Influence of intraseasonal surface wind variability on ENSO in CFS predictions Wanqiu Wang, Mingyue Chen, Arun Kumar, Yan Xue Climate Prediction Center, NCEP/NOAA NOAA's 34th Climate Diagnostics and Prediction Workshop October 26-30, 2009 in Monterey, CA

1.Background 2.Objective 3.The NCEP CFS forecasts 4.Influence of intraseasonal variability (ISV) on ENSO prediction Outline

1.ISV in the W. Pacific affects subsequent SSTs in E. Pacific. 2.A sequence of MJO events may result in the development of an ENSO event. 3.Strong ISV can lead to the termination of ENSO. Impacts of ISV on ENSO Background

1.Observed ISV that occurs before the start of the ENSO forecast may add to prediction skill. 2.Observed ISV that occurs during the forecast period could become a limiting factor for forecast skill. 3.Within an ensemble spanning a range of initial conditions, Individual forecasts may vary with the regime of initial ISV. How does ISV affect ENSO prediction? Background

Forecast with no clear separation among members Background IC: May 2006 Nino3.4: 190E-240E; 5S-5N Nino3.4 SST forecasts from the CFS

Forecast with separation among members IC: May 2005 IC: Aug 2008 IC: Nov 2006 IC: Jun 2007

1.To diagnose to what extent the spread and the separation among the forecast members arise from initial intraseasonal surface wind anomalies. 2.To examine the impact of the initial ISV on the ENSO prediction skill and the dependency on the intraseasonal activities during the forecast period. Objectives

1.Produced daily for 9 target months –2007:2 runs/day 2008 – Now:4 runs/day The NCEP CFS forecasts

U(t 0 ) observed initial surface wind T(t 0,  ) forecast Nino3.4 SST t 0 = 1Jan2005 to 31Dec2008  = 1 to 270 days Influence of ISV on ENSO prediction Intraseasonal anomalies with respect to initial time Applying a day filter to t 0 (NOT  ) gives U I (t 0 ) T I (t 0,  ) Intraseasonal anomalies with respect to initial time Raw anomalies

Intraseasonal anomalies with respect to initial time Raw anomalies CFS Nino3.4 SST anomalies T(t 0,  ) T I (t 0,  ) t 0 = 11 Jun to Jul 10, 2007  = 1 to 270 days

 < 60 days: Local wind influence Correlation: Initial intraseasonal U 10m and forecast Nino3.4 SST Where is the ISV that has strong impacts on ENSO prediction?  > 60 days: Remote impacts from W. Pac. Lead time (days)

Correlation: W. Pac (120E-160E) U 10m and forecast Nino3.4 SST How long does it take for the initial ISV to affect forecast ENSO ? Impacts of W. Pac. winds on Nino3.4 SST has a maximum around 80-day lags and the impacts persist throughout the entire target period.

Impacts of initial W. Pac. winds are carried through via subsurface Kelvin wave propagation. Correlation: initial W. Pac. U 10m and forecast SSH How are the impacts of ISV carried through in the forecasts?

Impacts of W. Pac. winds on SSTs at different longitudes. No effects on surface advection. We would otherwise see surface warming propagates from WPac to EPac. Correlation: Initial W. Pac. U 10m and forecast SST

CFS Nino34 SST (K) Substantial change in forecasts from Dec 1-5 to Dec S-10N U850 (m/s) Impacts of the MJO event in Dec 2006 Influence of ISV on ENSO prediction Dec 1 Dec10 Forecasts after Dec 5 Forecasts before Dec 5

Impacts of the MJO cycles in Nov-Jan 2007/2008 Observed U 10m anomalies CFS Nino3.4 SST Initial date Target date 1 Nov Oct 2008 t 0 = 1 Nov 2007 to 31 Jan 2008  = 1 to 270 days

CFS Nino3.4 SST anomalies U(t 0 ) T I (t 0,  ) t 0 = 1 Nov 2007 to 31 Jan 2008  = 1 to 270 days 1 Nov Oct 2008 U 10m (120E-160E average) Initial date Target date Intraseasonal anomalies with respect to initial time

Summary There exists a substantial spread among the ENSO forecasts started from different days, and at times, the ensemble members show a clear separation. The separation among the forecast members are found to be related to differences in subseasonal variability of surface winds in the western Pacific. It takes about 80 days for the impacts of the initial winds in the western Pacific to be carried through to the eastern Pacific by subsurface Kelvin waves. ENSO forecasts during Dec-Jan 2006/2007 and Nov-Jan 2007/2008 strongly depend on the phase of the MJO during these periods.