NASA is preparing to launch a satellite designed to study aerosols' influence on Earth's climate and continue a long-standing record of solar energy, measurements that could help improve the accuracy of climate models.
Known as Glory, the satellite is set to launch Feb. 23 from Vandenberg Air Force Base in Southern California aboard a Taurus XL rocket. Once in space, it will settle into an orbit roughly 440 miles above the Earth.
That will place Glory in a line of satellites known as the A-Train, named for their afternoon orbit around the equator. The four satellites that now comprise the A-Train carry 15 instruments that measure different properties of the atmosphere, including temperature, water vapor content, the structure of clouds, and the distribution of greenhouse gases.
Because the A-Train satellites fly in unusually close proximity to one another, they provide near-simultaneous measurements of different aspects of the climate system -- in effect, functioning as "the first-ever superobservatory," said Joy Bretthauer, NASA's Glory program executive.
"The highly accurate and precise data from Glory, in combination with observations from the rest of the A-Train, will enable researchers to improve our understanding of the Earth system by improving our ability predict future climate," she said.
Glory's payload consists of two scientific instruments: one facing the sun, the other facing Earth.
Pointed at the sun, the Total Irradiance Monitor (TIM) is designed to extend a 32-year record of fluctuations in the sun's energy output. Understanding how much energy from the sun reaches Earth is important because it can influence the climate over the long term, scientists said.
"The short-term fluctuations -- though large -- don't influence climate so much," said Greg Kopp of the University of Colorado, Boulder's Laboratory for Atmospheric and Space Physics, which developed the TIM instrument. "The climate can't respond so quickly to them. We'd like to know over the long term how the sun responds over decades or over centuries. That's much more relevant to climate change on the Earth."
Probing the mysteries of aerosols
The TIM instrument flying aboard Glory will replace a similar instrument already in space aboard a different NASA satellite. The version Glory will carry is "significantly more accurate than all its predecessors," said Michael Mishchenko, a Glory project scientist based at NASA's Goddard Institute for Space Studies.
The second scientific instrument carried aboard Glory is designed to measure how tiny particles called aerosols influence Earth's climate.
Different types of aerosols behave differently in the atmosphere. Some reflect sunlight, cooling the climate, while others absorb heat from the sun, warming the climate. Aerosols also affect the climate indirectly, by influencing the behavior of clouds and patterns of precipitation.
"Because of this important role that aerosols play in distributing energy within the global climate system, we need to understand their distribution with very high accuracy," said Mishchenko.
Scientists believe that aerosols exert an influence on climate roughly equal to that of greenhouse gases, but the current estimate of aerosols' climate effect carries a large margin of error.
Glory's Aerosol Polarimetry Sensor aims to change that. The instrument will measure how aerosol particles in the atmosphere reflect or absorb light. Combined with measurements from an instrument aboard NASA's Calipso satellite -- another member of the A-Train -- the data from Glory's APS will allow scientists to understand how different types of aerosols are distributed throughout the layers of the atmosphere.
Space agency officials said preparations for Glory's launch next month are proceeding on schedule. The satellite is now at Vandenberg Air Force Base, and NASA has completed all post-shipment tests and inspections. The agency will spend the next few weeks assembling the launch vehicle and preparing the satellite for its journey into space.