Reviewer
Sid Boukabara (NOAA/NESDIS)
Road Map
The review intends to shed light on possible strategies for the choice of observables in the cloud analysis system. The focus of this work is not to list the various observation types, but rather to study how they can be successfully "digested" within an operational data assimilation (DA) system. The question of non-linearity will be addressed, particularly for the radiative transfer model (RTM) in satellite data assimilation. The accuracy of the RTM and the range of linearity will be shown for various schemes. The literature comparing the assimilation of raw radiances and retrievals (practical advantages, specification of errors, information content, etc) will be summarized with a special focus on clouds and strategies to leverage experience from retrievals for radiance DA will be presented. The review will also include the specification of observation error covariances and will distinguish measurement, preprocessing and representativeness errors. Various strategies to alleviate the later will be presented, in particular methods to account for the scales (both spatial and temporal) of the observations vs. the background errors. The "super-observations" in radar DA could be used as an example.
Non-exhaustive list of publications and earlier reviews
Comparison of progress in assimilating cloud-affected microwave radiances at NCEP, ECMWF, JMA and the Met Office. Min-Jeong Kim, Steve English, Peter Bauer, Alan Geer, Kozo Okamoto. NWP-SAF Report 2008.
The capability of 4D-var systems to assimilate cloud affected satellite infrared radiances. CHEVALLIER, F.; P. LOPEZ, A. M. TOMPKINS, M. JANISKOVA and E. MOREAU. 2004. Q. J. R. Meteorol. Soc.130: 917-931.
Retrieval of cloud parameters from satellite sounder data: a simulation study. EYRE, J.R. and W.P. MENZEL. 1989. J. Appl. Meteorol.28: 267-275.
Lessons learnt from the operational 1D+4D-Var assimilation of rain- and cloud-affected SSM/I observations at ECMWF. A. Geer, P. Bauer, P. Lopez. 2008. Q. J. R. Meteorol. Soc. 134, 1513-1525.