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Summer 2001

Science Bits

Jurassic dunes reveal monsoon pattern

Within the sandstone arches and reefs found across the southern Great Basin of the United States are clues to monsoon rainfall that occurred 150 to 200 million years ago. Evidence of heavy summer rains during the Jurassic period appears in the geologic record of the Navajo sandstone cliff formations in Utah, according to David Loope, a geoscientist at the University of Nebraska–Lincoln. Loope's findings with UNL colleagues Matthew Joeckel and Clinton Rowe are featured in the 5 July issue of Nature.

During the Jurassic, southern Utah was located at around 15°N, toward the western margin of the supercontinent Pangaea. Strong heating of the land mass in summer is believed to have led to a regular monsoon pattern. Examination of the lower sandstone layer showed a sequence of contorted layers due to slumping of the sand after heavy rains. The contorted sections are separated by smooth, undisturbed layers that reflect more typical dune motion, especially during windy, dry winters. At one site, 24 slumps were indicated across a 37-year record.

Rowe will be factoring the new data into model simulations of the early Jurassic climate. Previous work had looked at average seasonal shifts in the atmospheric circulation. "Now, since we know that both seasonal [monsoonal] and shorter-term wind variations are recorded in the dune layers, we should be able to gain greater insight into regional weather patterns during the Jurassic," Rowe says.

University of Nebraska–Lincoln

A moistening stratosphere

The first comprehensive survey of water vapor data for the stratosphere and upper troposphere has been released by the Stratospheric Processes and Their Role in Climate project. SPARC was established in 1992 as part of the World Climate Research Programme, and the SPARC Data Center opened in 1999 at the State University of New York, Stony Brook.

According to the report, water vapor in the stratosphere has increased by around 2 parts per million by volume over the past 45 years, with current values ranging from 4 to 6 ppmv. For example, measurements of water-vapor mixing ratios from 15 to 25 kilometers (9.3–15.5 miles) above Boulder, Colorado, showed rises of about 1% each year from 1981 to 2000. Up to half of the global increase in stratospheric water vapor can be attributed to the oxidation of methane, but the source of the remaining increase is unclear. Lending credence to these results is the increasing quality of observations from both in situ and remote instruments, which generally agree to within a range of plus or minus 10%.

In contrast to the moistening above it, the upper troposphere has shown no solid trend in water-vapor levels. Satellites have collected data on relative humidity in this region for some 20 years; the SPARC team verified the quality of this satellite record, deeming it useful for climatological and process studies. Radiosonde data are less reliable at these altitudes, say SPARC researchers, although some aircraft- and ground-based techniques show promise.

World Climate Research Programme, SUNY–Stony Brook

New NYU center brings math to bear on atmosphere-ocean problems

The NYU Center for Atmosphere/Ocean Studies (CAOS) has been established by the Courant Institute of Mathematical Sciences and the Faculty of Arts and Science at New York University. Its goal is to provide a unifying mathematical framework for the interdisciplinary study of atmospheric science, physical oceanography, and climate dynamics. A degree-granting program since the fall of 2000, CAOS now offers a Ph.D. in atmosphere- ocean studies and mathematics. The program is also developing an interdisciplinary undergraduate presence and research links that will branch out into physics, chemistry, biology, and other disciplines.

"In just the last two decades, researchers have produced fairly reliable models of Earth's climate systems," says NYU mathematician Richard Kleeman. "But given their policy implications, these models need to be substantially more reliable. The goal of our center is to develop a common mathematical framework for use by the broad array of climate researchers. In this way, we can help substantially improve the accuracy and utility of their findings."

The research at CAOS will apply the Courant Institute's expertise in the analysis and numerical solution of partial differential equations (PDEs) to the realm of ocean-atmosphere models, which include some of the most complex PDEs ever studied. The distinct focus of the new program complements other institutions in the New York area, including the Lamont-Doherty Earth Observatory (Columbia University) and the Geophysical Fluid Dynamics Laboratory (Princeton University), whose members participate in CAOS colloquia and in collaborative research.

New York University

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Edited by Bob Henson, bhenson@ucar.edu
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Last revised: Wed Aug 8 17:05:07 MDT 2001