From initial clustering information provided by the user, a clustering algorithm is run to apportion each ensemble member into a cluster. Successive members are merged together by computing the correlation between members, combining the two closest members, and repeating the process until the required number of clusters is found.
A file called 'FFFFF_dendrogram.ps' (where FFFFF is the stash code of the field) is created which contains the clustering dendrogram, and the details about the cluster members are printed. Finally the average value of the field in each cluster is plotted at each data time. Note that the clustering is performed using data values at a single, user-specified, time.
The program allows up to 6 clusters; the actual number is determined by the difference in correlation between successive pairing of clusters. The cut-off is deemed to be where the difference in correlation between two-successive cluster joinings is greatest.
The IDL source code can be found at
The code uses library routines written by Andy Heaps (NCAS, University of
and these are accesssed by adding these two lines into your
export IDL_PATH=+/usr/local/itt , /data/nwp1/frbr/TIDLWorkspace/andy_lib/guide4.sh
The user must supply information as follows:
Currently, the clustering will work with only the members of the ensemble at a single time. The program needs to be re-run by the user (probably in batch mode using a unix script to generate the control file) if clusters at mnore than one time are required.
0 ; normalisation flag (0=off, 1=on) -1 ; spatial averaging flag 1 ; model level used for the clustering 4 ; N, where N'th time sample determines clustering 04203 ; field to be analysed 1 ; model level to be used for output /export/carrot/raid1/brugge/stefano/no_precip_run_fcst/ ; data directory _ppn_qwq114.oper ; XXX ; where filename is FFFFFXXXmmYYY .pp_001.nc ; YYY ; and mm is the member
where the records should been changed to reflect the input data and output requirements of the user. The text to the right of the ';' symbols can be kept as a reminder of the meaning of the data records.
The idl code can now been run in a batch job or, if run interactively, will loop through the specified cycles.
The figures show (a) a dendrogram showing how the clusters are generated, (b) a cluster plot using normalised data, and (c) a cluster plot based on the same inoput data - but this time not normalised.