The SAGE III mission is an important part of NASA's Earth Observation System and is designed to fulfill the primary scientific objective of obtaining high quality, global measurements of key components of atmospheric composition and their long-term variability. The primary focus of SAGE III on ISS will be to study aerosols, clouds, water vapor, pressure and temperature, nitrogen dioxide, nitrogen trioxide, and
chlorine dioxide.
Aerosols Aerosols play an essential role in the radiative and chemical processes that govern the Earth's climate. Since stratospheric aerosol loading has varied by a factor of 30 since 1979, long-term monitoring of tropospheric and stratospheric aerosols is crucial. SAGE III aerosol measurements will provide important contributions in the area of aerosol research.
Clouds Clouds play a major role in determining the planet's solar and longwave energy balance and, thus, are important in governing the Earth's
climate. SAGE III will provide measurements of mid and high level clouds including thin or "sub-visual" clouds that are not detectable by nadir-viewing passive remote sensors. These observations are important because while low clouds primarily reflect incoming solar radiation back into space (acting to cool the planet), mid and high level clouds enhance the "
greenhouse effect" by trapping
infrared radiation (acting to warm the planet). Also, the presence of thin cloud near the
tropopause may play a significant role in heterogeneous chemical processes that lead to
ozone destruction in mid-latitudes.
Water vapor Water vapor is the dominant greenhouse gas and plays a crucial role in regulating the global climate system. An improved understanding of the global water vapor distribution can enhance our ability to understand water's role in climate processes. SAGE III water vapor measurements will provide important contributions on the long-term effect of this green house gas.
Ozone ozone hole was equal to the record single-day largest area of 11.4 million square miles (29.5 million square kilometres), reached on 9 September 2000. The blue and purple colors are where there is the least ozone, and the greens, yellows, and reds are where there is more ozone. Ozone research has remained at the forefront of atmospheric science for many years because stratospheric ozone shields the Earth's surface (and its inhabitants) from harmful ultraviolet radiation. Since recent declines in stratospheric ozone have been linked to human activity, accurate long-term measurements of ozone remain crucial. It is important to monitor ozone levels in the lower stratosphere and upper troposphere since observed trends are the largest and most poorly understood at those altitudes. SAGE III's high vertical resolution and long-term stability make it uniquely well suited to make these measurements. SAGE III is also able to look at the relationship between aerosol, cloud, and chemical processes affecting ozone argue for simultaneous measurements of these atmospheric constituents (such as those made by SAGE III).
Pressure and temperature SAGE III temperature measurements will provide a unique data set for monitoring and understanding atmospheric temperature changes. In particular, the long-term stability and self-calibration capabilities of SAGE III may permit the detection of trends in stratospheric and mesospheric temperature that will be important diagnostics of climate change. SAGE III temperature measurements in the upper stratosphere and mesosphere will be a new source of long-term temperature measurements in this region of the atmosphere to complement existing long-term measurements made by satellites (MLS, ACE, SABER) and ground based lidar systems. SAGE III temperature measurements will also allow the monitoring of periodic temperature changes, such as those associated with the solar cycle and quasi-biennial oscillation, and the effects of radiative forcing by aerosols.
Nitrogen dioxide, nitrogen trioxide, and chlorine dioxide Nitrogen dioxide (NO2),
nitrogen trioxide (NO3), and
chlorine dioxide (OClO) play crucial roles in stratospheric chemistry and the catalytic cycles that destroy stratospheric ozone. SAGE III nitrogen dioxide measurements are important because the processes that occur in the Antarctic winter and spring and give rise to the ozone hole effectively convert NO2 to nitric acid (HNO3). Thus NO2 is an important diagnostic of ozone hole chemistry. Since it is measured during both solar and lunar occultation events, SAGE III observations of NO2 will improve our understanding of the strong diurnal (daily) cycles in stratospheric processes. In addition, SAGE III will make virtually unique measurements of nitrogen trioxide (NO3). Although it is short-lived in the presence of sunlight, NO3 plays an active role in the chemistry of other reactive nitrogen species such as NO2 and di-nitrogen pentoxide (N2O5) and, thus, indirectly in ozone chemistry. Since few other measurements of NO3 are available, SAGE III measurements, which are made during lunar occultation (nighttime) events, will provide crucial validation for our current understanding of reactive nitrogen chemistry. == Launch ==