Re: vector eof/pca (e.g. u- and v-component of current data)

Hi,

I read the Wilks reference, however it is still not clear to me how to
'technically' pass the two components (meaning how to structure it in
a matrix) to eofunc, either using the covariance or correlation matrix
(@jopt).
I tried to use the function array_append_record to combine the two
components prior to the eofunc call and de-combined them afterwards,
however the resulting pattern of my data set seems to be lacking
major features which emerge when performing an individual eof analysis
of each component.

Thanks,
Malte

2011/3/14 Malte Stuecker <malte.stuecker@gmail.com>:
> Hi,
>
> Thank you very much for the quick reply and the help so far!
> I will try to get a hold on the Wilks reference, it seems our library
> doesn't stock it.
> I assume the resulting EOF and also the interpretation will be quite
> different between the two mentioned methods:
>
> 1) eofunc of data(time,lat,lon,component)
> 2) eofunc of data(time,2xlat,lon)
>    with 2xlat meaning using merged u- and v- field along the meridional axis
> !?
>
>
> 2011/3/14 gibies george <gibies@tropmet.res.in>:
>>
>>
>> On 15 March 2011 10:31, gibies george <gibies@tropmet.res.in> wrote:
>>>
>>> Hello Malte,
>>> There is a slight different way, which I am using.
>>> We have
>>>  u(time,lat,lon)
>>>  v(time,lat,lon)
>>> I combine them into another variable
>>> data(time,lat,lon,component)
>>> where
>>> data&time = u&time   ; is also =v&time
>>> data&lat = u&lat         ; is also =v&lat
>>> data&lon = u&lon        ; is also =v&lon
>>> data&component = (/"uwnd","vwnd"/)
>>> data(time|:,lat|:,lon|:,component|0) = u(time|:,lat|:,lon|:)
>>> data(time|:,lat|:,lon|:,component|1) = v(time|:,lat|:,lon|:)
>>> Then find the EOF of the variable data.
>>>
>>> On 15 March 2011 01:56, Dennis Shea <shea@ucar.edu> wrote:
>>>>
>>>> Hello,
>>>>
>>>> D. S. Wilks
>>>> Statistical Methods in the Atmospheric Sciences
>>>> Academic Press (Elsevier), 2006
>>>>
>>>> pp 477-479:
>>>>
>>>> Section 11.2.2: Simultaneous PCA for Multiple Fields
>>>>
>>>> I would suggest you look at results from both the
>>>> correlation and covariance matrices.
>>>>
>>>> Good luck
>>>>
>>>>
>>>>
>>>>
>>>> On 03/14/2011 12:17 PM, Malte Stuecker wrote:
>>>> > Hi everyone,
>>>> >
>>>> > I have done EOF analysis for scalar fields (e.g. SST) with the NCL EOF
>>>> > functions, however I am struggling with the concept of how to do an
>>>> > EOF analysis of vector data (e.g. analyzing the u- and v- component of
>>>> > ocean current data at the same time). I understand that it is possible
>>>> > to represent both quantities as a complex number, however I am not
>>>> > sure about the practical (=programming) approach. Most literature that
>>>> > I found seems to cover only the theory, but there are not many 'HOW TO
>>>> > DO' sources out there.
>>>> > My idea was to just combine the u and v fields in one matrix along one
>>>> > of the spatial axis (e.g. combining a u (20E-40E,20S-20N) and v field
>>>> > (20E-40E,20S-20N) to a (20E-40E,40S-40N) field), calculate the EOF and
>>>> > afterwards split the eigenvector matrix into the u- and v- component
>>>> > and plot the resulting vectors. In this case, is it possible to
>>>> > interpret the eigenvalues + eigenvectors in the same way as you would
>>>> > doing an EOF analysis on a scalar field? It would be great if anyone
>>>> > could point me to some step-by-step introduction to this type of
>>>> > problem or knows maybe some software packages other than NCL that
>>>> > could deal with this type of analysis comfortably.
>>>> > Thank you very much in advance!
>>>> > _______________________________________________
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>>>
>>>
>>>
>>> --
>>> Gibies George,   CSIR-RF,
>>> Seasonal Scale Prediction Group,
>>> Climate and Global Modelling Division,
>>> Indian Institute of Tropical Meteorology,
>>> Dr. Homi Bhabha Road,
>>> NCL (P. O.), Pashan,
>>> Pune 411008, India.
>>>
>>> http://sites.google.com/site/gibiesge/
>>>
>>> Please Think about the environment. Save paper; Save Trees; and don't
>>> print this e-mail unless it is necessary.
>>
>>
>>
>> --
>> Gibies George,   CSIR-RF,
>> Seasonal Scale Prediction Group,
>> Climate and Global Modelling Division,
>> Indian Institute of Tropical Meteorology,
>> Dr. Homi Bhabha Road,
>> NCL (P. O.), Pashan,
>> Pune 411008, India.
>>
>> http://sites.google.com/site/gibiesge/
>>
>> Please Think about the environment. Save paper; Save Trees; and don't print
>> this e-mail unless it is necessary.
>>
>
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Received on Fri Mar 18 01:37:30 2011