen, Bob Henson, and Zhenya Gallon

Malé airport in the Maldives, where the C-130 is based during INDOEX, occupies its own island. (Photo courtesy of Adrian Neville on Hummingbird Helicopters.)

The upcoming months are unusually rich in field projects. The campaigns described here cover virtually the entire spectrum of research at UCAR. They also vary enormously in size, from scores of participants with aircraft, ships, and five or six ground-based observing systems to one scientist who has done everything from pouring concrete to analyzing data himself. We've focused on UCAR investigators and resources; for a more complete picture, start with the Web sites on the next page.

The biggest field projects this winter and spring are taking place in the tropics. Jeffrey Kiehl (NCAR Climate and Global Dynamics Division, or CGD), a principal investigator for the Indian Ocean Experiment (INDOEX), believes that these are only the vanguard for many upcoming campaigns. He lists the reasons. "The chemistry in the tropics is severely undersampled. There's biomass burning. There's El Niño. There's deep convection and massive anvil clouds. Also, in the future, pollution in the tropics will increase. So we'd better understand it now."

Locations of field projects.

A "natural laboratory" for aerosols: INDOEX

How much do sulfate aerosols cool the climate? That's one of the most pressing questions for understanding global climate change. To come closer to an answer, scientists are mounting a large and complex field project in the Indian Ocean this spring. Downwind of the polluted Indian subcontinent during the spring, yet extending into the pristine Southern Hemisphere, the region is a "natural laboratory on the direct versus indirect effects of aerosols," says Andrew Heymsfield (NCAR Mesoscale and Microscale Meteorology Division, or MMM), one of several UCAR scientists who will be participating in INDOEX. With a forecast of pleasant weather--calm, with little rain--the investigators should be able to sample both clean and dirty air in clouds and clear sky.

The direct effect of aerosols is the scattering that occurs when solar radiation bounces off the particles in clear air. The indirect effects have to do with sulfates' interactions with clouds. These aerosols are one of the chief sources of nuclei around which cloud droplets can condense (cloud condensation nuclei)--and the chief CCN source over the tropical oceans. Clouds with more CCN are brighter, reflecting more solar radiation back into space before it reaches the earth's surface.

In February and March 1999, more than 70 INDOEX researchers from a dozen nations are converging on the Maldive Islands. Paul Crutzen (Max Planck Institute for Chemistry, Mainz, Germany) and V. Ramanathan (Scripps Institution for Oceanography) are the chief scientists. The Maldive archipelago runs in a more or less north-south line from about 500 miles southwest of the tip of the Indian subcontinent to the equator. Since the islands are small, the personnel and observing systems are spread across several of them, with all transport by boat.

The resources include five aircraft, including the NSF/NCAR C-130 (three of these will be based in Mauritius); two research ships, the NOAA Ronald H. Brown and the Indian Sagar Kanya; and a host of ground-based systems. Satellite observations over the region are another key component, both for forecasting weather and the movement of pollutants and for measuring radiation at various altitudes.

This combination of ground, airborne, and satellite data is expected to vastly increase scientists' understanding of the nature and scope of aerosols' indirect effects. These are now so little understood that estimates in global climate models vary from almost no effect to more than enough cooling to offset global warming as a result of greenhouse gas increases. "A host of changes in cloud physical and microphysical properties are lumped under the term 'indirect effects,' " says CGD scientist William Collins. Collins will be estimating optical depths in clouds and the sizes of aerosol droplets from satellite measurements, hoping to refine data-retrieval techniques with the ground-based observations.

Heymsfield and MMM colleague Gregory McFarquhar will be studying some of the cloud microphysical changes using NCAR's Scanning Aerosol Backscatter Lidar (SABL) mounted on the C-130. Heymsfield did a "pre-INDOEX" project with the SABL on board the Sagar Kanya last year, so he has some idea of what to expect. However, he says, "From the plane you can much better characterize cloud top and bottom." The MMM scientists will observe the optical depth in both clear and cloudy aerosol-laden skies.

Kiehl has been involved in the design of INDOEX to assure that the project will collect the data needed to advance global climate modeling. Some physical and chemical processes are so complicated that modelers cannot simulate each detailed step. Unlike a process study, which focuses on a particular set of measurements to understand the detailed steps, INDOEX measurements will be made over long flight paths. These data will "provide a large number of statistics on a large number of processes," as Kiehl puts it. "We can actually test the way we treat aerosols against observations."

The government of the Maldives has been extraordinarily cooperative and accommodating, says Richard Dirks of UCAR's Joint Office for Science Support (JOSS), who is the operations director for INDOEX. "They're deeply concerned with climate change research. We are anticipating a fully successful intensive operations campaign."

Data from the remote Amazon: TRMM/Brazil and the LBA

The S-Pol radar site near Ji-Parana, Brazil. (Photo by Peggy Taylor, ATD.)

For INDOEX, the weather is expected to be delightful. For TRMM/Brazil, the forecast is rain--tropical deluges, with lightning to boot. But the kind of weather that wrecks your Club Med vacation is just what the scientists are hoping for.

The Tropical Rainfall Measuring Mission satellite, a joint project of NASA and Japan's National Space Development Association, has been in orbit for just over a year now, recording the distribution of rainfall around the globe between 35 degrees N and S latitude. About three-quarters of the energy that drives atmospheric circulation is latent energy from the evaporation of heated water, and this energy is released wherever and whenever it rains. Thus the TRMM data not only will improve scientists' knowledge of rainfall regimes in the little-observed tropical regions, but will also help modelers and others understand global circulation.

TRMM/Brazil, based in the tiny town of Ji-Parana on the western edge of Amazonia, is a ground-validation program for the satellite. It is funded mainly by NASA, with NSF and NOAA also contributing. Using a wide array of instruments and aircraft, scientists from Colorado State University (CSU), NCAR, NASA, the Massachusetts Institute of Technology, Rutgers and Texas A&M Universities, and the Universities of Utah and Alabama will collect data related to the dynamics and microphysics of tropical convection. The data will be used to produce four-dimensional maps of diabatic heating throughout the tropics, which are needed to improve global climate models.

Why Amazonia? "Brazil offers us an opportunity to look at the convective regime over the interior of a tropical continent," says Steven Rutledge (CSU), the lead TRMM/Brazil principal investigator. He explains that there are three areas of extensive convection in the tropics: Amazonia, equatorial Africa, and the so-called maritime continent around northern Australia and Indonesia. The latter has been studied the most, and equatorial Africa presents the greatest logistical and organizational problems. Brazil is the happy medium.

Also, Rutledge adds, "We're certainly motivated by the fact that Brazilian and European agencies are conducting LBA at the same time." The Large-Scale Biosphere-Atmosphere Experiment in Amazonia, led by a number of Brazilian agencies, is a multiyear initiative to study the climate, ecology, biogeochemical cycles, and hydrology of Amazonia and the impacts of deforestation both on these systems and on global climate. "We know from past research that deforestation affects the local and regional climate," says Rutledge. "One of the big questions is whether there's sensitivity on the larger scale." LBA is a long-term monitoring project with six missions (e.g., ecology and chemistry) located in various parts of Amazonia.

The TRMM/Brazil observing phase is 4 January through 28 February. Instrumentation includes NCAR's S-Pol radar and a NASA C-band radar, a NASA ER-2 aircraft and the University of North Dakota Citation, profilers, radiosondes, rain gauges, a lightning detection network, a tethersonde system, and a flux tower from the University of Virginia.

NCAR scientists James Wilson (Atmospheric Technology Division) and Jothiram Vivekanandan (Research Applications Program) will be going with the S-Pol. The radar has never been used in a truly tropical climate, and Wilson looks forward to the chance. "We're mostly supporting [the other scientists], although we'll do a little bit of [precipitation] particle typing and some precip estimation," says Wilson. "What's really interesting about Brazil is that we don't really know what the precip's like down there. We know there's a lot of it, but we don't know what percentage falls in thunderstorms, what percentage in stratiform rains, and so on. It's just so remote."

Monsoon season in the South Pacific: PEM-Tropics B

(Photo by Carlye Calvin.)

Looking for the cleanest air in the world? Some have speculated that it's in the South Pacific. Yet the tropospheric chemistry of the tropical Pacific has been largely unknown. To address the dearth of data, in early 1999 two research aircraft and about 100 scientists and support staff are heading back to the region for the second phase of the Pacific Exploratory Mission to the tropics.

In 1996, PEM-Tropics A took extensive samples during the dry season (August to October). Despite the "cleanest-on-earth" reputation, that detailed survey yielded significant levels of anthropogenic pollution, primarily from biomass burning. PEM-Tropics B is returning to gather baseline samples during the wet season, when the impact of biomass burning is expected to be much lower. The mission is part of the Global Tropospheric Experiment, an ongoing project of NASA's Tropospheric Chemistry Program.

PEM-Tropics investigators hope to increase their understanding of the oxidizing power of the troposphere and the impact of human activity on the oxidation process. The hydroxyl radical (OH) has been called "the detergent of the atmosphere" because it reacts with several gases that would otherwise be warming the troposphere or causing stratospheric ozone depletion. The tropics play a key role in determining the global oxidizing power of the atmosphere because high levels of humidity and ultraviolet radiation promote the formation of OH.

One of PEM-Tropics' goals is to establish baseline values for the chemical species that determine oxidizing power in the tropical Pacific. Data will also be gathered to evaluate the chemical and dynamic factors controlling levels of ozone, OH, and aerosols over the region.

During March and April 1999, data will be gathered over the tropical Pacific Basin in an area ranging from 165 degrees W to 80 degrees E longitude, with deployment sites at Hawaii, Christmas Island, Tahiti, and Fiji. PEM researchers will log over 320 hours of flight time on a NASA DC-8 jet and P-3B turboprop. Hundreds of species and compounds will be sampled by some 35 instruments. Thirty-one principal investigators from 17 universities and research laboratories are involved. The mission scientists are Doug Davis (Georgia Institute of Technology) and Daniel Jacob (Harvard University).

"With all the instrumentation on board you can provide serious constraints for model comparisons. You have so many measurements going on that it really does allow you to make some conclusions about the chemistry of sulfur species and the chemistry that's responsible for production and loss of tropospheric ozone," says Brian Ridley (NCAR Atmospheric Chemistry Division). Ridley and ACD colleague James Walega's team have a recently improved nitrogen oxides/ozone instrument flying on the P-3.

Four other ACD researchers will be collecting data in PEM-Tropics. Fred Eisele and Lee Mauldin will measure OH and four trace gases from the P-3. This is the first time that their instrument, a specialized spectrometer, will be used to measure some compounds from an aircraft, including ammonia and dimethylsulfide oxidation product, that have not been measurable by other techniques. Richard Shetter and Christopher Cantrell will fly radiometers on both aircraft to determine spectrally resolved actinic flux, a measure of photolysis.

Once the observations are done, Elliot Atlas and Frank Flocke (both of ACD), in collaboration with Donald Blake and Sherwood Rowland (both at the University of California, Irvine), will measure alkyl nitrates and selected halocarbons in whole-air samples from both aircraft. Steven Oncley (ATD) and Donald Lenschow (MMM) will use chemical measurements and the P-3's velocity to estimate fluxes.

The stable boundary layer: CASES-99

October nights in the U.S. southern plains often feature clear skies, calm winds, and cool temperatures. At first glance not very exciting for a meteorologist, these conditions create some vexing problems in atmospheric science. CASES-99, part of the multiyear Cooperative Atmosphere-Surface Exchange Study, will examine the stable nocturnal boundary layer and the poorly understood eddies that spin through it beneath the cloak of a seemingly calm night.

CASES-99 will take place throughout October 1999 across parts of the Walnut River watershed in south central Kansas, where CASES-97, the first experiment in the series, was also based. Normally, about 40% of October nights feature mostly clear skies and light winds near the ground. As these calm nights evolve, the lowest few hundred meters or so of the atmosphere (the nocturnal boundary layer) cool down most strongly, often forming an inversion. This layer decouples from the wind that may persist at higher altitudes, producing a sheared zone at the top of the boundary layer and terrain-forced flow at the surface. Through a set of processes that remain unclear, the upper-level wind periodically breaks through and can mix down to the surface. This, as well as other phenomena, can result in a burst of wind at ground level and a quick, concentrated exchange of heat, momentum, and moisture.

Computer models have trouble depicting these bursts. When conditions are less stable, such as during the daytime, turbulence occurs often enough to be more easily modeled in the aggregate, but these bursts appear to be so random and sporadic that they aren't easily characterized through an average. "This behavior is not conducive to success in a statistically based model or parameterization," says Greg Poulos (Colorado Research Associates, or CoRA), one of the coordinators of CASES-99. Whether models are global, mesoscale, or large-eddy scale, "they have problems when the conditions become statically stable."

The main goal of CASES-99 is to take the closest look to date at the nocturnal boundary layer, mapping its evolution and the sequence and sources of random turbulent bursts in detail. "No studies have comprehensively identified and quantified the sources of this intermittent nocturnal boundary-layer turbulence," says Poulos. "It's never been measured by a sufficiently large and capable suite of instruments."

The program will use the existing CASES network, including profilers, sodars, and instrumented towers. Pending approval, these may be supplemented by the University of Wyoming King Air, NOAA's Long-EZ aircraft, mobile microbarographs, a high-resolution wind profiler and Doppler lidar, a German Helipod (instrument pod tethered 40 meters [130 feet] below a helicopter), a volume-imaging turbulent eddy profiler and a frequency-modulating, continuous-wave radar from the U.S. Army, NCAR's integrated sounding system, and three of NCAR's mobile radiosonde systems. Collaborators from Europe will bring a range of other equipment, including a laser scintillometer for measuring turbulence, three sonic anemometers, and a backscatter lidar. Computer runs before, during, and after the experiment will focus on mesoscale modeling, large-eddy simulation, and direct modeling of the turbulent bursts.

Along with Poulos, the experiment's lead investigators are Bill Blumen (University of Colorado) and Dave Fritts (CoRA). Several MMM scientists have been involved in planning CASES-99, including Chin-Hoh Moeng, Donald Lenschow, Jielun Sun, and Margaret LeMone, who coordinated CASES-97. UCAR's JOSS will put the data from CASES-99 on its Web-based CODIAC catalog.

Alpine floods and mountain waves: MAP

From the Kansas plains to the Swiss Alps, the meteorological problems change as drastically as the landscape. From August through November 1999, the Alps will be the focus of a study on the effects of their topography. The Mesoscale Alpine Program's goals are to study the mechanisms behind severe mountain-induced flooding and to examine the dynamics of other mountain-related phenomena, including some that have never been systematically studied and some only recently discovered. Joachim Kuettner, who holds the UCAR Distinguished Chair for Atmospheric Science and International Research, is head of MAP's U.S. Project Office.

Dubbed "the water tower of Europe," the Alps feed the continent's major rivers (the Rhine, Danube, Rhone, and Po) and produce dramatic, sometimes catastrophic floods. The region's 150-year meteorological data set supports the choice of autumn as a prime time to observe major rainfall and mountain-wave events. MAP will examine the "breaking" of gravity waves in the stratosphere, using lidar-equipped aircraft, and will study airflow through passes, which Kuettner calls "a seriously neglected area" of research.

A big drawing card for the Alps is its instrument network, among the world's most dense. There are several hundred automated weather stations, over 6,000 rain gauges, and about 20 overlapping radars (mostly Doppler) in place. MAP is drawing on these systems for a 13-month general observing phase, which started in October and will lead into the actual field phase. During the field phase, these systems will be augmented by NCAR's S-Pol radar, the NSF/NCAR Electra aircraft, and NOAA's P-3 aircraft. Also expected to participate is Doppler on Wheels (University of Oklahoma/NCAR).

Another unique feature of MAP is its two-year modeling phase, also preceding next fall's field phase. The modeling will help gauge the predictability of phenomena to be studied and will help set the observing strategy.

"The advance of operational mesoscale models has led us into a new situation," says Kuettner. "The resolution of the latest models exceeds that of the observing network. Instead of trying to understand and model features observed in the atmosphere, we are now faced with the opposite problem: verifying and exploring features that are deduced from the models."

For instance, Swiss models have recently indicated that the Alps generate potential vorticity (PV) banners. Appearing in the models as alternating bands, these circulation features extend downstream up to 1,000 kilometers (600 miles) from major alpine peaks. PV banners may be involved in the formation of cyclones to the lee of the mountains. MAP planners hope to use airborne Doppler or flight-level wind data from aircraft to find PV banners and compare them to model predictions.

MAP is another multinational program. The participants are UCAR and NCAR, 8 U.S. universities, 12 weather services and 25 research institutes in Europe and Canada, NOAA, and the U.S. Naval Research Laboratory. Eight aircraft from the United States, France, Germany, and Switzerland will be involved.

Cold, clean air: ISCAT

The Amundsen-Scott South Pole Station. (Photo by Lee Mauldin.)

Like the South Pacific, the South Pole is a contender for the world's cleanest air. Air routinely sinks from higher altitudes to ground level there, and with the pole's elevation of nearly two miles, the air quality is comparable to that found elsewhere well above ground level. Lee Mauldin, before leaving for the South Pacific and PEM-Tropics B, is spending six weeks in Antarctica's very different climate in November and December to study sulfate chemistry in its natural state, without human influences.

Mauldin and ACD coinvestigator Fred Eisele are collaborating on the Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) with researchers from Drexel University, Georgia Institute of Technology, and the Universities of Minnesota, New Mexico, and California, Irvine. The team is sampling dimethyl sulfide and sulfur dioxide, the primary sources of sulfate aerosols. Since they are interested in the early stages of sulfate formation, they are using instrumentation from the University of Minnesota that can record particles of only 3 to 4 nanometers. Additionally, they will sample OH in a more stable setting than usual, a range of other chemicals, and aerosols in the size range of 15 to 400 nanometers.

This fall's field work was the first of two rounds scheduled for the four-year program, which is funded by NSF. The second field phase is scheduled for the fall of 2000 and will be keyed to answering questions that arise from this year's sampling. Years two and four will be devoted to data analysis.

Mauldin has another goal for ISCAT. He has set up a Web site (see p. 5) aimed at K-12 students around the world, giving them twice-weekly updates on what it's like to do science at the South Pole. The site also features photos Mauldin took with a digital camera and includes a link to his electronic mailbox. Most of the responses he's gotten "have to do with the cold, as you would expect," says Mauldin. "Things like how do you stay warm. Everyone who has responded likes the idea of the 'virtual field trip.' It should be fun to repeat for PEM-Tropics B."

Seeking planets from a chicken coop

Brown's telescope at last year's observing site. (Photo by Timothy Brown.)

Amid this wealth of big, international efforts, there's still a place for a one-man show. This winter, astrophysicist Timothy Brown (NCAR High Altitude Observatory, or HAO) is mounting his second field project to look for extrasolar planets. Until very recently, Brown did virtually everything himself, including staying up all night for six weeks last winter to take observations.

So far, some 17 extrasolar planets have been found around Sun-like stars. Most of these planets are roughly the size of Jupiter, but their orbits are much closer to their stars than Mercury's orbit is to our Sun, earning them the nickname "hot Jupiters." Even these giants could not be seen through a telescope from Earth, so scientists have spotted them by noting their gravitational pull on their stars.

Brown is observing a different phenomenon. When one of these huge planets crosses the face of its Sun-like star in a direction observable from Earth, it dims the light we receive from that star by about 1%. Theory states that planets made mostly of hydrogen, like Jupiter, have diameters that are the same within 10-20%, so Brown is looking for dimming in the 1% range for the length of time a planet would need to make the transit.

Brown's experiment stems from an observing system put together by Edward Dunham of Lowell Observatory in March 1997. To avoid "getting clouded out," Brown explained, he and Dunham decided to run two sites looking at the same patch of sky at the same time. Brown set up his telescope in a remodeled chicken coop outside Longmont, Colorado, part of which had been turned into an optics laboratory by Thomas Baur, a former HAO staffer.

To find a planet, you have to look at a lot of stars for a long time. Although about 3% of Sun-like stars that have been observed in other planet-finding efforts have a hot Jupiter, when factors such as the number of stars with close binaries are thrown in, it takes continuous observations of at least 1,500 eligible stars for four to six days to find a single planet. Allowing for bad weather and daytime, this means all night, every clear night, for four to six weeks. No observatory can afford to give a single program that much telescope time, which explains why Brown and Dunham devised their own system.

Even though it takes so much observing time, planet finding does not require a large, state-of-the-art telescope. It needs a big detector and short focal length to get a wide field. Brown describes his setup as "medium-scale amateur equipment, except for the detector, which is something amateurs couldn't afford, and the data analysis, which requires extensive computation." Brown bought his CCD detector and mount using HAO program funds and borrowed the lens, a surplus dating from the Korean War, from Lowell Observatory.

Due to problems in both locations, Brown and Dunham ended up having only three hours of observations on one night in common last year. Brown himself got 17 nights of data over six weeks, looking at the northern Milky Way. Analysis has turned up "lots of stuff that is almost surely spurious" in the 1% to 2% variation range, Brown says. For instance, some appear at the beginning or end of the night, when observations are most unreliable. "Right now, I'm swamped by false alarms. The chances are that one of them is real. Which one? The only way to find out is to improve our observations and analysis."

Brown is optimistic about this season. He's improved his observing system, fixing problems with the guiding, the shutter, the computer system, and the analysis. This winter he only has to turn the telescope on at sunset and off at dawn rather than staying at his post all night. Also, this winter Dunham and Brown will be joined by William Borucki at NASA Ames Research Center, whom Brown calls "the principal proponent of using [this] method to search for planets from space."

And finally, with a grant from NASA, HAO is hiring an additional person to analyze Brown's data. So HAO's planet-finding effort is now a two-person show.

On the Web:

INDOEX: The official INDOEX site is a wealth of background information. JOSS's INDOEX site gives up-to-the-minute reports on proposed flight tracks and other logistical questions.

TRMM/Brazil and the LBA: See the TRMM/Brazil home page and the LBA's home page. The TRMM mission site also includes general material on tropical meteorology.

PEM-Tropics B: See the project office's home page.

ISCAT: See Mauldin's K-12 page for ISCAT. His PEM-Tropics education site will be linked to ACD's home page.

CASES-99: The first CASES field project (CASES-97) includes some information about CASES-99. Also, see the JOSS data catalog.

MAP: See the international project office site.

Seeking planets: For a good introduction to the subject, see the Web site of Geoffrey Marcy, a planet finder at San Francisco State University.

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Edited by Carol Rasmussen, carolr@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Tue Apr 4 14:56:02 MDT 2000