HR: 1340h
AN: A43B-0094    [Abstracts]
TI: Testing retrieval algorithms from limb-scattered radiances observed by the Ozone Mapping and Profiler Suite (OMPS): Modeling water vapor absorption
AU: * Bergman, J W
EM: jbergman@cpi.com
AF: Computational Physics Inc., 1650 38th st, suite 105W, Boulder, CO 80301 United States
AU: Lumpe, J D
EM: lumpe@cpi.com
AF: Computational Physics Inc., 1650 38th st, suite 105W, Boulder, CO 80301 United States
AU: Hornstein, J S
EM: john.hornstein@nrl.navy.mil
AF: Naval Reasearch Laboratory, 4555 Overlook ave. SW, Washington, DC 20375 United States
AB: Radiatively active atmospheric constituents, such as water vapor, can corrupt retrievals of ozone profiles from the Ozone Mapping and Profiler Suite (OMPS) that will fly aboard the NPOESS Preparatory Project (NPP). However, incorporating water vapor into the limb scattering radiative transfer models used for testing ozone retrievals is challenging because water vapor absorption occurs in lines that are much thinner than the bandwidth of the observed radiances. Since these lines can saturate, the water vapor cross section is a nonlinear function of the water vapor density in the photon path. This nonlinearity complicates the calculation of limb-scattered radiances, which a linear relationship for efficiency. As a result, a rigorous calculation of water vapor absorption is computationally prohibitive. To incorporate water vapor into OMPS testing calculations, we consider three approaches. (1) The low density limit linearizes the effective cross-section by holding the cross-section per number density fixed at sub-saturation values. This overestimates the impact of water vapor on radiative fluxes and provides a `worse case scenario' for the corruption of retrievals by water vapor. (2) The high density limit holds the cross section per number density fixed at values appropriate for saturated lines. For realistic water vapor densities, this method underestimates the impact of water vapor on radiative fluxes. The difference between fluxes calculated from these two limiting cases provides a rough estimate of the error introduced by line saturation. (3) We have also developed a first order correction to the linear limits. This method exploits the relationship between the actual optical path length and the low-density limit. For conditions typical of the Earth's atmosphere, that relationship is, to a reasonable approximation, a single-valued function. This allows us to adjust optical path lengths from a low-density calculation to obtain more realistic estimates of water vapor absorption without explicitly calculating the true effective water vapor cross section for all photon paths.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0360 Radiation: transmission and scattering
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005