Climatology is interpolated from 1 degree monthly file to 1/4 degree daily grid file.
The base period is 1971-2000. This climatology is described in:
and paper at:
Xue, Y., T. M. Smith, and R. W. Reynolds, 2003: Interdecadal changes of 30-yr SST normals during 1871-2000. J. Climate, 16, 1601-1612.