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Science Briefing

Bill Mankin, Mike Coffey, and Jim Hannigan (Atmospheric Chemistry Division) are shuttling to and from the Arctic this month as part of a multinational study aimed at ozone depletion in middle and high latitudes. The Second European Stratospheric Arctic and Midlatitude Experiment (SESAME) is designed to build on the first such project, held in 1991-92. That study did much to quantify chemical ozone loss within the stratospheric polar vortex. SESAME hopes to extend the success beyond the vortex to midlatitudes, where some ozone loss has been documented in recent years but the causes (mixing of midlatitude and polar air, local chemical processing, or both) are not yet pinned down. Chlorine and nitrogen partitioning--the strong gradients between low and high levels of each--will be under particular scrutiny. SESAME also will look at the dynamics linking the midlatitude and polar parts of the lower stratosphere in the Northern Hemisphere. Mike and Bill are based in Sondrestromfjord (Kangerlussuaq), Greenland, just north of the Arctic Circle, for two-week stints each. They are measuring the infrared transmission spectrum of the atmosphere, from which they derive the amounts of a dozen trace gases involved in stratospheric chemistry.
On the other side of the globe, Bill traveled to New Zealand last month to attend a meeting of the Steering Committee of the Network for Detection of Stratospheric Change. He took the opportunity to visit the Airborne Southern Hemisphere Ozone Experiment, whose attention was focused on the cycle of ozone depletion now concluding above Antarctica. This austral spring brought stratospheric ozone lows that didn't quite match last year's all-time record for lowest ozone. However, the overall amount of depletion--as judged by the extent, depth, and duration of the "hole"--appears to have been as large as ever, according to Bill.

Investigators waiting with bated breath for the launch of a new experimental earth observing system will have to wait a while longer. The nominal launch date for the MicroLab-1 satellite, bearing the Global Positioning Satellite meteorological experiment (GPS/MET), has been pushed to 18 January 1995. "Launch dates are fickle critters, subject to many factors," says Mike Exner, program manager for GPS/MET with UCAR's University NAVSTAR Consortium. "The GPS/MET payload and the MicroLab-1 are essentially ready. However, other factors, in this case launch vehicle readiness, also affect schedules. Weather and range scheduling can also affect timing. Thus, it is quite difficult to predict the exact date of a launch." Exner's group is using the delay as an opportunity: some of the data processing software and algorithms that had been planned for development after the expected launch are now being developed in advance. If GPS/MET lives up to expectations, it will be able to provide frequent temperature and/or water vapor profiles throughout the earth's atmosphere.

The annual South Asian summer monsoon, provider of life-sustaining rainfall for India and nearby regions, is not a uniform phenomenon. It varies substantially from year to year--running weakest, on average, in summers that follow heavy winter snowfall in the mountains of Nepal and Tibet. In the 14 October issue of Science, Jerry Meehl argues that South Asian snowfall and monsoon patterns are tied to a third party: the tropical biennial oscillation (TBO) that is an integral part of El Nino and tropical air-sea interaction.
Jerry (Climate and Global Dynamics Division) analyzed a 50-year integration from a global coarse-grid, coupled ocean-atmosphere climate model developed at NCAR. The strongest monsoons in the model were preceded by anomalously high winter temperatures over South Asia, often associated with reduced snowfall. Actual data for the 1987-88 period, spanning one weak and one strong monsoon, back up the large-scale model findings with an unusually strong region of high pressure centered over Asia in the winter of 1988. Air-sea interaction in the tropics, associated with the TBO, results in sea-surface temperature variations and anomalous heat release from thunderstorms over the western Pacific warm pool (an area strongly tied to El Nino). These act in combination with similar heat releases from thunderstorms over equatorial east Africa to drive the large-scale circulation. The resulting midlatitude patterns favor high pressure and low snowfall over Asia the winter before a strong Asian summer monsoon. Low pressure and high snowfall over Asia the following winter, associated with fluctuations in tropical sea-surface temperatures and shifts in thunderstorm activity involved with the TBO, then lead to a weaker summer monsoon. Thus, the two-year oscillation comes about from a combination of processes involving air-sea interaction, tropical thunderstorm activity, large-scale midlatitude circulation, Asian snowfall, and Indian monsoon rainfall.

Rainfall and its role in the global hydrologic cycle is at the center of a multiyear study which gathered its forces at NCAR's Mesa Lab earlier this month. The UCAR Office of Field Project Support hosted a review session, modeling workshop, and science panel 1-4 November for the GEWEX (Global Energy and Water Cycle Experiment) Continental-scale International Project, or GCIP. The modeling workshop was held in tandem with the International Satellite Land-Surface Climatology Project (ISLSCP) to address the coupling of surface and atmosphere on scales from the single-column to the global. The GCIP science review featured a packed slate of 17 presentations over ten hours; topics included hydrologic modeling algorithms, the prediction of soil moisture and long-range temperature, and moisture budgets. The science panel included reports and posters on GEWEX and related projects. Organizers report that the meetings provided a good overview of ongoing collaborations involving GEWEX and ISLSCP.

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Edited by Bob Henson, bhenson@ucar.edu
Last revised: Wed Mar 29 12:20:53 MST 2000