Meteorologisk Institutt met.no

Radar beam refraction modelling

Uta Gjertsen, met.no, FoU

Nordic weather radar workshop Helsinki 3.10.-4.10.2002

Meteorologisk Institutt met.no

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.

Meteorologisk Institutt met.no

Today’s precipitation composite

• Spatial gauge adjustment with mean monthly gauge/radar factors

• Precipitation intensity

• Accumulated precipitation

Meteorologisk Institutt met.no

Accumulated precipitation

Meteorologisk Institutt met.no

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

Meteorologisk Institutt met.no

Beamsplitting:

Radar beam height as a function of distance modeled from radiosonde data 16.8.2002 (elevation = 0.5 degrees, radar Oslo)

Meteorologisk Institutt met.no

Beam shielding west of radar Oslo 16.8.2002

Blue line: measurement volumeRed line: meausrement volume

after beam blockageDashed red line: measurement

volume from standard atmosphere

• Lower edge height of radar beam

Meteorologisk Institutt met.no

Beam splitting east of radar Oslo 16.8.2002

Meteorologisk Institutt met.no

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