Engineers help unlock El Nino's secrets

Huntington Beach, CA--To millions of people and untold wildlife, the 1997-98 El Nino has meant floods, mudslides, drought, and even famine. Yet it contains a possible silver lining for scientists, meteorologists, and engineers. Delivered along with El Nino's wrath has been increased emphasis on the need to understand this often destructive weather phenomenon. This emphasis translates into opportunities for not only gathering vital information about the most recent El Nino, but also for developing next-generation equipment to better understand and forecast El Ninos in the future.

Great. But what exactly is El Nino? The phrase refers to a massive warming off the coastal waters of Peru and Ecuador that frequently extends more than 90 degrees of longitude. It's related to the Southern Oscillation, the atmospheric component of this phenomenon, and the two are often abbreviated ENSO. Typically, ENSO starts late in the spring or summer and builds to a peak at the end of the year, with the event usually over by the following summer. It's quasi-periodic, recurring on an average of two to seven years, and causes significant anomalous weather effects worldwide.

Vital to El Nino's study are technologies such as satellites, sensors, instruments, imaging systems, computers, and software. A sampling of systems and devices available today and under development include:

- ATLAS buoys. These form the Tropical Atmosphere Ocean (TAO) array in the equatorial Pacific. Next-generation, ATLAS II buoys just being deployed will extend the capabilities of the world's only real-time sub-surface thermal observation system.

- Jason 1. Follow-on to the TOPEX/Poseidon spacecraft, Jason 1 will continue tropical sea-surface height observations vital to understanding ENSO.

- SeaWinds. NASA's Micro-wave radar scatterometer will gather sea-surface vector wind data.

- TRMM. Launched in fall 1997, the Tropical Rainfall Measuring Mission uses a precipitation radar to measure rainfall.

- MODIS. The Moderate-Resolution Imaging Spectrometer will fly on AM-1 in late 1998 and PM-1 in 2000 and provide infrared sea-surface temperature.

- ALACE. Anomalous coastal effects from El Nino storms can be studied by the laser-based Airborne LIDAR Assessment of Coastal Erosion program which uses LIDAR beamed from low-flying aircraft to create detailed digital elevation models of coastline topography.

Water temperature wizards. The TAO array, comprised of 70 Autonomous Temperature Line Acquisition System (ATLAS) buoys, is considered one of the essential sources of El Nino information. Their data is more discrete and localized than that provided by satellites, but the buoys deliver something no orbital platform can: subsurface water temperatures to 500m.

The National Oceanic and Atmospheric Administration (NOAA) is just now mooring the first Next Generation ATLAS buoys, replacing those placed in the late '80s and early '90s. Reengineered by the Pacific Marine Environmental Laboratory (PMEL), changes were made to improve performance while easing manufacture and reducing cost. Reengineered buoys function similarly to their predecessors, but incorporate new electronics and sensors.

Most significant is the incorporation of inductively coupled sensors clamped directly to the wire-rope mooring line. This simplifies fabrication over the original ATLAS which had a separate sensor cable. Sub-surface temperature readings are supplied by YSI (Yellow Springs, OH) thermistors, and Paine (Seattle) model 211-30-660-01 pressure sensors determine depth. Interestingly, an inductive-coupling method is also used to time multiplex data transmissions from each sensor package to the buoy.

New electronics based on the Motorola MC68332 microprocessor retrofit into the original electronics packages. This change greatly reduced component count and improves reliability. All electronics now fit on a single PCB, replacing three boards. The board draws an average of 10-15 mW, and a simple battery pack of 84 D-cells will provide an 18-month deployment life.

Redesigned sensor modules sample and store data at predetermined intervals. Their cylindrical housings are made from polyethylene terephthalate (PET) and designed for depths up to 750m. Internal electronics are based on the Motorola MC68HC11 microcontroller with 256K of RAM. It's mounted to a dense, 8-layer board with surface-mount components. Three 9V batteries provide power for more than 400 days.

El Nino vs. big science. "Everyone's been talking about this El Nino because it just happens to be the biggest one this century," says Dr. Michael King, senior project scientist for NASA's Earth Observing System (EOS), the world's largest science program. Over the next decade many of EOS' 19 instrument science development teams and 71 interdisciplinary science investigations will focus on better understanding ENSO.

One critical piece of El Nino data EOS will provide is ocean sea-surface vector winds. NASA's SeaWinds microwave radar scatterometer will launch in 2000 on the ADEOS II. And a SeaWinds engineering spare will fire aloft in November 1998 on QuickSCAT, a rapid-development recovery mission intended to fill in for the Japanese-built ADEOS I, which failed last June. "Before it failed, the ENSCAT instrument on ADEOS I was improving some weather forecasts by 24 hours," says King.

Adding to the El Nino data pile will be MODIS with its sea-surface temperature and ocean color sensors, Jason 1 for sea-surface height, and TRMM for tropical rainfall. On the ground, the EOS Data and Information System (EOSDIS) ground computers will focus on processing, analyzing, and disseminating information gathered by this orbiting army of satellites.

Model behavior. Interpreting this pile of information is the job of Dr. Lisa Goddard, project scientist at the International Research Institute (IRI) in San Diego, CA. "Satellites only tell you what is happening now, not what will happen in the future," she says, "that's what prediction models are for."

AT IRI, Goddard and other researchers run El Nino models developed by organizations such as the National Center for Environmental Prediction (NCEP) on Cray J90 supercomputers. Even with 12 processors and gigabytes of RAM, the models take 2 to 3 days to complete, but it's worth it. "It's been only quite recently that anyone could make a statement as to what triggers El Nino, the atmosphere or the ocean," says Goddard. "We now know that the inertia for starting El Nino's is in the ocean."

Cybercontacts

El Nino Page at NOAA

http:www.elnino.noaa.gov/

ATLAS buoy info.

http:www.pmel.noaa.gov/toga-tao/buoy.html

EOS Project Science Office

http:eospso.gsfc.nasa.gov/

International Research Institutehttp:iri.ucsd.edu/