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Mission Synergy: Maximizing Science Results
The Aura instruments were selected and the satellite was designed to maximize science impact. The four Aura instruments have different fields of view and complementary capabilities. The instruments all observe the same air mass within about 13 minutes, a short enough time so the chemical and dynamic changes between observations are small.
Chemical and transport processes have led to changes in the stratospheric ozone layer, and scientists need measurements of many different chemical species to puzzle out the causes for these observed changes. Measurements of ozone-destroying radicals such as CLO, NO2, BrO, and OH and reservoir gases such as N2O5, CLONO2, and HNO3 help solve the chemical part of the puzzle. Measurements of long-lived gases such as N2O and CH4 tell scientists about the puzzling effects of transport. Ozone and some other constituents are measured by all the instruments; some constituents like hydrochloric acid are measured by only one. New Aura measurements, such as OH, will help us complete the picture. The new measurements are shown as detached pieces.
Stratospheric Ozone
Understanding stratospheric ozone change involves measurements of both the ozone profile and the total column amount, as well as the chemicals responsible for ozone change.
All of Aura’s instruments make ozone profile measurements. HIRDLS profiles have the highest vertical resolution and extend from cloud tops to the upper stratosphere. MLS measurements have lower vertical resolution than HIRDLS, but MLS can measure ozone in the presence of aerosols and upper tropospheric ice clouds. TES limb ozone measurements overlap the measurements from HIRDLS and MLS up to the middle stratosphere. OMI can also make broad ozone profile measurements using a modified SBUV technique.
To establish the scientific basis for ozone change, scientists must measure the global distribution of the source, reservoir, and radical chemicals in the nitrogen, chlorine, and hydrogen families. Together, the Aura instruments fill this requirement. For example, HIRDLS measures the halocarbons (chlorine source gases) and chlorine nitrate (one of the major chlorine reservoir gases), while MLS measures the radical chlorine monoxide and hydrogen chloride (the other major chlorine reservoir).
Stratospheric aerosols influence ozone concentrations through chemical processes that transform ozone-destroying gases. HIRDLS measures stratospheric aerosols with the best horizontal coverage and highest vertical resolution of Aura’s four instruments. TES provides a backup for HIRDLS. MLS and HIRDLS both measure nitric acid and MLS measures hydrogen chloride (HCl) and chlorine monoxide (ClO), two gases that are transformed by the chemical processes involving aerosols.
Air Quality
Measuring tropospheric ozone and its precursor gases is a major goal for Aura. Aura’s instruments provide two methods of tracking ozone pollution. First, TES measures tropospheric ozone directly. The second estimate of the total tropospheric ozone amount can be obtained by subtracting HIRDLS stratospheric ozone measurements from OMI’s total column ozone measurements. A similar procedure can be used to estimate the tropospheric amount of NO2, an important ozone precursor.
In the clear upper troposphere, Aura instruments provide overlapping measurements of CO (MLS, TES), H2O (MLS, TES, HIRDLS), HNO3 (MLS, TES, HIRDLS). Carbon monoxide (CO) is an ozone precursor and HNO3 is a reservoir gas for NO2. The combination of TES nadir measurements and MLS limb measurements through clouds will provide important new information on the distribution of CO and H2O.
An emerging problem in air quality is the increasing amount of aerosols in the air we breathe. OMI measures aerosols, and distinguishes between smoke, mineral dust, and other aerosols. Both TES and HIRDLS measure aerosol characteristics in the upper troposphere to help scientists understand how aerosols are transported.
Climate Change
Atmospheric chemistry and climate are intimately connected. Ozone, water vapor, and N2O take part in tropospheric chemical processes and are also greenhouse gases. Changes in these and other greenhouse gases can upset the atmosphere’s heat balance and alter climate. Measurements of these gases, their sources and sinks are essential if we are to understand how the climate is changing as a result of human activity. All of the Aura instruments provide information on tropospheric ozone. Clouds and aerosols are also important contributors to climate change. HIRDLS and MLS will measure cirrus clouds. OMI will measure aerosol distributions and cloud distributions and their heights.
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