The Future of Wind Measurements from Space

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The United States is about to lose its ability to measure wind speed and direction over the ocean. Immediate action is needed to restore these crucial measurements, or the nation will risk significantly higher future costs and delays as its environmental satellite observing system infrastructure continues to degrade.

Winds play key roles in weather and climate globally. In their most violent expression, they produce hurricanes, typhoons and midlatitude winter storms that threaten international shipping and the lives and property of people along the coasts. With the advent of the Quick Scatterometer (QuikSCAT) and its precursors, the last decade has seen a revolution in our understanding of ocean vector winds. In a recent congressionally mandated Earth Science Senior Review of operating satellites, the QuikSCAT mission was rated “outstanding” for scientific merit by an independent scientific panel and “very high utility” by a panel representing the national interest.

QuikSCAT has made major contributions to our nation’s ability to forecast weather. Organizations such as the National Oceanic and Atmospheric Administration (NOAA), the European Centre for Medium-range Weather Forecasts, the United Kingdom’s Meteorology Office and the Japanese Meteorological Agency routinely assimilate data provided by QuikSCAT to improve numerical weather models. QuikSCAT also provides the U.S. Navy with a unique capability for monitoring winds, including tropical cyclones, in regions far from the U.S. coasts. The operational utility of QuikSCAT for weather was recognized at a NOAA and Navy workshop, and the impact of QuikSCAT winds in the marine forecasting and warning environment was highlighted in a recent paper.

Among QuikSCAT’s major weather forecasting and warning accomplishments is the discovery that hurricane-force winds are more common than previously thought in the midlatitude winter storms in northern seas. These storms affect the U.S. east, west and Alaskan coastlines. For example, a mid-December 2006 extratropical cyclone caused widespread damage across Washington and Oregon, resulting in power outages for 1.5 million people. These extreme storms pose grave dangers to ocean shipping, which transports the majority of international trade. NOAA introduced a new hurricane-force QuikSCAT-based wind warning category for midlatitude winter storms. An independent assessment of the impact of the resulting improvements to warning and forecast services concluded that the container and bulk shipping industry saved $135 million annually by reducing its exposure to hurricane-force winds in nontropical storms by 44 percent.

The U.S. National Research Council of the National Academies, asked by NASA and NOAA to recommend the highest-priority missions to be flown in the next decade, strongly recommended that the next-generation scatterometer instrument, called the Extended Ocean Vector Wind Mission, be launched by NOAA in the 2013 to 2016 timeframe to mitigate the likely loss of QuikSCAT.

A single satellite in low Earth orbit cannot sample changes in wind adequately. The need for a constellation of satellites is understood, and other nations are contributing to implement the constellation. QuikSCAT is flying with the European ASCAT satellite. The Indian space agency recently launched an experimental scatterometer, and another one is expected to launch from China in a few years. However, these instruments do not provide the same spatial resolution or sensitivity to high winds as QuikSCAT. Furthermore, it is unknown whether data from India and China will be available to support operational weather forecasting and warnings. QuikSCAT, seven years beyond its design life, is ailing and is expected to become nonoperational in months. When this happens, the global ocean vector wind constellation will be broken, with major consequences to both weather forecasting and the continuation of a unique climate data record.

Although the utility of QuikSCAT was recognized, both the National Research Council and the operational data users have emphasized the need to go beyond QuikSCAT’s capabilities. This message, as well as the need for continued cross-calibrated observations by a constellation of satellites, was endorsed by an international meeting of scientists to chart the future of ocean observation, by a NASA-, NOAA- and Japan Aerospace Exploration Agency-sponsored meeting to assess the impact of scatterometers on climate science, and by the NASA Ocean Vector Winds Science Team.

The improvements required for the next-generation instruments are driven by the need to better study hurricanes, typhoons and coastal zones, with better fidelity across the wind speed range and higher spatial resolution. QuikSCAT and ASCAT capabilities are limited due to rain contamination and spatial resolution. Improved capabilities that have been endorsed by users at the National Hurricane Center, the Central Pacific Hurricane Center, the NOAA Alaska, East and West coast forecasting offices, and the scientific community would enable significantly better monitoring of hurricanes and other tropical cyclones, improving the safety of coastal populations. These capabilities also would allow an improved assessment of the heat exchange between the ocean and atmosphere, which has been hypothesized to be of major climate importance. Improved coverage of coastal regions would lead to better estimates of wind and wave power available for electrical energy generation.

A solely U.S.-built instrument launched on a U.S. rocket would be the fastest and least-complicated solution. NOAA asked NASA’s Jet Propulsion Laboratory to design the Extended Ocean Vector Wind Mission system recommended by the NRC. The design was shown to be feasible with current technology, but required more resources for a U.S. launch than are available at NOAA. To overcome this obstacle, NOAA and NASA have formed a partnership with the Japanese space agency to examine the feasibility of flying a next-generation instrument in Japan’s Global Change Observation Mission (GCOM) satellites. This unique opportunity would provide a low-cost solution (the Japanese agency would provide the launch vehicle, satellite, and a complementary instrument) for the United States to meet its needs for ocean wind monitoring.

Planning for the next-generation scatterometer (called the Dual-frequency Scatterometer) on GCOM has made significant progress over the last year. Five three-agency technical meetings have concluded that accommodating the instrument on the Japanese agency’s 2016 launch GCOM-W2 mission is feasible. An international working group, of which I am a member, has met multiple times and defined the mission goals and requirements that are consistent with the research and operational needs described above. The GCOM-W2 Dual-frequency Scatterometer-radiometer combination will be the first system to provide multi-|frequency active and passive simultaneous microwave observations, allowing for the near-optimal intercalibration of all wind measurement systems.

The GCOM-W2 mission, with the Dual-frequency Scatterometer instrument onboard, is ready to proceed to a mission concept review and a full mission start. Unfortunately, this unique opportunity is at risk. In order to fit in the GCOM schedule, the United States must make an investment during fiscal year 2011. The current fiscal year 2010 draft budgets in Congress do not contain any funds for the Dual-frequency Scatterometer. The Department of Commerce has not included any scatterometer as part of its budget request for the next year even though the nation’s environmental satellite observing system infrastructure continues to degrade. It would be a tragedy if this opportunity to meet critical U.S. needs for weather and climate wind measurements, at substantial savings to the taxpayer, were wasted. Failure to act now might easily set us back a decade, endanger our coasts and oceangoing commerce, and reduce our ability to monitor a key variable needed to understand, monitor and forecast climate change.

 

Mark Bourassa is the
NASA
Ocean
Vector Winds Science Team leader.