Retrieving cloud geometrical extents from MIPAS/ENVISAT measurements with a 2-D tomographic approach

Year: 2011

Authors: Castelli E., Dinelli B.M., Carlotti M., Arnone E., Papandrea E., Ridolfi M.

Autors Affiliation: Ist Sci Atmosfera & Clima CNR, Bologna, Italy
Ist Applicaz Calcolo Mauro Picone CNR, Florence, Italy
Univ Bologna, Dipartimento Chim Fis & Inorgan, I-40136 Bologna, Italy
Univ Bologna, Dipartimento Fis, Bologna, Italy

Abstract: Clouds represent a critical factor in regulating the Earth’s atmosphere and its energy balance. Satellite instruments can measure the energy balance and global atmospheric properties only through an accurate knowledge of the vertical profile of cloudiness, which is as yet one of the key shortages in atmospheric science. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on-board the ENVISAT satellite, designed to infer the amount of atmospheric trace-gases, demonstrated also sensitivity to the radiation emitted from clouds. In order to model the effect of the geometrical extent of a cloud on MIPAS measurements, we developed a retrieval model capable to simulate cloud effects on broad spectral intervals accounting for the two-dimensional (2-D) variability of the atmosphere in the satellite orbit plane. The 2-D analysis revealed a sensitivity of MIPAS spectra to both the vertical and horizontal extents and the position of clouds along the instrument line of sight. One-dimensional models were found to underestimate Cloud Top Height (CTH) by approximating clouds as an infinite horizontal layer with a finite vertical extents. With the 2-D approach, we showed it is possible, for optically thin Polar Stratospheric Clouds (PSCs), to retrieve both CTH and horizontal dimension by analyzing simultaneously all the limb observations that come across the cloud with their field of view. For a selected case study we found a very good agreement for both PSC CTH and horizontal extents retrieved from MIPAS measurements and those retrieved from coincident CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarisation) measurements. (C) 2011 OSA

Journal/Review: OPTICS EXPRESS

Volume: 19 (21)      Pages from: 20704  to: 2072

More Information: E. Arnone and E. Papandrea acknowledge support by ESA within the framework of the Changing Earth Science Network Initiative. The authors acknowledge ECMWF for having granted direct access to their archives of atmospheric data. CALIOP data were obtained from the NASA Langley Research Center Atmospheric Science Data Center.
KeyWords: POLAR STRATOSPHERIC CLOUDS; LIMB EMISSION-SPECTRA; MID-IR; SATELLITE MEASUREMENTS; MIPAS; PARAMETERS; SCATTERING; CIRRUS; VALIDATION; INSTRUMENT
DOI: 10.1364/OE.19.020704

ImpactFactor: 3.587
Citations: 4
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