Measurement and simulation of mid‐ and far‐infrared spectra in the presence of cirrus

Observed far‐infrared and mid‐infrared radiance spectra measured insitu above cirrus with both the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) and the Airborne Research Interferometer Evaluation System (ARIES) are presented. Two sets of upwelling spectra between wavenumbers 100 and 1415cm−1 taken over ice cloud of visible optical thickness 0.1 and 0.3 are shown. These observations address the need for more measurements of radiance from cirrus, particularly in the far infrared, where experimental data are lacking. A test of consistency in modelling in both the far infrared and mid infrared is performed by fitting a model calculation of radiances in the infrared window region, and comparing with the measured radiances. In this consistency check, the sampling of the surrounding atmosphere and the cloud is given extensive consideration. The model was not able to consistently reproduce the observed radiance across the entire region, and was particularly poor in the 330–600cm−1 region of the far infrared. Possible causes are thought to be primarily model input uncertainties arising from inadequate sampling of cloud and atmosphere. Copyright © 2010 Royal Meteorological Society and Crown Copyright.