|This satellite image from 7 October 1995, shows a well-developed cyclone over the North Atlantic, as indicated by the comma-shaped cloud. A cold front extends south and west from the low-pressure area, with a broad shield of clouds and rainfall to the north and east. (Photo courtesy National Aeronautics and Space Administration.)|
The project is called the Fronts and Atlantic Storm Track Experiment (FASTEX). Operations began on 6 January and will continue through February. The findings should lead to better forecasts for the west coasts of both Europe and North America, as well as a better understanding of how oceanic winter storms affect world climate.
Scientists from the United States, Canada, Iceland, Ireland, the United Kingdom (U.K.), Denmark, Norway, France, Portugal, Spain, and the Ukraine are involved in FASTEX. NCAR and NOAA are among the key U.S. scientific participants; UOP is providing logistical support.
Forecasting the development of oceanic storms is still a challenge, largely because there are fewer weather observations at sea than over land. Cyclones (low-pressure centers) that rake Europe tend to develop along slow-moving cold fronts that extend across the Atlantic. The cyclones often develop midway between North America and Europe and reach their peak strength a day or two later near the British Isles.
Even if a cold front is well forecast, the smaller cyclones that focus wind and rain along it are harder to predict. The researchers of FASTEX are hoping to identify precursors that may trigger cyclones once the precursors overtake the cold front. These precursors could include jet streaks (regions of higher wind speed inside the jet stream) and pockets of air that descend from the stratosphere. If such precursors can be located as they reach the North Atlantic, the cyclones they later generate might be better forecast up to two or three days in advance.
To follow the life cycles of precursors and cyclones, a wide array of observational tools stretches from continent to continent and extends from midlatitudes to polar regions.
Three turboprop aircraft are probing cyclones as they develop: the NCAR/NSF Electra, the NOAA P-3, and the U.K. C-130. The NCAR and NOAA planes eah feature an on-board Doppler radar that can trace wind and precipitation patterns inside the storms.
The NCAR/NSF Electra is teaming up with the NOAA P-3 to collect detailed Doppler radar data from within Atlantic cyclones. (Photo by Curt Zukosky.)|
Four ships (French, Icelandic, Ukranian, and U.S.) are stationed near longitude 35 degrees west to make measurements of heat and moisture exchange between the ocean and air, as well as to launch balloon-borne radiosondes.
Many other observing systems, such as radiosondes launched from land, drifting ocean buoys, and wind profilers, are contributing.
The decision-making process for instrument placement in FASTEX may lead to a model for everyday weather monitoring in the future. Computer models of the atmosphere (the main source of forecasting guidance) require a detailed picture of current weather in order to extend that picture into the future. Where data are limited--such as over the oceans--it may be worthwhile to focus data collection on a small area where storms are developing, rather than on a bigger area where relatively little is happening. Two major goals of FASTEX are to develop better techniques for targeting these sensitive regions and to measure how much the targeting will improve computerized forecasts. The prime spots for enhanced observation include developing cyclones as well as their precursors farther upstream.
The airborne Doppler radars aboard the NCAR/NSF and NOAA turboprop aircraft will be used to analyze mature cyclones at altitudes near or below 10,000 feet (3 km). One of the flight plans, called a "lawnmower" pattern, crisscrosses a cyclone to analyze the frontal rainbands that produce much of a cyclone's heavy precipitation. The rapid-scanning abilities of the Electra Doppler radar will help document the turbulent ascent and descent of air in shallow rain showers behind a cyclone's cold front.
Some results from FASTEX will be applicable to the Pacific as well as the Atlantic. For instance, precursors exiting Asia are likely responsible for some cyclones that reach the U.S. West Coast several days later. Techniques developed in FASTEX for identifying precursors and targeting observations could be used to improve forecasts for both North America and Europe. A follow-up field experiment is being considered for the North Pacific.
|The extensive reach of the FASTEX observational network includes radiosondes, aircraft, and ships. (Illustration courtesy David Jorgensen.)|
Thanks to the Internet and other communication tools, distance is no object in keeping track of FASTEX. A number of people in ATD and JOSS will be involved throughout the experiment in cataloguing data and assisting with field work from Boulder. "We're doing a lot of real-time monitoring here," says Charlie Martin (ATD). "It's quite a step forward in making our expertise available at a distance. We have scientists and engineers actively involved in the project from Boulder while the equipment is in the North Atlantic."
As with most field programs, FASTEX is bound to include stretches of quiet punctuated by episodes of intense work. "Typically, there will be a series of four or five cyclones in our study area over ten or more days," says Dick Dirks (JOSS). Dick will serve as operations director at Shannon in February, following Jim Moore in January. If the winter of 1997 proves to be a normal one in the North Atlantic, there will be a couple of these cyclone series during the two months. "The lows form in sequence, one right after the other. What happened on the [U.S.] West Coast around New Year's is a good analog."
Although FASTEX began with a huge upper-level high-pressure cell firmly in place over the study area, steering cyclones far to the north or south, the pattern had changed quickly enough to put the experiment into its first intensive operations period by 10 January. BH
The FASTEX operations plan reads: "During FASTEX an attempt will be made to position the ships beneath active weather such as surface fronts and/or jet streams." That spells seasickness for the typical NCAR staff member from Colorado who is used to firm, steady ground.
The initial two days from port were surprisingly smooth. However, it wasn't long before we were successful in finding a front. The third day out presented us with 8-meter swells and 22-meter-per-second (m/s) winds. It wasn't long before we newcomers were groaning in our bunks. Now, after a week on board, we are getting our sea legs, learning how to walk while swaying from port to starboard.
Today I was up on the flying bridge deck, fixing sensors, and could see pilot whales all around the ship. Winds were 18 m/s and the ship was rolling pretty strongly, so one had to hold on.
The Knorr is a well-outfitted ship for science: Ethernet throughout the ship, e-mail terminals for all on board, network printing services, and a data stream of meteorological parameters that is displayed in several places on board and can be tapped by user systems.
Weatherwise, the most surprising thing is how warm it is. The sea-surface temperature is typically about 17 degrees C, so the air outside is often near 15 degrees C.
That's the news from the roaring forties. [The Knorr was then stationed near longitude 40 degrees west.]