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There is a great need to accurately determine the water vapor
distribution since its uncertainty is a key limitation of models'
ability to simulate and predict the state of the atmosphere. For
example, the Working Group on Numerical Experimentation of the World
Climate Research Program indicated that the prime uncertainty of
greenhouse gas impact studies was caused by the treatment of
cloudiness which can produce a factor of two difference in predicted
temperature increases. With current uncertainties in global humidity
distribution and its variability due to dynamical meteorological
processes, the relative accuracy of different models, with different
convection schemes, cannot be determined. An initiative called the
Global Energy and Water Experiment (GEWEX) Vapor Program (GVAP) has
been undertaken to reduce uncertainties in the moisture field. Water
vapor uncertainties affect the initial diabatic forcing and subsequent
precipitation and wind fields, thus limiting the range of useful
prediction, particularly in the tropics. GIFTS will advance the GEWEX
objectives by providing accurate measurements of the tropospheric
water vapor distribution and its transport in response to climate and
weather processes. Most relevant to the science theme of this proposal is that the GIFTS will provide a unique four-dimensional water vapor and cloud tracer wind data set. Spaceflight demonstration is required to provide a constant sensor viewing area for the time period necessary to achieve accurate water vapor and cloud tracer vectors, which represent the atmosphere's wind velocity. With 1-2 km vertical resolution, wind vectors for at least six distinct vertical layers of the troposphere can be resolved. Assimilating these data directly and continuously into an accurate numerical model of the atmosphere's circulation will result in a greatly improved depiction of the atmosphere's four-dimensional wind field (as well as the temperature and water vapor fields.) |
