Global Distrubution of Diurnal Cycles and Long-term in Cloud Amounts from Surface Observations

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Abstract for ATM-9510170 Warren, Stephen, University of Washington Title: Global Distribution of Diurnal Cycles and Long-term Changes in Cloud Amounts from Surface Observations Clouds have large effects on the earth's radiation budget, both shortwave and longwave. These effects are different for different cloud types, and the net forcing usually changes sign from day to night. A study of how clouds have changed in the past may help to clarify the interactions of clouds with other parts of the climate system and to infer changes in cloud radiative forcing. For global-changes studies involving clouds, a long period of record with global coverage and with no change in observing procedures is necessary. Routine surface weather observations of clouds, beginning about 1952 from ships in the ocean and 1971 from land stations, meet these requirements. Creation of databases and analyses of those databases are proposed to determine the changes of cloud types and their diurnal cycles over the past 40 years. Surface weather observations from land and sea have previously been used to produce a global climatology of total cloud cover type amounts, covering the 30-year period 1952-1981 over the ocean and the 11-year period 1971-1981 over land. These results were published in a series of four climatic atlases, which have found numerous uses in climatic research. Recently an improvement to the analysis procedure has been developed establishing an illuminance criterion for nighttime observations. By screening nighttime observations based on the availability of sufficient moonlight or twilight more accurate diurnal cycles of cloud amounts can be obtained. This illuminance criterion will be used to determine the geographical distribution of cloud type amounts, their diurnal variations, interannual variations, and long-term trends. The trends will be analyzed separately for day and night, since cloud radiative forcing is generally negative in daytime but positive at night. The research consists of the creation of a hierarchy of three databases for climatic analyses of clouds, spanning the 45 years 1952-1996. (1) Edited Cloud Reports Archive (2) Global analysis of the average amounts and diurnal cycles of total cloud cover and eleven different cloud types, using the moonlight criterion. (3) Global analysis of the geographical distribution of interannual variations and multi-decadal trends in amounts of the different cloud types (1954-1996 for ocean; 1971-1996 for land). This work is important because cloud processes are among the most important in climate change and long-term data about clouds are essential to an improved understanding of cloud processes. This project is co-funded by NSF (ROCEW and Geosystem Databases) Global Change initiatives and NOAA's Office of Global Programs.