The HIRS instrument on the NOAA polar orbiting satellites is used to obtain coverage of outward-going longwave radiation across the global tropics and subtropics four times a day. Fractional coverage of cold cloud is obtained from this, which is then interpreted as rainfall rates. This information is introduced into the ECMWF data assimilation system as diabatic heating through the nonlinear normal-mode initialization scheme. Substantial impact on the analyses is found.
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Heckley et al. (1990) studied this question.