Monday, November 5, 2012

Negative PDO Struggling

A comparison of October 3 and October 31 sea surface temperatures show that the previously strong negative PDO (characterized by a warm body of water in the North Pacific with cool waters surrounding it) is now weakening.

We are no longer seeing that arm of extremely above normal water temperatures from Japan through the Northern Pacific. Cool water anomalies are beginning to filter in to the region now, and this is posing problems for what used to be a very solid negative PDO.

Some of you may not know what the PDO is, so let's break it down. The PDO is the Pacific-Decadal Oscillation. It has two phases- positive and negative. The two phases are actually not what you think they are. A negative PDO consists of warm water anomalies stretched across the Northern Pacific, like what was seen on October 3. A positive PDO holds cool waters across the North Pacific, like we are currently seeing fill in.

The positive PDO generally brings cool conditions to the East, while the negative PDO is very warm for the same region. The Gulf Coast gets much of the precipitation during -PDO years, while +PDO years favor a dry East US in general. The +PDO is associated with El Ninos, and the -PDO with La Ninas.



TriangleMan said...

Does this mean that the PDO will flip in the next few months, or is this just normal variation for a -PDO? Will there be implications for the NINO this winter?

Joshua Steiner said...

That link between Eastern weather and the PDO phase isn't always true. In fact, studies show that due to the NEGATIVE PDO regime during the 60's and 70's allowed for record cold conditions across the East. But that holds true for long term patterns. I do not believe that this is a significant trend. In fact, I believe it is just a small blip in the PDO patterns. In fact, because of the fact that the pattern is becoming more La NiƱa like, as indicating by the broad trough forecasted by the Euro and GFS ensembles to be in place across North America, as well as a strong Pacific jet stream will all aid in the redevelopment of a negative PDO signal. Especially if a significant ridge develops near the Japanese coast. I know that these factors are usually the effects of the PDO, not the causes, but I still think they may have some affect, as they are related to changes in the MJO, and thus changes in the ENSO patterns. In effect, I believe it just to be a blip caused by the kelvin wave propagation across the Atlantic, and will eventually transition back.

Anonymous said...

would the dryer east mean for a wetter west?

Anonymous said...

thespe22@ joshua steiner I find it interesting that even though Andrew is showing current data with the warm central pacific and the cold north and northwest of Hawaii that you choose to believe that La Nina like conditions will prevail because of 2 models . I must be very ill informed about how weather signals work.