Tuesday, 24 June 2014

Why will El Nino turn out potentially weaker then expected?

After expectation's were very high coming off a record breaking oceanic kelvin wave this past spring, tides have turned in the ENSO department with the prospect's of a strong el nino dwindling. Below are some of the factors I am looking at regarding ENSO:

1) Solar flux has dropped at or below 75 for the first time since november after a double peak this winter/spring period signifying a long and weak cycle. This should have some implications on ENSO this upcoming fall/winter.

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2) Despite negative 200mb CHI propagation into the central/eastern pacific this week, any WWB's over the WPAC are expected to remain weak/stationary over the next week. This displays that even period's which favour el nino strengthening are failing to produce major changes to the subsurface anomalies.
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3) Cooler than normal subsurface SST's have replaced the strong downwelling OKW that formed in the early spring period.

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4)AAO/Atlantic circumpolar wave forcing has helped keep the western IO cool while SST's in and around the maritime continent are well above normal. This makes it very difficult to keep the SOI predominantly negative. SOI values are expected to remain negative through early July with a reversal to positive values expected after ~7/3 as the MJO wave propagates east.

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5) A weak K/O current this spring means the JJA "summertime" AO anomaly should remain predominantly positive correlating to this SST anomaly setup.

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6) Underwater currents have shifted to an easterly anomaly after it was initially suspected that the base state of the pacific changed to a mean westerly anomaly as a result of the mega downwelling OKW in the spring. Obviously that claim was proven false.
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For these reasons i'm expecting a weakening and retrograding el nino anomaly as we head into winter. In the end, moderate ENSO strength is likely IMO in the trimonthly ONI dataset (+1.0 to+1.5c peak). Any questions/comments, feel free to shoot away in the comment section below.

Sunday, 22 June 2014

Are back to back Nino's on the way?

Looking at years following at least three winters with negative ONI conditions and at least one winter with ONI values <-1.00 for 3 or more trimonthly periods we get the following years as past analogs.

1957-58(Moderate El Nino) and 1958-59(Warm Neutral)

SST anomalies from 1957-58 on the right and 1958-59 on the left

1976-77(Weak/Moderate El Nino) and 1977-78(Moderate El Nino)

SST anomalies from 1976-77 on the left and 1977-78 on the right

1986-87(Moderate El Nino) and 1987-88(Moderate El Nino)
1986-87 on the left and 1987-88 on the right

2002-03(Moderate El Nino) and 2003-04(Warm Neutral)

1918-19(Moderate El Nino) and 1919-20(Weak El Nino)

1911-12(Moderate El Nino) and 1912-13(Cool ENSO Neutral Conditions)

As you can see, all of these setup's have a secondary el nino(sometimes considered warm neutral) that is weaker in terms of anomalies when compared to the first nino. The 1911-12 and 1912-13 couplet is the only exception, with ENSO neutral conditions occurring in the second winter(1912-13).

Now comes the question whether the current pattern we are in is considered a period of 3+ years with cooler then normal ENSO conditions. Unlike most negative ONI periods including 1 or more la nina events, trimonthly ONI managed to spike at or above +0.5c for two trimonthly period's in the fall of 2012. Although by official standards this is not considered an el nino, it can significantly alter the global climate system. The question for me was if I could find a good analog to see if it made a difference to the ENSO state following a long cool ENSO period with an el nino year afterwords. After some research, the mid 1930's matched up pretty well. Below are the ONI values in this period courtesy of Bob Tisdale. Note the long period of negative ONI values from late 1932 through mid 1939. This period included several spikes into warm neutral conditions(similar to the 2012 period) although official nino status was never met. Coming out of this period was not only a double nino, but a triple nino.

So what would be some potential effects of a double el nino if analogs hints verify?

1) A temporary spike in global temperatures.

2) Longer lasting temporary +PDO regime within a multidecadal -PDO phase. This means a relief from  drought conditions that currently exist over the SW and southern plains states.

3) Strength of ENSO in the 2015-16 winter could dictate the H5 pattern across the eastern U.S(stronger events correlate to very cold temperatures east of the rockies e.g 77-78 and 69-70 while warm neutral events correlate to warmth e.g 03-04).

4) Continued below normal ACE/tornadic activity over the next 2 years with a significant spike to follow.

Questions and comments are encouraged in the section below. You can tweet me with your questions, @blizzardof96.

Thursday, 19 June 2014

Early Thoughts on Winter

Few comparisons I made on twitter this morning, using an ONI base state between +0.7 and +1.5c. All el nino/-QBO years are on the right with nino/+QBO years on the left. We should be in a -QBO shear phase this DJF nearing the -QBO peak late winter. Note how the -QBO years tend to have a pretty strong -NAO block with lower heights surrounding the block and a -SAM/+PDO state in the means. Whether solar activity increases or decreases heading into winter will be very important as you run the risk of ending up similar to 91-92 although it's definitely not a guarantee either way.

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The PDO dataset is also pretty interesting with the positive years on the right. I am expecting the PDO to remain positive through next winter as the nino continues to gradually strengthen. This is consistent with the NMME/JAMSTEC suite's. Note how PNA and EPO ridging is stronger in the +PDO years and the state of the NPAC is completely opposite. This tends to favour areas further SE for the heavy snow's(mid atlantic and southern parts of the Northeast) as it takes any nina component out of the pattern.

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The few things i'll be monitoring besides solar:

1) Positioning of the NPAC warm pool. If it can retrograde, look for the storm track to want to shift further west. If it continues to shift East into a more classic +PDO horseshoe position, as I am expecting, the mid atlantic will be more favoured in terms of storm track/snow interests.

2) The warm SST's off the east coast tend to pump up a stronger SE ridge like 51-52 saw in the December-January period. 

3) Keeping an eye on the positioning of the nino. Currently favouring a slightly west based nino although it could very well end up providing more basin wide like forcing.

4) We just came out of a long lasting la nina period. ONI spikes coming after at least a double nina look like this with no ENSO sorting:
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5) SLP pattern across N Siberia in October. This goes hand in hand with SAI feedbacks, which looks at snow cover growth in october over southern siberia.

Below are Positive AO El nino december heights at 250mb with Oct SLP anoms on the left. Notice the negative SLP anomaly across N Siberia and the response across North America.
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-AO years are completely opposite in December. 8 of those 10 +AO December years remained persistent with a +AO in January as well. In feb it mattered little as troughiness still dominated over the northeast/great lakes. Any questions about the upcoming winter? Feel free to shoot me a question in the comment section below or you tweet me @blizzardof96.

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