1. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Interannual to Decadal Variability of the West Pacific Warm Pool in Remote Sensing Based and ECCO-assimilated Oceanographic Data Sets  Importance of the tropical warm pools in the global climate system  Objectives of this study and their relevance to the SSTST  Satellite remote sensing based and ECCO-assimilated oceanographic data sets  West Pacific Warm Pool variability  Small SST change? Yes, but a big impact on the global atmosphere!  Summary Vikram M. Mehta and Hui Wang Center for Research on the Changing Earth System (CRCES) Funded by NASA-Physical Oceanography Program Grants NNX08AH70G and NNX09AF36G

2. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Importance of the Tropical Warm Pools in Global Climate Much of the warmest ocean water on Earth Annual-average SST ≥ 28°C from 25°S- 25°N; pronounced annual cycle Saturation vapor pressure non-linearly related to SST  dramatic increase in atmospheric moisture content and convection when SST ≥ ≈28.5°C Indo-Pacific Warm Pool THE major source of heat for the global atmosphere Numerous studies of possible mechanisms of maintenance of time-average state of the Tropical Warm Pools Natural variability has not received much attention; influences ENSO and marine ecosystems, among others, at interannual timescales

3. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Project Objectives * To develop physical hypotheses of interannual and decadal variability of West Pacific and West Atlantic Warm Pools, using remote sensing based, multi-sensor oceanographic data; and * To identify important mechanisms of interannual and decadal Warm Pool SST variability. Relevant NASA SST Science Team Objective Scientific utilization of measurements and data products to understand SST uncertainty budget, as well as utilization of these (SST) measurements in combination with other ocean and atmosphere measurements to understand the general circulation of the ocean and air-sea coupling in the global climate system.

4. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010  NOAA Optimum Interpolation (OI) V2 AVHRR: SST; satellite era: 1982-present; monthly; 1° lon.-1° lat., 0°-360°, 90°S-90°N  QuikScat: Surface wind stress; 1999-2008; daily; 0.5° lon.-0.5° lat., 0°- 360°, 90°S-90°N WMerged TOPEX/Poseidon, Jason-1, and ERS-1/2: Sea surface height (SSH); 1993-2008; pentad; 0.33° lon. - 0.33° lat.; 0°-360°, 90°S-90°N WOSCAR: Surface currents; 1992-2007; pentad; 1° lon. - 1° lat.; 0°-360°, 69.5°S-69.5°N; geostrophic currents from SSH and ageostrophic from surface wind stress WGPCP: Rainfall; 1979-present; monthly; 2.5º lon. - 2.5º lat.; 0°-360°, 90°S-90°N WECCO: Currents, temperatures, budget terms, forcing fields; 1992-2004; monthly; 1° lon. - 1° lat.; 0°-360°, 60°S-60°N; 23 levels Remote Sensing Based and Model-assimilated Oceanographic Data

5. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Empirical Orthogonal Function Analysis of WPWP SSTs EOFs-PCs of monthly SST anomalies (w. r. t. average monthly climatology) within the boxed region where average SSTs above 28°C; PC time series projected on entire Indo-Pacific region within 40°S- 40°N EOF1: Largest signals in the WPWP and eastern Indian Ocean; EOF2: in WPWP and eastern equatorial Pacific “Decadal” appearance of PC1 variability; Interannual appearance, with major El Niño events prominent, of PC2 variability EOF 1 32% EOF 2 12% PC 1 PC 2

6. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 West Pacific Warm Pool SST and SSH

7. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Evolution of “Decadal” Pattern - 12 Months to 2 Months before EOF1 Peak Sea surface temperature

8. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Evolution of “Decadal” Pattern - 12 Months to 2 Months before EOF1 Peak Sea surface temperature Surface wind stress

9. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Evolution of “Decadal” Pattern - 12 Months to 2 Months before EOF1 Peak Sea surface temperature Surface wind stress Sea surface height

10. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Evolution of “Decadal” Pattern - 12 Months to 2 Months before EOF1 Peak Sea surface temperature Surface wind stress Sea surface heightRainfall

11. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Evolution of “Decadal” Pattern - 2 Months to 12 Months after EOF1 Peak Sea surface temperature Surface wind stress Sea surface heightRainfall

12. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Evolution of Interannual Pattern - 12 Months to 2 Months before EOF2 Peak Sea surface temperature Surface wind stressSea surface height Rainfall

13. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 West Pacific Warm Pool Variability in ECCO-GODAE Data Set Generally similar WPWP SST anomaly time series of OI and ECCO High correlation between WPWP SST tendency and net surface heat flux terms in ECCO; WPWP SST variability driven mainly by surface heat flux Horizontal, mainly zonal, heat advection drives mixed-layer and upper 50 m temperatures Average WPWP SST Anomalies in OI SST and ECCO-GODAE WPWP SST Tendency and Net Surface Heat Flux Anomalies

14. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Surface air temperature (shaded; ºC) and rainfall (mm/day) anomalies as simulated by FVGCM in response to positive and negative SST anomalies in the west Pacific Warm Pool region Preliminary experiments with an atmospheric GCM to quantify atmospheric sensitivity to WPWP SST variability Substantial, non-linear impacts of ±0.5°C SST anomalies on rainfall and temperature of the Asian-Australian monsoons A distinct annual cycle of response WP ∆SST = -0.5ºCWP ∆SST = +0.5ºC MAM DJF SON JJA Imposed SST pattern; 2-d Gaussian with  0.5°C at center

15. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Surface air temperature (shaded; ºC) and rainfall (mm/day) anomalies as simulated by FVGCM in response to positive and negative SST anomalies in the west Pacific Warm Pool region Substantial, non-linear impacts of ±0.5°C SST anomalies on North American rainfall and temperature A distinct annual cycle of response Small SST changes can drive substantial atmospheric changes if the SST changes are in convectively-active regions with average SSTs close to ~28°C WP ∆SST = -0.5ºC MAM DJF SON JJA WP ∆SST = +0.5°C

16. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Summary Some of the warmest ocean water in the world in Tropical Warm Pools; saturation vapor pressure an exponential function of SST  intensity of deep convection very sensitive to changes in SST over the warm pools 45% of monthly OISST variance in the Indo-Pacific Warm Pool region in two EOF-PC patterns Physically-consistent evolution of SST, SSH, surface wind stress, and rainfall in “decadal” and interannual patterns Thermally-direct variability of the Walker circulation associated with both patterns Associated variability in global atmospheric circulation  modulates the North Pacific and North Atlantic Oscillations In ECCO-GODAE data, WPWP SST variability driven largely by net surface heat flux variability; variability of mixed-layer and upper 50m temperature driven largely by zonal and meridional heat advections Substantial impacts on the global atmosphere of even small-amplitude SST anomalies in the WPWP region in idealized experiments with an atmosphere GCM

17. Vikram MehtaNASA SST Science Team Meeting, Seattle8 November 2010 Thank you!!