1. Beam Propagation modelling and blockage correction in the Nordic Weather Radar Network (NORDRAD)
Uta Gjertsen, met.no, Norway
Günther Haase, SMHI, Sweden
Joan Bech, Meteocat, Spain
Heikki Pohjola, FMI, Finland
ERAD, Barcelona,

2. Structure The NORDMET/NORA Beam Propagation Project
Examples from Korpoo, Hemse, Røst
Anaprop modelling
Beam blockage correction for standard conditions, example Bømlo
Summary blockage correction
Conclusions

3. NORDMET NORA Beam Propagation Project
Background: Issues concerning the beam propagation are of great importance for the quality of radar products.
Objectives: Coordinate the work carried out in the Nordic countries to define common algorithms.
Address typical “cold climate challenges” like beam propagation in inversion situations, shallow precipitation, snow …
Deliverables: beam blockage correction,
anaprop information

4. Radars Hemse, Sweden and Korpoo, Finland 4.7.2006

5. Radar Røst, 6 July UTC
Simulated height of the lower beam limit and beam blockage HIRLAM11 analysis at the radarsite
Simulated height of the lower beam limit and beam blockage radiosonde Bodo

6. Questions Refractivity:
What is normal beam propagation in the Nordic countries?
Is the BPM a useful tool? And what are the limitations?
Radiosonde or NWP model data for refractivity profiles?
Should anaprop be considered when correcting precipitation estimates for beam blockages?
When and where is anaprop most likely?
Refractivity:

7. ANAPROP variability Data from 2003 and 2004 Norwegian Radio Soundings
Shows only surface ducts

8. Summary ANAPROP
BPM produces reasonable output with radiosondes and HIRLAM
Radiosondes are not always representative for the conditions at the radar site, HIRLAM might be better
HIRLAM 6-hour forecast is good for the cases investigated
Potential for forecasting sea clutter, 1-dim. HIRLAM
Refractivity shows a latitude-dependent pattern

9. Correction field for precipitation
(BB=beam blockage, y=distance center beam - topography, a=radius radar beam cross section) BB
50%
bcorr
1.54
60%
1.77
70%
2.12
(bcorr=correction factor for precipitation, b=Marshall-Palmer b coefficient)

10. = * - = Radar Bømlo Correction filed Corrected precipitation
Uncorrected precipitation - =
Corrected precipitation
Uncorrected precipitation
Corrected areas

11. Blockage correction and VPR
G/R bias as a function of distance for 3 winter months at radar Bømlo

12. Summary blockage correction
The blockage correction reduces bias and scatter
Average bias reduction is 2.6 dB at ranges 40 to 160 km and blockage between 50-70%
Correction fields for standard conditions are good enough
Considering a decrease of reflectivity with height within the measurement volume improves the results

13. Conclusions
The BPM gives realistic output for normal conditions and in cases with anaprop
What is the most realistic profile of temperature, humidity and pressure at the radar site?
Correction fields produced by BPM reduce the gauge/radar bias and scatter
The improvement is dependent on the distance from the radar and the degree of blockage -> consider to correct for inhomogenous beam filling?
The blockage correction for standard conditions should be implemented in the Nordic countries
There is also a potential for sea clutter forecasting and radar site selection assessment (presentation by G. Haase)
We could use a set of VPRs in the future.
The quality information will be very useful in the future, also for hydrological applications of radar data.

14. Thank you for your attention!
Find a nice picture…..