# Presentation: 780906

## The Tropical Western Hemisphere Warm Pool

**Chunzai Wang**
**David B. Enfield**
**Physical Oceanography Division**
**NOAA Atlantic Oceanographic and Meteorological Laboratory**
**Miami, Florida**

**Wang, C., and D. B. Enfield, 2001: The tropical Western Hemisphere warm pool. **
**	*****Geophys. Res. Lett*****., 28, 1635-1638.**
**Wang, C., and D. B. Enfield, 2002: A further study of the tropical Western **
**	****Hemisphere warm pool.  *****J. Climate*****, in press.**

**Available at http://www.aoml.noaa.gov/phod/docs.html**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Outline

-  **What is the WHWP and Why is the WHWP important?**
** ****Annual variation of the WHWP**
** ****Interannual variability of the WHWP**
** ****A positive feedback for WHWP SST anomaly growth**
** ****Summary**

**Outline**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Define: ==> area of water warmer than 28.5°C
Depth of 28.5°C is close to average mixed layer depth (MLD)
Convenient (a closed region)
Significant impact on organized  tropical convection (e.g., Graham & Barnett 1987)

- _Define_: ==> area of water warmer than 28.5°C
- Depth of 28.5°C is close to average mixed layer depth (MLD)
- Convenient (a closed region)
- Significant impact on organized  tropical convection (e.g., Graham & Barnett 1987)

**The Tropical Western Hemisphere Warm Pool (WHWP)**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## The NCEP SST showing the seasonal variation of the tropical Western Hemisphere warm pool (WHWP)

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## The WHWP is a heating source of summer Atlantic Hadley circulation

- SST (larger than 28.5°C)

**The Tropical Western Hemisphere Warm Pool (WHWP)**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Five of the largest WHWPs (1958, 1969, 1983, 1987, and 1998) have come in the NH summer following El Niño events (EN [+1]).  However, large WHWPs fail to develop following four recognized 

**El Niño events (1966, 1973, 1977, and 1992).   The WHWPs of year EN [0] can be large or small.****  **

**Index of the WHWP**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Rainfall Composites for Early Summer (AMJ)

**Rainfall Composites for Early Summer (AMJ)**

**Nino [+1]  summers **
**with 4 largest WHWPs.**
**(El Niño  + WHWP)**

**Nino [+1] summers **
**without large WHWPs.**
**Consistent with El Niño effect **
**of Chen and Taylor (2002)**

**Difference: WHWP effect**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Relation to Atlantic Hurricanes

- Large WHWPs ==> low shear ==>  more hurricanes
- Knaff (1997) ==> Warm Caribbean <=> low shear

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## A clear summer moisture path from warm pool 

**A clear summer moisture path from warm pool **
**into the central U.S. ****(Bosilovich et al. 2002)**** **

- Arrows: q•V (moisture transport)     Contour: Evaporation > 5 mm/day

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## Warm pools strongly

**Warm pools strongly**
**affect climate patterns **
**over continent**

**AGCM studies by **
**Inatsu et al. (2000 and 2002)**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Simple slab model of annual heat budget

**Over 7°N-27°N, 110°W-50°W, h=25 m**

**                         ****Data Sets:**
**NCEP SST from 1950-99**
**NCAR-NCEP surface heat flux from 1950-99**
**Levitus climatological data**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Annual Variation of the WHWP SST

**Heat storage tendency: ∂H/∂t=********C****P****h ∂(SST)/∂t**
**Q****N****: net heat flux; Q’****N**** net heat flux considering penetration**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## WHWP Interannual Variability

**WHWP Interannual Variability**

**Composites of WHWP Warm Events (Dark Contour: Climatology)**

**July: Larger by 96%**

**September: Larger by 27%**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Our data analyses suggest that a tropospheric bridge

**Our data analyses suggest that a tropospheric bridge**
**transfers Pacific ENSO effect to the WHWP**
**The question is: After the ENSO-related initial warming,**
**what is process that amplifies WHWP SSTA growth?**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Correlations between WHWP Variables

**Correlations between WHWP Variables**

**R(SST,Q****LW****) is large, negative at zero lag, suggesting that longwave radiation**
**is a positive feedback (associated with clouds).**
**However, 3-month lagged positive (negative) correlation between  latent heat**
**(shortwave radiation) and SST anomalies, suggesting that latent heat & shortwave **
**radiation tend to damp/cool warm SSTA in the WHWP region.**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Composite of Longwave Radiation Anomalies

**Composite of Longwave Radiation Anomalies**

**SST and Longwave Radiation Anomalies in the WHWP Region**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

##  Positive feedback through momentum flux: ENSO (Bjerknes 1966, 1969)

**feedback operating through longwave radiation and associated**
**cloudiness is responsible for WHWP SST anomaly growth**

**SST Anomalies (+)**

**SLP Anomalies (-)**

**Convection and**
**Cloudiness (+)**

**Longwave Radiation**
**from the Surface (-)**

**It differs from:**
** ****Positive feedback through momentum flux: ****ENSO ****(Bjerknes 1966, 1969)**
** ****Positive feedback through latent heat flux: ****TNA ****(Carton et al 1996; Chang et al 1997)**
** ****Positive feedback through shortwave radiation: ****SE tropical Pacific ****(Philander et al 1996)**

- NOAA Atlantic Oceanographic & Meteorological Laboratory

## Summary

**Importance of the WHWP:**
- A heating source of summer Atlantic Hadley circulation
- Rainfalls in the United States, Caribbean, Central America, and northern South America
- Atlantic hurricanes
- A source of moisture for North America (Bosilovich et al. 2002)
- Subtropical westerly wind of North America (Inatsu et al. 2002)
**Seasonal cycle: Surface heat fluxes seem to be primarily responsible for warming of the WHWP.**
**Interannual variability: A positive ocean-atmosphere feedback through longwave radiation and associated cloudiness seems to operate in the WHWP.****   **

- NOAA Atlantic Oceanographic & Meteorological Laboratory