However, surface based observations of clouds are also affected by spurious trends. Therefore, we analyze long-term trends in low-clouds and total clouds observations over oceanic stratus regions from the Hahn and Warren archive and compare with clouds retrievals from satellites (Isccp corrected low plus mid level clouds and Patmos-x low clouds). There are extensive regions where surface based observations are not reliable due to poor sampling, but in regions in which archives from ships provided a continuous record of observations (e.g. SE Atlantic, NE Pacific) we see a good degree of agreement with satellites data. Looking at well-known correlations of low and total cloud cover with other variables, such as SST, SLP and EIS (Estimated Inversion Strength), we evaluate which category of data sets (surface observations rather than satellites) appears to be more reliable when there is discrepancy in the sign of cloud anomaly.
This analysis will help understand how cloud cover has changed over the last sixty years and if there has been a significant increase in the amount of incoming solar radiation at the top of the atmosphere due to decreased cloud cover.