Re: mean seasonal cycle

[verschel@xxxxxxxxxxxxxxxxxxxxx (Mark A. Verschell)]

Joerg reminded me of the @MOD function for calculating climatologies - I had
completely forgotten about it (this comes from using ferret from the
beginning!)

He wasn't sure how to use it properly, so I ran a few tests and here are the
results (kudos to Steve Hankin and his crew - this works great! - well except
for a few little quirks)

An example, adapted from the ferret manual V4.4 (page 73):

    ! use the predefined climatological axes
    USE climatological_axes
    CANC DATA climatological_axes

    ! use my wind set (34 years of monthly data, 408 values)
    SET DATA pacwinds

    ! calculate the 12 month climatology
    LET txc = tx[GT=month_reg@MOD]

    ! Define the anomaly
    LET txa = tx-txc

Now I have the climatology and anomalies defined. Here is the slight flakiness,
the time axis for the climatology isn't perfectly adapted for use with the
original data set. Sometimes I get core dumps, and other times I get
inconsistent data region messages. What seems to work for me is something like
the following:

    ! plot the anomalies at one point
    PLOT txa[l=1:408,x=180,y=0]

    ! save the anomalies to a file
    SAVE/file=pacanom.cdf txa[l=1:408]

You could also probably use the /t= syntax....

If the data you are using is not defined at the middle of the month you need to
do a linear interpolation when making a climatology. Refer to page 74 and 75 of
the ferret manual.

Mark


-- 
 Mark Verschell                     NASA/Goddard Space Flight Center
 verschell@neptune.gsfc.nasa.gov    Code 970/Lab. for Hydrospheric Proc.
 301-286-2027  Fax: 301-286-1761    Greenbelt, MD 20771