Wednesday, 9 July 2014
This work investigates the extent to which atmospheric properties, including cloud properties, can be retrieved from downwelling infrared spectra in the Arctic as a function of spectral resolution (for exact line-by-line simulations to 4 cm-1 resolution simulations). For this purpose, hundreds of spectra have been simulated that represent a large range of clear and cloudy conditions experienced in the Arctic. This dataset allows retrievals to be performed on many different realizations of the Arctic atmosphere to develop statistical knowledge of how well the retrieval system performs. Since simulated spectra are used, the atmospheric and cloud conditions are a priori and can be compared with what is retrieved. Retrieved properties include cloud base height and cloud microphysical properties. In addition, improvements are made to the first guess temperature profile and trace gas amounts. For cloud base height, the CO2-sorting method and Minimum Local Emissivity Variance method are tested. Retrievals of cloud microphysical properties are found to be relatively insensitive to the resolution of the infrared spectra because cloud properties vary slowly across the infrared spectrum.
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