ERA40 T106 Monthly Mean Analysis Fields on Pressure Surfaces, created at NCAR

DS129.1 represents a higher resolution version of ds126.1 [https://rda.ucar.edu/datasets/ds126.1/]. Both ds126.1 and 129.1 were implemented and computed by NCAR's Data Support Section, and form an essential part of efforts undertaken in late 2004, early 2005, to produce an archive of selected segments of ERA-40 on a standard transformation grid. In the case of ds127.1, ERA-40 monthly mean upper air variables on 23 pressure levels were transformed from either spherical harmonics (geopotential, temperature, vertical pressure velocity, vorticity, divergence, relative humidity), or a reduced N80 Gaussian grid (potential vorticity, specific humidity, ozone mass mixing ratio), to a 320 by 160 regular Gaussian grid at T106 spectral truncation. In addition, horizontal wind components were derived from spectral vorticity and divergence and also archived on a T106 Gaussian grid. All scalar fields were transformed using routines from the ECMWF EMOS library, whereas the horizontal winds were obtained using NCAR's SPHEREPACK library.

The ERA-Interim data from ECMWF is an update to the ERA-40 project. The ERA-Interim data starts in 1989 and has a higher horizontal resolution (T255, N128 nominally 0.703125 degrees) than the ERA-40 data (T159, N80 nominally 1.125 degrees). ERA-Interim is based on a more current model than ERA-40 and uses 4DVAR (as opposed to 3DVAR in ERA-40). ECMWF will continue to run the ERA-Interim model in near real time through at least 2010, and possibly longer. This data is available in ds627.0 [https://rda.ucar.edu/datasets/ds627.0/].