On Friday, 13 April 2018 11:02:12 UTC+1, Graham P Davis wrote:
On 13/04/18 09:08, wrote:
On Thursday, 12 April 2018 20:56:57 UTC+1, Graham P Davis wrote:
The Pacific Decadal Oscillation (PDO) Index has been positive for
50 straight months. This was the longest period that the index has
been in either positive or negative territory. However, last month,
the index slipped to -0.05. To put this value into some
perspective, the highest monthly value of the index on record has
been +3.5 and the lowest -3.6.


-- Graham P Davis, Bracknell, Berks. Web-site:
http://www.scarlet-jade.com/ "There is nothing more frustrating
than playing hide and seek with a deaf wolf." [Benton Fraser] OS:
Linux [openSUSE Tumbleweed]

What's the source of the PDO data that you're looking at?

The NOAA PDO index (https://www.ncdc.noaa.gov/teleconnections/pdo/)
seems to have been fluctuating between positive and negative for the
last 50 months:


http://research.jisao.washington.edu/pdo/PDO.latest.txt


--
Graham P Davis, Bracknell, Berks. Web-site: http://www.scarlet-jade.com/
"There is nothing more frustrating than playing hide and seek with a
deaf wolf." [Benton Fraser]
OS: Linux [openSUSE Tumbleweed]

Graham

Now I understand - that data I referred to is the NCEI PDO which is based on the Mantua PDO data as the NOAA website explains:

"The NCEI PDO index is based on NOAA's extended reconstruction of SSTs (ERSST Version 4). It is constructed by regressing the ERSST anomalies against the Mantua PDO index for their overlap period, to compute a PDO regression map for the North Pacific ERSST anomalies. The ERSST anomalies are then projected onto that map to compute the NCEI index. The NCEI PDO index closely follows the Mantua PDO index."

Which all sounds very complicated to me.

Bruce.