# Presentation: 097213

## Short Range Systematic Errors in the NCEP GFS

***Short Range Systematic Errors in the NCEP GFS***
**by**
**G. White, J. Alpert, K. Campana, P. Caplan. J. Derber, G. Gayno, Y. Hou, M. Iredell, H. Juang, R. Kistler, D. Kleist, S. Lord, S. Lu, J. Meng, K. Mitchell, S. Moorthi, H. Pan, S. Saha, J. Sela, R. Treadon, F. Yang, H. Wei, X. Wu, M. Young, Y. Zhu**
**Global Climate and Weather Modeling Branch**
**Environmental Modeling Center**
**National Centers for Environmental Prediction**
**DOC/NOAA/NWS**
- _[Glenn.White@noaa.gov](mailto:Glenn.White@noaa.gov)_
***I’m responsible for this presentation;***
***The others are responsible for the GFS***

## GFS Global Forecast System

***64 sigma layers***
***T382 to 180 hours, T190 to 384 hours 4 times a day ***
***Guidance for NWS aviation, hurricane, medium and extended range forecasts (12 hours-9 months)***
***Atmospheric model used in NWS Climate Forecast System for monthly, seasonal forecasts***
**GDAS Global Data Assimilation System***** ***
***SSI Spectral Statistical Interpolation 3DVAR—used as initial and boundary conditions for other systems***

## 500 hPa Height 5 day Anomaly Correlation

***30% of variance 1984***

***70% of variance 2006***

**Frozen cdas model**

**Operational GFS**

***More than doubled skill of forecasts in 22 years***

***Robert****** ******Kistler***

**500 hPa Height 5 day Anomaly Correlation**

## Today will discuss using short-range errors (day 1 or less) to diagnose GFS

- _[http://wwwt.emc.ncep.noaa.gov/gmb/noor/oct98op/text.html](http://wwwt.emc.ncep.noaa.gov/gmb/noor/oct98op/text.html)_
**--monthly, seasonal systematic errors in GFS 9/1998 on**
**--monthly comparison of GFS and other NWP centers **
**9/2003 on**
**Today will discuss using short-range errors (day 1 or less) to diagnose GFS**
**--comparison to other centers**
**--”transplant” experiments—running GFS model from ECMWF Analyses and ECMWF model from GFS analyses**
** **
**Poster Thursday on long range errors using multi-decadal ocean-atmosphere coupled integrations to diagnose GFS**

## Major implementation May 31, 2005

- --higher resolution 50 km to 35 km
- --improved analysis
- --new sea-ice, land-surface models
***--enhanced orographic height by 10% of mountain variance in calculation of mountain blocking dissipative forces***
***--reducing both background diffusion in free atmosphere and turbulent diffusion length from 150 to 30 m in stable cases***
***Last two tested (and tuned) in 1-day experiments on winter cases 2004-2005 (emphasized period in Feb. 2005 where our skill dropped off relative to ECMWF) and found to work together to improve forecasts***

## Negative bias in GFS Asian jet compared to 

***observations ***
***This suggested too much diffusion***
***Reducing diffusion did not eliminate bias***

**Bias in 200 hPa Wind speed 24 hr forecasts Jan 2005**

## old

**Reducing diffusion produces drier, warmer stratosphere**

**Zonal mean 5day error in ****temperature**** **

***old***

***new***

**47 day means Dec.-Jan**

## Day 1 error (left) implies problem with orography

***Day 1 error (left) implies problem with orography***
***Enhanced mountain blocking reduced error over Himalayas, Rockies***

**OLD**

**NEW**

***Day 1 error in 500 hPa height 47 day mean Dec-Jan***

## OLD

***Day 1 rms height error reduced over mountains***

**OLD**

**NEW-OLD**

***RMSE 1 day error 500 hPs height 47 days Dec.-Jan.***

## April 21-June 4, 2005

|  | Day 3 | Day 5 | Day 7 |
| --- | --- | --- | --- |
| Old GFS | .950 | .815 | .587 |
| New GFS | .958 | .844 | .635 |
| ECMWF | .967 | .868 | .693 |

***April 21-June 4, 2005***
***20-80N 500 hPa height ***
***Anomaly correlation***

## Examining day 1 errors indicated areas of concern in gfs. 

***Reducing day 1 errors improved medium-range forecasts.***
***Non-linear processes less time to act in shorter-range forecasts; source of error may be clearer.***

## GFS still large day 1 error

***GFS error against own analysis grows rapidly first 24 hours;***
***More slowly beyond day 1.***

**RMS Error vs. forecast time **
**Z 500 hPa**
**Dec. 2006**

***GFS still large day 1 error***

## Day 1 “errors” against own analyses comparable to analysis differences between different nwp centers December 2006

***Day 1 “errors” against own analyses comparable to analysis differences between different nwp centers *****December 2006**

**Differences in analyses**

**Day 1 error against own analyses**

**500 hPa height**

## Monthly mean GFS analysis difference from other centers

**Monthly mean GFS analysis difference from other centers**

**December 2006**

**500 hPa height**

**GFS-Canada**

**GFS-ECMWF**

**GFS-Met Office**

**GFS-FNMOC**

## 500 hPa Height

**500 hPa Height**

**December 2006**

**GFS-EC analysis**

**GFS 12hr error**

**GFS 1day error**

**GFS-EC 12 hr RMSE**

## GFS analysis doesn’t agree with other centers’ analyses

***GFS forecast model doesn’t agree with GFS analysis***
***GFS 1 day forecasts try to remove analysis differences from other centers***
***New GSI analysis appears to agree more with other analyses***

## GSI/Hybrid

***Hope to implement this spring ***
***gridpoint statistical interpolation and hybrid sigma pressure vertical coordinate***
***Grid space definition of background error***
***Improved balanced equations***
***Beats operational GFS at day 1; ***
***	******day 5 ?***

## GFS-EC

***GFS-EC***

***GSI-GFS***

**Analysis difference**

**RMSE 1 dy difference**

**500 hPa height**

**Aug15-Sep7 2006**

**August 2006**

***GSI-GFS***

***GFS-EC***

## GFS

**GFS**

**GSI**

***New analysis has much less day one error***

**1 day error 500 hPa hgt 500 Aug 15-Sep 7 2006**

## Transplant experiments

***--EC analyses and forecasts from 000 UT***
***--GFS analyses and forecasts from 000 UT***
***--ECGFS:  EC analyses to GFS model from 000 UT (Treat EC analyses as observations)***
***--EC analyses and forecasts from 1200 UT***
***--GFS analyses and forecasts from 1200 UT***
***--GFSEC:  GFS analyses to EC model from 1200 UT***
***--Are differences due to analysis or model?***
***GFS minus ECGFS effect of GFS assimilation***
***ECGFS minus EC effect of GFS model***

## RMSE 1 dy 500 height

***Effect of GFS model***

***Effect of GFS Assimilation***

***Much of day 1 error in 500 hPa height in GFS appears to come from GFS assimilation, not from GFS model***

**RMSE 1 dy 500 height**
**Aug 2006**

**GFS-EC**

**EC analysis GFS model-EC**

**GFS-EC analysis GFS model**

## T equator 

**T equator**** **

**GFS-EC**

**EC analysis GFS model -EC**

**ANL**

**1day**

**GFS model produces pattern in 24 hours**

**August 2006**

## ANL

**EC model reduces difference in 24 hours**

**ANL**

**1day**

**GFS-EC**

**GFS analysis EC model - EC**** **

**T equator**

**Aug 1-20 2006**

## --Differences in height appear largely due to assimilation

**--Differences in equatorial temperature structure reflect model differences**
**--Examination of short-range errors can help identify specific problems; need to determine whether assimilation or model to blame**
**--Reducing day 1 errors ***MAY*** reduce medium range errors**