Cloud Liquid Water Climatology from the Special Sensor Microwave/Imager

A Special Sensor Microwave/Imager (SSM/I) algorithm is developed to measure both cloud liquid water path (LWP) and cloud frequency (CF) over the oceans. For climate analysis, the LWP and CF parameters are computed on pentad and monthly timescales. Comparisons are made between cloud frequencies obtained from microwave and visible/infrared measurements. It is shown that the SSM/I CF correlates with International Satellite Cloud Climatology Program low- and middle-level cloudiness. Interannual variations of monthly LWP are found to be strongly correlated with El Niño and La Niña events. In general, positive LWP anomalies are associated with positive SST anomalies. However, positive LWP anomalies may also occur in regions of negative SST anomalies. This is probably due to an increase in warm top rain clouds, produced from low-level convergence. When pentads of outgoing longwave radiation data are compared to the LWP, they both show the detailed structure for atmospheric intraseasonal oscillations at 30–60-day periods. However, there are some interesting differences. Finally, as an important application, the monthly LWP is compared with simulations from a general circulation model. While the simulation captures the locations of observed maxima and minima, there is a large discrepancy between the model and measurement for the Northern Hemisphere in summer.