The EOFs are derived from a covariance matrix.
Only mathematical/numerical operations. *No* physics is involved.
Any physical interpretations are 'yours'.
On 01/04/2010 06:11 AM, Maurice.McHugh@noaa.gov wrote:
> Regarding the sign in EOF analyses, the point is that EOF analysis can tell where OLR values are varying out of phase -- having opposite signs -- the exact sign is irrelevant. You can simply multiply your results by -1. to change the sign if you so desire as you're not changing the nature of the covariance across your domain or between variables.
>
> Maurice
>
> ----- Original Message -----
> From: shinn wong<shinnshinnwong@gmail.com>
> Date: Sunday, January 3, 2010 11:59 pm
> Subject: Re: mjo
> To: ncl-talk@ucar.edu
>
>
>
>> Thanks. But I still feel a bit puzzled about it. So, if the sign of
>> the EOF
>> is arbitrary, does it mean that we cannot tell from the sign that
>> where is
>> the positive and negative OLR anomalies? If yes, how can i modify the
>> code
>> so that negative OLR anomalies can be distinguished from the positvie
>> OLR
>> anomalies? Thanks.
>>
>> 2010/1/4<shea@ucar.edu>
>>
>>
>>> The sign of the EOF is arbitrary.
>>>
>>> Good luck
>>>
>>>
>>>> Hi everyone,
>>>> I have a problem concerning with the mjo. I have used the example
>>>> mjoclivar_12.ncl<
>>>>
>>>> to
>>>> compute the univariate eof for 20-100 day band-pass filtered olr
>>>>
>> data
>>
>>>> from
>>>> 1987-2007, but the result seems to be different from that of the typical
>>>> one. The conventional EOF1 exhibits negative OLR anomalies (strong
>>>> convection) in the tropical Indian Ocean and positive anomalies in
>>>>
>> the
>>
>>>> western pacific (see figure 1 in
>>>>
>>>>
>>> ),
>>>
>>>> but the result of mine is just the opposite. Do anyone know the reason?
>>>> The
>>>> code can be seen in the attachment. Thanks.
>>>> shinn
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>>>
>>>
>>>
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-- ====================================================== Dennis J. Shea tel: 303-497-1361 | P.O. Box 3000 fax: 303-497-1333 | Climate Analysis Section | Climate& Global Dynamics Div. | National Center for Atmospheric Research | Boulder, CO 80307 | USA email: shea 'at' ucar.edu | ====================================================== _______________________________________________ ncl-talk mailing list List instructions, subscriber options, unsubscribe: http://mailman.ucar.edu/mailman/listinfo/ncl-talkReceived on Mon Jan 4 11:41:30 2010
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