DS127.1 represents a higher resolution version of ds124.1
[https://rda.ucar.edu/datasets/ds124.1/]. Both ds124.1 and 127.1
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
6-hourly 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/].