These data are the daily averages of the 3-hourly data provided by CPC, with the daily averages calculated over the same accumulation period used to produce the daily values produced by the CPC, namely 00Z to 00Z. There are some minor differences between these data the daily data provided by CPC (from Feb 2005) and are generally seen in portions of North America and Central Asia. Here is an example image of the difference between the daily and daily_calculated fields. Please refer to the CPC documentation for more information about potential sources for these differences.
For documentation, see the following web page: http://www.cpc.ncep.noaa.gov/products/janowiak/cmorph.shtml
The appropriate reference for this data set is the following:
Joyce, R.J., J.E. Janowiak, P. A. Arkin and P. Xie, 2004: CMORPH: A Method that Produces Global Precipitation Estimates from Passive Microwave and Infrared Data at High Spatial and Temporal Resolution. J. Hydrometeorology, 5, 487-503.
The following information is excerpted from the "readme" file associated with the 3-hourly data from which the daily averages are calculated:
CMORPH 0.25 degree 3-hourly Information
Last Update: November 8 2004
The 0.25 degree 3-hourly CMORPH can be found on the ftpprd.ncep.noaa.gov
server in the /pub/precip/global_CMORPH/3-hourly_025deg/ directory
The data are compressed using the standard Unix compress function (files have a
suffix of ".Z"). Each file is composed of 16 direct access binary
("big_endian") records that are defined as follows:
Record 1: contains the merged microwave precipitation only for 00 UTC
Record 2: contains the "CMORPH" precipitation estimates for 00 UTC
Record 3: contains the merged microwave precipitation only for 03 UTC
Record 4: contains the "CMORPH" precipitation estimates for 03 UTC
.
.
.
Record 15: contains the merged microwave precipitation only for 21 UTC
Record 16: contains the "CMORPH" precipitation estimates for 21 UTC
All units are "mm/hr". Missing data are denoted by values of "-9999."
Each record contains a 1440 x 480 REAL*4 array of data which is oriented
from 0.125E EASTward and from 59.875N SOUTHward, with a grid increment
of 0.25 degrees of latitude and longitude. Thus, the grid locations
are the centers od a 0.25 degree lat/lon grid box. Note that these
estimates represent spatial averages, so the data are grid-centered,
rather than lattice-centered.
For example (1,1) is 0.125E, 59.875N
(2,2) is 0.375E, 59.625N, etc.
There is an associated GrADS ctl file with this data set:
CMORPH+MWCOMB_025deg-3hr.ctl
Below is FORTRAN code (run on an SGI) that will read the data sets:
program cread
c program cpc_advt+comb_read.f
parameter (IRMAX=1440, JRMAX=480, PMAX=2)
real*4 ssmipropREG(IRMAX,JRMAX,PMAX)
character*115 in1ssmipropREG
iyrmndy = 20031110
irec = 0
c Open input regional blended sensor rainfall file for 3
c hour CPC micro rainfall file
in1ssmipropREG = '/export-2/sgi109/irstat/blended_tech/cpc/data/02
&5deg/YYYY0M0D_3hr-025deg_cpc+comb'
write (in1ssmipropREG(54:61),'(i8)') iyrmndy
write(6,'('' file '',a88)') in1ssmipropREG
open (unit=15, file=in1ssmipropREG, access='direct',
& recl=1440*480*2*4, form='unformatted')
c Loop over 8 3 hourly periods for one day
do ihr = 0, 21, 3
irec = irec + 1
write(6,'(//,''proc 3 hr starting '',i8,i4)') iyrmndy, ihr
read (15, rec = irec) ssmipropREG
write (6,'(/,'' cpc combined MW '')')
do jreg = 271, 280
write(6,'(15(f5.1))') (ssmipropREG(ireg,jreg,1),ireg=1161,1175)
enddo
write (6,'(/,'' CMORPH '')')
do jreg = 271, 280
write(6,'(15(f5.1))') (ssmipropREG(ireg,jreg,2),ireg=1161,1175)
enddo
c End 3 hour loop
enddo
close (15)
stop
end