# Presentation: 709754

## Systematic errors in the GFS Dec. 2005-Feb. 2006

- --model has trouble with low-level stratus clouds over the southeast Pacific off South America, initially displacing them further off-shore and then acting to dissipate them
- --this disturbs the surface radiative and heat budget and introduces thermal errors
- --may be related to too much convection over South America and too much sinking over stratus clouds region, perhaps reflecting difficulties with convection over orography

## 850 hPa winds Dec. 2005-Feb. 2006

- 1

***850 hPa winds Dec. 2005-Feb. 2006***

- analysis

- Error in 1day forecasts

- Error in 3 day forecasts

- Error in 5 day forecasts

## analysis

- 15 day forecasts

- 15 day forecasts error

- GFS forecasts weaken low level southerly jet near western South American coast

## 150 hPa winds Dec2005-Feb 2006

- 1

***150 hPa winds Dec2005-Feb 2006***

- Analyses

- Error in 1 day forecasts

- Error in 3 day forecasts

- 1 day forecasts show increased outflow over South America and convergence over stratus cloud region
- GFS 15 day forecasts show increased trough over northern South America, squeezing anticyclone to south

## Analyses

- 15 day forecasts

- Error in 5 day forecasts

- Error in 15 day forecasts

## Horizonal divergence at 200 hPa Dec. 2005-Feb. 2006

***Horizonal divergence at 200 hPa Dec. 2005-Feb. 2006***

- Analyses

- 1 day forecasts

- 5 day forecasts

- 15 day forecasts

## GFS forecasts act to increase upper level divergence over Andes, increase convergence over ocean to south

***GFS forecasts maintain divergence over South America better than they do over Indonesia.***

## Difference between 1day forecasts and analyses

- 3 day forecasts minus analyses

- 5 day analyses minus analyses

- 15 day forecasts minus analyses

## Longitude-pressure cross-section of horizontal divergence at 30S

## GFS forecasts tend to increase slightly upper level convergence, lower level divergence near 80W. 

## GFS forecasts act to increase rising motion over Andes—possible problem with orography and convection?

- Vertical velocity at 500 hPa Dec. 2005-Feb. 2006

- Analyses

***GFS forecasts act to increase rising motion over Andes—possible problem with orography and convection?***

- 1 day forecasts minus analyses

- 3 day forecasts minus analyses

## 5 day forecasts

- 15 day forecasts

- 5 day forecasts minus analyses

- 15 day forecasts minus analyses

## 925 Temperature

***925 Temperature***

***850 Temperature***

- 1 day error

***5 day error***

- 1 day error

***5 day error***

## Temperature 700

***Temperature 700***

***Off west coast of South America, forecasts act to warm temperatures at 850 and 920, cool temperatures at 700.  Warming occurs sooner than cooling.***

***1 day error***

***5 day error***

## 1 day error

***Vertical cross-section of temperature at 30S ***
***Dec. 2005-Feb. 2006***

***1 day error***

***3 day error***

***Off west coast of South America, model warms in boundary layer, cools in mid-troposphere***

## 5 day error

- T with zonal mean removed

- Analyses

- 15 day forecasts

***5 day error***

***15 day error***

## 925 relative humidity—drying off west coast of South America

***850 relative humidity drying in tropical convergence zones***

## Analyses

- 3 day error

- 15 day error

***Analyses***

***15 day forecasts***

***Relative humidity 925***

## 5 day error

***5 day error***

- 15 day error

***Relative humidity 850***

## Total cloud cover

***Total cloud cover***
***GFS analysis cycle has less clouds in South American stratus region than Air Force nephanalysis cloud estimates ***

- Air Force

- GFS 0-6 hr forecasts

- GFS minus Air Force

## Forecasts further decrease clouds in South American stratus region

- 0-24 hr forecasts minus 0-6 hr forecasts

- 48-72 hr forecasts minus 0-6 hr forecasts

## Low clouds Dec. 2005-Feb. 2006

- GFS 0-6 hr forecasts displace South American stratus clouds to west and have less clouds than Air Force estimates

- Air Force

- GFS 0-6 hr forecasts

- GFS minus Air Force

## 0-6 hr forecasts

- 336-360 hr forecasts

- 0-24hr minus 0-6h

- 48-72 hr minus 0-6 hr

## GFS forecasts displace low stratus clouds further to west off South America.

- 96-120 hours minus 0-6 hr

- 336-360 hours minus 0-6 hr

## Boundary layer clouds Dec. 2005-Feb. 2006

***Boundary layer clouds Dec. 2005-Feb. 2006***
***GFS 0-6 hr forecasts have more clouds in boundary layer than Air Force estimate***
***(Definition of layers may differ)***

- Air Force

- GFS 0-6 hr forecasts

- GFS minus Air Force

## 0-6h forecasts

- 336-360 hr forecasts

- 0-24 hr minus 0-6 hr

- 48-72 hr minus 0-6hr

## GFS forecasts decrease boundary layer stratus clouds to west of South America

***GFS forecasts decrease boundary layer stratus clouds to west of South America***

***96-120 hr minus 0-6 hr forecasts***

***336-360 hour minus 0-6 hour forecasts***

## Surface net short wave

- 0-6 hr forecasts

- 336-360 hr forecasts

- 0-24 hr minus 0-6hr forecasts

- 48-72 hr minus 0-6 hr forecasts

## Surface net long wave

- 0-6 hr fcsts

- 336-360 hr fcsts

- 0-24 hr minus 0-6 hr fcsts

- 54-72 hr minus 0-6 hr forecasts

## Surface net radiation

***Surface net radiation***

- 0-6 hr forecasts

- 336-360 hr forecasts

- 0-24 hr minus 0-6 hr fcsts

- 54-72 hr minus 0-6 hr forecasts

## Evaporation

## Surface net heat flux

***Surface net heat flux***

## Changes in stratus clouds off South America are associated with increased surface radiative fluxes and more downward surface net heat flux.

***While SST is prescribed in these forecasts, the same atmospheric model is used in coupled seasonal forecasts.  Too little low-level stratus clouds in the east Pacific appears to be a problem in the coupled integrations.***
***GFS has stronger east Pacific ITCZ, more precipitation over Amazon, less over Andes than independent estimate***

## Precipitation

***Precipitation***

- CAMS/OPI

- 0-6 hr forecasts

- 0-6 hr minus CAMS/OPI

- 0-24 hr minus CAMS/OPI

## 0-6 hr

- Horizontal divergence of 10 m wind

***0-6 hr***

***0-24 hr***

***0-24 hr minus 0-6 hr***

***48-72 hr minus 0-6 hr***

## Speed of 10 meter wind

***Speed of 10 meter wind***

- 0-24hr minus 0-6 hr

- 48-72 hr minus 0-6 hr

- Forecasts weaken low-level convergence and divergence associated with east Pacific ITCZ and weaken 10 m wind speed in east Pacific

## --GFS forecasts fail to maintain low level stratus clouds off the west coast of South America, increasing net radiative fluxes and downward surface net heat flux.  

- --GFS precipitation over and near South America disagrees with independent estimates, suggesting that GFS divergent flow may be incorrect.