# Presentation: 858245

## Forecasting the Onset of El Niño Based on GPCP Precipitation:

**Validation and Future Work**
- Scott Curtis
- Joint Center for Earth Systems Technology
- University of Maryland, Baltimore County
- NASA/Goddard Space Flight Center

- Robert F. Adler
- NASA/Goddard Space Flight Center

- George J. Huffman
- SSAI/NASA/Goddard Space Flight Center

- Curtis, S., G. J. Huffman, and R. F. Adler, 2002:  Precipitation Anomalies in the Tropical Indian Ocean and Their Relation to the Initiation of El Niño,
*Geophysical Research Letters*, 29(10), 1441, doi:10.1029/2001GL013399.

## DATA:  Precipitation, Surface Winds, and SST

- •  GPCP Pentad Precipitation (Xie et al. 2003) + GPROF SSM/I Pentad Precipitation
- (2.5°, global, 1979-present)
- •  NCEP Daily (avg. to pentad) Reanalysis 1000mb Winds
- (2.5°, global, 1979-1999)
- •  TRMM Daily (avg. to pentad) 3B42 Precipitation (Adler et al. 2000)
- (1°, tropics, 2001-2002)
- •  TRMM Daily (avg. to pentad) SST
- (0.25°, tropics, 2001-2002)
- Acknowledgement:  TMI-SST data were produced by Remote Sensing Systems and sponsored by NASA’s Earth Science Information Partnerships (ESIP)
- •  QuikSCAT 12 Hourly (avg. to pentad) Sea Surface Winds
- (0.5°, near-global, 2001-2002)
- Acknowledgement:  Data obtained from the NASA / NOAA sponsored data system Seaflux, at JPL through the courtesy of W. Timothy Liu and Wenqing Tang

## The Indian Ocean and El Niño

- “observational summaries suggest important teleconnections of these zonal winds over the near-equatorial southern Indian Ocean and the subsequent onset of the El Niño in the equatorial Pacific Ocean” (Krishnamurti et al. 2000).
- However, no uniform response in MJO in the eastern Indian Ocean has been related to El Niño (Fink and Speth 1997, Vincent et al. 1998).

**The Indian Ocean and El Niño**
- Longitude-time sections of Equatorial **850mb zonal wind anomalies** from daily forecast values
- (Krishnamurti et al. 2000, Figure 1)

- 1991-92

- 1993-94

- 1994-95

- 1997-98

## GPCP Pentad Precipitation and NCEP 1000mb Winds (1979-1999)

**Hastenrath et al. (1993), **
**Saji et al. (1999), Webster et al. (1999)**
- (autumn during El Niño)

**Eastern Equatorial Indian Ocean**
- (autumn-winter before El Niño)

**GPCP Pentad Precipitation and NCEP 1000mb Winds (1979-1999)**

- Curtis et al. (2002)

## Results from Curtis et al. (2002)

- 1.  Greatest relationship with El Niño found in an index of the gradient of precipitation anomalies (SE minus NW)
- 2.  Two Dimensional Solution:
- 	A)  Interannual average (2-7 year filter) of the gradient is a positive 		maximum
- 	B)  Followed 3-4 months later by significant intraseasonal variability in 	the gradient (30-60 day power from a wavelet analysis)
- 3.  These conditions only occurred before El Niños **(****1982-83,**** ****1986-87,**** ****1991-92,**** ****1994-95,**** ****and**** ****1997-98****)**

## Summary

- Enhanced westerlies
- over several months

- Air-sea interaction
- (Kelvin wave)

- El Niño development

- MJO ?

- Eastern Indian Ocean

- Western Pacific Ocean

- Wind has been well observed (on sub-monthly time scales) from buoys in the Pacific, but not the Indian Ocean.  However, precipitation/cloud patterns (observed from satellites over the past two decades) offer an indirect measure of global wind variations (eg. the MJO in the Indian Ocean).

## An Experimental “Onset Predictor” Index

- 2-7 year filter was replaced with trailing 37 pentad (half-year) average
- Ignore the 30-60 day power for pentads with 6-month trailing mean < 0
- Real-time updates beginning in 2001
- Index exceeded positive forecast conditions for the first time on Jan. 21-25 2002 (calculated in early Feb.)
- Based on past events, we called for onset to occur        6-9 months from January (July-October)

## 30-60 day power (mm day-1)2

- 30-60 day power (mm day-1)2

- Trailing 37-pentad average (mm day-1)

## Validation

**Validation**

- Black = “miss”
- Blue = 1-4 months
- Green = 5-8 months
- Pink = 9-12 months
- Red = +12 months

**LEGEND**

- Nino3.4

**30-60 day power (mm/d)^2**

**Nino3.4 (°C)**

*4.33*

*4.17*

*3.58*

*2.92*

*6.25*

## Slide 10

## Future Work

- Precipitation is not THE answer.  We are currently investigating intraseasonal variations in wind, SST, and rainfall from satellites in the equatorial Indian Ocean sector (96-97; 01-02)
- Extension of the analysis back in time
*The western Pacific*
*Extended-MJO time scales (60+ days)*
*Communication, dialogue, and feedback*

## Air-sea coupled MJO

**Air-sea coupled MJO**
**(30-day variability in 2002)**

- 15-day difference in
- daily pentad averages
- Precipitation:** ****	**-30 to 30 mm/day
- Zonal winds:**	**** **-15 to 15 m/s
- SST:** ****	****	**-2.5° to 2.5° C
- Start:
-    Jan 6-10 2002 minus Dec 22-26 2001
- End:
-    Feb 15-19 2002 minus Jan 31 - Feb 4 2002
- See also:
-   Harrison and Vecchi 2001
-   Woolnough et al. 2000
-   Wang and Xie 1998

## Gridded Global Historical Climatology Network Precipitation Anomalies

**Cocos (Keeling)**
**Islands, Australia**

- Darwin, Australia

**Gridded Global Historical Climatology Network Precipitation Anomalies**
**October 2000**

- Intraseasonal variability from monthly data

- 4 zero-line crossings required
- 60-day oscillations, with max/min at mid-month

- 0 mm

## * 10 out of the 13 strongest El Niños (Jan-Feb SOI) were preceded (< 12 months) by oscillations

- * Darwin precipitation also shows a similar relationship