Comparison between measured and simulated far-infrared spectra

The spectral region between 15 µm and 100 µm is referred to as the far-infrared (far-IR) portion of the spectrum. The far-IR radiation is an important component of the radiation budget of the earth-atmosphere system. However, the spectral characteristics and information content of the far-IR radiation have not been studied extensively in comparison with their counterparts at shorter wavelengths. The novel Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument developed by NASA (Mlynczak et al. 2006), which is a Michelson interferometer, provides unprecedented data sets to understand far-IR radiation. This presentation reports on the analyses of the FIRST spectra obtained in Chile in 2009. In addition, we have integrated a radiative transfer package based on a combination of the line-by-line radiative transfer model (LBLRTM, Clough et al. 1992) and the discrete ordinate radiative transfer (DISORT, Stamnes et al. 1988) model to simulate far-infrared spectra. In the model simulations, cirrus optical models based on extensive in situ observations of cirrus microphysical properties and single-scattering properties of ice crystals computed from state-of-the-art methods are used. The spectral characteristics of the FIRST spectra, particularly, under cloudy cirrus conditions are discussed in detail.