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February 1998

Science Briefing

Targeting observations across the Pacific

MMM director Bob Gall is spending the last half of January as flight scientist for NOAA's new Gulfstream-IV high-altitude jet, one of three research aircraft on patrol from Hawaii to Alaska. The planes are collecting weather data across the North Pacific through February to help sharpen the vision of computer forecast models. Researchers from NOAA, the Naval Research Laboratory (NRL), and NCAR will use the two-month experiment to learn how much the enhanced Pacific data can improve weather forecasts from California to Europe, with an emphasis on the central and eastern United States.

A minireunion of MMM directors took place during the recent American Meteorological Society meeting in Phoenix, Arizona. Phil Merilees (left), who preceded Bob Gall (right) at the helm of MMM, is now at the Naval Research Laboratory, one of the lead agencies in NORPEX. Phil and Bob were at the Sky Harbor International Airport on 15 January for a NORPEX press conference, as NOAA's Gulfstream aircraft (background) stopped at Sky Harbor en route from its Tampa home to its NORPEX base in Honolulu. (Photo by Bob Henson.)

The North Pacific Experiment (NORPEX) involves the Gulfstream-IV and two Air Force C-130 turboprop aircraft. The Gulfstream has been based in Honolulu 15-31 January; the C-130s will operate from Anchorage 15 January-15 February and from Honolulu 15-28 February. Together, the planes will be able to cover critical regions above the data-poor Pacific with a net of upper-air observations as dense as that over the contiguous United States. Mel Shapiro (NOAA Environmental Technology Laboratory) is the NORPEX program coordinator.

NORPEX is an outgrowth of an ongoing NOAA project that uses the hurricane-hunting Gulfstream-IV to investigate winter storms off the East and West Coasts. The goal is to provide computer models with targeted observations, an experimental method of growing interest. NORPEX will send planes into data-sparse "hot spots" identified in model output from NRL and NOAA's National Centers for Environmental Prediction (NCEP). Hot spots are regions where extra observations of current weather systems would have the most impact on forecasts for regions affected 12 hours to several days later in another part of the world.

Such hot spots are especially common in the North Pacific, according to Bob, and their effects can be far-reaching. "If you pick an area in the middle United States and you want to optimize the forecast there, then what are the sensitive areas? It turns out that, in the 36-hour time frame, the most sensitive area is often the Gulf of Alaska," a focus area for NORPEX flights. Testing the technique of backtracking from the forecast area to the propagation area during NORPEX is one step, according to Bob, in helping shape a vision for a next-generation observing system that could eventually extend from Japan eastward to Europe. An additional, immediate payoff could be improved forecasts of daily weather possibly influenced by the current El Niño, since the warming of the equatorial Pacific normally has its greatest effect on U.S. weather during the winter months.

NCAR and other agencies explored the potential of targeting observations last winter across the Atlantic in the Fronts and Atlantic Storm Track Experiment (FASTEX). But the benefits from targeting the Pacific could be greater than for the Atlantic--even for predictions in Europe--because the Pacific Ocean (and thus its data void) is larger and because systems there are a few days further away from Europe. The European Center for Medium-Range Weather Forecasts, based in Reading, England, will provide some of the target guidance for NORPEX and, in turn, the center will use the NORPEX aircraft data to improve its own model forecasts for Europe.

This map is an example of the guidance being provided for NORPEX by the Naval Research Laboratory. The NRL models first are run out to 72 hours in advance; then, after a few hours, the model output is checked against reality. Areas where enhanced data could have provided a better short-term outlook are identified, and the guidance is used to help NORPEX aircraft collect data that can improve the next model run. In this image, "hot spots" across the North Pacific (numbered contours) correspond to areas where better temperature input at high altitudes could have improved the 72-hour outlook for the central and eastern U.S. (boxed at right).

Forecasters at NCEP and the U.S. Navy weather service will select the chief forecast problem for the day; NRL will then prepare target area maps (see diagram) and develop flight plans. Also providing support will be the Universities of Hawaii and Washington, the National Weather Service in Anchorage and Honolulu, and NOAA's Pacific Marine Environmental Laboratory. After the experiment ends, NORPEX data will be analyzed in more detail by Xiaolei Zou (NCAR/Florida State University) and colleagues to determine how targeted observations can best be incorporated into forecast models and linked to satellite data.

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Edited by Bob Henson, bhenson@ucar.edu

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