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 the Surface Pressure has a level of 1 but is valid at the earths surface.