MSC Introductory Weather Radar Course

The portion of power scattered back in an incident direction.

There are many methods, e. g. the Norwegian one documented in Gjertsen and Dahl (2002), for the blockage correction. In this method the number of beam traces are determined using altitude vertical angle, refractivity, atmospheric pressure, temperature data and data of water vapour partial pressure. This computed beam trace is used in a distributed model, where each point is taken in cylindrecal coordinate system if a point on the topografic map is higher than a computed one. The pre-calculated beam closest to the topografic data is used as minimum measurement height in that point.

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Problems

Vertical profiles of temperature, pressure and humidity affect radar beam propagation, especially when there is low elevation angle at the radar site. Actually, normal propagation conditions are dominant but there are also significant seasonal variations in the median and monthly dispersion of the vertical refrectivity gradient.

Problems in Radar Products

Bird flocks look like precipitation on the radar picture, especially during migration. There are some algorithms that use pattern recognition or study the doppler spectra.

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A core of weak equivalent reflectivity in a thunderstorm which identifies the location of a strong updraft. The updraft is so strong that large precipitation particles do not have time to form in the lower and mid levels of the storm and are prevented from falling back into the updraft core from above. See also Weak Echo Region.

Rapidly moving crescent shaped echo which is convex in the direction of motion. Typically associated with strong straight-line winds. See also Line Echo Wave Pattern.

Bragg scattering is the phenomenon of sharp inhomogenities in the refrective index of the atmosphere. This is most important for the radars of longer wavelength, especially those which are vertically pointed. The turbulence is responsible for producing the large-scale refractive index gradients which result in return of incident radar power.

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In radar, indicates the melting point of a snowflake. High intensity return is caused by the water surrounding the ice crystal, hence appearing large.