This data is on the original <a href="http://dss.ucar.edu/datasets/common/ecmwf/ERA40/docs/eta-ab">60 model levels</a>. <br>
 For most variables, level 1 denotes the highest level near the top of the atmosphere and level 60 denotes the lowest level near the earths surface.  However,
 the Log of the Surface Pressure and Geopotential have a level of 1 but are valid at the earths surface.