Thursday, April 10, 2014

El Nino and Spring

One of our readers posted a comment today asking if the maps from last month's post on "El Niño and Summer" could be reproduced for April and May instead of June and July.  This is easy enough to do with the computer code I used before, so here are the corresponding maps for spring:

Top 10 El Niño years in April and May:

 Years falling in the El Niño tercile and the positive PDO tercile:

Years falling in the El Niño tercile and negative or neutral PDO terciles:


Top 10 positive PDO years in April and May:

Compared to the earlier maps for June and July, the El Niño effect by itself is apparently much stronger for temperature in spring, as above-normal temperatures are very likely indeed when strong El Niño conditions prevail.  However, the PDO phase is still very important, as we see that colder than normal conditions are most likely when the PDO is neutral or negative, even when the Niño regions are warm.  Presumably this means that strong El Niño episodes in spring are almost always accompanied by a significantly positive PDO phase (I verified this, 8 of 10 strong El Niño years in April-May had a substantially positive PDO phase at the same time).

With regard to current conditions, the PDO is still quite strongly positive (though not quite in the top 10), but El Niño conditions have not yet developed.

1 comment: