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Better Weather Detection, Prediction For Fliers

NCAR Developing System To Aid Transoceanic Flights

POSTED: 7:13 pm MDT July 7, 2009
UPDATED: 7:54 pm MDT July 7, 2009

Flying in severe weather is never easy, and there is an effort here in Colorado to give pilots important information that will keep fliers safer when the weather turns rough.

The National Center for Atmospheric Research (NCAR) is developing a system that will provide aircraft with updates about severe storms and turbulence as they fly across remote ocean regions.

The system is designed to help guide pilots away from intense weather, such as the storms that Air France Flight 447 apparently encountered before crashing into the Atlantic Ocean on June 1.

The NCAR system, being developed with funding from NASA, combines satellite data and computer weather models with cutting-edge artificial intelligence techniques to identify and predict rapidly evolving storms and other potential areas of turbulence.

The system is based on products that NCAR has developed to alert pilots and air traffic controllers about storms and turbulence over the continental United States.

"Pilots currently have little weather information as they fly over remote stretches of the ocean, which is where some of the worst turbulence encounters occur," said NCAR scientist John Williams, one of the project leads. "Providing pilots with at least an approximate picture of developing storms could help guide them safely around areas of potentially severe turbulence."

NASA
A prototype system could provide commercial airline pilots with key weather and turbulence forecasts when flying over remote regions of the ocean where little real- or near-real-time data is available now. The NASA-funded system, being developed by the National Center for Atmospheric Research (NCAR), combines computer models and data from five operating NASA satellites with an artificial intelligence system to predict turbulence. The system is on track for testing next year, with the goal of ultimately giving pilots a regularly updated picture of potential storms over the ocean so that they can fly away from or around danger. This photograph, acquired in February 1984 by an astronaut aboard the space shuttle, shows a series of mature thunderstorms in southern Brazil. More

The component of the system that identifies major storms over the ocean is already available for aircraft use on an experimental basis.

The entire prototype system, which will identify areas of turbulence in clear air as well as within storms, is on track for testing next year.

Pilots on selected transoceanic routes will receive real-time turbulence updates and then provide feedback on the system to NCAR. The researchers will adjust the system as needed.

When the system is finalized in about two years, it will provide pilots and ground-based controllers with text-based maps and graphical displays showing regions of likely turbulence and of storms.

Pinpointing turbulence over the oceans is far more challenging than over land because of sparse observations. Weather satellites are often the only source of information over these remote regions. But the satellites tend to provide images less frequently than over land, which can make it difficult to capture fast-changing conditions, and they do not directly measure turbulence.

Pilots of transoceanic flights currently get preflight briefings and, in certain cases involving especially intense storms, in-flight weather updates every four hours. They also have onboard radar.

All this information, however, is of limited value. Thunderstorms may develop quickly and move rapidly, rendering the briefings and weather updates obsolete. Onboard radars are designed to detect clouds and precipitation, but turbulence is often located far from the most intense precipitation.

As a result, pilots often must choose between detouring hundreds of miles around potentially stormy areas or taking a chance and flying directly through a region that may or may not contain intense weather.

NASA
A 2009 astronaut photo from the International Space Station (ISS) of deep convective clouds, seen from above, over the Atlantic Ocean. Free standing and embedded towering convective clouds are particularly dangerous to aircraft flying over the open ocean. More

In contrast, NCAR provides real-time maps of turbulence at various altitudes over the continental United States. Such a system, had it encompassed remote ocean regions, could have alerted the pilots of the doomed Air France flight to the stormy conditions along their flight path.

The cause of that disaster has not been determined, and it is impossible to know whether the system could have prevented it.

"It seems likely that the information provided by a real-time uplink of weather conditions ahead would have, at a minimum, improved the pilots' situational awareness," Williams said.

Williams and his colleagues have recently completed two critical steps in identifying turbulence over the oceans:

- The team has created global maps of clear air turbulence based on global computer weather models that include winds and other instabilities in the atmosphere. Clear air turbulence consists of erratic movements of air masses that occur in the absence of clouds and sometimes buffet aircraft.

- Drawing on satellite images of storms, the scientists have created global views of the tops of storm clouds. Higher cloud tops are often correlated with intense storms, although not necessarily with turbulence.

NASA
NASA and NCAR are working to develop a near-real-time forecast that identifies turbulence from breaking gravity waves that are generated by rapidly rising deep convection. This image from NASA's MODIS instrument (Moderate Resolution Imaging Spectroradiometer) shows gravity waves over the ocean. Atmospheric gravity waves (also called atmospheric internal waves) occur either when a uniform layer of air blows over a large obstacle, like a mountain or island or when rapidly rising, deep convection perturbs a stable layer from below, as in the oceanic case we have illustrated. When the air hits the obstacle or is disturbed by rising convection from below, the horizontal ribbons of uniform air are disturbed, which forms a wave pattern. This wave pattern in the air impresses itself onto sea waves when it touches the surface of the ocean. In addition to the surface mimicking the wave pattern, wave clouds can form as well, creating potential turbulence for aircraft. More

The next step is to identify areas of possible turbulence within and around intense storms. To do so, the team will study correlations between storms and turbulence over the continental United States where weather is more closely observed. The scientists will then infer the likelihood of turbulence associated with storms over the oceans, keying in on satellite indicators such as rapidly expanding clouds or places where the tops of storm clouds are cooling quickly.

They will also develop mathematical equations to account for differences in cloud systems over the United States compared to over the oceans, including the tropics.

In addition to providing aircraft and ground controllers with up-to-the-minute maps of turbulence, the NCAR team is turning to an artificial intelligence technique, known as "random forests," to provide short-term forecasts of turbulence.

The random forests, which have proven useful for forecasting thunderstorms over land, consist of many decision trees that each cast a yes-or-no "vote" on crucial elements of a storm at future points in time and space. This enables scientists to forecast the movement and strength of the storm over the next few hours.

"Our goal is to give pilots a regularly updated picture of the likely storms ahead as they fly over the ocean so they can take action to minimize turbulence and keep their aircraft out of danger," explains NCAR scientist Cathy Kessinger, a project team member. "Even over the middle of the ocean, where we don't have land-based radars or other tools to observe storms in detail, we can still inform pilots about the potential for violent downdrafts, turbulence, and possibly lightning."


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