1. Radar beam refraction modelling
Nordic weather radar workshop Helsinki
Radar beam refraction modelling
Uta Gjertsen, met.no, FoU

2. For the quantitative use of weather radar data in Norway it is essential to correct for beam shielding. The degree of beam shielding is variable due to changes in atmospheric humidity and temperature profiles. In the near future we will implement a model deriving the degree of beam blockage from actual radiosonde profiles. The model will increase the accuracy of the shielding correction and identify regions where data is missing due to anaprop. The model gives also an indication on situations with beam splitting. Beam splitting can produce large errors and is difficult to identify from NWP model or radar data alone.

3. Today’s precipitation composite
Spatial gauge adjustment with mean monthly gauge/radar factors
Precipitation intensity
Accumulated precipitation

4. Accumulated precipitation

5. Radar Oslo: Mean daily precipitation for a winter and spring season, beam blocking and topography

6. Beamsplitting: Radar beam height as a function of distance modeled from radiosonde data (elevation = 0.5 degrees, radar Oslo)

7. Beam shielding west of radar Oslo 16.8.2002
Lower edge height of radar beam
Blue line: measurement volume
Red line: meausrement volume after beam blockage
Dashed red line: measurement volume from standard atmosphere

8. Beam splitting east of radar Oslo 16.8.2002

9. Examples for vertical humidity and temperature profiles causing anaprop.
Condition
dN/dh
Trapping
< -157
Superrefraction
-157 to -79
Normal
-79 to 0
Standard
-39
Subrefraction
> 0