# Presentation: 358599

## The 2007/08 La Niña Cycle: Evolution and Prediction

_***Yan Xue***_***, Boyin Huang, Wanqui Wang, ***
***Arun Kumar, ******Philip Pegion and Michelle L’Heureux***
**Climate Prediction Center**

**33****rd**** CDPW and CLIVAR Drought Workshop, Lincoln, ****Nebraska, ****Oct. 21-24 2008.**

## Slide 2

## Data Sources and References

**  ****Optimal Interpolation SST (OI SST) version 2 (Reynolds et al. 2002) **
**  ****SST 1971-2000 base period means (Xue et al. 2003)**
**  ****NCEP CDAS 850 mb winds (****Kalnay et al. 1996)**
**  ****NCEP CDAS2 wind stress (****Kanamitsu et al. 2002)**
**  ****NESDIS Outgoing Long-wave Radiation (OLR)**
**  ****NCEP’s Global Ocean Data Assimilation System temperature, heat content, ****currents (Behringer and Xue 2004)**
**  ****Ocean Surface Current Analyses – Realtime (OSCAR) (****Bonjean and Lagerloef, 2002**)

## Evolution of Pacific NINO SST Indices

_**Evolution of Pacific NINO SST Indices**_

**Nino 3**

**start**

**end**

## Comparison with Historical La Nina Events

_**Comparison with Historical La Nina Events**_

**- According to CPC’s ENSO definition based on ERSST (NINO3.4 =< -0.5C for five consecutive overlapping 3-month seasons), there were seven La Nina winters during 1982-2008 (84/85, 88/89, 95/96, 98/99, 99/00, 00/01 and 07/08).**
** ****The 2007/08 La Nina has a similar strength as that of the 1999/00 La Nina.**
** ****The moderate-to-strong 2007/08 La Nina was ****noteworthy since ENSO variability has been relatively weak during 2001-2006.**

## Evolution of Equatorial Pacific SST, Heat Content, TAUX, and Surface Zonal Current Anomaly 

** ****Negative SSTA propagated westward and positive SSTA appeared in far E. Pac. in early spring 08.**
** ****Negative heat content  (upper 300m temperature average) anomaly presented in central-eastern Pacific in January 07, and persisted until early spring 08 with little propagation.**
** ****Easterly (westerly) wind stress anomaly in the central (eastern) Pacific propagated westward during August 07 – April 08. **
** ****Westward surface zonal current anomaly (ZCA) switched to eastward ZCA in February 08.**

_**Evolution of Equatorial Pacific SST, Heat Content**__**, **__**TAUX, and Surface Zonal Current **__**Anomaly**__** **_

## Central and Eastern Pacific SSTA for Seven La Nina Winters

**The onset of the 07/08 La Nina was similar to that of the 95/96 La Nina during which negative SSTA in the far E. Pac. led negative SSTA in the C. Pac by 4-6 months.**

** ****During the decay phases of La Nina, negative SSTA in the far E. Pac. tend to return to near-normal in early spring of the following year and then cool down to a second cold phase in next fall.**
** ****Compared to all other early spring warmings in the far E. Pac., the 08 spring warming was stronger and persisted much longer.**

**onset**

**decay**

_**Central and Eastern Pacific SSTA for Seven La Nina Winters**_

## Warm Water Volume and NINO 3.4 Index in 1982-2008

_**Warm Water Volume and NINO 3.4 Index in 1982-2008**_

## NINO3.4, Surface ZCA of OSCAR and GODAS for Seven La Nina Winters

** ****Zonal current anomaly (ZCA) of GODAS agrees well with that of OSCAR in the central-eastern equatorial Pacific except during the 97/98 El Nino. However, GODAS has substantial mean biases, positive in the central-eastern Pacific and negative in the W. and far E. Pacific (not shown).**
** ****ZCA tends to lead SSTA by a few months.**
** ****ZCA usually switches from negative to positive during the peak phases of La Nina in late winter. **

_**NINO3.4, Surface ZCA of OSCAR and GODAS **__**for Seven La Nina Winters**_

## Impacts of MJO-related Winds on Heat Content Anomaly

** ****MJO-related easterly wind anomaly during November-December 06 contributed strongly to the sudden switch of heat content anomaly from positive to negative in January-February 2007.**
** ****A pair of westerly and easterly wind bursts during May-June 07 contributed to a positive heat content anomaly in the central-eastern Pacific.**
** ****A pair of easterly and westerly wind bursts during December 07 – January 08 and a westerly wind event  in the far E. Pacific in February-March 08  had contributed to the sudden switch of heat content anomaly from negative to positive in the central-eastern Pacific in April 08. **

_**Impacts of MJO-related Winds on Heat Content Anomaly**_

## Heat Budget Anomaly & SSTA for (170W-120W, Eq)

_**Heat Budget Anomaly & SSTA for (170W-120W, Eq)**_

**Zonal advection followed the SSTA tendency well, suggesting a dominant role of zonal advection in controlling the evolution of the La Nina.**

**Vertical entrainment at the bottom of the mixed layer contributed to negative SSTA tendency during Feb-Apr and Sep 07 – Mar 08. **

**Net heat flux is a damping term to SSTA.**

## Onset Phase

_**Onset Phase**_

## Development Phase

_**Development Phase**_

## Mature Phase

_**Mature Phase**_

## Decay Phase

_**Decay Phase**_

## 2007 CFS Nino34 forecast with mean bias correction

## 2007 CFS Nino34 forecast with PDF correction

## Slide 18

## Slide 19

## NINO3.4, WWV_West and WWV_East  for Seven La Nina Events

** ****During the onset phases of La Nina, negative WWV_West anomaly usually leads negative WWV_East anomaly, indicating a slow eastward propagation of negative heat content anomaly.**
** ****But, during the 07/08 La Nina, near-zero WWV_West anomaly led negative WWV_East anomaly, suggesting no eastward propagation of heat content anomaly. **
**The onset phase of the 07/08 La Nina was similar to that of the 99/00 La Nina during which WWV_West was near-normal. **

** ****During the decay phases of La Nina, negative WWV_East and positive WWV_West anomaly both weakened quickly in early spring of the following year.  **

**decay**

**onset**

_**NINO3.4, WWV_West **__**and WWV_East **__** for Seven La Nina Events**_

## Impacts of MJO-related Winds on Surface ZCA

** ****MJO-related easterly wind anomaly during November-December 06 forced westward zonal current anomaly (ZCA).**
** ****A pair of westerly and easterly wind bursts during May-June 07 forced eastward and westward ZCA in the western-central Pacific.**
** ****A pair of westerly and easterly wind bursts during November - December 07 had contributed to the switch of ZCA from westward to eastward in the central-eastern Pacific in January-February 08. **

_**Impacts of MJO-related Winds on Surface ZCA**_

## Slide 22