Sometimes, not often, but sometimes I'm interested in things that are approximately observations. Following the Lake Arrowhead workshop on Parameterizations of the PBL, I wanted to take a closer look at the so-called Klein line - the empirical relationship between lower tropospheric stability and low cloud fraction described by Klein & Hartmann (1993). Here are a series of plots from the ERA-40 reanalysis. The dataset being used was obtained from the NCAR website, and is gridded on a 1.25 degree grid that is close to what the CAM produces using T85.

The plots are all the same. Each one is a different monthly mean, spanning 1990 through 2001. The horizontal axis is lower tropospheric stability (difference of potential temperature between 700 hPa and near surface (2m) potential temperature). The vertical axis is low cloud fraction. The points are all the ocean points, and those within 30 degrees of the equator are red crosses (plotted on top of the gray dots of the total distribution). A blue dashed line shows the least squares best fit line through the tropical points, while the gray dashed lines shows the Klein line (as defined in the CAM's cloud parameterization). The axes should be the same in all cases, and the month and year are shown on the upper left of each plot.

The format is png, which is good for the web, but the quality is not great. I have the original pdf files, which can be provided upon request, but they are ~10MB each.