Cloud liquid water retrievals from aqua AMSU/HSB

The aqua satellite of NASA´s Earth observing system carries, among other instruments, the atmospheric infrared sounder, the advanced microwave sounding unit-A, and the humidity sounder for Brazil, which are used cooperatively to retrieve numerous geophysical parameters, including profiles of atmospheric temperature, ozone, water vapour, and cloud liquid water. This paper discusses the method of obtaining nonprecipitating cloud liquid water and some results form the first year of operation; for example, images of retrieved cloud liquid water show the positions of weather fronts. The retrieval process consists of several stages; cloud liquid water is estimated in the first stage, using the microwave channels. This algorithm seeks to minimize, by iteration, a cost function composed of quadratic functions of the differences between observed and computed brightness temperatures and the differences between the retrieved and a priori atmosphere/surface parameters. The algorithm uses internally a condensation model that relates water vapour and cloud liquid water to a single profile of a humidity variable, through which the a priori statistics of water vapour are introduced. The transition between vapour and liquid (saturation point) is a parameter found by the algorithm, thus allowing for possible error in the retrieved temperature profile. In simulations, the integrated cloud liquid water has rms errors of 50g/m² over water surfaces, and 150g/m² over land surfaces.