SOI drop needs to be watched

[hurricanetrack]

In case you have not noticed, the SOI has plummeted over the last several days- more than a week- and is now quite negative in the daily and 30 day avgs. This is likely just a bump and the overall trend has been up since last year but this decent amount of time of negative SOI could certainly lead to a westerly wind burst. This could slow down the anticipated La Nina. Of course, this is just my observation based on looking at the SOI each day like I always do. Note too the strong trough carved deep in to the East now- bringing very cold air with it after a period of above normal temps.

Does anyone out there understand how these pressure differences between Darwin and Tahiti work? Why is the SOI down so much lately? Is there a way to predict that it will come back up or even stay negative? There are a lot of variables in the weather that can ultimately affect an entire hurricane season. I am just wondering if I am seeing the beginning to another "we had no idea the El Nino was coming" with this recent trip south of the SOI.

[HURRICANELONNY]

It does seem a little perplexing to me. I have no idea what the relationship is. I hope another El Nino does come. That would rattle the pros. But I think the chances are slim to none. I would like to understand the relationship betwen the two. If anyone has a better understanding. Please post.

[cycloneye]

Mark,do you have a link to the data?

What I found is the the SOI drop is not drastic and in fact from -7.3 in January it's at -1.4 in March.

ftp://ftp.bom.gov.au/anon/home/ncc/www/ ... ntext.html

[HURRICANELONNY]

Here's the daily:http://www.longpaddock.qld.gov.au/SeasonalClimateOutlook/SouthernOscillationIndex/30DaySOIValues/

[cycloneye]

http://www.bom.gov.au/climate/enso/soi.dt3

Right now it's at -6.3 down from -5.3 on April 2,interesting to say the least.

[MiamiensisWx]

Personally I believe the developing La Nina will not reach intense status if it forms. The Kelvin Wave has largely collapsed over the past several weeks and the persistent SOI drops and subtropical jet activity (and unfavorable OLR despite a developing +PDO) and persistent warm subsurface west of 140W (within the NINO 3.4 and NINO 4 zones) supports a weak to moderate Nina peak if it develops. The overall CONUS pattern now resembles the features of a developing El Nino in some aspects. I think we may experience a weakening trend with the cool anomalies beneath the surface as they expand westward. I expect a low-end moderate La Nina peak (per the three to five month Australian standards) as we enter the 2007 winter.

[WeatherEmperor]

Im a little bit confused. What effects will a negative SOI have compared to a positive SOI?

<RICKY>

[vacanechaser]

Im a little bit confused. What effects will a negative SOI have compared to a positive SOI?

<RICKY>

negative SOI, usually leads to the development of el nino conditions if it continues over a significant period of time... positive anomalies is the oppsite.. la nina conditions develop if it is positve over a significant period of time.. these relate to pressure differences between darwin and tahiti i believe... positive numbers usually reveal east to west winds across the equator in the pacific is is an upwelling wind along south america's west coast.. this causes the water to cool leasding to neautral or la nina conditions... the opposite is true with negative numbers.. west to east causing warmer water to develop and "pile up" for lack of a better term, near the coast and central pacific to create el nino conditions...



Jesse V. Bass III
http://www.vastormphoto.com
Hurricane Intercept Research Team

[SouthFloridawx]

Even if there is a -SOI, it appears from cycloneyes link that there is a lag time from -SOI to the pacific being classified as El Nino.
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
2006 12.7 0.1 13.8 15.2 -9.8 -5.5 -8.9 -15.9 -5.1 -15.3 -1.4 -3.0
2007 -7.3 -2.7 -1.4

A Constant Negative SOI if at least -5.0beginning in May of '06 lasted until October of 2006. Perhaps, looking at this data it appears that there is a lag time of about 3-5 Months of persistant - or positive features until Nina/Nino is Declared.

While we are in a -SOI, I appears as though its not as severe as in May - Oct. of last year. In fact if the trend continues we'll probable see the SOI go positive, however that remains to be seen.

In November we saw the SOI go from -15.0 to -1.4... This lead to a pending La Nina, which was then repressed a little bit as the SOI dropped into -7.0's.

I am going to have to agree with, MiamiensisWx...

Unless SOI bombs below -7.0's I don't think we'll see a El Nino during the summer. We'll also have to watch the SOI and see if it moves into the Positive range... if it does it may lengthen La Nina.

[hurricanetrack]

I sure hope it goes back to positive. This recent cold snap in the East is likely correlated with the drop of the SOI and other related factors. I like warm to hot weather and am tired of the cold- it has been a rather nasty winter in the U.S. as far as temps go. Not used to that as of the last few years- so it was not pleasant.

If one looks at the MJO as of late http://www.cpc.ncep.noaa.gov/products/g ... thly_1.gif you can see that the Pacific is mostly in the sinking motion phase....once the green moves in to the Pacific, perhaps we will see the SOI come back up and in a big way.

I think it is interesting, just another piece of the puzzle that we can watch on a daily basis- if one is so inclined....

[cycloneye]

2007022820070329 .6
2007030120070330 -.9
2007030220070331 -2
2007030320070401 -3.3
2007030420070402 -4.2
2007030520070403 -5.1
2007030620070404 -5.3
2007030720070405 -6.3
2007030820070406 -7.8

http://www.bom.gov.au/climate/enso/soi.dt3

Still creeping down Mark.As of the 6th of April it's now down -7.8 from -6.3 one day earlier.

[deltadog03]

this should go to show yall that the la nina will be la nada this year. That SOI has driven the el and la nina and ninos.

[hurricanetrack]

Still quite negative in the dailies. Will be watching the MJO to see if it influences a change to turn things around.

[HURRICANELONNY]

Don't think so Delta. Look at 98's Soi when a strong La Nina formed. It takes time for the SOI. By May it should average more +.

[deltadog03]

im saying it will rise. I am not sold on the la nina crap...I guess that was my point! There will not be a strong la nina imo.

[Ptarmigan]

this should go to show yall that the la nina will be la nada this year. That SOI has driven the el and la nina and ninos.

Neutral years have been very active, 2004 and 2005 come to mind.

[hurricanetrack]

It has gone down even more today- yikes!

Daily contributor to SOI calculation: -28.84


Hmm....wonder how long this will last. As long as it stays negative, I would not get too excited about a La Nina. Of course, this makes sense- if it were indeed to stay negative, then it would naturally lead to other factors that would then lead to a lessening of the trades and so forth and so on....but before I go THAT far, let's see if this comes up anytime soon. It probably will....we'll see....

[AussieMark]

ironically enough during the El Nino we had days of +15 or +20

[MiamiensisWx]

The lack of the subtropical jet (a trademark feature of Ninos) during the previous El Nino during the winter of 2006 and 2007 may have been related to the PDO change. Some evidence suggests the PDO flip to positive (negative) phase (with a warmer North Pacific subsurface and cooler equatorial Pacific) may have already occurred during the last few years. When combined with the warmest subsurface temperatures mainly restricted to the eastern equatorial Pacific (NINO 1 and NINO 2) we may not have seen the typical relay into atmospheric patterns (via a stronger subtropical jet) with this recent El Nino. This may have also contributed to its rapid demise during January and February. With the developing La Nina transitioning into a cool ENSO episode with the coolest subsurface mainly within NINO 1 and NINO 2 (like the aforementioned El Nino), we may not be seeing a "typical" atmospheric pattern characteristic of some other developing Nina cases.

['CaneFreak]

ironically enough during the El Nino we had days of +15 or +20

You made a great point here and I just want to make sure that everyone here interpreted this correctly. What we're saying here is that you can NOT look at the daily values of the SOI when you are trying to develop trends from the data because you are likely to encounter many errors when doing so. That is why they only include the three month averages and or monthly averages because that is based on 30 or 90 individual daily SOI values. If you based the SOI totally on just one days numbers from Tahiti and Darwin, you would never be able to predict a pending La Nina or El Nino scenario. Of course, there are many other factors that help you determine a pending El Nino and La Nina but I hope you get the general idea. I also think from looking at this data that you can link a negative SOI value (pressure difference from Darwin to Tahiti) troughiness pattern, with a trough in the Eastern US through the theory of teleconnections. There is a lot you can learn from the SOI values.

Back to AussieMark's point about the daily values of +15 and +20. You can have many days of -SOI in a La Nina pattern, but in GENERAL, when you average all the daily SOI values for the month, in a TYPICAL LA NINA PATTERN you will GENERALLY see positive numbers for THE MONTH. Good points here in this discussion topic.