Unless you are a modern day Rip Van Winkle,
you know that we have been experiencing a major El Nino in the topical Pacific.
As we'll see it's one of the strongest on the record,
and it's having effects that are being felt worldwide,
particularly in terms of patterns of weather variability, but also, ecosystem impacts in
the ocean as well as on land.
The news has been awash in the past year with stories like this.
These are some of the classic impacts:
Drought and out of control wildfires in Indonesia,
deficient Indian summer monsoon rainfall,
flooding in California, Texas, the Gulf States, and Florida.
It's been a record tropical storm year in the Pacific because of all the warm water,
but it's also been a quiet Atlantic hurricane season.
These are all classic signatures of major El Ninos.
El Nino and the Southern Oscillation, we all know,
is a year-to-year fluctuation of the climate system that originates in the tropical Pacific.
It's mediated by wind and sea surface temperature feedbacks.
The warm phase we refer to as "El Nino" and the cold phase "La Nina".
We are interested in this because it is the largest year-to-year fluctuation of the climate
system on the planet
and it also has tremendous socio-economic impacts because of its effects on weather,
ecosystems, and fisheries.
Here is the star of our show.
These are December 2015 sea surface temperature anomalies, global anomalies,
and you see there in center stage are the warm anomalies associated with the El Nino
between 2.5-3 degrees centigrade.
There are other warm anomalies out there; the Indian Ocean is warm.
This is typical during El Nino events. The Indian Ocean basin warms up as the El Nino
matures.
How well this event compares with others is illustrated here.
This is one commonly used index. There are several for El Ninos.
This is the Nino 3.4. It's a large areal index of deviations from normal in the central Pacific.
It's a region where the atmosphere is particularly sensitive to underlying changes in sea surface
temperature, which is why it's a major focus region.
It starts in 1980 and it goes to last month--December 2015.
The red peaks are El Nino years. The blue troughs La Ninas.
We define El Nino when the temperatures rises above 1/2 degree centigrade for 5 months or
more.
And so you see can the big El Ninos of the last 35 years.
Here is 97-98. This is by some measure the strongest in the instrumental record that
goes back to the 1800s.
Before that we had a really big one in 82-83,
and then right at the end of the record is 2015-2016.
And you can see by eye that the anomalies we are seeing in this region are comparable
to those in 1997-98.
But we can highlight that a little bit more if we chop this record up into 2 and 1/2 year
segments
and we'll stack the El Ninos on top of one another and you can see how they compare in
a little bit more detail.
So actually, for this, I'm going back to the 50s, so we're going back 60 years ago.
There are 15 El Ninos that we're stacking up in this way, plus the 2015-16.
So we start in July the year before the El Nino and we end January the year after.
Here's the 1/2 degree centigrade line, that's the threshold for El Nino.
Black is the average of these 15 El Ninos
and you can see they peak about a degree and a half or so.
They began to develop in the boreal spring, peak in November, December, January and roll
off the following boreal spring.
The purple line is 97-98, the blue is 82-83, and thick red line is the current event.
A couple things to note. This event is far above average in its amplitude,
and you will note that, in fact, in the Nino 3.4 region,
November-December were the warmest November-December on record,
so it's a pretty extraordinary event.
A couple other things to note about this El Nino:
You remember the El Nino that failed to happen last year--the monster El Nino that never
materialized.
Although it never materialized, it left the somewhat elevated temperatures on which the
El Nino that failed to occur last year,
helped to jumpstart the big El Nino this year by just providing a higher starting point.
The other thing to notice is that these 15 El Ninos here--
nine of them transit into cold phase in the following year.
That's 9 out of 15, so just based on statistics,
you might say that there is a 60% chance that this El Nino will revert to La Nina conditions
by mid-year 2016.
You might say this is the strongest El Nino on record,
but we want to be a little bit careful, because there is spatial variability to the patterns.
If we move just a little bit further to the east, here is the same presentation for the
Nino 3,
and you can see 97 wins in this comparison.
So depending on which index you use,
I think we can safely say it's one of the 3 strongest El Ninos on record.