The two main elements of the Atmospheric Infrared Sounder Radiative Transfer Algorithm (AIRS-RTA) are described in this paper: 1) the fast parameterization of the atmospheric transmittances that are used to perform the AIRS physical retrievals and 2) the spectroscopy used to generate the parameterized transmittances. We concentrate on those aspects of the spectroscopy that are especially relevant for temperature and water vapor retrievals. The AIRS-RTA is a hybrid model in that it parameterizes most gases on a fixed grid of pressures, while the water optical depths are parameterized on a fixed grid of water amounts. Water vapor, ozone, carbon monoxide, and methane profiles can be varied, in addition to the column abundance of carbon dioxide.
An intercomparison of radiation codes used in retrieving upper-tropospheric humidity (UTH) from observations in the v2 (6.3 /xm) water vapor absorption band was performed. This intercomparison is one part of a coordinated effort within the Global Energy and Water Cycle Experiment Water Vapor Project to assess our ability to monitor the distribution and variations of upper-tropospheric moisture from spaceborne sensors. A total of 23 different codes, ranging from detailed line-by-line (LBL) models, to coarser-resolution narrowband (NB) models, to highly parameterized single-band (SB) models participated in the study. Forward calculations were performed using a carefully selected set of temperature and moisture profiles chosen to be representative of a wide range of atmospheric conditions. The LBL model calculations exhibited the greatest consistency with each other, typically agreeing to within 0.5 K in terms of the equivalent blackbody brightness temperature (T b ). The majority of NB and SB models agreed to within ±1 K of the LBL models, although a few older models exhibited systematic T b biases in excess of 2 K. A discussion of the discrepancies between various models, their association with differences in model physics (e.g., continuum absorption), and their implications for UTH retrieval and radiance assimilation is presented.
Electrostatic ion cyclotron wave fields are determined in a magnetized and weakly collisional plasma. A phased-locked Laser Induced Fluorescence (LIF) diagnostic is used to directly measure the wave perturbed ion velocity distribution. Comparing these local LIF measurements with a theoretical model uniquely determines the wave parameters, such as the wave potential, the three-dimensional wave vector, and the effective wave damping. The self-consistent wave–particle interaction is modeled by Boltzmann–Poisson equations in the limit of weak collisions. The wave parameters determined from local measurements agree with those determined from spatial scans.
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