# Presentation: 515478

## El Niño/La Niña and the Southern Oscillation Index (ENSO) 

**Southern California Current Conditions**

## ENSO and Southern California  Outline

- Current ENSO state and predictions
- ENSO indices/predictions
- Precipitation and temperature forecasts
- What is ENSO and how is it measured
- Basic description of ENSO
- Determination of ENSO
- ENSO statistics
- Indices
- Models
- Southern California Observations

## Current ENSO State(February 5, 2009)

- ENSO Alert System Status: La Niña Advisory
-  Negative Oceanic Niño Index (ONI = -0.6 ̊C; DJF 2008/2009)
- _[http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml](http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml)_
- Forecast weak La Niña conditions into the Spring and then a gradual weakening with an eventual transition to ENSO-neutral conditions
- Below normal rainfall - next 90 days
- Above normal temperature - next 90 days

**(top) Weekly sea surface temperature (SST) ( ̊C) centered on 28 January 2009. (bottom) Same as the top except for SST anomalies.**

**Time series of area-averaged sea surface temperature (SST) anomalies ( ̊C) in the Niño regions.**

## NCEP CFS Niño 3.4 SST Prediction

**NCEP Climate Forecast System (CFS) Niño 3.4 SST prediction indicates a weak La Niña event (ONI >/= -0.5) with a gradual weakening with eventual transition to ENSO-neutral conditions. **

## One Month Temperature Outlook:February 2009

## One Month Precipitation Outlook: February 2009

## Three Month Temperature Outlook:FMA 2009

## Three Month Precipitation Outlook:FMA 2009

## US Drought Monitor: August 2008

## Western US Drought Monitor: August 2008

## Slide 13

## What is ENSO and how is it monitored/measured? 

## ENSO Talking PointsENSO Alert System

**El Niño or La Niña Watch**
- Issued when conditions are favorable for the development of El Niño or La Niña conditions within the next three months.
**El Niño or La Niña Advisory**
- Issued when El Niño or La Niña conditions are observed and expected to continue.
**Final El Niño or La Niña Advisory**
- Issued after El Niño or La Niña conditions have ended.
**NA:** ENSO Alert System is not active

## General El Niño Talking Points

- El Niño refers to a particular climatological condition and not a specific weather event.
- The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea surface temperatures across the central and east-central equatorial Pacific.
- El Niño represents the warm phase of the El Niño/Southern Oscillation, or ENSO, cycle, and is sometimes referred to as a Pacific warm episode.
- Can work to enhance our typical storms.
- Has greatest impact on Southwest U.S. in the winter and spring.
- Typical El Niño effects include warmer-than-average temperatures over the western and northern United States and wetter-than-average conditions over portions of the U.S. Gulf Coast, California, and Florida, while drier-than-average conditions can be expected in the Ohio Valley and the Pacific Northwest.

## General La Niña Talking Points

- La Niña refers to a particular climatological condition and not a specific weather event.
- The term La Niña (the opposite of El Niño) refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic cooling in sea surface temperatures across the central and east-central equatorial Pacific.
- La Niña represents the cold phase of the El Niño/Southern Oscillation, or ENSO cycle, and is sometimes referred to as a Pacific cold episode.
- Can work to inhibit precipitation production in our typical storms.
- Has the greatest impact on the Southwest U.S. in the winter.
- Typical La Niña effects include drier than normal conditions in the Southwest in late summer through the subsequent winter. Drier than normal conditions also typically occur in the Central Plains in the fall and in the Southeast in the winter. In contrast, the Pacific Northwest is more likely to be wetter than normal in the late fall and early winter with the presence of a well-established La Niña. Additionally, on average La Niña winters are warmer than normal in the Southeast and colder than normal in the Northwest. In addition, Atlantic hurricane frequency increases during La Niña.

## Southern California El Niño Talking Points

- The majority of past strong El Niño’s have a history of much above normal winter rainfall in Southern CA. Weak El Niño’s typically bring wetter-than-average conditions but not always. Moderate El Niño’s typically result in near or slightly above normal conditions.  Some El Niño’s have even been drier than normal.
- El Niño brings an increased threat of heavy rain events, resulting in flooding, debris flows, and higher than normal surf.
- The debris flow project will continue with the most sensitive areas being this and last year’s fires. Details on this project can be found at:
- http://www.wrh.noaa.gov/lox/main.php?suite=hydrology&page=debris-flow_project

## Southern California El Niño Talking Points Continued

- El Niño has a repeat cycle of _**2-7**_ years.  **Avg. = 4 yrs**.
- The recent past strong El Niño’s (72’-73’, 82’-83’ and 97’-98’) have a history of much above normal winter rainfall in Southern CA.
_**Strong El Niño’s**_
- Most dramatic effect on local rainfall.
- Seasonal totals _**average 150-200% of normal.**_
- Less predictable effect in the mountains than at lower elevations for reasons that are not clear.
- ENSO index between 0.5-0.9
_**Moderate El Niño’s**_
- Feature more normal to slightly above normal rain than weak or strong El Niño’s.
- Seasonal totals _**average 100-120% of normal.**_
- ENSO index 1.0-1.8
_**Weak El Niño’s**_
- Feature an _**earlier start**_ to the rainy season.
- Seasonal totals _**average 120-150% of normal.**_
- The reason weaker El Niño’s tend to have a greater effect is poorly understood at this point.
- ENSO index stronger than 1.9

## Southern California El Niño Talking Points Continued

- Weak and strong El Niño’s have produced more rain than moderate El Niño’s.
- Less consistency exists with regard to temperature.
- Seasonal rainfall correlations are still being fine tuned as the database of El Niño events continues to develop.
- Forecasts produced by CPC (Climate Prediction Center) are the official long range forecast.
- Telephone # 301-763-8000

## Southern California La Niña Talking Points

- The majority of past La Niña’s have a history of below normal winter rainfall in Southern CA.
- There have been 16 recorded La Niña’s since 1950.
- There is no clear signal between weak, moderate, and strong events.
- The 3rd wettest year on record in Los Angeles occurred during a La Niña year – 1889-1890.
- The last La Niña was 2007-2008 (moderate strength reaching -1.5 ENSO index)
- La Niña’s re-occur every 1 to 7 years with an average of every 3.7 years.

## ENSO Monitoring

- El Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe.
- Atmospheric and oceanic conditions in the tropical Pacific are monitored by the Tropical Atmosphere Ocean Project maintained by NOAA’s Pacific Marine Environmental Lab (PMEL) that consists of an array of moored buoys shown above

## Normal Oceanic Conditions

- Warm sea surface temps are common in the western Pacific (Australia, Indonesia, etc.)
- Thermocline depth is deep in the Western Pacific and shallow in the Eastern Pacific
- Upwelling of cool, nutrient rich ocean water are common in the Eastern Pacific (South America) creating a productive fishery region.
- Updrafts and thunderstorms form over the Western Pacific with little activity over the Eastern Pacific.

## El Niño Oceanic Conditions

- Warm sea surface temps spread across the entire Pacific via the leading front of an oceanic wave.
- Thermocline begins to deepen across the Pacific reducing and/or shutting off the upwelling of cool, nutrient rich ocean water along the South American coast reducing fishery productivity with possible fish kills occurring.
- Convective events and thunderstorms generation shift eastward over the Central Pacific.
- This influences a subtropical jet stream over southern U.S. with storm tracks that normally occur over the Pacific Northwest to be shifted to the south over CA

## La Niña Oceanic Conditions

- Cooler sea surface temperatures now move westward as the oceanic wave is reflected off the Southern American Coast.
- Thermocline depth is now very shallow allowing cooler, nutrient ocean water to once again upwell along the South American coast increasing fishery productivity.
- Convective and thunderstorm genesis once again occurs in the western Pacific.
- Sub-tropical jet stream is impacted but in contrast to during an El Niño event, the jet stream moves further north cooling and producing more precipitation in the Pacific Northwest and drying the Southwest.

## El Niño/La Niña Jet Stream

- El Niño produces a near horizontal jet stream causing wet conditions in the Southwest
- La Niña produces a arching jet stream to the north producing wetter conditions in the Pacific Northwest

## El Niño/La Niña Classification

- Key to defining the strength of a El Niño/La Niña event is the Sea Surface Temperature Anomalies (SSTA).
- The main monitoring location for SSTA along the equator is the Niño 3.4 region.
- CPC classifies an El Niño with an anomaly of 0.5 degrees or lower for 5 consecutive months
- CPC classifies a La Niña with an anomaly of -0.5 degrees or lower for 5 consecutive months.

## 2002-2003 Moderate El Niño

- ENSO Index 1.5

## 2007-2008 Moderate La Niña

- ENSO Index -1.5

## Current Weak La Niña

## DESCRIPTION: Warm (red) and cold (blue) episodes based on a threshold of +/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v3 SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)], based on the 1971-2000 base period. For historical purposes cold and warm episodes (blue and red colored numbers) are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons. 

## DESCRIPTION: Warm (red) and cold (blue) episodes based on a threshold of +/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v3 SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)], based on the 1971-2000 base period. For historical purposes cold and warm episodes (blue and red colored numbers) are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons

## DESCRIPTION: Warm (red) and cold (blue) episodes based on a threshold of +/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v3 SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)], based on the 1971-2000 base period. For historical purposes cold and warm episodes (blue and red colored numbers) are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.

- DESCRIPTION: Warm (red) and cold (blue) episodes based on a threshold of +/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v3 SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)], based on the 1971-2000 base period. For historical purposes cold and warm episodes (blue and red colored numbers) are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.

| Year | DJF | JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 2002 | -0.1 | 0.1 | 0.3 | 0.4 | 0.7 | 0.8 | 0.9 | 0.9 | 1.1 | 1.3 | 1.5 | 1.3 |
| 2003 | 1.1 | 0.8 | 0.6 | 0.1 | -0.1 | 0.0 | 0.3 | 0.4 | 0.5 | 0.5 | 0.6 | 0.5 |
| 2004 | 0.4 | 0.2 | 0.2 | 0.2 | 0.3 | 0.4 | 0.7 | 0.8 | 0.9 | 0.9 | 0.9 | 0.8 |
| 2005 | 0.6  | 0.5 | 0.3 | 0.4 | 0.5 | 0.3 | 0.2 | 0.0 | 0.0 | -0.2 | -0.4 | -0.7 |
| 2006 | -0.8 | -0.7 | -0.4 | -0.2 | 0.0 | 0.1 | 0.3 | 0.4 | 0.7 | 0.9 | 1.1 | 1.1  |
| 2007 | 0.8 | 0.3 | 0.1 | -0.1 | 0.0 | -0.1 | -0.2 | -0.5 | -0.8 | -1.1 | -1.2 | -1.4 |
| 2008 | -1.5 | -1.4 | -1.1 | -0.7 | -0.5 | -0.4 | -0.1 | 0.0 | 0.0 | -0.1 | -0.5 | -0.6 |

## All El Niño and La Niña events since 1950, based on the Niño 3.4 observations

| Warm Episodes   max | Cold Episodes      min |
| --- | --- |
| JAS 1951 - NDJ 1951/52                   0.7
MAM 1957 – MJJ 1958                      1.6        | ASO 1949 – FMA 1951                     -1.8
MAM 1954 – DJF 1956/57                -2.1 |
| JJA 1963 – DJF 1963/64                   1.0 | ASO 1961 – MAM 1962                    -0.6 |
| MJJ 1965 – MAM 1966                      1.6 | MAM 1964 – JFM 1965                     -1.1 |
| OND 1968 – AMJ 1969                      1.0 | SON 1967 – MAM 1968                    -0.9 |
| ASO 1969 – DJF 1969/70                  0.7 | JJA 1970 – DJF 1971/72                  -1.4 |
| AMJ 1972 – FMA 1973                      2.1 | AMJ 1973 – JJA 1974                      -2.0 |
| ASO 1976 – JFM 1977                      0.8 | ASO 1974 – AMJ 1976                     -1.8 |
| ASO 1977 - DJF 1977/78                  0.8 | ASO 1983 – DJF 1983/84                -0.9 |
| AMJ 1982 – MJJ 1983                      2.3 | SON 1984 – MJJ 1985                     -1.1 |
| JAS 1986 – JFM 1988                       1.6 | AMJ 1988 – AMJ 1989                    -1.9 |
| AMJ 1991 – MJJ 1992                      1.8 | ASO 1995 – FMA 1996                    -0.8 |
| FMA 1993 – JJA 1993                       0.8 | JJA 1998 – MJJ 2000                      -1.6 |
| MAM 1994 – FMA 1995                    1.3 | SON 2000 – JFM 2001                     -0.7 |
| AMJ 1997 – MAM 1998                    2.5
AMJ 2002 – FMA 2003                     1.5
JJA 2004 – JFM 2005                       0.9 | NDJ 2005 - JFM 2006                   - 0.8
JAS 2007-AMJ 2008                        -1.5 |
|  |  |

## El Niño Years Since 1950

| Weak* | Moderate* | Strong* |
| --- | --- | --- |
| 1951-52 | 1957-58 | 1972-73 |
| 1969-70 | 1963-64 | 1982-83 |
| 1976-77 | 1965-66 | 1997-98 |
| 1977-78 | 1968-69 |  |
| 1992-93 | 1986-87 |  |
| 2004-05 | 1987-88 |  |
|  | 1991-92 |  |
|  | 1994-95 |  |
|  | 2002-03 |  |

- *Weak is Niño Oscillation Index between 0.5 and 0.9.  Moderate between 1.0 and
- 1.8.  Strong is greater than 1.9.

## Global El Niño Impacts

- Warm episodes have weather relationships around the globe

## El Niño Temperature Extreme Risk

## El Niño Precipitation Extreme Risk

## La Niña Years Since 1950

| Weak* | Moderate* | Strong* |
| --- | --- | --- |
| 1961-62 | 1949-51 | 1954-56 |
| 1967-68 | 1964-65 | 1973-74 |
| 1983-84 | 1970-72 | 1988-89 |
| 1995-96 | 1974-76 |  |
| 2000-01 | 1984-85 |  |
| 2005-06 | 1998-00 |  |
|  | 2007-08 |  |
|  |  |  |
|  |  |  |

- *Weak is Niño Oscillation Index between -0.5 and -0.9.  Moderate between -1.0 and
- -1.8.  Strong is greater than -1.9.

## La Niña Jet Stream and Precipitation

- Upper level high pressure over Gulf of Alaska begins to weaken and retreat westward
- Polar jet begins to split and undercut the high pressure
- Undercutting polar jet also may phase with subtropical jet
- Undercutting polar jet becomes steering mechanism for trans- Pacific storms/deep moisture
- Sometimes referred to as the “Pineapple Express” since the moisture origins are often south and west of Hawaii

## Typical La Niña Relationships

**Typical La Niña Relationships**

## Summer La Niña Impacts

- Cold & wet conditions in the Pacific NW
- Warm and dry in the Midwest and NE
- Wet in the southeast
- Dry in Texas
- Higher Frequency of Atlantic & Caribbean Hurricanes
- No California signal

## Fall La Niña Impacts

- Cold & wet conditions in the Pacific NW
- Warm throughout the Mississippi River Valley and Texas
- Wet in the southeast
- Dry in Texas
- Higher Frequency of Atlantic & Caribbean Hurricanes
- No California signal

## Winter La Niña Impacts

- Cold & wet conditions in the Pacific NW
- Warm and wet throughout the southeast but dry in Florida
- Cold across the northern Rockies and Great Plains
- Very dry across California

## La Niña Temperature Extreme Risk

## La Niña Precipitation Extreme Risk

## El Niño/La Niña and Southern California 

- Records clearly show that during almost all La Niña’s, January - March precipitation anomalies are negative

**mm / month**

## Percent of Normal Rainfall during La Niña (for climate division 6)

**Climate Divisions**

## Slide 50

## Weak El Niño’s feature an earlier start to the rainy season. 
The pattern becomes more consistent and parallels normal patterns later in winter, with totals settling around 150% of normal, on average.

**Weak El Niño’s feature an earlier start to the rainy season. **
**The pattern becomes more consistent and parallels normal patterns later in winter, with totals settling around 150% of normal, on average.**

## Moderate El Niños tend to feature a more modest increase in rainfall than weak or strong El Niños.  Seasonal totals average around 100-120%.
The reason weaker El Niños tend to have a greater effect is poorly understood at this point.

**The reason weaker El Niños tend to have a greater effect is poorly understood at this point.**

## Strong El Niños have the most dramatic effect on local rainfall with seasonal totals averaging 150-200% of normal.
Immediate coastal areas tend to see a greater increase in rainfall with lesser effects inland.

**Strong El Niños have the most dramatic effect on local rainfall with seasonal totals averaging 150-200% of normal.**
**Immediate coastal areas tend to see a greater increase in rainfall with lesser effects inland.**

## Weak El Niños tend to feature higher precip than moderate El Niños.
There is more variability with respect to normal in precip before January.   Thereafter precipitation tends to level out to a more consistent and steadier pattern, but rates are higher compared to normal. This extends into the Spring.
Strong El Niños have a less predictable effect in the mountains than at lower elevations for reasons that are not clear.

**There is more variability with respect to normal in precip before January.   Thereafter precipitation tends to level out to a more consistent and steadier pattern, but rates are higher compared to normal. This extends into the Spring.**
**Strong El Niños have a less predictable effect in the mountains than at lower elevations for reasons that are not clear.**

##  The El Niño signal is not quite as consistent in the northern Sierra.

-  **The El Niño signal is not quite as consistent in the northern Sierra.**
** ****Strong El Niño’s still produce the most precip (125%) but weak and moderate events are similar – near to slightly below normal.**

## Winter Storms are consistently wetter-than-normal in winter and spring in both weak and strong El Niño’s.

**Winter Storms are consistently wetter-than-normal in winter and spring in both weak and strong El Niño’s.**
**Strong and Weak El Niño’s produce more precipitation than Moderate El Niño’s.**

##  4 out of 5 El Niño years used in this composite were weak events. The fifth was moderate.

** ****4 out of 5 El Niño years used in this composite were weak events. The fifth was moderate.**
**This composite shows much closer to normal seasonal rainfall totals than typical weak El Niño’s.**

## El Niño has a repeat cycle of 2-7 years with an average repeat cycle of approximately 4 yrs.