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Understanding the dynamics of climate, the transport of chemical agents in the atmosphere and their distribution over the surface of the Earth, and the rainfall and evaporation that control the growth of vegetation requires a precise knowledge of the global atmospheric circulation, temperature profiles, and water vapor content. AIRS along with its partner microwave instrument, Advanced Microwave Sounding Unit (AMSU-A), will observe and characterize the entire atmospheric column from the surface to the top of the atmosphere in terms of surface emissivity and temperature, atmospheric temperature and humidity profiles, cloud amount and height, and the spectral outgoing infrared radiation. These data and scientific investigations will answer long-standing questions about the exchange and transformation of energy and radiation in the atmosphere and at the Earth's surface.

1. Determination of the factors that control the global energy and water cycles

The study of the global hydrologic cycle and its coupling to the energy cycle is a key to

understanding the major driving forces of the Earth's climate system.

AIRS/AMSU will measure the major components of these driving forces

including the thermal structure of the surface and the atmosphere, the outgoing

longwave infrared radiation, and the atmospheric water vapor content.

2. Investigation of atmosphere-surface interactions

The high spectral resolution of AIRS will provide several spectrally transparent window channels that will observe the surface with minimal contamination by the atmosphere and will allow the determination of accurate surface temperature and infrared spectral emissivity. In addition, the narrow spectral channels in the short-wavelength infrared region will observe the atmospheric layers near the Earth's surface with the highest vertical resolution possible by passive remote sensing. The observations will enable investigations of the fluxes of energy and water vapor between the atmosphere and the surface, along with their effect on climate.

3. Improving numerical weather prediction

Numerical weather prediction models have now progressed to the point where they can predict atmospheric temperature profiles to an accuracy of 2 K, which is equivalent to the accuracy of current satellite data. Further improvement in our knowledge of temperature profiles is essential in order to improve forecasting accuracy. AIRS/AMSU temperature profiles with radiosonde accuracy of 1 K in 1 km-thick layers are key to improving the accuracy and extending the range of weather forecasts.

4. Detection of the effects of increased greenhouse gases

AIRS will map the concentration of carbon dioxide and methane globally. In addition, the ability to provide simultaneous observations of the Earth's atmospheric temperature, ocean surface temperature, and land surface temperature and infrared spectral emissivity, as well as humidity, clouds and the distribution of greenhouse gases, makes AIRS/AMSU a primary space instrument to observe and study the response of the atmosphere to increased greenhouse gases.

5. Assessing climate variations and feedbacks

The accuracy and high spectral resolution of AIRS provide a powerful new tool for climate studies. AIRS' high resolution infrared coverage from 3.74 to 15 μm will give researchers the ability to validate numerical models and to study different climate processes as needed. For example, emission to space by strong and weak water vapor lines is a critical climate feedback mechanism in the middle and lower troposphere. Numerical models must reproduce such lines as an indication of their ability to describe the climate system.

Science Objectives