Decadal modulation of the ENSO impact on the Hydroclimate over the United States

1. Decadal modulation of the ENSO impact on the Hydroclimate over the United States Kingtse Mo Climate Prediction Center NCEP/NWS/NOAA

2. Composites of drought indeces All drought indices indicate Cold ENSO=> Drought overthe Great Plains, Southwest and Gulf states

3. Questions The impact of ENSO does not always obey the ‘composites’. WHY? • Each ENSO is different • ENSO impact on regional climate is modulated by decadal modes

4. Decadal modes • Trends • Atlantic Multi decadal oscillation (AMO) • Pacific Decadal Oscillation (PDO) • PDO Barnett and Cayan (1998), Gershunov and Barnett (1998) Decadal: fluctuations with time scales longer than 6 yrs

5. Observational Data100 yr data set is not long enough P and Tsurf • Monthly Precipitation (P) and surface temperature (T) over the United States from 1915-2006 (U. of Washington) • SST and SLP • SST- Smith reconstructed SSTs 1915-2006 • SLP – Trenberth and Paolino (1987) • Anomaly- departure from monthly mean Climatology from 1915-2006

6. Atlantic Multi decadal Oscillation AMO composite warm-cold phase Decadal influence is small. You can filter to get clearer signal, but the percentage of variance is small, so the net influence is small. AMO warm 1930-1959,1992-2006 AMO cold 1915-1925,1965-1990

7. AMO influence through ENSO Composite of SPI6 with all seasons together for different phase of the AMO Mo et al. 2009

8. Trends • Composites were formed for each season for (a) 1915-1960 and (b) 1962-2006 • ENSO – Nino 3.4 index over 0.8 std (less -0.8 std) • Results are given as composites: warm –cold weighted by the number of events • Statistical significance is determined by the Monte Carlo method

9. Surface temperature ENSO composites warm-cold Tsurf: Strongest signal is in winter and Spring In the recent decades 1. Cooling over the Southeast, the Gulf States has been weakening . 2. Warming over California and cooling over the Plains occur in Spring

10. It used to be….. • Warm ENSO  cold over the South and warming over the North. • Things are changing • Cooling over the South has been weakening in winter. • For California and the Southwest, spring is warmer in the recent decades. • The great Plains is cooler in spring ENSO-T

11. ENSO-P • Strongest impact is in winter • In the recent decades, influence on California increases • Over the Pacific Northwest, impact comes in Fall

12. Changing in SSTAs Warming centered at the eastern Pac Warming centered At the Central Pac Ref: Yeh et al. (2009) , Kug et al. (2009), Kao and Yu (2009), Ashok et al. (2007)

13. SLP anom composites

14. ENSO teleconnections are changing • The impact of ENSO on P and Tsurf over the United States is not stationary. • More warm ENSO events in the recent decades • Warming over the Northern U. S. and cooling over the Southeast and the Gulf states are weakening • Impact over the Southwest and California intensified in the recent decades (Warm=> wet, Cold=> drought) • Impact over the Pacific Northwest comes early in Fall. (Warm= > drought, cold=> wet) With such small sample, are these real???

15. Two kinds of ENSO Eastern PAC X Central Pac x Yeh et al.2009(nature)

16. Composites of EP & CP ENSO Events were taken from Yeh et al. (2009) P Tair C Pac 7 events • Different type of ENSO contributes to the variability of impact • If models are able to capture two types of ENSO and impact, then they can be used for diagnosing phycical mechanisms E Pac 21 events

17. IPCC runs (focus on winter) • 20th Century simulations from 1880 to 2000 runs (20C3m) • Models: • GFDL_CM2.1 (700yrs) • GFDL_CM2.0 (412 yrs) • MicroC3.2-medres (453 yrs) • UKMO_HadCM3 (280 yrs) • MPI_Echam5 (814 yrs) • These are simulations with realistic ENSO (Meehl et al. 2007, Oldenborgh et al 2005) Data from the Earth system grid WCRP CMIP3

18. IPCC (JFM) • For each run, compute anomalies as the departure from the model mean • Form SSTA Nino 34 and Nino 3 indices • Select events when both indices are greater than 0.6-0.8 standard deviations • EP events when Nino34> Nino3 + d with a clear Maximum over the eastern Pacific, d= 0.1 to 0.3 • 5. CP events when Nino3>Nino34 +d with a clear maximum over the central Pacific

19. Ensemble ipcc model Central Pac Eastern Pac • Tsurf : more north-south warming/ cooling for the E-PAC and East-west contrast for the C-PAC • Cooling over the South weakens for the C –PAC • More rainfall over California and the Southwest and less for the Southeast for the C-PAC Eastern Pac Central Pac

20. Physical mechanims were examined using the GFDL_CM2.1 model runs • Physical Mechanisms • Eastern Pac: • Positive P anomalies are located over the area extending from 160W to 90W. • Walker circulation puts less rainfall over northern Brazil • The weakening of Hadley circulation implies more rainfall over the Southeast. • Central Pac: • Positive P anomalies are located over the deadline Precip (shaded), Chi wind (vectors)

21. GFDL CM2-1 • E-PAC • the North American jet extends to the Atlantic • Strm 200 –more zonal structure • Central Pac • jet extends to the west coast • Pacific-North American wavetrain

22. Decadal changes of ENSO impact • For forecast and monitoring: • Impact on the U. S. depends on both ENSO pattern as well as magnitudes. • Pay attention to the precip anomalies in the Tropics. • Different tropical convection pattern different wind and circulation responses  different impact • These changes are not linear. The OCN magic may not work