Long-term observations of cloud liquid, water vapor, and cloud-base temperature in the North Atlantic Ocean

Measurements of precipitable water vapor, cloud liquid, and cloud-base temp erature made at Porto Santo Island, Madeira Archipelago, are presented. The observations were made continuously over a 1-yr period from July 1992 to J une 1993. Instrumentation consisted of a 20- and 31-GHz ground-based microw ave radiometer for measurement of water vapor and cloud liquid, and a 10.7- mu m infrared radiometer for measurement of cloud-base temperature, A stati stical summary of the data is presented for clear and cloudy conditions, co nsidered both separately and combined. The mean and variance of precipitabl e water vapor are smaller during clear than during cloudy periods. Values o f water vapor during the winter are 26% smaller than during summer months. The mean decorrelation time of precipitable water vapor is generally found to be less than 12 h.