1. 07/22/031 Doppler radar wind data assimilation in HIRLAM 3D-Var SRNWP/COST-717 WG-3 Session on assimilation of 'non-conventional data' 8.10.2003 Kirsti Salonen (FMI), Heikki Järvinen (FMI), Magnus Lindskog (SMHI)

2. 07/22/031 Contents ● Superobservations ● Variational data assimilation ● Observation operator for Doppler radar radial winds ● Fit of the observations with the model counterpart ● Future plans

3. 07/22/031 Superobservations (1) ● Available: raw radial wind data with high temporal and spatial density. ● Observations represent partly phenomena which are not resolved by the NWP model. ● Calculating spatial averages, Superobservations (SO), decreases the representativeness error. ● To minimize horizontal correlation, each piece of raw data is allowed to influence only one SO.

4. 07/22/031 Superobservations (2)

5. 07/22/031 3D Variational data assimilation ● Based on minimization of the cost function ● Observation operator H produces the model counterpart of the observed quantity.

6. 07/22/031 Observation operator for Doppler radar radial winds Interpolation of the NWP model wind (u,v) to the observation location. Projection of the interpolated NWP model wind towards the radar: v h =u sin  +v cos  Projection of v h on the slanted direction of the radar beam v r =v h cos(  +  ).

7. 07/22/031 Broadening of the radar beam Gaussian averaging kernel The effect of radar horizon is taken into accout. An empirical upper limit for the averaging kernel is set to 1.5 times the half- beamwidth.

8. 07/22/031 Bending of the radar beam Taken into account by using Snell's law Beam path is accumulated until the radar beam reaches the observation location. Effective elevation angle is calculated and used in the projection of v h.

9. 07/22/031 The fit of the observations with the model counterpart TEMP Radar

10. 07/22/031 Free parameters associated to SO ● Number of polar bins used in the SO generation (NPB). ● Measurement range. ● Variance of the raw radial wind values forming a SO (VRW).

11. 07/22/031 Distribution of the observations Non-meteorological targets: Birds Ships Remaining ground clutter Aliasing problems.

12. 07/22/031 Applying quality criteria ● Measurement range less than or equal to 100km. ● NPB more than or equal to 5. ● VRW less than or equal to 10 m/s.

13. 07/22/031 Future plans ● Parallel data assimilation experiments with Finnish and Swedish radar data. ● Make use of novel de-aliasing algorithm. ● Summer and winter months. ● Impact studies of using radar wind data on forecasting severe weather events. ● Studies with Luosto radar data.