Data Assimilation Meetings at Reading

Date Meeting type Speakers
7 Mar 2012 informal DARC meeting


Cristina Prates (University of Reading)
IASI retrievals in the presence of clouds
The new generation of vertical sounders such as the Infrared Atmospheric Sounding Interferometer (IASI) with its high spectral resolution provides the possibility to retrieve atmospheric temperature and humidity profiles at much higher resolution than that achieved by previous sounders. However, to make effective use of IR satellite measurements in the presence of cloud is still one of the major challenges faced by the numerical weather prediction (NWP) community as it requires the parameterisation of radiative cloud effects within the observation operator (radiative transfer models). The radiative transfer models that are currently used to assimilate infrared cloudy radiances are based on simple cloud schemes in which clouds are assumed to be single-layer grey bodies of negligible depth despite observational evidence that the majority of cloud formations in the atmosphere are more complex than the single layer configuration. A new cloud scheme enabling an additional cloud layer (two-layer cloud representation) to be treated in a one-dimensional variational retrieval (1D-Var) has been developed and tested using both observed and simulated IASI measurements. The cluster information based on a detailed radiance analysis of co-located Advanced Very High Resolution Radiometer (AVHRR) pixels inside each IASI field of view is used in this study as an independent source of information to characterise the cloud formation within IASI pixel.

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