Spacecraft and Instruments
Microwave Limb Sounder (MLS)
The scientific priorities and objectives of the MLS investigation are to improve understanding of the following processes and parameters vital to global change research and environmental policy:
Chemistry of the lower stratosphere and upper troposphere — MLS measures lower stratospheric temperature and concentrations of H2O, O3, ClO, BrO, HCl, OH, HO2, HNO3, HCN, and N2O, for their effects on (and diagnoses of) ozone depletion, transformations of greenhouse gases, and radiative forcing of climate change. These measurements will be especially valuable for diagnosing the potential for severe loss of Arctic ozone during the critical period following the turn of the century when an abundance of stratospheric chlorine will still be high, and slight cooling of the stratosphere could exacerbate ozone loss due to chlorine chemistry. The measurements will help determine whether the stratosphere is responding as expected to the effects of the Montreal Protocol agreements for phasing out ozone-depleting substances. MLS also measures upper tropospheric H2O, O3, CO, and HCN for their effects on radiative forcing of climate change and for diagnoses of exchange between the troposphere and stratosphere.
Chemistry of the middle and upper stratosphere — MLS observes the details of ozone chemistry by measuring many radicals, reservoirs, and source gases in chemical cycles which destroy ozone. This set of measurements will provide stringent tests on the understanding of global stratospheric chemistry, will help explain observed trends in ozone, and can provide early warnings of any changes in the chemistry of this region.
Water in the upper troposphere— the Upper Atmosphere Research Satellite (UARS) has demonstrated the MLS capability of measuring upper tropospheric water vapor profiles, knowledge of which is essential for understanding climate variability and global warming but which previously has been extremely difficult to observe reliably on a global scale. MLS is unique in its ability to provide these measurements in the presence of tropical cirrus, where important processes affecting climate variability occur. MLS also provides unique measurements of cirrus ice content. The simultaneous MLS measurements of upper tropospheric water vapor, ice content, and temperature, under all conditions and with good vertical resolution, will be of great value for improving our understanding of processes (such as El Niño) affecting the distribution of atmospheric water, climate variability, and tropospheric-stratospheric exchange. The simultaneous measurements of dynamic tracers CO and N2O enhance the value of this data set by helping identify source regions of the air masses being observed.
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