November 26, 2012
Credit: Credit: NASA
Frank Morring, Jr. Goddard Space Flight Center
A new climate-study spacecraft just entering environmental test here is expected to sharpen weather-forecasting models in ways that would have given forecasters a better handle on the back-to-back storms that slammed the U.S. Mid-Atlantic coast this fall.
The Global Precipitation Measurement (GPM) mission, a U.S.-Japanese follow-on to the Tropical Rainfall Measurement Mission (TRMM) launched 15 years ago by NASA and the precursor to the Japanese Aerospace Exploration Agency (JAXA), will give unprecedented detail in its measurements of rainfall, snowfall and temperatures inside storms like Hurricane Sandy and the Nor'easter that followed it into New York Harbor and the New Jersey shore.
That, in turn, should allow meteorologists to tweak their computer models for better predictions of the track and intensity of violent storms. As has been the case with other weather-science instruments, there may be a future operational role for the sorts of data GPM will generate.
“If we demonstrate over the coming years after this thing is launched that, man, this thing is really helping in improving our ability to forecast snowstorms, that may bring to light a real need to have that type of system in an operational capacity,” says J. Marshall Shepherd, an atmospheric scientist at the University of Georgia who is president-elect of the American Meteorological Society. “From a hardware standpoint, ideally we'd really like to have these active radar-type systems in a geosynchronous satellite system.”
Before taking his academic appointment, Shepherd was deputy project scientist for the GPM mission. The spacecraft, which entered thermal vacuum testing here Nov. 13, carries two Japanese-built synthetic aperture radars (see photo) collectively dubbed the Dual Frequency Precipitation Radar (DPR). The radars will scan down through the atmosphere in Ka- and Ku-band frequencies (35.5 GHz and 13.6 GHz, respectively) to provide better three-dimensional data on precipitation structures, including very light rainfall and snow. The precursor TRMM spacecraft carries a single Ku-band radar in a 35-deg., 350-km (220-mi.) orbit.
The newer spacecraft also carries an advanced radiometer—the GPM Microwave Imager (GMI)—that passively measures energy from falling precipitation in 13 frequency channels. Set for launch in 2014 on a Japanese H-IIA rocket to a 65-deg. orbit at 407 km altitude, the spacecraft—formally known as the GPM Core Observatory—will allow scientists to calibrate radiometer data from as many as eight other present and planned satellites in a variety of orbits. The GPM constellation's deluge of data will yield precipitation measurements over 90% of the Earth's surface updated every 3 hr.
In the short term, forecasters will be able to predict the track of a storm approaching landfall, and measure temperature phenomena in the storm-eye wall called heat towers that signal changes in its intensity, according to Gail Skofronick Jackson, GPM deputy project scientist. The more heat towers—essentially thunderstorms riding from the cyclone's eye—that appear, the more intense the storm will become.