A Survey of Changes in Cloud Cover and Cloud Types over Land from Surface Observations, 1971–96

Abstract

From a dataset of weather observations from land stations worldwide, about 5400 stations were selected as having long periods of record with cloud-type information; they cover all continents and many islands. About 185 million synoptic reports were analyzed for total cloud cover and the amounts of nine different cloud types, for the 26-yr period 1971-96. Monthly and seasonal averages were formed for day and night separately.Time series of total-cloud-cover anomalies for individual continents show a large decrease for South America, small decreases for Eurasia and Africa, and no trend for North America. The largest interannual variations (2.7%) are found for Australia, which is strongly influenced by ENSO. The zonal average trends of total cloud cover are positive in the Arctic winter and spring, 60°-80°N, but negative in all seasons at most other latitudes. The global average trend of total cloud cover over land is small, Ϫ0.7% decade Ϫ1, offsetting the small positive trend that had been found for the ocean, and resulting in no significant trend for the land-ocean average.Significant regional trends are found for many cloud types. The night trends agree with day trends for total cloud cover and for all cloud types except cumulus. Cirrus trends are generally negative over all continents. A previously reported decline in total cloud cover over China and its neighbors appears to be largely attributable to high and middle clouds. Global trends of the cloud types exhibit trade-offs, with convective cloud types increasing at the expense of stratiform clouds, in both the low and middle levels.Interannual variations over Europe, particularly of nimbostratus, are well correlated with the North Atlantic Oscillation; significant correlations are also found across northern Asia. Interannual variations in many parts of the Tropics are well correlated with an ENSO index. Little correlation was found with an index of smoke aerosol, in seven regions of seasonal biomass burning.In the middle latitudes of both hemispheres, seasonal anomalies of cloud cover are positively correlated with surface temperature in winter and negatively correlated in summer, as expected if the direction of causality is from clouds to temperature.

A high-quality monthly total cloud amount dataset for Australia

“…Comparison between TCA timeseries for the Australian region provided by Warren et al (2007) and our results, for the common period , reveals negative trends of similar magnitude. This similarity occurs despite the fact that two analysis are based on different number of stations (74 and 165 respectively) and Warren et al include neighboring Pacific Islands.…”

“…A comprehensive study of global trends in cloud amount was undertaken by Warren et al (2007). The study found a small negative trend in global average cloud cover over land for the period 1971 to 1996, which was compensated by a small positive trend over the ocean, resulting in almost no trend for global average cloud cover over the period considered.…”

Clouds in the atmospheres of extrasolar planets

“…The corresponding global and temporal average cloud coverages resulting from long-term surface observations have been published by e.g. Warren et al (2007) and are given in Table 1. The measured cloud coverages already include a certain amount of overlap between the different cloud layers, which was not further specified by Warren et al (2007).…”

“…Warren et al (2007) and are given in Table 1. The measured cloud coverages already include a certain amount of overlap between the different cloud layers, which was not further specified by Warren et al (2007). Average properties of Earth clouds, for instance the cloud top temperature and pressure as well as their optical depth have been derived by long-term satellitebased measurements within the International Satellite Cloud Climatology Project (ISCCP) for example.…”

“…To study the basic climatic effects, our cloud scheme has been coupled with a one-dimensional A&A 511, A66 (2010) Notes. (a) Taken from surface observations (Warren et al 2007), the global mean coverages have been derived by a weighted average from the coverages over ocean (70%) and land (30%). (b) From satellite observations within the ISCCP (see Rossow & Schiffer 1999, for details).…”