Assessments of cloud liquid water algorithms using advanced technology microwave sounder （ATMS） observations

Cloud liquid water path is an important parameter in climate analysis and weather applications and is often retrieved from satellite microwave observations. The algorithm requires the data measured at two frequencies at 23.8 and 31.4 GHz. Using the Advanced Technology Microwave Sounder (ATMS) observation data, the physical and empirical algorithms for retrieving the cloud liquid water path were compared. It is shown that both algorithms can well depict the distribution of cloud phase clouds, although the magnitudes at some regions are different. The cloudy areas detected by the physical retrieval algorithm are more consistent with that shown in satellite visible images. The performance of the empirical algorithm, however, is more affected by the season, especially in the mid-high latitudes. The sensitivity analysis indicates that the errors of the physical algorithm are affected by cloud layer temperature, sea surface temperature and sea surface wind speed. The uncertainty in cloud layer temperature is likely a major source of errors in cloud liquid water retrievals. In addition, sea surface temperature errors influence the retrieval of clouds liquid water having a high amount while sea surface wind has more impacts on cloud liquid water having a low amount.