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

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 0.5 - 1.0 oC at flight level.

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

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

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.

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

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

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

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

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.

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.