GLORY: Explaining the Earth's Energy Budget

WHY GLORY?

The Sun provides heat to our planet. However, only about half of the sunlight heats the surface of the Earth. A third of the sunlight is reflected back into space by the surface and atmosphere, while one sixth is absorbed in the atmosphere and then re-emitted. This energy budget of "heat in" versus "heat out" directly influences the Earth's short-term and long-term climate trends.

An accurate description of Earth's energy budget is important for scientists in order to anticipate future changes to our climate. Shifts in the global climate and the associated weather patterns impact human life by altering landscapes and changing the availability of natural resources. Scientists are actively working to better understand exactly how and why this energy budget changes. The NASA Goddard Space Flight Center (GSFC) Glory mission will provide significant contributions toward this critical endeavor.

GLORY SCIENCE

Scientists who study the Earth's energy balance consider the difference between energy entering and energy leaving the lowest layer of Earth's atmosphere (generally, energy entering has a warming effect while energy leaving has a cooling effect).

Specifically, the Glory mission is intended to meet the following two scientific objectives:

1. Measure solar energy entering the Earth's atmosphere to determine its long-term effects on the Earth's climate record
2. Collect data on the properties of natural and human-caused aerosols in the Earth's atmosphere

The Sun Factor The primary input to the Earth's energy balance comes from a natural source Ð our Sun. To find out the contribution of this giant space heater to the Earth's energy budget, scientists will measure the amount of energy that reaches the Earth's atmosphere over a given period of time. The current estimate is approximately 1,361 watts per square meter. That's enough energy incident on the Earth to continuously power nearly half a million 60-watt light bulbs per person. Previous sensors have provided a data record spanning the past 30 years, but these measurements of solar intensity contain slight offsets. That's one reason why scientists must maintain a continuous solar measurement record; Glory will provide continuity of this measurement. Energy from the Sun fluctuates depending on solar changes, such as sunspots, which peak in number with an 11-year average period. While it is easy to recognize that the Sun contributes to the "heat in" portion of the Earth's energy budget, it is not so simple to account for the subtle changes in the Sun's intensity in this budget analysis. The data from the instruments on Glory will help to answer some of these questions.

Particle Puzzles A second factor affecting the Earth's energy balance is the influence of aerosols, which are tiny particles suspended in the atmosphere. Aerosols come from both natural sources such as volcanoes, fires and desert dust, and from human sources, such as the burning of fossil fuels. Aerosols impact the Earth's energy balance by either absorbing or reflecting solar energy. Black carbon aerosols, for example, absorb the heat and then re-radiate some of that energy, contributing to more "heat in." Non-absorbing aerosols, such as sulfates, reflect the Sun's energy back into space causing cooling, or "heat out." In addition, aerosols also indirectly impact atmospheric cooling by changing the properties of clouds and altering precipitation patterns. Both natural and human-caused aerosols have an impact on global temperatures. Over the past century, the average temperature of the Earth has increased by approximately 1.3 degrees F (0.7 degrees C). Accurately attributing this increase and the accompanying climate change to natural events, human sources, or a combination of both is of primary importance to scientists and policy makers. The aerosol sensor on Glory will provide scientists with accurate measurements of aerosols in our atmosphere and will help scientists better understand how they influence the climate. The impact of solar variability and aerosols on the Earth's climate is believed to be comparable to the impact posed by greenhouse gases. Still, aerosols remain poorly measured and may represent the largest uncertainty in our understanding of climate changes. The root of the problem is that the Earth's atmosphere and its surface have a complex relationship, which leads to large uncertainties in simulations that scientists use to describe and understand this system. The objective of the Glory mission is to reduce these uncertainties.

GLORY'S INSTRUMENTS

The Glory spacecraft is equipped with the following scientific instrumentation: The Total Irradiance Monitor (TIM); and the Aerosol Polarimetry Sensor (APS), along with its two supporting Cloud Cameras.

Total Irradiance Monitor The Total Irradiance Monitor (TIM) instrument is built by the University of Colorado's Laboratory for Atmospheric and Space Physics in Boulder, Colorado. The instrument measures the amount of solar energy that enters the Earth's atmosphere. This information will help researchers understand any long-term changes in the amount of energy coming from the Sun and how those changes affect Earth's climate. The accuracy of Glory's TIM instrument is expected to be better than that of any other solar irradiance instruments currently in space. It will follow a record of observations made by an earlier TIM instrument flown on the SOlar Radiation and Climate Experiment (SORCE) mission, and continue an uninterrupted series of solar observations that span the past 30 years. The TIM instrument will monitor the Sun during the daylight portion of each Glory orbit. Data acquired in 50-second intervals will track changes in the total solar energy, which will then be averaged to provide both 6-hourly and daily values. This virtual continual monitoring will help diagnose short-term solar mechanisms causing energy budget changes and will contribute to the vital long-term solar record.

Aerosol Polarimetry Sensor The Aerosol Polarimetry Sensor (APS) instrument is built by Raytheon Inc. in El Segundo, California. This instrument will measure the size, quantity, refractive index, and shape of aerosols. This is the first space-based instrument to be able to identify different aerosol types, which will help researchers distinguish the relative influence of natural and human-caused aerosols on our global climate. The aerosol characterization capabilities of APS, coupled with the cloud identification function performed by the two on-board Cloud Cameras will allow scientists to determine, with very high accuracy, the global distribution of aerosols and cloud properties. The Glory Cloud Cameras are built by Ball Aerospace and Technologies Corporation (BATC) in Boulder, Colorado. Glory will complete a series of 233 orbits of the Earth along differing ground tracks to create a net of observations. This pattern is repeated every 16 days. Such complete coverage of the Earth will help scientists learn about aerosols and their impacts across the globe.

GLORY SPACECRAFT

The Glory Spacecraft is built by Orbital Sciences Corporation, in Dulles, Virginia. The spacecraft has two deployable solar array wings, is 3-axis stabilized, and has X-band/S-band RF communications capabilities. The structure is an octagonal aluminum space frame and there is a blowdown hydrazine propulsion module which contains enough fuel for much more than the 36 month baseline mission. The spacecraft bus provides payload power; command, telemetry, and science data interfaces, including onboard storage of data. The attitude control subsystem supports instrument pointing requirements in the 10's of arc-seconds.

GLORY LAUNCH AND ORBIT

The Glory satellite is scheduled for launch in 2009 on a Taurus XL launch vehicle from the Vandenberg Air Force Base, located on the central coast of California, and will orbit as part of the Afternoon Constellation, also known as the A-Train, which is a series of Earth-observing satellites flying in close formation. The A-Train orbits the Earth once every 100 minutes.

WHY FLY IN THE A-TRAIN

From its A-Train orbit, Glory will enhance existing satellite science data through a comparison of Glory science data with data from other instruments located on satellites orbiting in the A-Train through a process known as co-observation.

WORKING TOGETHER TO MAKE GLORY WORK

Getting Glory into space, and maintaining it once it is in orbit, will require the collaboration of numerous organizations across the United States.

Orbital Sciences Corporation is responsible for operating the spacecraft from the Mission Operations Center in Dulles, Virginia.

The Laboratory for Atmospheric and Space Physics in Boulder, Colorado will provide the capability to command the TIM instrument, monitor its performance, and generate science data products.

The Goddard Institute for Space Studies in New York City will schedule APS instrument activities, monitor instrument (APS and Cloud Cameras) performance, and generate aerosol and cloud data products.

The TIM, APS and Cloud Camera data products will be archived and distributed by the Goddard Earth Sciences Data and Information Services Center (GES DISC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, Maryland.