El Nino/La Nina question

[Jim Cantore]

I know the conditions how to be there for 3 months, but how much of an Anomaly is required?

[AussieMark]

for NOAA its 0.5C across Nino 3.4

for BOM its 0.8C across Nino 3.4

i.e for El Nino its either +0.5C or +0.8C

or for La Nina

-0.5C or -0.8C

thats the anomalities



weekly values across Nino 3.4 are as follows over the last 3 months

Week ending
Aug 13: +0.30C
Aug 20: +0.53C
Aug 27: +0.55C
Sep 03: +0.72C
Sep 10: +0.72C
Sep 17: +0.79C
Sep 24: +0.81C
Sep 24: +0.81C
Oct 01: +0.70C
Oct 08: +0.64C
Oct 15: +0.95C
Oct 22: +0.87C

the 12 week average of 3 month average is +0.70C (unless I am wrong)

[Jim Cantore]

Awsome, thanks.

[P.K.]

13 weeks in three months Mark . I make the anomaly +0.64C to 22/10.

[Jim Cantore]

One more question, where is the line drawn between a mild El Nino/La Nina, and a strong one?

[AussieMark]

lets look at the anomalities of strong ones for example

1997/98
Apr-Jun: +0.9C
May-Jul: +1.4C
Jun-Aug: +1.7C
Jul-Sep: +2.0C
Aug-Oct: +2.3C
Sep-Nov: +2.4C
Oct-Dec: +2.5C
Nov-Jan: +2.5C
Jan-Mar: +2.4C
Feb-Apr: +2.0C
Mar-May: +1.4C
APr-Jun: +1.1C

a fully moderate one was 1965/66
Jun-Aug: +1.0C
Jul-Sep: +1.2C
Aug-Oct: +1.4C
Sep-Nov: +1.5C
Oct-Dec: +1.6C
Nov-Jan: +1.5C
Jan-Mar: +1.2C
Feb-Apr: +1.1C
Mar-May: +0.8C

from this I assume a very strong event has ssts anomalites over 2C
and a moderate around the 1.5C range

[Jim Cantore]

lets look at the anomalities of strong ones for example

1997/98
Apr-Jun: +0.9C
May-Jul: +1.4C
Jun-Aug: +1.7C
Jul-Sep: +2.0C
Aug-Oct: +2.3C
Sep-Nov: +2.4C
Oct-Dec: +2.5C
Nov-Jan: +2.5C
Jan-Mar: +2.4C
Feb-Apr: +2.0C
Mar-May: +1.4C
APr-Jun: +1.1C

a fully moderate one was 1965/66
Jun-Aug: +1.0C
Jul-Sep: +1.2C
Aug-Oct: +1.4C
Sep-Nov: +1.5C
Oct-Dec: +1.6C
Nov-Jan: +1.5C
Jan-Mar: +1.2C
Feb-Apr: +1.1C
Mar-May: +0.8C

from this I assume a very strong event has ssts anomalites over 2C
and a moderate around the 1.5C range

1997-1998 was in a class of it's own, for now.

[rainbird]

Have an elementary question: What is anomaly? (Thought I ask because of related topic/question) There was thread/posts in Talking Topics a while ago - discussing sub-surface anomalies/equatorial temperature anomaly - Had no idea what everyone was referring to - Am I correct that these anomaly/anomalies are related in determining El Nino and El Nina?? Please correct me if I am wrong - Again, thank you all so much - Always inquiring and learning on Storm2K!!!

[AussieMark]

anomalites mean how much above normal or below normal they are.
in this el nino is determined after prolonged warming

[AussieMark]

lets look at the anomalities of strong ones for example

1997/98
Apr-Jun: +0.9C
May-Jul: +1.4C
Jun-Aug: +1.7C
Jul-Sep: +2.0C
Aug-Oct: +2.3C
Sep-Nov: +2.4C
Oct-Dec: +2.5C
Nov-Jan: +2.5C
Jan-Mar: +2.4C
Feb-Apr: +2.0C
Mar-May: +1.4C
APr-Jun: +1.1C

a fully moderate one was 1965/66
Jun-Aug: +1.0C
Jul-Sep: +1.2C
Aug-Oct: +1.4C
Sep-Nov: +1.5C
Oct-Dec: +1.6C
Nov-Jan: +1.5C
Jan-Mar: +1.2C
Feb-Apr: +1.1C
Mar-May: +0.8C

from this I assume a very strong event has ssts anomalites over 2C
and a moderate around the 1.5C range

1997-1998 was in a class of it's own, for now.

1997/98 or 1982/83 were both severe events. 1982/83 had much lower SOI. but 1997/98 had slighly warmer ssts

1982/83
Jun-Aug: +0.8C
Jul-Sep: +1.0C
Aug-Oct: +1.5C
Sep-Nov: +1.9C
Oct-Dec: +2.2C
Nov-Jan: +2.3C
Dec-Feb: +2.3C
Jan-Mar: +2.0C
Feb-Apr: +1.6C
Mar-May: +1.2C
Apr-Jun: +1.0C

[AussieMark]

looking at SOI of those 2 events

1982/83
Apr: -3.8
May: -8.2
Jun: -20.1
Jul: -19.3
Aug: -23.6
Sep: -21.4
Oct: -20.2
Nov: -31.1
Dec: -21.3
Jan: -30.6
Feb: -33.3
Mar: -28.0
Apr: -17.0

1997/98
Mar: -8.5
Apr: -16.2
May: -22.4
Jun: -24.1
Jul: -9.5
Aug: -19.8
Sep: -14.8
Oct: -17.8
Nov: -15.2
Dec: -9.1
Jan: -23.5
Feb: -19.2
Mar: -28.5
Apr: -24.4

[wxmann_91]

One can also use the Multivariate Enso Index (MEI):

0.5-1.0 Weak Nino
1.0-1.5 Mdt Nino
>1.5 Strong Nino

http://www.cdc.noaa.gov/ENSO/enso.mei_index.html

Bimonthly MEI values: http://www.cdc.noaa.gov/people/klaus.wo ... table.html

Here's a good website which shows several ways to determine strength of ENSO: http://ggweather.com/enso/years.htm

[Ptarmigan]

1997/98 or 1982/83 were both severe events. 1982/83 had much lower SOI. but 1997/98 had slighly warmer ssts

1982/83
Jun-Aug: +0.8C
Jul-Sep: +1.0C
Aug-Oct: +1.5C
Sep-Nov: +1.9C
Oct-Dec: +2.2C
Nov-Jan: +2.3C
Dec-Feb: +2.3C
Jan-Mar: +2.0C
Feb-Apr: +1.6C
Mar-May: +1.2C
Apr-Jun: +1.0C

National Geographic had an article about the 1982/83 El Nino. That El Nino sure made Texas cold in December of 1983.

[AussieMark]

I got some emails from BOM in recent weeks and as rule as thumb this is their classification

SSTS on Nino 3.4
+0.8 to +1.1°C: weak
+1.1 to +1.5°C: moderate
+1.5 to +2.2°C: strong
above +2.2°C: very strong

SOI
-5 to -10: weak
-10 to -15: moderate
-15 to -20: strong
below -20: very strong

I also would assume the opposite would be the case to their La Nina classifications