Winds
In the United States, hurricanes have been responsible for at least 17,000 deaths since 1900 and hundreds of millions of dollars in damage annually. Worldwide, there were 10 hurricanes in 1998, making that the worst hurricane season in the last 200 years. One of them, Mitch, killed over 10,000 people in Central America. The beginning of a hurricane can be observed as winds swirling off the coast of Africa days before clouds form. Ocean surface wind measurements are crucial to understanding and predicting hurricanes, other storms, and climate change.
This is a view of Hurricane Ivan in the Caribbean Sea on September 9, 2004. It shows the wind speeds 10m above the ocean surface. The false color image was created from SeaWinds scatterometer data. Dark purple shows high winds around the eye of the hurricane and small lines (or barbs) that indicate wind speed and direction. Sea surface winds can help show accurate locations of hurricanes, especially when they are far from land and difficult to reach with airplanes. Early on September 9, 2004, the SeaWinds scatterometer aboard NASA's QuikSCAT satellite saw through Ivan's swirling clouds to measure wind speed 10 meters above the ocean surface. The result was this multi-colored image of the storm. Purple in the center of the storm shows the highest wind speeds, and green fringes around the outside of the storm show the lowest wind speeds. The black barbs indicate wind speed and direction at QuikSCAT's nominal 25 km resolution; white barbs indicate areas of heavy rain.
Wind is the largest source of momentum for the ocean surface, impacting individual surface waves and complete current systems. When observing and analyzing ocean phenomenon, it is critical to consider wind in our measurements.
Ocean surface wind speed and direction, when incorporated into weather forecasting models, have been shown to significantly improve forecast accuracy. Winds over the ocean help transfer heat, moisture, gases, and particulates into and out of the ocean. Modulation of these transfers regulate the interaction between the atmosphere and the ocean, which establishes and maintains both global and regional climates. Combined with measurements from other scientific instruments, scientists can better understand the mechanisms of global climate change and weather patterns.
Measuring the Wind Through the Clouds
NASA's QuikSCAT satellite carries the SeaWinds instrument, a scatterometer. A scatterometer is a microwave instrument that measures the microwaves reflected or scattered back to the instrument from the sea surface. The SeaWinds scatterometer is a specialized microwave instrument that measures near-surface wind speed and direction all the time, even when it is cloudy.
Although designed for measurements over the ocean, SeaWinds can also collect data over land and ice. In a continuous 1,800-kilometer-wide band, Sea Winds makes approximately 400,000 measurements covering 90% of Earth's surface every day. QuikSCAT is a joint mission with NASA and the National Space Development Agency of Japan (NASDA).
Putting the Data to Work
Data derived from ocean scatterometers is vital to scientists studying air-sea interaction, ocean circulation and their effects on weather patterns and global climate. These data are also useful in the study of unusual weather phenomena such as El Niño and changes in the sea-ice masses around the polar regions. These play a central role in regulating global climate.
In recent years, the ability to detect and track severe storms has been dramatically enhanced by the advent of weather satellites. Data from the SeaWinds scatterometer is augmenting traditional satellite images of clouds by providing direct measurements of surface winds to compare with the observed cloud patterns in an effort to better determine a hurricane's location, direction, structure, and strength. Rotating winds over the ocean's surface are precursors to tropical cyclone development. Scatterometers can detect these winds before other instruments, providing even earlier notice of developing storms to forecasters and scientists. Specifically, these wind data are helping meteorologists to more accurately identify the extent of gale-force winds associated with a storm, while supplying inputs to numerical models that provide advanced warning of high waves and flooding.
Ocean Winds in 3-D
To facilitate our ability to forecast weather conditions over the oceans, near real-time sea surface wind data are integrated into models that generate 3-D satellite images. These images are then used to create increasingly accurate forecast systems. Thus, computer modeling of global atmospheric dynamics for the purpose of weather forecasting has become an important tool to scientists and meteorologists.
The Big Picture
NSCAT (NASA Scatterometer) and SeaWinds, are part of a global monitoring system were designed to observe the tropical oceans, predict El Niño and other irregular climatic variations, and make climate predictions readily available for planning purposes. By improving our ability to anticipate how climate and weather will change over time, ocean scatterometers can help us better manage global agriculture, water reserves, and other resources.
Ocean surface winds play a vital role in the water cycle as the tropical Pacific Ocean and overlying atmosphere react with, and influence each other. Easterly surface winds along the equator control the quantity and temperature of the water that upwells (moves or flows upward) to the surface. This upwelling of cold water determines sea-surface temperature distribution, which affects rainfall distribution. This in turn determines the strength of the easterly winds - creating a continuous cycle.
Data derived from ocean scatterometers are key to our understanding of how the ocean plays a central role in regulating global climate, and ocean surface wind data are vital to scientific studies of air-sea interaction and ocean circulation. The data are also useful for studying unusual weather phenomena such as El Niño, the long-term atmospheric effects of deforestation on our rain forests, and changes in the sea-ice masses around the polar regions.
Ocean Surface Winds and People
By measuring global ocean surface wind speed and direction, scatterometer data can help meteorologists more accurately predict the winds and waves that affect everyday human life. Examples of the practical uses of ocean surface wind data follow:
- Weather Forecasting - Data from ocean scatterometers greatly enhance overall weather-forecasting skill. The data are delivered to the National Oceanic and Atmospheric Administration (NOAA) within two hours, where they are used for timely, accurate weather forecasting.
- Storm Detection - The ocean scatterometer data can determine the location, direction, structure and strength of storms at sea.
- Ship Routing - Knowledge of ocean wind behavior will enable ship masters to choose routes that avoid heavy seas, or high headwinds that may slow the ship's travel, increase fuel consumption, or possibly cause damage to vessels and loss of life.
- Environmental Impact - Safe, efficient drilling operations depend upon the specific location and understanding of current wind and wave conditions and timely and accurate warning of impending storms. Further, in the event of an oil spill, surface-wind information is key to determining how and where the oil will spread.
- Food Production - Finally, perhaps the oldest use of the ocean is seafood harvesting. Detailed wind data from the scatterometers can aid in the management of commercial seafood crops.