1. Impact of aircraft data in the MSC forecast systems
Stéphane Laroche and Réal Sarrazin
AMDAR meeting
Toronto, 20 October 2011

2. Some features regarding the assimilation of aircraft reports in NWP
Easy to assimilate;
Observations (wind, temperature and humidity) directly related to NWP model variables, as oppose to radiances from satellite data for instance;
The quality of these data is now as good as radiosonde data;
Can easily be used for verification;
However, temperature (those assimilated) from most aircraft data providers are bias (warm) with respect to NWP, reaching oC at flight level.

3. Impact of the main global observing systems on NWP in terms of gain in predictability
Z500 over Northern Hemisphere
Northern Hemisphere Extra-Tropics
12 hours
6 hours
A few hours
Case impact
Neutral
SSMI
AMV
SCAT
GPS-RO
AMSU/A
IASI
AIRS
Buoys
Aircraft
Radiosonde
~6 hours
Gain in predictability of the main global observing systems
Source: 4th WMO workshop on the impact of various observations on NWP (2008)
Current contributions to some parts of the existing observing system to the large-scale forecast skill at short and medium-range. Green colour means the impact is mainly on the mass and wind field. Blue colour means the impact is mainly on humidity field. The contribution is primarily measured on large-scale upper-air fields. The read horizontal bars give an indication of the spread of results among the different impact studies sofar available (for several observing systems the quantity of impact studies is too small and the spread is not quantified).
Results from data denial experiments
with the MSC global forecast system
and 3D-Var, January 2009

4. Observations assimilated in the MSC global forecast system
March 2009
About 2.0 million observations
are assimilated in the global
forecast system daily
12 hours
6 hours
A few hours
Case impact
Neutral
SSMI
AMV
SCAT
GPS-RO
AMSU/A
IASI
AIRS
Buoys
Aircraft
Radiosonde
Gain in predictability for various observations
in the Northern Hemisphere
Distribution of the various data
type assimilated at 00 and 12 UTC

5. OSEs carried out at MSC in 2007
In this study, the impact of a given observing network (here aircraft or radiosonde) on NWP is assessed by denying the data in the global forecast system during the period of January and Febuary 2007 over North America. Forecast differences between those from the data-denial and the control experiments are used to evaluate the impact.
The time-averaged root-mean-square forecast error (RMSE) of 500-hPa geopotential height (Z500) and 250-hPa zonal wind speed (U250) and the Forecast Impact (FI), which is the normalized time-averaged RMSE difference between the data-denial and control experiments are used to measure the impact.

6. Aircraft reports assimilated during January and February 2007
and radiosonde stations (black dots)

7. RMSE differences for Z500 Impact of aircraft reports
January and February 2007
Impact of aircraft reports
Impact of radiosonde data 0h
24h
48h

8. Forecast impacts (FI%) over regions of North America
Z500

9. Forecast impacts (FI%) over regions of North America
U250

10. Main findings from OSEs
The quality of NWP over Canada heavily relies on the radiosonde network, especially over the northern regions;
Over areas of dense aircraft data such as the eastern United States, aircraft data provide the main positive impact on short-range forecasts.
The impact of aircraft data is more important on wind field at the jet level than on mass field;
The amount of aircraft data over Canada is relatively small. The data volume from the Canadian AMDAR program represents roughly 4% of all aircraft data.

11. Expected impacts of additional aircraft data over Canada
NWP over the Canadian regions would greatly benefit from a larger amount of aircraft data. The nature of the impact will depend where additional aircraft data will be deployed:
Widely distributed ascent and descent reports over data sparse regions like northern Canada would greatly benefit to global NWP systems and would improve longer range forecasts over Europe for instance;
More frequent reports over highly populated areas such as southern Canada would greatly benefit to regional and high-resolution NWP, improving short-range forecasts.