The next step in sophistication in the retrieval of atmospheric state variables is to assume either temperature or humidity in order to retrieve the other. In climate research, efforts are being made to treat the index of refraction, dry pressure and dry temperature, in addition to bending angle as state variables that can be directly compared to model output of the same quantities.
Dry temperature, in contrast, is always less than the kinetic temperature. Dry pressure is always greater than kinetic pressure, and the difference increases the moister the environment becomes. Instead, they retrieve pressure and temperature as if there were no water vapor present and call those quantities dry pressure and dry temperature. The most basic retrieval schemes do not attempt a resolution of the wet-dry ambiguity. Prior uncertainty in humidity propagates to a greater (lesser) uncertainty in the index of refraction than does prior uncertainty in temperature in the lower troposphere (upper troposphere and stratosphere). Qualitatively, GPS RO can be considered a humidity sounder in the lower troposphere and a temperature sounder above. Many techniques, almost all of which are a type of variational data assimilation, have been incorporated to resolve the wet-dry ambiguity. The hydrostatic equation constrains the solution, but there is still one too many unknown variables, a problem that is known as the wet-dry ambiguity in GPS RO. There is no single way to convert profiles of the index of refraction to profiles of temperature, pressure, and humidity. Leroy, in Encyclopedia of Atmospheric Sciences (Second Edition), 2015 RO: Retrieval of Atmospheric State Variables
0 kommentar(er)
