# Presentation: 321069

## Global Air-Sea Flux Data Sets 

*Glenn White*
*Global Climate and Weather Modeling Branch*
*EMC/NCEP*
*NWS/NOAA/DOC*
*Glenn.White@noaa.gov*

## Sources of air-sea fluxes:

**--COADS ship observations**
**--satellite-based estimates**
**	****SRB surface radiation estimates**
**--numerical weather prediction data assimilation**
**	****operational**
**	****reanalyses**
**--FSU surface winds, stress**
**--Yu, Sun and Weller-objective analysis of ships, buoys, satellite retrievals, NWP output**
**	**

## 2) SEAFLUX-emphasis on air-sea fluxes from satellites

**a) Report on our current knowledge of air-sea fluxes **
**b) Workshop proceedings**
**http://www.soc.soton.ac.uk/JRD/MET/WGASF**
**Or from WMO/WCRP**
**New group being organized**

**2) SEAFLUX-emphasis on air-sea fluxes from satellites**
**http://paos.colorado.edu/~curryja/ocean**

**3) SURFA—Peter Gleckler and Jan Polcher**
**Comparison of operational NWP centers’ surface fluxes (land and ocean) to high quality in-situ measurements**

## Fluxes from COADS data

***Da Silva et al.--UWM***
***Josey et al.--SOC***
***Careful corrections applied to ship data***
***Global imbalance***
***Not truly global coverage***

## (left) Correlation of monthly mean evaporation from NCEP1 reanalysis with COADS;(right) number of COADS ship reports/month

- Results similar for sensible heat, net heat flux and wind stress
- Reanalyses agree well with COADS where COADS has data.  Reanalyses have observations other than ship data.
- Indicates that reanalyses’ latent and sensible heat and wind stress are reasonable.

## Surface radiation budget (SRB-1) Jul. 83-June 91Satellite measurements TOAISCCP cloudsRadiative transfer modelSatellite-based short wave estimates often higher than surface observations (BSRN)SRB NLW Global mean of 48 W/m2Kiehl and Trenberth  (1997) 66 W/m2SRB Net radiation fairly large, implying larger evaporation than any other estimate

## Global Mean Ocean Heat Budget

***Global Mean Ocean Heat Budget***

## Best way to assimilate satellite data is to assimilate what satellite actually measured into system that considers all other data and applies laws of physics—an atmospheric data assimilation system

**Independent estimates of surface fluxes needed to keep data assimilation estimates honest**

## Precipitation Estimates

***Global Precipitation Climatology Project***
***CMAP (Xie and Arkin) ***
***Based on rain gauges, satellite-based estimates***
***OPI—quick-look CMAP***
***Magnitude over ocean uncertain***
***Satellite algorithms may be more tuned to tropics than midlatitudes***

## Which is correct?

- (CMAP)

## lower bound on uncertainty in precipitation

- CMAP
- Precip
- 1988-92

- GPCP-CMAP

## NCEP-1 with CMAP

- NCEP-2 with CMAP

- Monthly mean precipitation anomalies from NCEP reanalyses correlated with CMAP

## Forecasting a system's behavior is a tough test (not the only test) of how well you understand that system.

- need reliable estimates of fluxes and near-surface fields           at regular spatial and temporal intervals
- a few hours after observation time
- produced from vast amount of quality-controlled data carefully interpolated in space and time by laws of physics, in which information about surface fields is extrapolated from other fields,
- carefully monitored continuously by diverse, critical users,
- rigorously tested for its accuracy.
- That’s data assimilation for NWP.
- Forecasting a system's behavior is a tough test (not the only test) of how well you understand that system.

## Problems:

***"spin-up"--initial adjustment of fields ***
***ERA-15 recommended use of 12-24h forecasts for fluxes, not 0-6. ***
*** ******NWP systems continually being improved******.******                    ******Discontinuities introduced, can be significant in fields more defined by model physics than by observations.***
***Changes to improve forecasts, not to improve air-sea fluxes***
***Timeliness requirement may limit use of best parameterizations, highest resolution, relevant data******.***

## Spin-down in tropics;

- more like OPI
- Spin-up in mid-latitudes;
- less like OPI

- Operational GFS

## Global mean DSW increased                               from 198 to 211 W/m2.

**The changes increased forecast skill,                   reduced model biases and                                introduced more physical cloudiness**.
***Surface net short wave is now too high;                       new cloudiness needs adjustment.                                New cloud microphysics is being tested.***

***Global mean DSW increased                               from 198 to 211 W/m******2******.***

## New-Old Operational GFS

***New-Old Operational GFS***

## Increased resolution,                          minor analysis changes                            in late Oct. 2002                           increased global mean precipitation                                from 3.02 to 3.22 mm/day.

## NCEP

- Uses analyzed SST, currently averaged over a few days
- No diurnal cycle in SST
- doesn’t use TOGA-COARE parameterization
- doesn’t adjust ship obs for ship height
- observations at island station assimilated as if typical of ocean
- Output every 6 hours
- No wave model in GFS

## Reanalysis--use frozen data assimilation system to reanalyze past and present meteorological data, producing long record uncontaminated by changes in system, but still contaminated by changes in observations.

*** ***

## Reanalyses available

**1) NCEP-1 1995 model, T62, 1948-present CDAS**
**2) NCEP-2 1979-present**
**     ****Same resolution, analysis system, almost same data**
**     ****Corrected mistakes**
**     ****Updated physics**
** ****3) ERA-15 12-24 hr twice daily forecasts to avoid "spin-up"**
**     ****1979-93, T106**
**4) ERA-40 higher resolution, improvements, esp. to land surface  ****In progress****           **
**  **

## NCEP1--stratus clouds in eastern subtropical oceans

- 	stress too weak in equatorial Pacific
- 	ocean surface albedo wrong
- 	discontinuity at beginning of 1979
- NCEP2--reasonable stress in equatorial Pacific
- 	used to produce reasonable ocean reanalysis at NCEP
- 	correct ocean surface albedo
- 	lack of stratus clouds in eastern oceans
- ERA15--lack of stratus clouds in eastern oceans
- 	discontinuities due to problems with satellite radiances
- 	best precip pattern of first reanalyses
- ERA40--problems with radiances due to Pinatubo

## Reanalyses have problems with surface radiative fluxes.

**—****cloudiness and moisture poorly known and modeled.**
**Reanalyses’  sensible and latent heat and wind stress are more realistic.**
**--Parameterizations dependent on near-surface fields, which NWP data assimilation can infer from atmospheric fields.**
**--Reanalysis estimates may be as realistic as any global fields of sensible and latent heat and wind stress**
**CMAP precip more realistic than reanalyses, except possibly over high latitude oceans**

## Surface fluxes—GDAS(current system) vs. CDAS (NCEP1)

- GDAS—higher resolution
- better evaporation at high wind speed
- better precipitation pattern
- better wind stress in equatorial Pacific
- Corrected ocean surface albedo
- Precipitation and evaporation greater
- Sensible heat less
- Surface energy balance more out of balance

## 5S-5N

**5S-5N**

**Pacific FSU**

**1980-93 SOC**

**Time-mean**
**U****s**

- NCEP-1 too weak; NCEP-2 better

- COADS

**NCEP-1**

## Anomaly correlation with FSU--Pacific

**Anomaly correlation with FSU--Pacific**

**NCEP-1**

**NCEP-2**

- Zonal surface stress

## NCEP-1 minus SRB-1

***Surface NSW 1985-1991***

## Net short wave over No. Pacific in July from SRB-1 and 3 reanalyses.  ERA-15, NCEP-2 show no evidence of stratus clouds.

- SRB-1

- ERA-15

- NCEP-1

- NCEP-2

***Surface NSW ***
***July 1983-90***

## Operational

- SRB-1

***Surface NSW ***
***July 03***

***July ***
***1983-90***

## Stratus displaced from coast in operational

- Air Force nephanalyses

- Operational

***Low cloud cover July 2003***

## Operational

- OPI (quick look CMAP)

- NCEP-1

***Precipitation DJF 02/03***

## NCEP-1

- Operational

- COADS

*Evaporation DJF 02/03*

## Operational

- NCEP-1

- COADS

***Sensible heat flux DJF 02/03***

## Operational

- NCEP-1

- SRB-1

- Surface downward short wave
- DJF 2002/2003

## NCEP-1

- Operational

- SRB-1

- Surface NSW DJF 02/03

## Net heat flux into ocean 

***Net heat flux into ocean ***
***DJF 02/03***

- Operational

- CDAS

- COADS

## My preferences

- Precipitation--CMAP or GPCP
- Net Short Wave--SRB
- Sfc. Stress--NCEP2, ERA or FSU
- Sensible heat--NCEP1 or ERA
- Latent heat--NCEP1, NCEP2 or ERA
- Net heat flux--combine SRB NSW and reanalyses

## Need to improve knowledge of air-sea fluxes, especially clouds, magnitude of hydrological cycle, atmospheric moisture.

**Need to improve knowledge of air-sea fluxes, especially clouds, magnitude of hydrological cycle, atmospheric moisture.**
**Cloudiness major problem in NWP fluxes.**
**Test air-sea fluxes by using different data sets in ocean models**

## Time for another NCEP global reanalysis?Is operational system ready for the last 56 years?How to reduce effects of changes in observations?

## Global Mean Balances 

***Aug02-Jul03***

## Zonal mean net short wave over ocean

- Reanalyses much different from satellite estimate.

## Zonal mean net heat flux into ocean DJF 02/03

***Zonal mean net heat flux into ocean DJF 02/03***

- COADS

- NCEP-1

- Operational