A new NASA-developed technique to improve numerical weather prediction – one that looks to the ground as well as the clouds – may one day help forecasters increase the accuracy of spring and summer weather predictions.
Atmospheric scientist Bill Lapenta, of the Global Hydrology and Climate Center, based at the National Space Science and Technology Center (NSSTC) in Huntsville, Ala., is researching a new method for improving numerical weather prediction in the Southeast United States. Funded through the U.S. Weather Research Program, the research is a cooperative effort between NASA and the National Oceanic and Atmospheric Administration (NOAA).
Numerical weather prediction is a complicated business, which uses data from many sources and combines them to form a prediction of tomorrow’s weather. Like a chef creating a favorite dish, Lapenta’s recipe, or equation, for weather prediction includes ingredients used by many, along with specialty items used by few.
In addition to standard data – such as current air temperature, humidity, and wind speed – he adds a dash of specialized data from Geostationary Operational Environmental Satellites maintained by NOAA.
Using the satellite data adds detailed ground-level information to the numerical forecasts – something Lapenta believes can help forecasters increase the accuracy of predictions. “Understanding weather is more than understanding what’s happening high in the clouds,” he said. “The satellite data takes into account conditions at ground level, where the weather impacts most people.”
This method incorporates factors such as variations in the way different land surfaces react to the energy emitted by the sun.
“From prior NASA research, we know that parking lots, which absorb and hold heat, tend to become much hotter during the day than forests, which are cooled by evaporation,” he said.
“Also, the amount of water in the top layers of the soil affects how the Sun’s energy heats the overlying air. If the soil is wet, more energy is used to evaporate moisture than to heat the land and air. We adjust the initial estimate of moisture availability so that the predicted air temperature follows what the satellite senses. The satellite data helps the model to account for such differences in the temperature of the land surface.”
Even though the weather-prediction equations are complex, the concept is quite straightforward. Lapenta’s model uses an array of geographic grid points. Using these points, the method starts by creating a “snapshot” of the current state of the atmospheric winds, temperatures, and humidity. The next step is to use mathematical equations to predict the evolution of the atmosphere over the course of 48 hours.
“Many details are factored into the weather-prediction equations,” he said. “For example, today’s rainfall may become tomorrow’s humidity through evaporation from the wet soil.”
When all standard factors are calculated into his formulas, there is enough information for an initial forecast, but that’s not where it ends. He then adds the satellite data, which makes adjustments to the soil moisture availability at each grid point – this can have a dramatic impact on the original prediction.
Lapenta is concentrating on spring and summer weather, because precipitation during warm-weather seasons has been traditionally more difficult to predict.
In addition to improving the accuracy of short-range (0 to 48-hour) predictions of temperature, humidity, and precipitation, Lapenta’s goal is seeing this new method implemented within other models, including those used by the National Weather Service. He also sees potential for using the method to improve urban and air quality modeling.
This is a joint research project with Dick McNider of the University of Alabama in Huntsville, and supported by Ron Suggs and Gary Jedlovec, NASA scientists in the Global Hydrology and Climate Center, who process the satellite data. All are located at the National Space Science and Technology Center.
A collaboration that enables scientists, engineers and educators to share research and facilities, the NSSTC is a partnership with NASA’s Marshall Space Flight Center in Huntsville, Alabama universities and federal agencies. Opened in 2000, it focuses on space science, materials science, biotechnology, Earth sciences, propulsion, information technology, optics and other areas that support NASA’s mission.
