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March 2005

An overview of projects throughout the organization

Solar rotation

Unlike a solid body such as Earth that rotates once a day at all latitudes, the Sun has a differential rotation that ranges from 25 days at the equator to about 35 days at the poles. Intriguingly, this differential rotation is confined to the convection zone (about the outer 30% of the Sun), while the radiative core has an approximately even rotation. The differential rotation varies with depth in a way that current models do not fully explain.

HAO’s Matthias Rempel is trying to understand these rotational patterns, and his work may shed insights into other important solar processes as well. He is focusing on a stable, stratified area of the Sun, called the tachocline, which is sandwiched between the radiative core and the overlying convection zone. Using a two-dimensional hydrodynamic model, Matthias has demonstrated that disturbances in the tachocline may hold the key to the differential rotation. He’s found that variations in entropy, originating in the tachocline and spreading into the convection zone through the transport of heat, can produce a differential rotational pattern that closely resembles observational records.

The next step is for one of Matthias’s colleagues in HAO, Mark Miesch, to investigate the implications of these results in the context of global solar convection simulations. If confirmed, Matthias’s work may help to improve our understanding of internal solar processes such as the subsurface movements of plasma between pole and equator, called the meridional flow, that influence sunspots.

This three-dimensional COMET graphic shows the structure of a rip current, which is one segment of a larger nearshore circulation of water. Under certain conditions, energy from incoming waves may interact with a longshore current to produce a narrow and potentially deadly rip current that flows rapidly away from shore before dispersing. (Illustration courtesy COMET.)

Rip current forecasts

Rip currents, which are narrow, powerful currents of water that flow swiftly away from shore, rank among the more significant weather-related hazards in coastal and lakeshore communities. The U.S. Lifesaving Association (USLA) estimates that rip currents kill more than 100 people each year in this country; in Florida alone, more people were killed by rip currents from 1998–2004 than from lightning, tornadoes, and hurricanes combined.

COMET’s Kevin Fuell and Katherine Olson are working with the National Weather Service (NWS) to produce four Web-based modules to help coastal and lake shore meteorologists learn more about rip currents and make better forecasts. The first module presents an online lecture about the need for rip current forecasts and the characteristics and terminology of rip currents (which are sometimes referred to, incorrectly, as rip tides). It also discusses the partnership between the NWS, the USLA, and NOAA SeaGrant universities to educate the public and develop improved methods for observing and forecasting rip currents. Subsequent modules, using three-dimensional animations, video footage, and interactive exercises, discuss the circulation of water near the beach; the use of buoy observations and model output to assess the threat of rip currents; and regional rip current case studies.

The first two modules are on the Web; the final two should be available by the end of this year. Kevin notes that society has the tools for improved rip current forecasting, thanks to advances in wave modeling and buoy technology. However, few forecasters with atmospheric degrees have taken courses in physical oceanography, and some areas have only limited buoy observations. “These modules help fill a knowledge gap for atmospheric forecasters in coastal areas who will be responsible for informing the public of the daily rip current hazard level,” Kevin explains.

Leaf emissions

James Greenberg, Alex Guenther, Peter Harley, and Thomas Karl (ACD), and Mark Potosnak (Desert Research Institute) are studying how leaves in the Brazilian rain forest emit different amounts of the chemical isoprene depending on the season. Isoprene is a volatile organic compound (VOC) that plays a role in ozone formation and can elevate particulate matter when combined with human-generated nitrogen oxides. Isoprene may also play a role in aerosol production, one of the more uncertain areas of climate modeling.

Last year, Mark took isoprene measurements at the Santarém research station in the Brazilian rain forest and discovered that the leaves emit twice as much isoprene in the dry season compared to the wet season. Seasonal differences in light and temperature can only partially account for the higher emissions. “Physiologically, the plants are changing how they behave from wet season to dry season, not just responding to different temperatures and light,” says Mark, a postdoctoral researcher in ASP until last year. “We’re trying to understand why there is such a strong seasonal cycle.”

The work is especially important because isoprene from the tropics accounts for about 80% of the global isoprene budget. The scientists will be able to provide inputs for climate and chemical models at a higher level of resolution by pinpointing how the isoprene emissions vary seasonally, as opposed to simply determining the total amount of isoprene emitted each year.

NSDL portals

The National Science Digital Library (NSDL) is collaborating with outside organizations to add a series of portals to the online library to help teachers of kindergarten through college find the materials they need more quickly. These new “pathways projects,” funded by NSF grants, organize materials by subject area, grade level, and other categories. The goal is to provide specific audiences with a customized view of NSDL so they will not have to search the entire library, which currently comprises more than 400 collections.

The Eisenhower National Clearinghouse for Mathematics and Science Education is creating the first portal, which is designed for middle schools. The portal helps science, math, and technology teachers find a variety of materials—including lesson plans, articles, video clips, and still images—that are appropriate for their students. When fully functional, it also will enable teachers to create customized collections and search for materials to meet state educational standards.

WGBH, a Boston-based public broadcasting station, is building another portal for teachers who want to tap into a variety of the station’s multimedia materials. Additional portals are under construction for undergraduate math teachers, community and technical colleges, and computational science educators. NSDL’s Susan Jesuroga is managing the work on pathways projects.

Also in this issue...

RICO field project: Cool heads prevail during a complicated study of warm rain

It’s playtime: Parents give high marks to
UCAR Child Care Center

Rotating scientists recall time at NSF

Greg Holland, MMM’s new director

Python interface to NCL’s graphics library now available

Steve Schneider’s 60th

Delphi Questions

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