This data set contains the results of the Weighted Anomaly of Standardized Precipitation (WASP), developed by Bradfield Lyon of the IRI, applied to several monthly gridded precipitation analyses available in the IRI Data Library.
The precipitation data sets to which the WASP has been applied here
include the CAMS-OPI
v0208 data set
from the CPC, the latest version of the CPC Merged Analysis of
Precipitation (CMAP)
analysis version 2
(which excludes model predictions from the estimate), the NASA Global
Precipitation Climatology Project (GPCP)
Version 2 merged satellite-gauge data set, and the University of East Anglia, Tyndall
Centre TS2.1
monthly gridded precipitation
data set.
The WASP uses overlapping multi-month sums (1, 3, 6, 9, and 12-month
sums are given in this data set) of standardized precipitation
anomalies weighted according to the fraction of mean annual
precipitation at the given time of year, to produce a measure of
interannual precipitation variability. Because of differences in
data availability in each data set, the base periods used for computing
climatological mean values and standard deviations in each data set are
different. For the CAMS-OPI, CMAP, and GPCP, the base period is
1979 to the most recent full year available. For the University
of East Anglia TS2.1 data set, the base period is 1961-1990.
The following references provide a full explanation of the WASP:
Lyon, B., 2004: The strength of El Niño and the spatial
extent of tropical drought. Geophysical
Research Letters, 31,
L21204.
Lyon, B, and A. G. Barnston, 2005: ENSO and the spatial extent
of interannual precipitation extremes in tropical land areas. J. Climate, 18, 5095-5109.
