|
The
Oceanic Niño Index (ONI) has become the
de-facto standard that NOAA uses for identifying El Niño (warm) and
La Niña (cool) events in the tropical Pacific; often collectively
called ENSO (El Niño
- Southern Oscillation). The ONI
is
the running 3-month mean
SST anomaly for the Niño 3.4 region (i.e.,
5oN-5oS,
120o-170oW). Events are defined as 5
consecutive months at or above the +0.5o anomaly for warm
(El Niño) events and at or below the -0.5 anomaly for cold (La Niña)
events. The threshold is further broken down into Weak (with a 0.5
to 0.9 SST anomaly), Moderate (1.0 to 1.4) and Strong (≥
1.5) events. For the purpose of this report for an event to be
weak, moderate or strong it much have equaled or exceeded the
threshold for at least 3 months.
El Niño
Events:
Weak:
51-52, 63-64, 68-69, 69-70, 76-77, 77-78, 04-05, 06-07
Moderate: 86-87, 87-88, 94-95, 02-03
Strong: 57-58, 65-66, 72-73, 82-83, 91-92, 97-98
La
Niña Events:
Weak:
50-51, 56-57, 62-63, 67-68, 71-72, 74-75, 84-85, 95-96, 00-01
Moderate: 54-55,
64-65, 70-71, 98-99, 99-00, 07-08
Strong: 55-56, 73-74, 75-76, 88-89 |
|
click to enlarge |
A period of November - March was chosen as "winter"
for this study because approximately 85% of the California rainfall is
during that period.
Warm Event (El Niño)
Anomalies:
Winter (November, December, January, February, March) Impacts
| click graphics to
enlarge |
All Warm Events |
Weak |
Moderate |
Strong |
|
ONI |
≥ +0.5 |
+0.5 to +0.9 |
+1.0
to +1.4 |
≥ +1.5 |
|
Years |
50-51, 57-58, 63-64,
65-66, 68-69, 69-70,
72-73, 76-77, 77-78,
82-83, 86-87, 87-88,
91-92, 94-95,
97-98, 02-03, 04-05, 06-07 |
50-51, 63-64, 68-69, 69-70, 76-77,
77-78, 04-05, 06-07 |
86-87, 87-88, 94-95, 02-03 |
57-58, 65-66, 72-73, 82-83, 91-92, 97-98 |
| Precipitation Anomaly |
 |
 |
 |
 |
| 500-hPa Anomaly |
 |
 |
 |
 |
|
Cool Event (La Niña)
Anomalies:
Winter (November, December, January, February, March) Impacts
| click graphics to
enlarge |
All Cool Events |
Weak |
Moderate |
Strong |
|
ONI |
≤ -0.5 |
-0.5 to -0.9 |
-1.0
to -1.4 |
≤
-1.5 |
|
Years |
51-52, 54-55,
55-56, 56-57,
62-63, 64-65, 67-68,
70-71, 71-72,
73-74, 74-75,
75-76, 84-85,
88-89, 95-96,
98-99, 99-00, 00-01,
07-08, |
51-52, 56-57, 62-63, 67-68, 71-72,
74-75, 84-85, 95-96, 00-01 |
54-55, 64-65, 70-71, 98-99, 99-00,
07-08 |
55-56, 73-74, 75-76, 88-89 |
| Precipitation Anomaly |
 |
 |
 |
 |
| 500-hPa Anomaly |
 |
 |
 |
 |
|
|
