# Presentation: 784287

## Atmospheric Hydrological Cycle in the Tropics in Twentieth Century Coupled Climate Simulations

- Hailan Wang and William Lau
- Laboratory for Atmospheres, NASA/GSFC

- 30th Climate Diagnostics and Prediction Workshop
- October 26, 2005

- Climate Model Evaluation Project (CMEP)

## Motivation

- Identify and understand long-term change of tropical hydrological cycle in 20th Century climate simulations by Coupled GCMs
- Precipitation
- Clouds
- Provide input for IPCC AR4 in 2007

## Coupled GCMs

- State-of-the-art
- Fully coupled
- Time signature differs
- Driven by time-varying external climate forcings
- No agreed-upon forcing functions
- The diversity in external forcing in the CGCMs is regarded as a measure of forcing uncertainties

## NASA GISS_E

- /research/modeling/

## Coupled GCMs (Cont’d)

- 16 CGCMs analyzed
- 1 run of each CGCM used
- Monthly mean fields
- 1900-1999
- Linear trend (actual linear change over time period concerned)
- Models: 1950-1999
- Observations
- 1979-1999 for GPCP precip
- 1984-1999 for ISCCP clouds

## USA: 5; France: 2; Japan: 2; UK: 2; 

| Model No. | Model Acronym | Modeling group | Country | Atmosphere Resolution | Ocean 
Resolution at Equator |
| --- | --- | --- | --- | --- | --- |
| 1 | CGCM3.1(T47) | CCCMA | Canada | T47L31  |  1.851.85L29 |
| 2 | CNRM-CM3 | CNRM | France | T63L45 | 20.5L31 |
| 3 | CSIRO-Mk3.0 | CSIRO | Australia | T63L18 |  1.8750.84L31 |
| 4 | GFDL-CM2.0 | GFDL | USA | 2.52L24 |  11/3L50 |
| 5 | GFDL-CM2.1 | GFDL | USA | 2.52L24 |  11/3L50 |
| 6 | GISS-EH | NASA/GISS | USA | 54L20 | 22L16 |
| 7 | GISS-ER | NASA/GISS | USA | 54L20 | 54L13 |
| 8 | FGOALS-g1.0 | LASG/IAP | China | T42L26 | 11L33 |
| 9 | INM-CM3.0 | INM | Russia | 54L21 | 2.52L33 |
| 10 | IPSL-CM4 | IPSL | France | 3.752.5L19 | 21L31 |
| 11 | MIROC3.2(hires) | CCSR/NIES/FRCGC | Japan | T106L56 | 0.280.1875L47 |
| 12 | MIROC3.2(medres) | CCSR/NIES/FRCGC | Japan | T42L20 | 1.40.5L43 |
| 13 | ECHAM5 | MPI | Germany | T63L31 | 1.51.5L40 |
| 14 | CCSM3 | NCAR | USA | T85L26 | 1.1250.27L40 |
| 15 | UKMO-HadCM3 | UKMO | UK | 3.752.5L19 | 1.251.25L20 |
| 16 | UKMO-HadGEM1 | UKMO | UK | 1.8751.25L38 | 11/3L40 |

**USA: 5; France: 2; Japan: 2; UK: 2; **
**Australia: 1; Canada: 1; China:1; Germany: 1; Russia: 1**

## Linear Change of Surface Temp

**HadCRU (#17); NCEP CAMS (#18); **
**NOAA extended SST (#19)**

- Annual Mean 1950-1999

**Notes:**
HadCRU (#17), NCEP CAMS (#18), and NOAA extended SST (#19).

## GPCP (#17)

- Linear Change of Precip
- Annual Mean 1979-1999

## Linear Trend of 

**Linear Trend of **
**Surface Temp (1950-99) and Precip (1979-99)**

**16 AR4 Model EnsMean**

**Obs**

## Distribution of GPCP Rain as a function of Rain Rate

- Rain Rate

**Light: ****	****<1mm/day**
**Medium: ****	****2-8mm/day**
**Heavy: ****	****>9mm/day**

**Distribution of GPCP Rain as a function of Rain Rate**
**Annual Mean 1979-1999; Tropical Ocean**

- Clim

- Trend

## Trend_Model*4

- GFDL CM2.0

- NASA GISS ER

- MIROC3.2 hires

- NCAR CCSM3

- UKMO HadCM3

- GPCP

**Trend_Model*4**

## ISCCP (#17)

**Linear Change of Total Cloud Cover**
**Models (1950-1999) vs ISCCP/4 (1984-1999)**

## Clim and Linear Trend of 3-D Cloud in GFDL CM2.0

**[30S-30N]**

**[0-360E; 30S-30N]**

**Clim and Linear Trend of 3-D Cloud in GFDL CM2.0**

## Clim

**Clim**

**Linear Trend**

## 500mb

**OLR reduces**

**Chen et al (2002); **
**Wielicki et al (2002)**

**Linear Change over 1950-1999**

- 500mb

**OLR at TOA**

## Cool Climate

**Cool Climate**

- Tropical Ocean

- Tropopause

- OLR

- Surface Evaporation

- Tropopause

- OLR

- More cold and bright high cloud at tropopause and lower stratosphere

- Less mid-to-low cloud

- Less high cloud

- Less OLR

*Enhanced *
*heavy rain*

*Greatly reduced*
*moderate rain*

*Increased *
*light rain*

- Intensified
- deep convection

- Strengthened
- updraft

- Ocean surface

- Warmer Tropical Ocean

**Warm Climate**

- Ocean surface

- Enhanced Surface Evaporation

## Conclusions

- CGCMs are reasonably consistent in depicting aspects of long term changes in the 20th Century climate and the tropical hydrological cycle:
- Surface warming over tropical ocean and land
- Increasing/decreasing precipitation over tropical ocean/land
- Increasing heavy and light rain, but decreasing moderate rain
- A reduction in total cloud cover in the tropics.
- CGCMs significantly underestimate the magnitudes of the observations, by a factor of at least 4.
- This likely leads to gross errors in model simulation of tropical radiative fluxes
- Difference between CGCMs and observations
- Time scale
- CGCMs: certain processes may be missing
- Obs: e.g. problems in retrieving high level thin clouds

## Future

- Improvement in representing physical processes associated with clouds and their interaction with radiation in the CGCMs
- Observational data
- Quality
- Long term